WO1985002271A1

WO1985002271A1 - Fiber optic coupler/connector device and electronic/fiber optic interface device

Info

Publication number: WO1985002271A1
Application number: PCT/US1984/001686
Authority: WO
Inventors: Karel Jan Kosman; Richard Francis Cantwell; Robert Edward Dutton; William Allen Gibson; Vernon Roy Hargrave; Matthew Lee Mcconnell; David William Roecker; Jerry Leo Fife
Original assignee: Raycom Systems, Inc.
Priority date: 1983-11-15
Filing date: 1984-10-17
Publication date: 1985-05-23
Also published as: AU3553784A; EP0162861A4; EP0162861A1; AU580740B2; JPS61500457A

Abstract

A fiber optic coupler/connector device (400) provides simultaneous bi-directional transmission of optical signals over a single fiber optic link cable (398) and precisely aligns and longitudinally separates transmit and receive lightguide fibers (426, 428) to reduce reflection. A high-packing ratio density is provided by stripping the transmit and receive lightguide fibers (426, 428) and applying recladding (450) having a substantially smaller thickness than the original cladding. A stable, triangular configuration is used, which provides for self-centering and stability. Mode stripping reduces reflections resulting from high order modes of propagation of the optical signal. A fluoropolymer heat shrink tube (452, 454, 482, 510) provides precise mechanical alignment of the light guides and link cables (398), as well as decreasing light divergence at the fiber optic lightguide ends. An electronic/fiber optic interface device (10) provides dual electronic serial data ports so that multiple devices can be interconnected by a single interface device (10). Reinforcement of optical data at several predetermined pulse frequencies provides a means for transmission of state operational information over the fiber optic link (95, 102) to control automatic device switching and resource sharing and to eliminate the need for mechanical switches. The fiber optic link (95, 102) cable is immune to electromagnetic and radio frequency interference, shorts, grounding problems and static discharges. The fiber optic link cable provides data security by providing a fiber monitor indicating a loss of integrity in the link cable. The system provides a low-loss, high bandwidth communications link, which can operate with no external power.

Description

FIBER OPTIC COUPLER/ CONNECTOR DEVICE AND ELECTRONIC/ FIBER OPTIC INTERFACE DEVICE

Cross-Refercnce to Related Applications This application is a continuation-in-part of U. S. patent application Serial No. 552,030 filed November 15, 1983 by Karel J. Kosman et al. , entitled "Fiber Optic Coupling Device Method and System".

Background of the Invention The present invention pertains generally to communication systems and more particularly to optical communication systems using fiber optic cables.

With the advent of the proliferation of data processing equipment, communications between user devices such as computers and peripherals is of great interest to the computer industry. Modems (modulation/demodulation units) have been universally usort in the industry as a means of communicating between user devices. Although standard modem devices ire capable of using standard network and telecommunication systems to transmit data, modems suffer from several disadvantages and limitations. For example, data transmission baud rates may be limited to the particular modem utilized. Although baud rates have increased substantially over the past few years, the speed at which data is communicated via modems is slow when compared to other methods of communicating data. This is due, in part, to the limited bandwidth resulting from the frequency at which modems operate. Moreover, the baud rate at which a modem is designed must be matched to the baud rate of the data processing device to which it is communicating. This additionally limits the versatility of such communication systems. Also, modems are subject to electromagnetic interference and radio-frequency interference (EMI/RFI) , and eavesdropping and data link taps. Other disadvantages of modems are set forth in U.S. Patent No. 4,399,563 issued August 16, 1983 to Greenberg.

Other methods of communicating data have been used to overcome disadvantages and limitations of typical modem devices. For example, microwave links have been used to provide high-speed transmission of digital data between user devices. However, microwave links comprise an expensive, means of transmitting data and have physical limitations which rule out the use of such systems in many applications.

The use of fiber optic links overcomes many of the disadvantages and limitations of the prior art by providing a means of communicating data optically which is immune to electromagnetic and radio-frequency interference. However, due to the complexity of transmitting data by fiber optic cables, typical prior art systems are extremely complex. Such systems are expensive and have been unable to economically compete with standard modem devices. Typical fiber optic communication systems are disclosed in U.S. Patent No. 4,381,881 issued May 3, 1983 to Bell; U.S. Patent No. 4,399,563 issued August 16, 1983 to Greenberg; U.S. Patent No. 4,366,565 issued December 28, 1982 to Herskowitz; U.S. Patent No. 4,289,373 issued September 15, 1981 to Sugimoto et al; U.S. Patent No. 4,362,358 issued December 7, 1982 to Hafle and U.S. Patent No. 4 ,341 , 438 issued July 27 , 1982 to Seki et al , which are specifically incorporated herein by reference for all that they disclose. A significant disadvantage of typical fiber optic data links is the necessity of using two fiber optic cables so that optical data can be transmitted and received simultaneously. Use of two fiber optic cables essentially doubles the cost of the fiber optic data communication line. To overcome these disadvantages and limitations, various coupling devices have been devised for using a single fiber optic cable. For example. Bell discloses an expensive and complex fiber optic cross-bar switch for automatically patching optical signals. The Bell system requires the use of multiple optical detectors and multiple LED's (light emitting diodes). Greenberg discloses a time division multiplexing scheme in which problems due to reflections in a Y-coupler device are eliminated by disabling each receiver when a corresponding transmitter is transmitting data. In a similar manner, Herskowitz uses angular division multiplexing to allow for simultaneous bi-directional transmission of data over a single optic fiber. Sugimoto et al, Hafle and Seki et al all disclose wavelength multiplexing to enable bi-directional transmission of optical data over a single fiber optic cable. Again, such systems require complex multiplexing schemes which are expensive to implement.

Summary of the Invention The present invention overcomes the disadvantages and limitations of the prior art by providing a fiber optic coupling device for providing simultaneous bi-directional transmission of optical data over a single fiber optic cable comprising: receive fiber means for receiving optical input signals; transmit fiber means for transmitting optical output signals; combined coupler/connector means for coupling and connecting the receive fiber means and the transmit fiber means with the fiber optic cable to axially and angularly align the receive and transmit fiber means with the cable means to provide simultaneous bi-directional optical coupling of the optical input sicmals from the link cable to the receive lightguide means, and the optical output signals from the transmit lightguide means to the link cable.

The present invention may also comprise a bidirectional fiber optic communication device comprising fiber optic cable means for bi-directionally communicating optical input signals and optical output signals; transmit fiber means for transmitting the optical output signals; receive fiber means for receiving optical input signals; combined coupler/connector means for axially and angularly aligning the transmit and receive fiber means with the fiber optic cable means to allow simultaneous bi-directional coupling of the optical input and output signals between the transmit and receive fiber means and the fiber optic cable means in the coupler/connector means; receiver assembly means for detecting the optical input signals and producing electrical input signals representative of the optical input signals; transmitter assembly means for producing the optical output signals in response to electrical output signals.

The present invention may also comprise a fiber optic interface device for connecting a plurality of user devices in a communications network comprising line receiver means for receiving electronic data input signals and ready-in-signals from a plurality of user devices; fiber receiver means for receiving input optical data signals and input optical state signals and decoding the input optical data signals to produce a decoded fiber data signal, and decoding the optical data signals and the optical state signals to produce a fiber activity signal; synchronous state means for receiving the ready-in-signals and the fiber activity signal and producing switching signals, ready-out-signals and state signals from a state logic decision table addressed by the ready-in-signals and the fiber activity signal; line driver means for transmitting the ready-out-signals and data-out-signals over an electronic serial data port; fiber transmitter means for transmitting output, optical data signals and output optical state signals which are indicative of the operational state of the fiber optic interface device; data steering means for receiving the electronic data signals, the switching signals and the decoded fiber data signal and for selecting a single output signal from the electronic data signals and the decoded fiber data signal in response to the switching signals.

The advantages of the present invention are that it provides an asynchronous data transmission device which is capable of transmitting data at high rates of speed (up to 100Kbps) with automatic speed selection.

Automatic speed selection is also provided by the present invention to eliminate the necessity for matching baud rates between modems and associated user devices. The present invention also provides dual electronic serial data ports so that multiple devices can be connected to a single fiber optic interface device. Transmission of state operational signals over the fiber optic link allows automatic device switching and resource sharing and eliminates the need for mechanical switches. Simultaneous bi-directional transmission of data over a single fiber optic cable is achieved by use of a coupler device which is integrated in a standard fiber optic ferrule connector. The combined coupler/connector is convenient, inexpensive, and provides high optical coupling efficiency. The fiber optic cable is immune to electromagnetic and radio-frequency interference, short circuits, grounding problems and static discharges. The fiber optic cable eliminates environmental safety hazards permitting easy installation and provides data security by protecting information against eavesdropping and data link taps. The system provides a low-loss, high bandwidth communications link which can operate with no external power and can be used in a networking system permitting resource sharing over long distances. Also, the fiber optic cable can be routed with fewer constraints. For example, the cable can be routed within a suspended ceiling with fluorescent lighting and through elevator shafts, and is suitable for noisy environments, such as manufacturing. For additional installation flexibility, the fiber optic interface units can operate either in self-powered mode or be externally powered from the connected devices or by an auxiliary power module.

Objects of the Invention

It is therefore an object of the present invention to provide an improved fiber optic communications system.

Another object of the present invention is to provide a fiber optic communications system which is easy to maintain and install and is durable.

Another object of the present invention is to provide a fiber optic communications system which permits resource sharing between multiple user devices.

Another object of the presont invention is to nrovide a fiber optic communications system which is capable of high-speed, full duplex, asynchronous data transmission over a single fiber with automatic speed selection.

Additional objects, advantages and novel features of the invention are set forth in part in the description which follows and will be understood by those skilled in the art on examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realised and obtained by means of the instrumentalities and combinations particularly pointed cut in the appended claims.

Brief Description of the Drawings

An illustrative and presently preferred embodiment of the invention is shown in the accompanying drawings, wherein:

Fig. 1 comprises a schematic block diagram of the fiber optic interface device of the present invention.

Fig. 2 comprises a typical point-to-point data link.

Fig. 3 comprises a schematic block diagram of a multi-point data link.

Fig. 4 comprises a schematic block diagram Illustrating bridging between fiber optic interface devices.

Fig. 5 comprises a schematic block diagram of the fiber optic interface device.

Fig. 6 comprises a schematic diagram of the power conditioner and supply device.

Fig. 7 comprises a schematic diagram of the line receiver device.

Fig. 8 comprises a schematic diagram of the fiber receiver and data decoder.

Fig. 9 comprises a schematic block diagram of the state logic and control device.

Fig. 10 comprises a state diagram.

Fig. 11 comprises a schematic diagram of the LED control circuit.

Fig. 12 comprises a schematic diagram of the data steering device.

Fig. 13 comprises a schematic diagram of the line driver.

Fig. 14 comprises a schematic block diagram of the encoder and fiber transmitter. Fig. 15 comprises a schematic diagram of the transmitter circuit.

Fig. 16 comprises a schematic diagram of the sub-assembly device, splice bushing, fiber optic link cable and the transmitter receiver board.

Fig. 17 is a schematic diagram of a fiber optic link cable.

Fig. 18 is a schematic diagram of the manner in which the fiber optic lightguides are assembled prior to insertion in the ferrule.

Fig. 19 is a schematic cut-away diagram of the fiber optic lightguides mounted in the sub-assembly ferrule.

Fig. 20 is an end view of the sub-assembly ferrule and fiber optic lightguides mounted therein.

Fig. 21 is a schematic cut-away diagram of the fiber optic lightguides surrounded by a mode-stripping medium within the sub-assembly ferrule.

Fig. 22 is an end view of the sub-assembly ferrule and fiber optic lightguides surrounded with the mode-stripping medium.

Fig. 23 is a top view of the insert device.

Fig. 24 is an end view of the insert device.

Fig. 25 is a side view of the insert device.

Fig. 26 is an exploded view of the components of the receiver assembly.

Fig. 27 is an end view of the PIN diode and receive fibers.

Fig. 28 is a schematic cut-away view of the receiver assembly.

Fig. 29 is a cut-away view of the transmitter assembly.

Fig. 30 is a schematic side view of the fiber optic link cable illustrating cable end preparation prior to assembly on the cable ferrule.

Fig. 31 is an exploded schematic view of the fiber optic interface device. Fig. 32 is a graph of attenuation and reflection versus gap width in the combined coupler/connector.

Detailed Description of Invention Fig. 1 schematically illustrates the fiber optic interface 10 utilized in accordance with the present invention. As shown in Fig. 1, fiber optic interface 10, has two electronic serial data ports 12, 14, which may comprise a standard RS232C compatible, networkable link. The electronic serial data ports 12, 14, are also capable of providing network links via other interfaces including ETA standards RS422, RS423, and RS449and other electrical interfaces such as coaxial cable interfaces.

Fiber optic interface 10 provides an interface device for connecting various devices such as micro-computors, mini-computers, main frame computers, controllers, terminals, peripheral units, and other such devices, via a fiber optic, bi-directional cable, which is immune to electro-magnetic and radio-frequency interference, short circuits, grounding problems and static discharges. Additionally, the fiber optic link provides data security by protecting information against eavesdropping and data link taps. As illustrated in Fig. 1, the fiber optic link cable is coupled to the fiber optic interface 10 at fiber optic bi-directional input/output port 16. Fiber optic interface 10 provides interconnection with other fiber optic interface devices using bi-directional communications over a single, fiber optic cable. Bidirectional communication is accomplished by the use of an asymmetric bi-directional Y-coupler incorporated in a conventional ferrule connector which eliminates the necessity for separate fiber optic transmitter and receiver cables between fiber optic interface devices. Control and monitoring of device connections are accomplished by transmission of state operational signals ever the fiber optic link cable 20 (Fig. 2) . Dual serial data ports 12, 14 provide for resource sharing, network applications, and daisy-chaining, as illustrated in Figs. 2 through 4.

Fig. 2 illustrates a typical point-to-point data link between a user device 18 and a user device 26. User devices 18, 26 can comprise data processing units, such as microcomputers, minicomputers, main frame computers, etc. and/or peripheral devices, such as printers, terminals, etc. for connection in various combinations. User device 18 communicates with fiber optic interface 17 via electronic serial data communications link 19. As stated above, electronic serial data link 19 can comprise a standard RS232C transmission link or other suitable means for communicating electronic data in a serial fashion between user device 18 and fiber optic interface 17. Fiber optic interface 17 transforms the electronic serial data produced by user device 18 into optical transmission data, which is transmitted via fiber optic link cable 20. Additionally, fiber optic interface 17 receives optical data transmitted by fiber optic interface 22 and transforms the optical data into electronic serial data having the proper format for communication with user device 18. Fiber optic interface 22, electronic communications data link 24 and user device 26 function in the same manner. They provide a point-to-point, full duplex data communications link between user device 18 and user device 26. Fiber optic interface units 17, 22 utilize a bi-directional fiber optic coupler, described in more detail infra, which allows a single fiber to simultaneously transmit two-way optical information on a single optic fiber. This reduces the cost of the fiber optic communications link by one half over conventional dual fiber optic cable links. Fig. 3 is a schematic diagram of a multi-point data link using the fiber optic interface devices of the present invention. As illustrated in Fig. 3, user devices 32, 34 communicate with fiber optic interface device 28 via electronic serial data communication lines 36, 38 which couple to the dual electronic serial data ports provided in fiber optic interface device 28. The fiber optic interface devices 28 , 30 are coupled together by a single fiber optic cable 40, in the same manner as disclosed supra. User devices 42, 44 communicate with fiber optic interface 30 by way of electronic serial data communication lines 46, 48 in the same manner as electronic serial data communication lines 36 and 38. Using the fiber optic interface units 28, 30, any pair of the four user devices 32, 34, 42, 44 can inter-communicate at any given time. Other than the two interconnected devices, no other user devices on the network can access the inter-communications thereby assuring the privacy and security of each connection. Control signals generated by the user devices are communicated through the fiber optic, interfaces to control access between user devices. Logic circuitry in the fiber optic interface units provides protocol for determining which pair of user devices will be coupled together, in an automatic fashion, and thereby which can eliminate the need for mechanical switching.

Fig. 4 is a schematic diagram of the manner in which the fiber optic interface units of the present invention can be coupled together to provide daisy-chaining and bridging. As illustrated in Fig. 4, resource sharing of devices can be accomplished as in Fig. 3 at three or more locations (Fig. 4) , while simultaneously allowing the total communications link to be extended to a distance of approximately 10 km. Fig. 4 illustrates two user devices 60, 62 which communicate to fiber optic interface 50 by way of communication lines 64 and 66. At a different location, user devices 70, 72 communicate with fiber optic interface units 52, 54, respectively, via communication link 74, 76. Fiber optic cable 68 provides the communications link between the two locations. Fiber optic interface units 52, 54 are bridged together by the electronic serial data ports of each unit using electronic serial data link 78. Fiber optic interface 54 communicates with fiber optic interface 56 by way of fiber optic cable 57. User devices 80, 82 communicate with fiber optic interface 56 by way of data links 84, 86 in the same manner as fiber optic interface 50. Consequently, each of the user devices 60, 62, 70, 72, 80, 82 can be coupled to another device at one of the three locations to provide network resource sharing between user devices. For example, one or more computers could share the resources of one or more printers at various locations. Again, state signals generated by the user devices are transmitted throughout the network to provide a protocol for the communication links which are established in the network between user devices.

Electronics Fig. 5 is a schematic block diagram of the fiber optic interface device of the present invention. As illustrated in Fig. 5, the fiber optic interface device has a line receiver 90 for receiving "data" and "ready" signals via an RS232C port from a user device. Similarly, the fiber optic interface device has a line driver 92 for transmitting data and ready signals via RS232 outputs 93 to the user device. Since each fiber optic interface device has dual electronic serial data ports, such as RS232C ports 93, data and ready signals are indicated by channels A and B. In addition, a "ready-in-bridge" signal is received by line receiver 90 and produced by line driver 92 indicating the ready condition of an additional fiber optic interface device connected in a bridge configuration. The line receiver functions to adjust the electronic serial data input signal levels to levels suitable for use with the CMOS logic circuitry utilized in the fiber optic interface device. In a similar manner, line driver 92 adjusts the CMOS signal levels to BS232 voltage levels.

The fiber receive and data decode device 94 receives fiber optic input signals from fiber optic input lightguides 95, which uses two fibers, and produces a decoded fiber data signal which comprises an electronic serial data signal which has been decoded from the optical signal transmitted over the fiber optic input lightguides 95 using transition decoding. The fiber receive and data decode device also produces a fiber activity signal which indicates the approximate pulse repetition rate of fiber optic signals being received. Three different states can be indicated by the fiber activity signal. A zero state signifies that no activity is occurring over the fiber optic line, indicating a disruption in the fiber optic link. Thus continuity of the fiber optic link is constantly monitored even in the absence of actual transmission of data across the link. A mark 1 state indicates activity on a 40 millisecond basis, and a mark 2 state indicates activity on a 15 millisecond or less basis. The fiber activity signal is directed to state logic and control device 98, while the decoded fiber signal is directed to data steering device 100.

The fiber optic interface device 10 has an encoding and fiber transmitter device 96 which receives a "data out" fiber signal from the data steering device 100 and performs transition encoding for transmission in the proper format over fiber optic output lightguides 102. Transmit F1 and transmit F2 signals produced by data steering device 100 are also received by encoding and fiber transmitter 96 to control the transmission rate of encoding and fiber transmitter 96. The transmit F1 signal indicates a mark 1 transmission interval of 40 milliseconds between pulse, while the transmit F2 signal indicates a transmission interval of mark 2 or data at 15 milliseconds or less between pulses.

State logic and control device 98 receives ready signals from line receiver 90 and a fiber activity signal from fiber receive and data decode device 94. In response to these signals, the state logic and control device 98 utilizes a read-only memory (ROM) lock-up table to produce switching signals used by data steering device 100 and "ready out" signals transmitted by line driver 92 to control access between various user devices coupled in a network of fiber optic interface units. The state logic and control device 98 also produces an LED control signal and four OEM control signals which indicate the condition which has been established between fiber optic interface units. The OEM control signals are machine readable signals, while the LED control signal is applied to LED control device 104 which causes an LED to flash at three different rates to indicate the condition of the link. The transmit F1 and F2 signals comprise state operational signals which indicate the state of operation of the fiber optic interface device.

Fig. 5 also discloses power conditioner and supply device 106 which is capable of providing positive and negative voltage sources to power the fiber optic interface device 10 from either an auxiliary power source or from the electronic serial data RS232 inputs. A power-up reset signal is also supplied by the power conditioner and supply device 106 which indicates the availability of power from the power supply circuitry.

Fig. 6 is a schematic circuit diagram of power conditioner and supply device 106. The power conditioner and supply device 106 is capable of deriving power from the RS232 input lines 108 which comprise the "ready-in-A", "ready-in-B", "ready-in-auxiliary-A", "ready-in-auxiliary-B", "data-in-A" and "data-in-B" lines. These signals are all produced by the user devices. The terminal ready signals 110 are coupled to current limiting resistors 112 and diodes 114 to accumulate positive voltage signals. In a similar manner, data signals 116 are coupled through current limiting resistors 118 and diodes 122 to collect positive voltage signals, and through diodes 120 to accumulate minus voltage signals. Positive voltage signals at the output of diodes 122 are applied via line 124 to the positive voltage signals supplied by the terminal ready signals 110. Isolation resistor 127 isolates the positive voltage signals collected on data terminal line 116 from the positive voltage signals collected from the terminal ready lines 110. Fositive voltage at the output of diodes 122 is also applied to voltage inverter 126 which inverts the plus voltage to a minus voltage for application to the minus voltage produced at the output of diode summing circuit 120. Current limiter circuits 128, 130 limit the amount of current supplied by terminal ready lines 110 and data terminal lines 116, respectively, during the power-up phase. Current limiters 128, 130 function to place 1 K ohm resistors 136, 138 in series with the positive and negative voltage supply sources during the power-up phase of the fiber optic interface unit. As soon as the power-up phase is over, transistors 148, 150 are driven into saturation by connecting the base terminals to each other by way of analog switch 140, via lines 132, 134. Termination of the power-up phase is indicated by a power-up reset signal 142 produced by comparator 144. The positive voltage level is sampled at the output of current limiter 128 and compared in comparator 144 with a reference voltage produced by voltage generator 146. When the power drain exceeds the capacity of the power supply, causing the positive voltage level to fall below the reference voltage level, the power-up reset level is removed, thereby disabling transmission of fiber optic output data and forcing the unit to standby state. The power-up reset signal is applied to analog switch 140 via conductor 152 to connect conductors 132, 134.

Auxiliary power is available through the J3, J4 pins and unused pins of the RS232 port. LC filtering circuits 154, 156 filter the auxiliary power and protect the remainder of the circuit from transients. Current limiting resistors 158, 160 limit the current of the auxiliary power supply. Conditioned auxiliary power is available to the fiber optic interface device 10 through connections 162, 164. Diodes 166, 168 provide coupling between the auxiliary power source and the power derived from the terminal ready and data input signals. The power derived from the terminal ready and data input signals is combined with the auxiliary power at nodes 170, 172. Zener diodes 174, 176 control the positive and negative supply voltages, while capacitors 178, 180 filter the output voltage signal.

Fig. 7 comprises a schematic diagram of line receiver device 90. The line receiver device 90 receives five input signals from a user device via the RS232 input. These five input signals comprise the "ready-in-bridge", "ready-in-B", "ready-in-A", "data-in-A", and "data-in-B" signals. The five input signals to the line receiver device 90 originate from five RS232 inputs provided by the user equipment or a bridged fiber optic interface device 10. Transistor switching network 192 comprises a single common emitter amplifier for each channel of input data. The line receiver functions as a low power RS232 line receiver which detects a "1" as any input greater than approximately 2.1 volts +.5 volts. Any input less than .8 volts ±.5 volts is detected as a "0". These data signals are low-pass filtered by RC filters 182, 186. Resistor network 186, 188 provides a resistive divider network which functions to adjust the voltage of the input signals to appropriate levels to drive transistor switches 192 . The voltage at the collectors of 192 is appropriate to interface with CMOS circuitry used throughout the remainder of the device. The circuit is protected against large and negative voltage signals provided on the RS232 input lines by diode network 190. Open collector pull-up resistors 194 provide the bias current for transistor switching network 192.

The fiber receiver and data decoder 94 is disclosed in Fig. 8. The fiber receiver and data decoder 94 functions to receive an optical signal 200 and discriminate valid optical pulses from reflected pulses. Valid pulses are then decoded to provide CMOS level encoding utilized by the fiber optic interface device 10. An optical pulse 200 representative of a logic 0 is encoded for fiber optic transmission as two 500 nanosecond pulses separated by 1.5 microseconds (a double pulse). A logic 1 is encoded by a single 500 nanosecond pulse. The fiber receive and data decoder 94 decodes the fiber signal to produce a CMOS level 1 when a single pulse is detected and a CMOS level 0 when a double pulse is detected.

Referring to Fig. 8, PIN photo diode 202 receives the optical signal 200 transmitted by the fiber optic link cable and produces an electric pulse signal in response to the optical signal 200. The PIN photo diode 202 is biased with a supply voltage. When an optical signal impinges upon PIN diode 202, current flows causing a voltage to be generated across resistor 204. Stray capacitance 206 limits the response time of the photo diode 202. Since the current level of the PIN photo diode 202 is small, amplifier stages 208, 210 are provided to increase the current pulse level. Amplifier 208 is a unity gain buffer, while amplifier 210 comprises an inverting amplifier having a gain of approximately -6. Capacitor 212 provides AC coupling between amplifier 208 and amplifier 210. Feedback is provided between the output of amplifier 210 and the input of amplifier 208 via resistor 214 and capacitor 216 to improve the pulse response of the fiber receiver. The output of the amplification stages is AC coupled to the remainder of the circuit by capacitor 218. The detected signal is then applied to bias network 220. Resistors 222 and 224 provide a voltage divider network to generate a reference voltage signal across resistor 224. Capacitor 225 ties resistor 224 to AC ground while resistor 226 maintains resistor 224 at a positive DC voltage level.

Resistor 224 establishes the threshold of comparator 228. The selection of the threshold level is critical to the proper operation of the fiber receiver and data decoder 94. The threshold must be chosen such that the largest reflected signal is not detected by the receiver, while the smallest non-reflected signal is detected.

Comparator 228 comprises a low-power, bi-polar comparator which is capable of producing an output signal whenever the threshold level established by resistor 224 is exceeded on data line 230. Comparator output 232 is applied to decoder circuit 234 which differentiates between single pulses and double pulses. Comparator output 232 is applied to the input of toggle flip flop 236 and one-shot multi-vibrator 238. Toggle flip flop 236 changes state at output 240 each time a pulse is applied to input 242. The initial pulse received by toggle flip flop 236 causes the toggle flip flop 236 to change from a 0 state to a 1 state at output 240. If a second pulse is applied to toggle flip flop 236, output 240 changes from a 1 state to a 0 state. One-shot multivibrator 238 produces a pulse at the end of three microseconds from the detection of the first pulse to latch data provided at output 240. Consequently, if only one pulse is received by toggle flip flop 236 during the three microsecond period, output 250 of flip flop 248 will have a 1 output. If two pulses are received by toggle flip flop 236 during the 3 microsecond period, flip flop 248 will be latched with a 0 output. One-shot multivibrator 238 also functions to clear toggle flip flop 236 on reset line 244. Output 250 therefore provides a decoded fiber signal indicating either 0 or 1 states for single or double pulses, respectively. One-shot multivibrator 238 also produces a fiber activity signal 252 indicative of the pulse repetition frequency of data detected by one one-shot multivibrator 238. One-shot multivibrator 238 produces a pulse that occurs each time either a single or a double pulse is detected at the output of comparator 228. The fiber activity signal therefore indicates the rate of occurrence of data provided on the fiber optic input. Fig. 9 is a schematic diagram of state logic and control device 98. State logic and control device 98 comprises a synchronous state device. Clock 254 comprises a 100 hertz clock which generates a clock signal which is applied to KA 1/KA 2 detector 256, data-in-latch 258, power control 260, output latch 262 and output latch 264. Clock 254 comprises an RC oscillator which uses a CMOS timer. Clock 254 synchronizes the entire state logic of state logic and control device 98. Fiber activity signal 252 from one-shot multivibrator 238 of fiber receiver and data decoder 94 (Fig. 8) is applied to the input of KA I/KA II detector 256. At each clock pulse produced by clock 254, detector 256 provides data which is latched indata-in-latch 258 pertaining to the fiber activity state, i.e., either KA I or KA II. Detector 256 distinguishes between 3 types of fiber activity; namely data arriving at the KA I rate (about every 40 ms) , data arriving at the KA II rate (about every 15 ms) , and no data on the fiber optic cable. A down counter is used to implement the KA I/KA II detector 256. In a similar manner, data-in-latch 258 latches the current state of data from ready-in-A input 266, ready-in-B input 268 and ready-in-bridge input 270.

The five latched signals from data-in-latch 258, comprising the two fiber activity signals (KA I and KA II) and the ready signals (reday-in-A, ready-in-B, and ready-in-bridge), are applied as an address to read-only-memory 272. The additional six address signals are comprised of a phase signal and five feedback signals.

The phase signal addresses the ROM such that 16 output bits pre generated from the 8 output bits of the ROM 272. The data contained in ROM 272 comprises a state logical decision table which produces an 8 bit output. Two sets of 8 bit output signals are produced by ROM 262 for each address location in accordance with phase signal 265. When the phase signal 265 is low, output latch 262 is enabled via connector 261 and a first set of 8 bit data is latched into output latch 262. When the phase signal 265 is high, output latch 264 is enabled via connector 263 and a second set of 8 bit data is latched output latch 264.

Alternatively, the state logic and control device can comprise an asynchronous combinational logic device which can employ LSI technology. Such a device utilizes a series of combinational logic gates and flip flops to produce the switching signals, ready-out signals and fiber optic data transmission rate signals (transmit F1 and transmit F2) .

The feedback signals (S0, S1, S2, F2-1, and F2-2) allow outputs to be generated that are a function of past inputs as well as current inputs. The eleven input data is an address of the memory location to be accessed in the read-only-memory. Read-only memory 272 utilizes a 2048 times 8 bit memory.

Power control device 260 applies power to readonly-memory 272 only when access must be made. At other times, ROM 272 is turned off. This provides a power savings of 3 orders of magnitude over a continuous use of the read only memory. In operation, power control device 260 applies power to ROM 272 so that access can be made. The output data is then Latched on output latches 262, 264 and power is then removed from ROM 272. Since 16 bits of output data is required, the phase signal 265 causes the ROM 272 to operate in two phases, with 8 bits read from memory during each phase and alternatively applied to output latches 262, 264.

Output latch 262 provides 8 output signals. Three switching signals, i.e., "switch A-B", "switch A-F (fiber optics), and "switch B-F", are applied to data steering device 100. Transmit F1 and transmit F2 signals are applied to encoding and fiber transmitter 96. Transmit F1 and transmit F2 comprise state operational signals indicating the operational state of the fiber optic interface device to cause encoding and fiber transmitter device 96 to generate transmission signals at the KA I or KA II data transmission. Ready-out-A, ready-out-B and ready-out-bridge are applied to line driver 92. The ready-out-A signal is a CMOS signal indicating the ready-out-state of the A port of the fiber optic interface device 10. The ready-out-B indicates the ready-out-state of the B port. The ready-out-bridge signal is a CMOS signal used to control bridging. The switch A-B signal is a CMOS signal used to establish a full duplex data path between ports A and B. The switch A-F signal is a CMOS signal used to establish a full duplex data path between the A port and the fiber optics signal. The switch B-F is a CMOS signal used to establish a full duplex data path between the B port and the fiber optics signal. The transmit F1 and transmit F2 signals are CMOS signals which indicate to the transmitter to re-enforce data at the KA I or KA II rate, respectively.

Output latch 264 produces three LED control signals to indicate the current operational state of the fiber optic interface device 10. Three state bits, S0, S1 and S2 are generated by ROM 272 to keep track of the current state of the state logic and control device. Two additional feedback bits, F2-1 and F2-2, are used to keep track of the fiber activity state (KA I, KA II, or no activity).

The three state bits S0, Si and S2, together with one LED bit appear on the OEM control signal connector disclosed in Fig. 5.

The three state bits, S0, S1, and S2, encode the eight operational states of the fiber optic interface device. These states are numbered as folloss: NUMBER STATE

0 Stand-by 1 Active 2 Bridging Active

3 Connect A-to-B 4 Link A 5 Connect F to A 6 Link B 7 Connect F to B

The fiber optic interface unit can assume one of eight states of operation, determined by the status and history of the ready-in-A, ready-in-B, ready-in-bridge and fiber optic link signals. In the standby state, the unit is powered but all ready-in (A, B, bridge) signals are off and no signal is being received by the fiber. In the active state, three conditions exist; active A, active B and active F. In these states, the unit is powered and one ready-in (A, B, bridge, or F signal) is on. In the linking state, two linking conditions exist; linking A and linking B. In these states, the unit is powered on, a ready-in signal is received and an active fiber signal is received. The fiber optic interface device 10 has not yet received acknowledgement of an end to end connection. The bridge-active-A state occurs only when units are bridged. In this state, the A port is ready and the bridge signal from the other unit is active. In the connected state, three connected conditions exist; connected A-B, connected A-F (fiber-optics), and connected B-F (fiber-optics).

The following table summarizes the state of the fiber optic interface device 10 and the inputs and outputs associated with each piece therein.

Inputs : d don't care

IN F=0 no signal in last 150 millisec; IN F=1 reception spaced by 30 to 150 ms. IN F=2 reception spaced by less than 30 ms.

Outputs :

A The data input on Part A will be signalled over the indicated output port

B The data input on Port B will be signalled over the indicated output port

F The data input on Port F will be signalled over the indicated output port

A+B The signal "OR" of the date input on port

A and B will be signalled over the fiber port

A+F The logical "OR" of the data input on port A and F will be signalled over the

B port

B+F The logical "OR" of the data input on port B and F will be signalled over the

A port

MKl A logical O is sent over fiber at the

KA I rate

LED

ON Flash 100 times/sec (appears on steady) FST Flash 10 times/ sec SLW Flash 1 time/sec MK A logical 0 sent over RS-212 interface Notice from the preceding table that two distinct operational modes exist for the fiber optic interface device 10. The device will operate in a secure full duplex mode with any two devices on a network able to communicate at any time. It will also operate in a broadcast mode with one device talking and the remaining device listening.

When operating for secure full duplex operation the device establishes a connection between the first two devices connected to a network that request a connection. In secure full duplex only the two connected devices user devices receive data. Devices request a connection by setting a ready-in lead high. The device 10 uses the LED status indicator to inform the user about the status of other devices on the network, as well as about the status of the fiber Linking a device with its neighbor. In the case that two devices request a connection to a third previously ready resource, the following convention is used to resolve contention:

Case 1) A Remote device is ready, and both A and B request service simultaneously: Device B is connected to the remote device;

Case 2) A is ready, and both B and a remote device request service simultaneously: Device B is connected to device A;

Case 3) B is ready, and both A and a remote device request service simultaneously: Device A is connected to device B;

Case 4) Device A or B is ready, and two remote devices, one on either side of this node request service simultaneously: the remote device closest to this node will be connected to device A or B. (Closest is used here to to mean least number of intervening nodes.) ;

Case 5) Device A or B is ready, and two remote devices, both on the same side of this node request service simultaneously: the connection can not be predicted; either the device closes to this node will be connected to device A or B, or the two devices requesting service will be connected to each other (established in the state logic control).

Operating in the broadcast mode can be performed when no devices attached to the network have activated Ready-In, or when the transmitting device has activated Ready-In. All devices but the transmitting device must have Data-in at "mark" (logical 0) . Any data sent by the transmitting device is received at all other ports on the network. Broadcast operation will not work if more than one device transmits (has Data-in not at "mark") at any time or if any non-transmitting device has an active Ready-In.

An alternative embodiment employs a board version which is intended for installation into a host product. The board version has a single connector providing the electrical interface. Using wiring options, the user may configure the board version to work in several different operational modes. The two ports of the board version are designated A and B. The A port is a TTL level port. (TTL is an electrical interface standard typified by 0 to .8 volts as a "0" and 2.1 to 5 volts as a "1".) The B port, which is also used for daisy-chaining units together, may be configured as an RS-232 port or as a bridge-only port. (RS-232 is an electrical interface standard typified by -3 to -15 volts as a "off" or "mark" and +3 to +15 volts as an "on" or "space".)

Two options are available for powering the board version: with a +5 and +/-12 V supply, or with a +5 and +12 V supply. The +5, +/-12 V supply allows TTL operation of the A port and RS-232 operation of the B port. The +5 and +12 V option allows only the TTL operation of the A port (RS-232 operation of the B port is not supported, but the B port can still be used as a bridge).

The following table identifies each I/D signal, its pin, and the signal name for the board version:

Type Pin Signal Name

TTL 16 Data in A

TTL 18 Ready in A

TTL 11 Data out A

TTL 14 Ready out A

RS-232 2 Data in B

RS-232 3 Ready in B

RS-232 12 Ready in bridge

RS-232 1 Data out B

RS-232 3 Ready out B

RS-232 17 Ready out bridge

TTL 9 State-0

TTL 10 State-1

TTL 8 State-2

TTL 6 State-3

Power 19 Ground

Power 5 PWR+In

Power 20 PWR-In

Power 15 +5V

Power 7 PwrProg1/Ground

Power 13 PwrProg2

Two options are available for PWR-In:

RS-232 Operation The PWR-In input must be less than -10V and greater than -15V referenced to ground, (typically -12V with less than 2V ripple). Zener shunt regulation is used so if the input voltage increases the required current will also increase. At -10 V input 20 mA is required, at -12 V input, 45 mA is required and at -15 V input 100 mA is required.

TTL Only Operation The PWR-In input is connected to ground, and pins 7 and 13 are connected together. The selection of the power options, e.g. TTL only operation or RS-232 operation, is made with two power option programming pins. These pins are used to select the minus voltage powering option. Minus Voltage Operation:

Pins 7 and 19 are connected to ground Pin 13 is left open Plus Voltage Only Operation:

Pin 19 is connected to ground Pins 7 and 13 are connected together, but not to anything else.

Four signals are available to the user which completely describe the state of operation of the board version. These indicators State-3, State-2, State-1, and State-0 make up a 4-bit code. State-3 is the most significant bit, and State-0 is the least significant bit.

The codes are defined as follows:

Operational States Code State Meaning

0 Standby No Fiber Signal Received, No Ready Input

1 Active If No Ready Inputs - KA I on fiber if one Ready Input - no fiber signal

2 Bridge Act A No Fiber Input, Ready-In-Bridge and

Ready-In-A high

3 Connect A-B Connection between A and B ports

4 Not Used

5 Connect A-F Connection between A and F ports

6 Link B Ready-In-Bridge high and KA I on fiber

7 Connect B-F Connection between B and F ports

8 Not Used

9 Active No Ready Inputs, KA II on fiber

10 Bridge Act A KA I on fiber, Ready-in-Bridge and

Ready-In-A high

11 Not Used

12 Link A Ready-In-A high and KA I on fiber

13 Not Used

14 Link B Ready-In Bridge high and KA I on fiber

15 Not Used

Fig. 10 comprises an operational, state diagram of the operation of the present invention which complements the above table to fully describe the operation of the synchronous state machine.

Fig. 11 comprises a schematic diagram of the LED control device of the present invention. The LED control circuit 104 drives a diaσnostic, light emitting diode (LED) which is visible to the user at one of three flash rates to indicate the current state of the fiber optic interface device 10. A slow flash of about 1 flash per second indicates an end to end connection has been established with a user device coupled to another fiber optic interface unit. A fast flash, of about 10 flashes per second, indicates a fiber link is in place between connected fiber optic interface units. A flash rate of 100 flashes per second which appears to the user as a steady "ON" signal indicates a common resource is available on the network. LED "off" indicates interruption in the fiber link between two interface devices 10 or it represents that the interface devices are off (not powered).

State logic and control device 98 produces three LED control signals 278, 280, and 282. These control signals are applied to a RC oscillator which utilizes a comparator device 290. The oscillator circuit is capable of producing three flash rates, dependent upon the RC time constant of resistors 284, 286, 288, and capacitor 292. For example, the RC time constant of resistor 284 and capacitor 292 is different from the RC time constant of resistor 288 and capacitor 292. Consequently, different oscillation rates can be produced by applying inputs to the various control lines 278, 280, and 282. Diodes 294 provide protection from the reverse flow of current, whenever lines 280, 282 are not activated. Feedback resistors 296, 298 provide the appropriate feedback to produce oscillation. A bias voltage is provided on line 284 to resistor 302. Base resistor 304 limits the current to the base of transistors 306 and 308.

The LED control can operate the LED at two different brightness levels depending upon whether external auxiliary power is available. If auxiliary power is available, current passes through both transistors 306 and 308 to provide more current to LED 276. If auxiliary power is not available, only transistor 306 conducts at a much lower current level, so that LED 276 has a much lower brightness level. Both transistors 306 and 308 are driven to saturation when the voltage level goes low at base resistor 304 assuming V+ power and Aux + power are available.

Fig. 12 is a schematic diagram of data steering device 100. Switching signals from state logic and control device 93 are applied to the data steering device 100 to control the data channel to be transmitted over line driver 92 and encoding and fiber transmitter 96. The switching control signals comprise switch A-F, switch B-F, switch A-B. As illustrated in Fig. 12, the three switching control signals are applied to the data steering device 100 in conjunction with the data-in-A, data-in-B, and data-in-F signals. The data signals and switching control signals are applied to six AND gates 314, 316, 318, 320, 322, and 324. The output of the AND gates is applied to OR gates 326, 328, and 330 to produce either a data-out-A, data-out-B, or fiber-data-out signal. The switching control signals function to select the data channel which is to be activated at the output of the full duplex data steering device 100. For example, when switch A-B is active, data-in-A is connected to data-out-B and data-in-B is connected to data-out-A. The data-out-A and data-out-B channels are applied to line driver 92, while the data-out-F signal is applied to encoding and fiber transmitter 96 for transmission over fiber optic output cable (transmit lightguide) 102.

Fig. 13 illustrates one channel of line driver 92. Line driver 92 generates five RS232 outputs from five CMOS inputs. The five CMOS inputs comprise data-cut-A, data-out-B, ready-out A, ready-out B, and ready-out bridge signals. Each signal is applied to a separate channel, such as the channel illustrated in Fig. 13. The data and ready signals are applied to the driver-in line 332 to operate CMOS switch 334. A high level on driver input 332 causes CMOS switch 334 to be coupled to positive voltage supply 336 in the manner illustrated in Fig. 13, while a low level causes CMOS switch 334 to couple to a negative voltage supply 338. The voltage levels provided by positive voltage supply 336 and negative voltage supply 338 cause current to flow through current-limiting resistors 340 and 342 to produce RS232 voltage levels and impedances at output 344. The voltage supply sources provided at 336, 338 are capable of providing the drive capability necessary for RS232 communications. Diodes 346, 348 provide protection from the presence of voltage levels at output 344.

The line driver circuit 92 has the ability to operate with two different source impedances depending upon the availability of external auxiliary power. If external auxiliary power is available, the output source impedance is approximately 1.4K ohms. Without external auxiliary power, the output source impedance increases to approximately 3.2K ohms as a result of resistors 354, 356. Diodes 358, 360 isolate the auxiliary power supply when auxiliary voltages are not available. The change of impedance limits the amount of power that is supplied to all of the RS232 outputs when external power is not available.

Fig. 14 schematically illustrates the encoding and fiber transmitter 96. The encoding and fiber transmitter device uses transition encoding to encode

CMOS logic signals produced by the fiber optic interface device 10 into a transition code which is transmitted by transmitter circuit 362. In the event no new data is available, marking signals are sent down the fiber optic cable in response to pulses produced by mark 1/mark 2 oscillator 364. Fiber optic data signals are received from data steering device 100 and are applied to input 366 of encoder and fiber transmitter

96. The fiber optic data signals are applied to edge detector 368 and latch 372. Edge detector 368 produces a pulse for data transitions from either positive to negative or negative to positive. Each pulse from the edge detector 368 fires one-shot multivibrator 370 which produces a pulse lasting for 6 microseconds. At the end of the 6 microsecond period, latch 372 latches the data at input 374 which produces a corresponding output at output 376 which comprises either a low or high signal indicating a logic 1 or 0. The logic 1 or

0 is then encoded as either a single pulse for a logic 1 or a double pulse for a logic 0. The encoded signal is then sent to transmitter circuit 362 for transmission over the fiber optic cable. The function of the one-shot multivibrator is to ensure that pulses do not occur at a rate faster than 6 microseconds. Since the edge detector fires on both positive to negative and negative to positive transitions, one-shot multivibrator causes both logic 1 and logic 0 levels to be latched in latch 372. The mark 1/mark 2 oscillator 364 runs at a selected rate determined by the transmit F1 signal at input 380 or the transmit F2 signal at input 382. Summing circuit transmits the mark 1/mark 2 oscillator signal and changes in data levels are occurring at input 366 to 370. The transmit F1 and transmit F2 signals are generated by the state logic and control device 98 which determines the pulse repetition rate of the idling pulses. to be transmitted by transmitter circuit 362. This means that if no activity is on fiber optic data out 366, the last level is repeated at the mark 1 or mark 2 rate.

Fig. 15 comprises a schematic diagram of transmitter circuit 362. Fig. 15 comprises a schematic illustration oftransmitter circuit 362. The encoded fiber optic signal is received from the encoded fiber transmitter circuit and applied to the gate of a field effect transistor 384. Current limiting resistor 380 is connected between a voltage source and an infrared LED 382. Encoded pulses at input 386 cause field effect transistor 384 to conduct causing current to flow through LED 382 to produce illumination.

Fiber Optics The present invention uses functionally integrated, reconfigurable, fiber optic assemblies which allow key fiber optic functions to be efficiently integrated. Typical prior art fiber optic interconnect systems utilize many types of active (electro-optical) and passive (optical) components. Active components include transmitters, capable of emitting modulated light, and receivers capable of detecting light. Passive components are used to guide, couple and direct light, and such components include optical fibers (cables), connectors and couplers. Connectors provide a means for connecting and disconnecting fiber optic cables from other active or passive components and can employ commercially available connector devices such as ferrules. Couplers function to coup'le light from active or passive components to other active or passive components.

The number of passive components in a transmission path has direct bearing on the losses of light caused by optical discontinuities (e.g., glass/air interfaces), divergence and absorption of light, and mechanical misalignment. The fewer the number of discrete components used in a system, the lower the systems losses, complexity and cost.

Physical integration of the following functions, in accordance with the present invention, decreases the number of discrete components, and consequently reduces systems losses, complexity and cost. Accordingly, the present invention uses a sub-assembly device employing a combination coupler/connector which can integrate the following functions:

1. Launching: The injection of emitted light from a transmitter onto one of several fibers.

2. Reception: The routing of light onto a detector.

3. Splitting: The branching of transmitted light into several directions.

4. Joining: The merging of several light transmission paths into a single transmission path.

5. Reconfiguration: The altering of a transmission path, either abruptly, e.g., by connecting or disconnecting, or gradually, e.g., by adjustment. 6. Feedback: The looping back of a portion of transmitted light for monitoring, self- alignment, or self-test. The feedback function is often associated with the reconfiguration function.

To effect the desired functions in accordance with the present invention, fibers and groups of fibers are positioned against each other and against active components so that light is appropriately guided through the fibers and transferred between other fibers and the active components. Relative movement of such fibers and groups of fibers provides for reconfigurability. Light is transferred between fibers by aligning and abutting ends of the fibers with one another. The gap between the facing fiber ends may be filled with air, a recladding material, a refractive index matching material, an optical material, or a combination of such materials. Spaces between fibers in a parallel group may be filled with a recladding material or a mode stripping material.

In general, the manner of implementation of the various functions recited above are described, in general, below.

The function of launching is accomplished by positioning the faces of one or several fibers against a transmitter. Light emitting diodes (LED's) having a suitable wavelength (e.g., 820 nanometers), are suitable for use as transmitters due to the ability of the optic fibers to transmit light with high efficiency at such IR frequencies. Of these, micro-lensed devices which incorporate an optical focusing sphere have been found particularly effective for launching light in fiber optics. Both windowed (hermeti- cally sealed) or windowless active devices may be used. Exposed fiber ends are surrounded by a recladding material and aligned for the desired amount of light to be launched.

The reception function is implemented by positioning one or more fiber ends in facing alignment with a detector which can comprise a PIN photo diode. The space between the fibers and the photo detectors is filled with an index matching material and a conformal material if the detector chip is exposed.

The splitting function is performed by positioning a fiber, or group of fibers, against at least two other fibers so that any 1 ight emitted from the fiber or first group of fibers split among the other fibers. Various splitting ratios can be achieved by utilizing fibers of different diameters and varying position.

The joining function comprises the reverse function of the splitting function, whereby light from more than one fiber is directed onto another fiber, or another group of fibers.

The reconfiguration function is accomplished by eiltering the relative positions between groups of fibers or between fibers in active components to change the pattern of light transferred between groups of fibers or between fibers and active components. The change can be either binary, i.e., on or off, or continuous, e.g., over a range of splitting ratios. The change can be introduced manually, e.g., on mating a connector, or automatically, e.g., by an electric actuator.

The feedback function is accomplished by splitting a portion of a transmitted signal so that one output fiber is connected to a local receiver.

The single fiber optic link cable is used to communicate bi-directionally between a plurality of fiber optic interface units 10. As illustrated in Fig. 5, each fiber optic interface device 10 has fiber optic input lightguides 95 and a fiber optic output lightguide 102. In order for data to be transmitted en a single fiber optic cable, fiber optic input lightguides 95 and fiber optic output lightguide 102 must be coupled to a single fiber optic link cable. The present invention combines an asymmetric bi-directional Y-coupler device with a commercially available fiber optic connector ferrule, in a single device, to reduce attenuation due to lightguide coupling and reflection. Reflections at the combined coupler/connector interface are reduced in accordance with the present invention by mean recladding and/or mode stripping media which surround the individual glass fibers, and by precise longitudinal spacing providing a predetermined separation gap between the ends of the fibers and which is established by relative position of the fiber optic interface device ferrule and the single fiber optic link cable ferrule. The individual glass fibers can be glass fibers with soft cladding stripped therefrom, glass fibers with hard cladding intact, or a combination thereof. When a group of fiber lightguides is assembled in a coupler, such as in the asymmetric bi-directional coupler/connector of the present invention, a value known as the packing ratio is used to define the coupler's effectiveness. This is the ratio of the light accepting or transmitting areas of the cores, at the face of the coupler, to the overall area onto which light may fall or be transmitted. The more spacing between the adjacent cores, the lower the packing ratio and the relatively lesser portion of light guided into the cores. For best packing efficiency, a tight alignment of lightguide cores, stripped of all cladding, would be desirable. Such close contact, however, would lead to a leakage of light between the cores resulting in excessive reflection into the input lightguides. It has been determined that for optimum results the cores should be separated by cladding having a thickness of between 4 to 15%, and at any rate no more of 30%, of the core diameter.

Another important consideration is the spacing between the faces of the coupler, i.e. the longitudinal separation of the lightguides and link cable. The designed spacing is related to the geometry of the gap and diameter of the fibers. With tight spacing, much of the reflection falls back on the output lightguide from where it was transmitted. As the gap increases, some reflected light reaches the input lightguides where it can be ultimately confused for an incoming transmission over the link cable.

Fig. 32 represents plots of relative forward attenuation and relative reflection of bi-directional fiber optic links, versus the width of the gap between the face of the coupler assembly and the face of the link cable. Each test link consisted of a length of 200 micron PCS cable, terminated according to the illustration in Fig. 30, connected to a bi-directional coupler at each end. A calibrated LED transmitter was used to launch a constant amount of light power into the transmit lightguide at the near end of the link and received power was measured from the receive lightguide at the far end of the link. A simultaneously reflected power reading was taken at the receive lightguide of the near end coupler. A dual head Photodyne model 22XLA fiber optic multimeter was used for all power readings. Two experimental "reclad" couplers built as depicted in Fig. 19, and two experimental "mode-stripping" couplers built essentially in accordance with Fig. 21, were tested. Four link configurations were measured, namely:

1) A one kilometer link with two "reclad" couplers, one at the each end;

2) A 100 ft. link with two "reclad" couplers;

3) A one kilometer link with two "mode-stripping" couplers;

4) A 100 ft. link with two "mode-stripping" couplers. Each link was measured twice in both directions and averages computed of the four readings.

Referring again to Fig. 32, function 550 illustrates the effect of the near-end gap (between the transmitting coupler and the link cable) on the signal received over a 1 km "reclad" link, relative to signal power measured with 1 micron gaps (=OdB) . It shows a flat level of -0.8 dB for gaps between 10 and 50 microns, beyond which the signal drops with increasing gap spacing.

Function 552 illustrates the effect of the far-end gap measured in the same set-up.

Function 554 illustrates a near-end reflection πeasured concurrently with function 550, relative to the reflection at 1 micron (=OdB) .

Function 554 shows reflection increasing considerably as the gap increases beyond 50 micron.

Function 556 discloses the signal energy received over a 100 ft link using a "reclad" coupler, versus the near gap, relative to the 1 km value at 1 micron (= OdB reference).

Function 558 discloses the near end reflection, with a 100 ft link using "reclad" couplers, measured concurrently with function 556. For the near end gap of between 5 and 40 micron this reflection is fairly constant and it is approximately 3 dB higher than reflection from a kilometer link. The assumption is that in a short link reflection from the far end of the cable is added to, and causes the measured increase of, the reflection at the near end.

Function 560 discloses the reception over a 1 km link using "mode-stripping" couplers, measured under conditions otherwise identical to function 550.

Function 562 discloses the reflection from a 1 km link with "mode-stripping" couplers, measured concurrently with function 560. Function 564 is a plot of reception over a 100 ft. link using "mode-stripping" couplers, measured to confirm the effect of mode-stripping on a short link loss (Ref. the table below). From these results it has been determined that it is desirable to maintain the face to face spacing, in the present invention, between 5 and 40 microns.

Fig. 32 indicates that the baseline reflection from the shorter, 100 ft cable, is about 3 dB higher than from the long cable. This is due to the reflection of light from the far end of the cable which is understandably more prominent in the shorter cable. This effect can be controlled, in part, by defining a minimum attenuation of the link, cable, e.g. minimum attenuation can be provided by using a minimum length cable. The bulk of customer interconnect requirements are between 100 ft and 1 km which is the range of the current invention using standard silica core cable. More lorsy media, such as plastic core cables, can be used to maintain adequate reflection return attenuation in very short links (below 100 ft). Reflection can be further controlled by the finish as well as separation and alignment of the mating faces. As the link operates bi-directionally, the finish and separation gap of the end surfaces should be the same at both ends. It has been found that by judicious choice of surface roughness as set forth infra, at both the near and far end faces, the aggregate reflection can be maintained at an adequate level, even with short cables. Reduction in internal reflection within the link cable as a result of a predetermined surface roughness, e.g. rough polishing with 3 micron abrasive paper, is believed to result from the generation of higher order modes due to the angle at which transmitted radiation is reflected from the end surfaces of the link cable. These higher order modes of reflected radiation attenuate rapidly as they propagate through the link cable due to the higher angle of incidence with the link cable surface which causes attenuation at a rate proportional to the angle of incidence.

Additional control of reflection can be accomplished by surrounding a section of the lightguides with mode stripping medium. Light propagates through large core light guides in many modes distinguished by the angle between its trajectory and the direction of the lightguide. Zero order mode is defined as a mode propagating along the axis of the lightguide. The highest order modes hit the core's surface close to the critical angle of total internal reflection. Due to surface imperfections, high order modes tend to leak into the cladding and eventually get absorbed. It has been observed that after several hundred feet the highest modes are substantially removed from the link cable.

Mode stripping is a process whereby the removal of high order modes can be accelerated over a relatively short section of lightguide by reducing the thickness of cladding and surrounding it with a light absorbing material of higher index of retraction than the cladding. Such material is called a mode stripping medium.

The purpose of mode stripping is to remove, within the coupler, those higher order modes which are more likely to leak from one lightguide to another and cause harmful reflection, yet which contribute little to overall transmission over the longest link. Mode stripping increases the loss of shorter links since it removes the higher order modes normally capable of carrying some light across the short cable. The following table shows the effect of mode stripping in the current invention, where it favorably reduces reflection as well as the range of signal power between the shortest and the longest link. Mode Reccsived Power Dynamic Reflection

Stripping: 100 ft 1 km Range @ 1 km

No -16 dBm -26 dBm 10 dB -41 dBm

Yes -18 dBm -27 dBm 8dB -43 dBm

Additionally, the manner in which the fiber optic link cable is polished reduces the reflected signal intensity in the combined coupler/connector, as well as the use of index matching material in the combined coupler/connector, alignment of the link cable and lightguides so that the faces of the link cable and lightguides are parallel and perpendicular to a common axis, and the choice of a link cable with a minimum designed attenuation. The mechanical attachment of the fiber optic lightguides by the fluoropolymer shrink tube ensures fiber alignment and prevents divergence of light for better optical coupling efficiency. Optical coupling gels are also used to provide refractive index matching between the lightguides and the transmitter and receiver circuits.

Fig. 16 illustrates the sub-assembly device 390, transmitter receiver board 392, splice bushing 394, fiber optic link cable end 396 and fiber optic link cable 398. The sub-assembly device 390 utilizes a sub-assembly combination coupler/connector 400 which utilizes a sub-assembly ferrule 402 and screw coupling cap 404. Three fiber optic lightguides 406 are disposed in sub-assembly ferrule 402 so that sub-assembly coupler/connector 400 functions both as a connector for connecting the sub-assembly device 390 to fiber optic link cable 398 and a coupler which functions as an asymmetric bi-directional Y-coupler for transmitting and receiving signals on a single fiber optic link cable 398. Sub-assembly coupler/connector

400, splice bushing 394 and fiber optic link cable end

396 mechanically position the three fiber optic lightguides 406 in alignment with fiber optic link cable 398. Splice bushing 394 has tapers which match tapers 412, 414 on sub-assembly ferrule 402 and link ferrule 410, respectively. Caps 404, 408 position and hold sub-assembly ferrule 402 and link ferrule 410 on splice bushing 394 with the proper tension to ensure axial and angular alignment between fiber optic link cable 398 and fiber optic lightguides 406. Caps 404, 408 maintain proper longitudinal separation between the ends of sub-assembly ferrule 402 and link ferrule 410 when disposed in splice bushing 394. Axial alignment and angular alignment between the ends of fiber optic lightguides 406 and the end of fiber optic link cable 398 ensure minimal loss resulting from transmission and reception across the air gap maintained between sub-assembly ferrule 402 and link ferrule 410. An appropriate spacing of less than approximately one half of the core diameter of the smallest of the three bundled lightguides, e.g., 40 microns for 110 micron lightguiding, should preferably be maintained to ensure adequate coupling of optical energy, while maintaining a separation to prevent damage to the fiber cores of link cable 398 and lightguides 406 as a result of the ends of the fiber cores touching and causing damage to the surfaces of the fiber cores, which would otherwise reduce optical coupling efficiency. To control the longitudinal separation between the ends of sub-assembly ferrule 402 and link ferrule 410, both ferrules as well as splice bushing 394 in which the ferrules are disposed are preferably manufactured to predetermined tolerances. In the present invention, the preferred results are achieved by grinding the ferrules to 6.26 ± 0.005 mm and grinding the splice bushing to 12.545± 0.005 mm length. The splice bushing can also be around to eliminate larger tolerances in the plastic parts caused by the plastic molding process. The resulting preferred separation gap in the current invention is then (12545 ± 5) - 2x (6260 ± 5) = 25 ± 15 micron. To increase optical coupling efficiency, an optical coupling gel can be used between the end of sub-assembly ferrule 402 and link ferrule 410 having an index of refraction which is substantially equal to the index of refraction of fiber optic link cable 398 and fiber optic lightguides 406. Use of an optical coupling gel reduces reflective losses at the air/glass interface of link cable 398.

Fiber optic lightguides 406 are mounted in sub-assembly ferrule 402, in a manner described infra, and cable sleeving 416 is placed over the fiber optic lightguides 406 and mounted in ferrule neck 418. Strain relief is provided by shrink tube 420 which is placed over the outer portions of cable sleeving 416, ferrule neck 418 and flange 424. Heat is applied to shrink tube 420 to prevent movement between strain relief insert 422 and ferrule neck 418 which might cause strain on fiber optic lightguides 406. Strain relief insert 422 is mounted directly in the fiber optic interface enclosure such that strain relief is integrated in the enclosure. In other words, forces produced on sub-assembly coupler/connector 400, or other portions of sub-assembly device 390, will be transmitted through strain relief insert 422 via strain relief projection 424 to the fiber optic interface device enclosure, thereby preventing strain from being produced on fiber optic lightguides 406 which might cause longitudinal displacement of the fiber optic lightguides 406 in sub-assembly ferrule 402. Additionally, cable sleeving 416 is mounted in strain relief insert 422 to further relieve strain on fiber optic lightguides 406, as a result of forces produced on the sub-assembly device 390, or the fiber optic link cable end 396 and fiber optic link cable 398.

Fiber optic lightguides 406 are threaded through cable sleeving 416. At the point at which the cable sleeving ends, the receive lightguides 426 are separated from the transmitter lightguide 428. Receive lightguides 426 are threaded through cable sleeving 430. Transmit lightguide 428 is threaded through cable sleeving 432. Shrink tube 434 is placed around the outer surface of cable sleeving 416, 430 and 432 and heat is applied to provide strain relief between each of the cable sleeving members. Receive lightguides 426 and cable sleeving 430 are attached to receiver assembly 436. Transmit lightguide 428 and cable sleeving 432 are connected to transmitter assembly 438. Receiver assembly 436 and transmitter assembly 438 are connected to transmitter receiver board 392 which is mounted on the mother board disposed within the fiber optic interface enclosure.

Fig. 17 is a schematic diagram illustrating the components of a typical fiber optic link cable. The fiber optic link cable comprises a glass fiber core 440 having a cladding 440 formed concentrically around the outer surface of the glass fiber core 440. The cladding 442 comprises a material having an index of refraction which is less than the index of refraction of the glass fiber 442 so that total internal reflection of light travelling through glass fiber 240 occurs whenever the light impinges upon the interface of the glass core and cladding at any angle between the critical angle and the surface of the fiber. Glass fiber core 440 can vary in diameter in accordance with its use. In the present invention, fiber optic lightguides 406 have glass fiber cores which are approximately 110 microns in diameter, while fiber optic link cable 398 has a glass fiber core of approximately 200 microns in diameter. Using these diameters, the glass fiber cores of the three fiber optic lightguides 406 can easily align with the glass fiber core of the fiber optic link cable 398, when cable ferrule 410 and sub-assembly ferrule 402 are coupled together by splice bushing 394. In accordance with the present invention, the outer diameter of cladding 442 on lightguides 406 is approximately 125 microns, and the diameter of cladding 442 on link cable 398 is approximately 330 microns in diameter. These diameters provide substantial overlapping of the face of the 200 micron glass core of link cable 398 with the faces of the three 110 micron glass cores of lightguides 406 which are placed in a tightly spaced triangular configuration. Buffer 444 comprises a protective layer which surrounds cladding 242 to protect the cladding material from abrasion or other damage. Inner tube 445 provides an additional protective layer. Strength member 446 comprises a braided material, preferably of a polyaramid plastic, to provide strength and reduce strain on glass fiber 440. Outer jacket 448 comprises a PVC protective layer for strength member 446.

The optical fibers can comprise all glass fibers, i.e., glass on glass, plastic coated silica (PCS) and all plastic fibers. Plastic coated silica fibers have been used in accordance with the present invention having fused silica cores with a refractive index of 1.46 and a RTU type of silicone elastomer cladding having a thickness which is approximately 30% of the core diameter of the PCS fiber. Soft cladding can be stripped from the core and reclad applied to the core where close positioning of adjacent cores of other lightguides is required, e.g., the assembly of fiber optic lightguides in sub-assembly ferrule 402, as illustrated in Fig. 18. For grouping of lightguides in a closely spaced configuration to achieve the requisite optical coupling efficiency required by the present invention, the cladding material should be 4% to 15% of the diameter of the core of the optical fiber, but no more than 30%. Sufficient optical coupling efficiency is not achieved with the thicker cladding since thicker claddings take more space, reduces packing efficiency and consequently require coupling to fiber optic cables of greater diameter and lower efficiency.

Fig. 18 comprises a schematic diagram of the assembly of fiber optic lightguides 406 in sub-assembly ferrule 402 (Fig. 16) . In forming the sub-assembly, three single fiber lightguides 406 are cut to length (as indicated by the distance between the sub-assembly ferrule 412 and transmitter/receiver board 392 in Fig. 16) . Each lightguide 406 comprises a light guiding core having an optical cladding formed concentrically around it. The cladding maintains light trapped in the core by virtue of total internal reflections a result of the index of refraction of the cladding being less than the index of refraction of the core of the lightguide 406.

The lightguides are supplied with a protective buffer tube 444 and they are presently commercially available. In some lightguides the optical cladding comprises RTV silicone type material, while in some others there is a layer of hard cladding material between the glass core and the silicone cladding. Lightguides 406 can be all soft clad, all hard clad or any combination thereof. In either case, the outer silicone cladding is removed with the buffer 444 when the lightguides are prepared for assembly. Since the glass fibers 440 have such high purity, they must be protected after they have been exposed to the atmosphere to prevent absorption of moisture. Each of the exposed glass fibers is dipped in a reclad solution after being cut to prevent water absorption and degradation. The recladding solution preferably comprises a solution of approximately 26% kynar, 74% acetone and a fractional percentage of polycarbonate. Such recladding solutions are available commercially. The purpose of cladding on the fiber optic core is to guide light within the core by creating a radial drop in the index of refraction. When cladding is stripped for termination or assembly of the optical fiber, the core must be reclad to prevent loss of light. Fluoro-polymers, such as TFE (Teflon), in the form of heat shrinkable tube work well to provide a lower index of refraction layer around the core of the material and help to guide light through the core of the optical fiber by reducing light divergence. The length of fiber required between sub-assembly ferrule 402, and receiver assembly 436 and transmitter assembly 438 (Fig. 16), is measured and cleaved at the receiver and transmitter assembly ends, in the manner described infra.

Referring again to Fig. 18, after recladding 450 has been applied to fiber optic lightguide 406, a fluoropolymer (TFE) heat shrink tube 452, such as a Teflon brand of fluoropolymer is placed over the ends of fiber optic lightguides 406 to hold the fiber optic lightguides 406 in a closely spaced triangular configuration. The closely spaced triangular configuration provides a naturally self-supporting structure having an outer surface area which automatically provides for self-centering in the sub-assembly ferrule. Recladding 450 which is relatively soft, conforms to the compression of the shrunk tube 452 by filling the voids between lightguides 406 within heat shrink tube 452 (Ref. Fig. 20) . The self-supporting triangular configuration allows the fibers to be closely spaced to one another in a configuration which is not prone to self-movement or misalignment. In addition to holding fiber optic lightguides 406 in a tightly spaced triangular configuration, heat shrink tube 452 also functions in conjunction with recladding 450 , to maintain light which is transmitted and received by fiber optic lightguides 406 in an axial direction, since heat shrink tube 452 has an index of refraction which is lower than the glass core of glass fiber 440. After heat shrink tube 452 is applied to fiber optic lightguides 406, an additional fluoropolymer heat shrink tube 454 is placed between and over the ends of heat shrink tube 452 and buffer 444 to provide strain relief and support to the structure. Vinyl heat shrink tube 456 is then placed over the buffer portion of the fiber optic lightguides 406 to provide additional support to the assembly.

Fig. 19 discloses the fiber assembly illustrated in Fig. 18 mounted in sub-assembly ferrule 402. The fiber assembly illustrated in Fig. 18 is inserted in opening 458 of sub-assembly ferrule 452 until heat shrink tube 454 abuts against abutment surface 460 in opening 458. At the point at which heat shrink tube 454 abuts against abutment surface 460, the glass fiber and recladding extend slightly from the end surface 461 of sub-assembly ferrule 402. The closely spaced triangular configuration causes the fiber optic assembly to be self-centered in ferrule 402. After the fiber optic assembly is placed in sub-assembly ferrule 402, a syringe is used to inject low viscosity epoxy in the void areas of opening 458. Any commercially available low viscosity curable epoxy resin is suitable for use. After the epoxy is allowed to harden, the glass fiber cores and recladding 450 which extend beyond the end surface of sub-assembly ferrule 402 is removed by air abrasive cutting. The entire assembly illustrated in Fig. 19 is then stress-relieved for 48 hours to allow the epoxy to fully cure and thereby prevent pistoning of the fiber optic lightguide.

The end surface of the sub-assembly ferrule 402 is then rough polished with 15 micron abrasive disc or the like mounted on a turntable. A 6.3 millimeter long polishing bushing is used for rough polishing on the 15 micron abrasive disc. The ferrule end surface is then final polished on 3 micron abrasive disc using a polishing bushing of 6.26 millimeters. The entire surface is then cleaned with nitrogen and a dust cap is placed over the end surface of the sub-assembly ferrule 402. The fiber optic lightguide 406 are then threaded through cable sleeving 416 and shrink tube 420 is placed over cable sleeving 416, ferrule neck 418 and flange 424 of strain insert 422, as illustrated in Fig. 16. Heat is then applied to shrink tube 420 and a hot melt adhesive on the inner surface of shrink tube 420 adheres shrink tube 420 to ferrule neck 418 and flange 424. Receive lightguides 426 are then separated from transmit lightguide 428 and cable sleeving 430, 432 is placed over the respective lightguides. Shrink tube 434 is then applied to cable sleeving 416 and cable sleeving 430, 432, as described above, to provide strain relief. A small amount of adhesive is applied to the end portions of cable sleeving 430, 432 to attach the fiber optic lightguides 406 to cable sleeving 430, 432.

Fig. 20 is an end view of sub-assembly ferrule 402. As illustrated in Fig. 20, end surface 460 has an opening 458 formed therein, in which lightguides 406 are disposed. As clearly illustrated in Fig. 20, fluoropolymer heat shrink tube 452 mechanically aligns the glass fibers in a closely spaced triangular configuration so that the glass fibers are centrally aligned in opening 458. The remaining spaces around lightguides 450 are then substantially filled with recladding 450. The proper alignment is then provided by the closely spaced triangular configuration and the use of a fluoropolymer heat shrink tube 452 of the proper cross-sectional thickness to fit within opening 458. Epoxy 462 holds the glass fibers and recladding 450 in place in the sub-assembly ferrule 402.

An alternative assembly method is available using those lightguides which exhibit a hard cladding material over the light guiding glass core. In this case the protective buffer 444 and the silicone cladding material are stripped, but the lightguide need not be reclad as the core is still protected with the hard cladding layer, as illustrated in Fig. 21.

In the current invention hard clad fiber optic lightguides are used in which the lightguiding core diameter is about 110 microns and the thickness of the hard cladding is approximately 7 microns. This thin cladding allows some portion of light incident at higher angles to leak across the core-cladding boundary. The beams of such higher angle of incidence are known as higher order modes of light propagation and it has been determined that they contribute substantially to the reflection of light backwards at the glass-air-glass boundary in the combined coupler/connector. When the lightguide is surrounded with light absorbing medium over a sufficient length, the leaking higher order modes are removed by process known as mode stripping, resulting in lower reflection at coupler/connector sub-assembly 400.

Fig. 21 discloses the alternative assembly employing a mode stripping medium disposed in sub-assembly ferrule 402. The protective buffer 444 and silicone cladding are removed so that approximately 1/2 inch of the hard clad lightguide is exposed. The lightguides comprising the glass fiber core and hard cladding 443 are held in a tight triangular configuration by the vinyl heat shrink tube 445 and introduced in the sub-assembly ferrule 402 which is filled with mode stripping medium 447, which is a commercially available black potting epoxy compound. Some excess length of the three lightguides is allowed to extend beyond the end of the ferrule, where the lightguides are held in position by a centering orifice until the mode stripping medium 447 has hardened.

After the mode stripping medium has cured, any excess lightguides and mode stripping medium are trimmed by air abrasive cutting and the rest of the process is identical to that described in connection with Fig. 19.

Fig. 22 shows the end surface of the finished sub-assembly ferrule 402 assembled with the mode stripping medium 447, indicating the space around and between hard cladding 449 filled with the mode stripping medium 447. The manner in which hard cladding 449 surrounds glass fiber core 451 is also illustrated in Fig. 22.

Figs. 23 through 25 illustrate strain relief insert 422. Fig. 23 is a top view of strain relief insert illustrating the manner in which strain relief projection 424 protrudes from vertical portion 464. Horizontal portion 466 joins vertical portion 464 at a substantially right angle, as further illustrated in Fig. 25. Fig. 24 discloses opening 468 formed in vertical portion 464 which functions to hold the fiber optic lightguides 406 and cable sleeving 416 in a fixed relationship after heat shrink tube 420 has been secured to flange 424.

Fig. 26 comprises an exploded cut-away view of the components of the receiver assembly 436. As illustrated in Fig. 26, the receiver assembly 436 comprises a PIN diode which is capable of detecting IR radiation transmitted by receive lightguides 426. PIN diode 470 is mounted on a standard TO-18 base having a predetermined outside diameter. Brass sleeve 472 has an inner diameter which allows brass sleeve 472 to be placed over the outer surface of PIN diode 470. In a similar manner, brass sleeve 472 has an outer diameter which fits within the inner diameter of quartz tube 474, in the manner illustrated in Fig. 26.

Fig. 27 is a top view of PIN diode 470. Detector surface 476 is disposed on the top of PIN diode upper surface 478. PIN diode 470 is received from the manufacturer without a protective window over the PIN diode upper surface 478 such that detector surface 476 is directly open to the environment. Fig. 27 also illustrates the manner in which receive lightguides 426 are positioned over detector surface 476. A fluoropolymer heat shrink tube 482 holds receive lightguides 426 in a closely spaced configuration adjacent the end portions of receive lightguides 426. The receive lightguides 426 are aligned with the longitudinal direction of detector surface 476 and centered thereon to provide maximum transmission of light from receive fibers 426 onto detector surface 476. Heat shrink tube 482 prevents divergence of light to provide better optical coupling efficiency.

Fig. 28 comprises a side cut-away view of receiver assembly 436. Optical coupling gel 484 with a refractive index of approximately 1.4 to 1.5 is placed over the PIN diode upper surface 478 adjacent detector surface 476 and is maintained within brass sleeve 472. A typical optical gel suitable for use with the present invention comprises a soft dielectric gel having a refractive index of approximately 1.407. Optical coupling gel 484 is a silicon gel having an index of refraction which approximates the index of refraction of receive fibers 476 to increase optical coupling efficiency between receive lightguides 426 and detector surface 476. The optical coupling gel comprises a conformal coating which functions to fill the air gap between the receive lightguides and the detector surface, and it seals PIN diode upper surface 478 from the environment.

The receive lightguides 426 are positioned above the detector surface 476, as illustrated in Fig. 27, and a UV curable adhesive 486 is placed in the reservoir formed by quartz tube 474. Typical UV curable adhesive suitable for use with the present invention include those currently used in optical assemblies. UV curable adhesive 486 extends beyond the upper surface of quartz tube 474 to ensure that the lower portion of cable sleeving 430 is secured by UV curable adhesive 486 so as to provide a secure assembly. When receiver fibers 426 are properly positioned in the receiver assembly 436, UV radiation is applied to UV curable adhesive 486 to secure the receive fibers and cable sleeving 430 in receive assembly 436.

Fig. 29 is a schematic cut-away view of transmitter assembly 438. Transmitter assembly 438 uses a light emitting diode 490 which is capable of transmitting infrared light at approximately 820 nanometers. The supporting structure of LED 490 is surrounded by a brass sleeve 492, which is in turn surrounded by quartz sleeve 494, in the same manner as receiver assembly 436, illustrated in Fig. 26. Also, an optical coupling gel 496 is disposed within quartz sleeve 494 to increase optical coupling efficiency. Transmit lightguide 428 is positioned on optical window 499 in alignment with optical focusing device 500 to provide a balance between transmitted and reflected light. When properly positioned, transmit fiber 428 and cable sleeving 432 are secured in place by UV curable adhesive 498. Optical coupling gel 496 can be replaced with a clear UV curable adhesive with a refractive index which is capable of increasing optical coupling efficiency.

In order to provide a proper surface for receipt and transmission of data in and out of transmit and receive lightguides 428, 426, the ends of the fiber cores must be cleaved in a particular manner to create a smooth perpendicular end surface. Cleaving is achieved by applying a predetermined bending moment and a predetermined tension to each lightguide. The glass core is then scored along the outer radial surface to create a crack which propagates through the fiber so as to form a damage-free surface. The crack must propagate at a predetermined speed dependent upon the tension and bending moment to prevent imperfections on the cleaved surface.

The manner in which receiver assembly 436 and transmitter assembly 438 are assembled is referred to as pigtailing. The pigtailing procedure requires the use of a micro-positioner which comprises a five axis positioner for aligning receive lightguide 426 with PIN diode 470 and transmit fiber 428 with optical focusing device 500. Receive lightguides 426 are aligned with the longitudinal direction of detector surface 476 and positioned for a maximum output reading on PIN diode 470. The receiver assembly 436 is assembled prior to assembly of transmitter assembly 438. Transmit light-guides 428 is subsequently aligned by maximizing the transmitted light at sub-assembly coupler/connector 400, while minimizing the output of receiver assembly 436 as a result of reflections at sub-assembly coupler/connector 400 . In the manufacturing process, transmit lightguide 428 is aligned to produce a desired level of transmitted light while maintaining the level of the reflected signal detected by receiver assembly 436 below a set limit.

The manner in which the ends of the sub-assembly link cable 398 are polished minimizes reflections between transmit lightguide 428 and receive lightguides 426 at the interface point between link ferrule 410 and sub-assembly ferrule 402 in sub-assembly coupler/connector 400. The final polishing using 3 micron abrasive paper produces a surface which is sufficiently rough to diffuse the reflected energy at the air/glass interface of fiber optic link cable 398. This procedure, in combination with the high tolerance alignment and spacing of sub-assembly ferrule 402 and cable ferrule 410, and the alignment of receiver assembly 436 and transmitter assembly 438, allow simultaneous distinguishable bi-directional optical communication of data using a combined coupler/connector which is convenient and easy to use. Additionally, the precise setting of threshold levels in the fiber receiver and data decoder 94 using resistor 224 in combination with the use of a link cable having a minimum designed attenuation, resulting from either the particular materials used /or the length of the cable, ensures that reflected signals at the combined coupler/connector will not be detected as received signals.

Fig. 30 is a schematic side view of fiber optic link cable 398 (Fig. 16) . Fig. 30 illustrates the manner in which the end of the fiber optic link cable 398 is prepared prior to insertion in cable ferrule 410. First, outer jacket 502, strength member 504, innertube 506, and buffer 508 ar stripped to the proper lengths. Both the buffer 508 and cladding surrounding glass fiber 514 are stripped. Glass fiber 514 is then dipped into a recladding solution. Buffer 508 is then abraded with sandpaper to produce a coarse layer. A. fluoropolymer of heat shrink tube 510 is placed over the end portion of buffer 508 and glass fiber 514. The heat shrink 510 is heat crimped at a location 512 to hold heat shrink 510 in the proper position. Heat is then applied to the heat shrink 510 to shrink heat shrink 510 over glass fiber 514. The cable end is then inserted in the ferrule 410 until it abuts against the inner taper in the ferrule. Glass fiber 514 and heat shrink 510 protrude slightly from the end of cable ferrule 410. The cable end is bonded to the ferrule with epoxy using a bonding fixture device. A heat shrink tube (not shown) is placed over the outer jacket 502 and cable ferrule 410 to provide strain relief. The entire assembly is then placed in the oven to cure. After curing, the protruding fiber is abrasively removed from the tip of the ferrule by air abrasive cutting. The assembly is then allowed to sit for 48 hours so that the epoxy can fully cure and thereby provide stress relief. The end of the ferrule is then polished in the same manner as the coupler to produce the substantially non-mirrored surface.

Fig. 31 comprises an exploded schematic view of the fiber optic interface device 10 of the present invention. Fiber optic interface unit 10 employs a protective lid 520 which is connected to enclosure 524 by way of wire hinge 522 which is disposed in holes

523. Enclosure unit 524 is coupled to base unit 526 by way of screws 542 disposed through holes 546 and mounted in posts 544 and which are covered by label 548 received in recess 549 to cover the recessed screwhead

(542). Subassembly coupler/connector 400 is disposed through opening 525 in enclosure unit 524 upon assembly. Shrink tube 420 of subassembly 390 is secured to flange 424 of strain relief insert 422 by applying heat to shrink tube 420, as described above.

Strain relief insert 422 is then mounted in enclosure unit 524 by inserting strain relief insert 422 in opening 527. Flange portions 529 resiliently expand in opening 527 and hold strain relief insert 422 in rigid engagement with enclosure unit 524. In this manner, subassembly 390 is integrally secured to enclosure unit

524 to provide strain relief for subassembly 390.

Fiber optic link cable 398 is inserted in rounded groove 536 having a predetermined radius of curvature which is sufficiently large to allow transmission of optical data through fiber optic link cable 398 without significant attenuation. Cable locking devices 538,

540 are formed in enclosure unit 524 and function to securely hold fiber optic link cable 398 in engagement with enclosure unit 524 to provide strain relief for fiber optic link cable end 396. Disposed in each base unit 526 are two plug units 528, 530 which comprise electronic serial data ports such as RS232 electronic serial data ports. Additionally, two plug units 532,

534 comprise power plugs for applying auxiliary power to the fiber optic interface unit 10. Consequently, auxiliary power can be applied at either end of the unit depending upon which is more convenient for the user.

Consequently, the present invention provides an optical communication device which is capable of simultaneous bi-directional transmission of optical energy over a single fiber optic link cable at high data transmission rates using a inexpensive device which is capable of operating with or without auxiliary power. The system provides maximum data security with total immunity to EMI/RFI. Resource sharing is achieved between multiple user devices by transmission of state operational signals between fiber optic interface units. Simultaneous bi-directional transmission eliminates the need for expensive multiplexing devices associated with each user unit. LED indicator lights provide information to the user as to the current state of operation of the units, as well as functioning as a continuity monitor to maintain data and transmission integrity and security against eavesdropping and data link taps. Bridging of units provides for extended range capabilities and networking between multiple user stations.

The assembly of the fiber optic cable units and the use of an insert which is integrated into the fiber optic interface enclosure provides strain relief to the fiber optic lightguides utilized in the present invention and, consequently, increases the reliability and durability of the system. Use of a standard connector ferrule as both a connector and coupler, reduces costs and provides a more convenient system for the user and installer. The combined coupler/connecter can also be easily cleaned so as to minimize maintenance costs. The use of a fluoropolymer heat shrink tube provides precise mechanical alignment of the lightguides and link cable as well as decreasing light divergence at the fiber optic lightguides ends. Use of the reclad solution after cutting and stripping the optical lightguides protects the integrity of the glass core as well as decreasing light divergence and enhancing optical coupling efficiency. Use of a mode stripping medium in the ferrule provides for the removal of higher order modes of light guidance, thereby reducing the amount of reflection resulting from the higher order modes.

The foregoing description of the invention has been present for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and other modifications and variations may be possible in light of the above teachings. The embodiment was chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and various modifications as are suited to the particular use contemplated. It is intended that the appended claims be construed to include other alternative embodiments of the invention except insofar as limited by the prior art.

Claims

WHAT IS CLAIMED IS:

1. A fiber optic coupling device for providing simultaneous bi-directional transmission of optical signals over a single fiber optic link cable comprising: receive lightguide means for receiving optical input signals; transmit lightguide means for transmitting optical output signals; combined coupler/connector means for coupling and connecting said receive lightguide means and said transmit lightguide means with said fiber optic link cable to align and longitudinally separate said receive and transmit lightguide means with said link cable so as to be capable of simultaneous bi-directional optical coupling of said optical input signals between said receive lightguide means and said link cable, and said optical output signals between said transmit fiber means and said link cable.

2. The device of claim 1 wherein said receive and transmit lightguide means comprise: fiber optic core means for transmitting said optical signals, said fiber optic core means having a predetermined core diameter; cladding means surrounding said fiber optic core means for guiding said optical signals in said fiber optic core means, said cladding means having a thickness which is sufficiently large to substantially prevent leakage of light from said cladding means and which is less than 30% of said predetermined core diameter so as to maintain a high packing ratio of active to non-active areas in said combined coupler/connector and optimize optical coupling between said receive and transmit licjhtguide means and said link cable while minimizing the fiber optic core diameter of said fiber optic link cable whereby the number of optical modes of transmission are reduced in said fiber optic link cable and the transmission bandwidth and data transmission rate of said optical signals transmitted over said fiber optic link cable are increased.

3. The device of claim 1 wherein said receive and transmit lightguide means comprise: fiber optic core means for transmitting said optic signals, said fiber optic core means having a predetermined core diameter; cladding means surrounding said fiber optic core means for guiding said optical signals in said fiber optic core means, said cladding means having a thickness which is from 4% to 15% of said predetermined core diameter so as to minimize the core diameter of said fiber optic link cable to maximize the packing ratio of said fiber optic cores and minimize leakage between the fiber cores.

4. The device of claim 3 further comprising: optical absorbing means surrounding said cladding means for absorbing higher order modes of said optical signal which have leaked through said cladding means.

5. The device of claim 1 wherein said fiber optic link cable has a surface which is abrasively polished to form a substantially non-mirrored surface.

6. The device of claim 1 wherein said combined coupler/connector means comprises: sub-assembly ferrule means for aligning said receive lightguide means and said transmit light- guide means; link ferrule means for aligning said link cable; splice bushing means for aligning said sub- assembly ferrule means and said link ferrule means.

7. The device of claim 6 wherein the length of said sub-assembly ferrule means, said link ferrule means and said splice bushing means are preselected to provide a predetermined longitudinal separation between the ends of said fiber optic link cable and said fiber optic core means.

8. The device of claim 6 further comprising: receive and transmit lightguide assembly means for holding said receive lightguide means and said transmit lightguide means in a closely spaced configuration and reducing light divergence in said combined coupler/connector means.

9. The device of claim 8 wherein said receive and transmit lightguide assembly comprises: recladding formed around end portions of said receive lightguide means and said transmit light- guide means; first heat shrink tubing means for holding said receive lightguide means and said transmit lightguide means in a closely spaced, triangular configuration; additional heat shrink tubing means coupled to said first heat shrink tubing means for providing support. and strain relief to said receive and transmit .lightguide assembly.

10. The device of claim 9 wherein said sub-assembly ferrule means and said cable ferrule means are longitudinally separated by approximately one quarter but less than one half of the diameter of the smallest of the fiber optic core diameters of said receive and transmit lightguide means.

11 . A bi-directional fiber optic communication device comprising: fiber optic link cable means for bi-directionally communicating optical input signals and optical output signals; transmit lightguide means for transmitting said optical output signals; receive lightguide means for receiving optical input signals; combined coupler/connector means for axially and angularly aligning said transmit and receive lightguide means with said fiber optic link cable means to allow simultaneous bi-directional coupling of said optical input and output signals between said transmit and receive lightguide means and said fiber optic link cable means in said coupler/connector means; receiver assembly means for detecting said optical input signals and producing electrical input signals representative of said optical input signals; transmitter assembly means for producing said optical output signals in response to electrical output signals.

12. The device of claim 11 wherein said receiver assembly means comprises: detector means for detecting said optical input signals; optical coupling means for increasing optical coupling efficiency between said detector means and said receive lightguide means; adhesive means for securing said receive lightguide means in optical alignment with said detector means.

13. The device of claim 12 wherein said receiver assembly means further comprises: heat shrink means disposed around said receive lightguide means for holding said receive lightguide means in a closely spaced configuration.

14. The device of claim 13 further comprising: receive lightguide cable sleeving means surrounding said receive lightguide means and adhesively secured to said adhesive means so as to provide strain relief for said receive lightguide means.

15. The device of claim 11 wherein said transmitter assembly means comprises: transmitter means for generating said optical output signals in response to said electrical output signals; optical coupling means for increasing optical coupling efficiency between said transmit means and said transmit lightguide means; adhesive means for securing said transmit lightguide means in optical alignment with said transmitter means.

16. The device of claim 15 wherein said transmitter assembly means further comprises: means for retaining said optical coupling means adjacent to said transmitter means.

17. The device of claim 16 further comprising: transmit lightguide cable sleeving means surrounding said transmit lightguide means and adhesively secured to said adhesive means so as to provide strain relief to said transmit lightguide means.

18. The device of claim 11 wherein said transmitter a ssembly means comprises: transmitter means for generating said optical output signal in response to said electrical output signal; adhesive means for securing said transmit lightguide means in optical alignment with said transmitter means and for increasing optical coupling efficiency between said transmitter means and said transmit lightguide means by providing refractive index matching.

19. The device of claim 12 wherein said fiber optic link cable means has an abrasively polished surface to form a substantially non-mirror surface.

20. The device of claim 12 wherein said receive and tranrmit lightguide means have cleaved surfaces at the ends of said receive and transmit lightguide means which are disposed in said receiver and transmitter assembly means.

21. The device of claim 12 wherein said combined coupler/ connector means comprises : sub-assembly ferrule means for aligning said receive lightguide means and said transmit light- guide means; link ferrule means for aligning said link cable means; splice bushing means for aligning said sub- assembly ferrule means with said cable ferrule means.

22. The device of claim 21 wherein the length of said sub-assembly ferrule means, said link ferrule means and said splice bushing means are preselected to provide a predetermined longitudinal separation between the ends of said fiber optic link cable and said fiber optic core means.

23. The device of claim 21 further comprising: receive and transmit lightguide assembly means for holding said receive lightguide means and said transmit lightguide means in a closely spaced self-supporting triangular configuration and reducing light divergence in said combined coupler/connector means.

24. The device of claim 23 wherein said receive and transmit lightguide assembly comprises: recladding formed around end portions of said receive lightguide means and said transmit light- guide means; first heat shrink tubing means for holding said receive lightguide means and said transmit lightguide means in said closely spaced, self- supporting triangular configuration; additional heat shrink tubing means coupled to said first heat shrink tubing means for providing support and strain relief for said receive and transmit lightguide assembly.

25. The device of claim 24 wherein said sub- assembly ferrule means and said link ferrule means are longitudinally separated by approximately one quarter but not more than one half of the diameter of the smallest of the fiber optic core diameters of said receive and transmit lightguide means.

26. The device of claim 15 wherein said fiber optic link cable means has an abrasively polished surface to form a substantially non-mirror surface which generates high order modes of reflected radiation within said fiber optic link cable.

27. The device of claim 15 wherein said receive and transmit lightguide means have cleaved surfaces at the ends of said receive and transmit lightguide means which are disposed in said receiver and transmitter assembly means.

28. The device of claim 15 wherein said combined coupler/connector means comprises: sub-assembly ferrule means for aligning said receive lightguide means and said transmit light- guide means; link ferrule means for aligning said coupling cable; splice bushing means for aligning said sub- assembly ferrule means and said link ferrule means.

29. The device of -claim 28 wherein the length of said sub-assembly ferrule means, said link ferrule means and said splice bushing means are preselected to provide a predetermined longitudinal separation between the ends of said fiber optic link cable and said fiber optic core means.

30. The device of claim 28 further comprising: receive and transmit lightguide assembly means for holding said receive lightguide means and said transmit lightguide means in a closely spaced self-supporting triangular configuration and reducing light divergence in said combined coupler/connector means.

31. The device of claim 30 wherein said receive and transmit fiber assembly comprises: recladding formed around end portions of said receive lightguide means and said transmit light- guide means; first heat shrink tubing means for holding said receive lightguide means and said transmit lightguide means in said closely spaced, self- supporting triangular configuration; additional heat shrink tubing means coupled to said first heat shrink tubing means for providing support and strain relief to said receive and transmit lightguide assembly.

32. The device of claim 31 wherein said sub-assembly ferrule means and said link ferrule means are longitudinally separated by approximately one quarter but no more than one half of the diameter of the smallest of the fiber optic core diameters of said receive and transmit lightguide means, when disposed in said splice bushing means.

33. The device of claim 12 wherein said transmitter assembly means comprises: transmitter means for generating said optical output signals in response to said electrical output signals; optical coupling means for increasing optical coupling efficiency between said transmit means and said transmit fiber means; adhesive means for securing said transmit lightguide means in optical alignment with said transmitter means.

34. The device of claim 21 further comprising: link assembly means for insertion in said link ferrule means, said link assembly means having a heat shrink tube which is heat crimped over a buffer portion of said link cable means and covering a portion of said link cable means extending beyond said buffer.

35. The device of claim 28 further comprising: link assembly means for insertion in said link ferrule means, said link assembly means having a heat shrink tube which is heat crimped over a buffer portion of said link cable means and covering a portion of said link cable means extending beyond said buffer.

36. A fiber optic interface device for connecting a plurality of user devices in a communications network comprising: synchronous state means for producing switching signals, ready-out-signals indicative of the ready status of said user devices and state signals indicative of the current state of operation of said fiber optic interface device, said switching signals, ready-out-signals and state signals produced in response to ready-in-signals produced by said user devices which indicate the ready status of said user devices and a fiber activity signal indicative of the data transmission rate at which optical pulses are being received by said fiber optic interface device from an additional fiber optic interface device; line driver means for transmitting an electronic output data signal and said ready-out-signals to at least one user device connected to said fiber optic interface device; fiber transmitter means for transmitting an encoded fiber output data signal and to said additional fiber optic interface device at a preselected data transmission rate to indicate said current state of operation of said fiber optic interface device; data steering means for selecting an output data signal for transmission from said electronic output data signals and said encoded fiber output data signals in response to said switching signals produced by said synchronous state means.

37. The device of claim 36 wherein said fiber optic interface device is capable of transmitting data which is received by all user devices connected to said communications network.

38. The device of claim 36 wherein secure full duplex communication can be established between any two user devices connected to said communications network.

39. The device of claim 36 wherein said fiber optic interface device is capable of providing resource sharing between a user device connected to said fiber optic interface device and a user device connected to said additional fiber optic interface device.

40. The device of claim 36 wherein said fiber optic interface device is capable of providing resource sharing and full duplex communication between multiple user devices connected to said fiber optic interface device and said additional fiber optic interface device.

41. The device of claim 36 wherein said synchronous state means comprises: diagnostic means for producing an indication of the current status of operation of said fiber optic interface device and for indicating a loss of integrity in a fiber optic link cable connecting said fiber optic interface device and said additional fiber optic interface device.

42. The device of claim 41 wherein said diagnostic means comprises a light emitting diode.

43. The device of claim 41 wherein said diagnostic means comprises a means for producing a machine readable signal.

44. The device of claim 36 wherein said input data signals comprise: an additional encoded fiber data signal and an additional state signal produced by said additional fiber optic interface device; electronic input data signals produced by said user devices.

45. The device of claim 36 further comprising: fiber receiver means for producing a decoded fiber signal from said additional encoded fiber signal and said fiber activity signal from said additional encoded fiber signal and an additional state signal produced by said additional fiber optic interface device.

46. The device of claim 36 further comprising: line receiver means for producing level adjus.ted electronic input signals in response to said electronic input data signals produced by said user devices.

47. The device of claim 32 further comprising: power supply means for deriving power from said input data signals and said ready-in-signals.

48. The device of claim 47 wherein said power supply means comprises: first diode summing means for accumulating a positive voltage supply from said ready-in-signals; second diode summing means for accumulating a positive voltage supply from said input data signals; third diode summing means for accumulating a negative voltage supply from said input data signals.

49. The device of claim 48 further comprising: current limiting means for limiting the amount of current supplied by said first and third diode summing means; comparator means for generating a control signal to control said current limiting means.

50. The device of claim 49 further comprising: auxiliary power source means coupled to said positive and negative voltage supplies; power conditioner means coupled to said positive and negative voltage supplies to provide a conditioned voltage source.

51. The device of claim 36 further comprising: means for causing said line driver means to operate with dual output impedances depending upon the availability of auxiliary power.

52. The device of claim 42 further comprising: light emitting diode control circuit means for causing said light emitting diode to operate at two brightness levels depending upon the availability of auxiliary power.

53. The device of claim 36 further comprising: power control means for systematically providing power to said synchronous state means to decrease the duty cycle of said synchronous state means and reduce power consumption of said synchronous state means.

54. The device of claim 36 further comprising: transition encoding means for producing a transition encoded fiber data signal from said input data signals to reduce power consumption of said fiber optic interface device.

55. The device of claim 45 further comprising: transition decoding means for producing a transition decoded fiber signal to reduce power consumption of said fiber optic interface device.

56. The device of claim 54 further comprising: transition decoding means for producing a transition decoded fiber signal to reduce power consumption of said fiber optic interface device.

57. The device of claim 47 further comprising: transition encoding means for producing a transition encoded fiber data signal from said input data signals to reduce power consumption of said fiber optic interface device; transition decoding means for producing a transition decoded fiber signal to reduce power consumption of said fiber optic interface device.

58. The device of claim 36 further comprising: receive lightguide means for transmitting said additional encoded fiber signal and said fiber activity signal to said fiber receiver means; transmit lightguide means for receiving said encoded fiber data signal and said state signal from said fiber transmitter means; single fiber optic link cable means for simultaneously bi-directionally transmitting said additional encoded fiber signal, said fiber activity signal, said encoded fiber data signal and said state signal between said fiber optic interface device and said additional fiber optic interface device; combined coupler/connector means for axially and angularly aligning said receive and transmit fiber means with said single fiber optic cable means in a connector device which provides simultaneous bi-directional coupling of said additional encoded fiber signal, said fiber activity signal, said encoded fiber data signal and said state signal between said receive and transmit fiber means and said single fiber optic cable means.

59. The device of claim 58 wherein said fiber receiver means comprises: threshold means for distinguishing between said additional encoded fiber signal, said fiber activity signal and reflections in said combined coupler/connector of said encoded fiber data signal and said state signal.

60. The device of claim 36 further comprising: transmit lightguide means .coupled to said fiber transmitter means for transmitting said encoded fiber data signal and said state signal.

61. The device of claim 36 further comprising receive lightguide means coupled to said fiber receiver means for receiving said encoded fiber data signal and said state signal.

62. A fiber optic communications system for providing resource sharing between a plurality of user devices comprising: first user means for generating first ready- in-signals which indicate the ready status of said first user means and first data signals for transmission; first fiber optic interface means for generating:

1) a first optical data signal having a predetermined data transmission rate indicative of the current state of operation of said first fiber optic interface means;

2) first ready-out-signals indicative of the ready status of said first fiber optic interface means; and

3) first electrical data signals; second user means for generating second ready-in-signals which indicate the ready status of said second user means and second data signals for transmission; second fiber optic interface means for generating:

1) a second optical data signal having a predetermined data transmission rate indicative of the current state of operation of said second fiber optic interface means;

2) second ready-out-signals indicative of the ready status of said second fiber optic interface means; and

3) second electrical data signals; first steering means disposed in said first fiber optic interface means for providing secure full duplex communication of said first electrical data signals between two user devices of said first user means in response to said first ready-in-signals and said first ready-out-signals, and for providing transmission of said first optical data signal to said second fiber optic interface means for secure full duplex communication between a user device of said second user means and a user device of said first user means in response to said second optical state signal; second steering means disposed in said second fiber optic interface means for providing secure full duplex communication of said second electrical data signals between two user devices of said second user means in response to said second ready-in-signals and said second ready-out-signals, and for providing transmission of said second optical data signal to said first fiber optic interface means for secure full duplex communication between a user device of said first user means and a user device of said second user means in response to said first optical state signal; link cable means for bi-directionally and simultaneously transmitting said first and second optical data signals between said first and second fiber optic interface means; whereby said full duplex communication established between said two user devices of said first user means, said two user devices of said second user means and said user device of said first user means and user device of said second user means provides full access resource sharing.

63. The system of claim 62 further comprising at least one additional set of fiber optic interface pairs bridged to said system for providing daisy-chaining of additional user devices.

64. A fiber optic communications system for providing resource sharing between a plurality of user devices comprising: first user means for generating first ready- in-signals which indicate the ready status of said first user means and first data signals for transmission; first fiber optic interface means for generating:

1) a first optical data signal having a predetermined data transmission rate;

2) first electrical ready-out-signals indicative of the ready status of said first fiber optic interface means; and

2) second electrical ready-out-signals indicative of the ready status of said second fiber optic interface means; and

3 ) second electrical data, signals; first data steering means disposed in said first fiber optic interface means for directing transmission of said first electrical data signal produced in response to said first data signals generated by a user device of said first user means to all other user devices of said first user means in response to said first ready-in- signals and said first ready-out- signals, and for simultaneously directing transmission of said first optical data signal produced in response to said first data signals to said second fiber optic interface means, and for directing data from said second optical data signal to all of said user devices of said first user means; second data steering means disposed in said second fiber optic interface means for directing transmission of said second electrical data signal produced in response to said second data signals generated by a user device of said second user means to all other user devices of said second user means in response to said second ready-in-signals and said second ready-out-signals, and for simultaneously directing transmission of said second optical data signal produced in response to said second data signals to said first fiber optic interface device, and for directing data from said first optical data signal to all said user devices of said second user means; single link cable means for bi-directionally transmitting said first and second optical data signals between said first and second fiber optic interface means; whereby broadcast operation is established between any single user device connected to said communications network and all other user devices connected to said communications network.

65. A fiber optic interface device for connecting a plurality of user devices in a communications network comprising: fiber receiver means for receiving optical input transition encoded data signals which have a data transmission rate indicative of the operational state of an additional fiber optic interface device and for decoding said optical input transition encoded data signals to produce a decoded fiber data signal, and for detecting said data transmission rate of said optical input transition encoded data signals to produce a fiber activity signal; synchronous state means for receiving ready-in-signals produced by said user devices and said fiber activity signal and for addressing a logic decision table with said ready-in-signals and said fiber activity signal to produce switching signals, ready-out-signals and state signals; line driver means for transmitting said ready-out-signals and data-out-signals over one of a plurality of electronic serial data ports; fiber transmitter means for transmitting an optical output transition encoded data signal over a single fiber optic link cable; data steering means for receiving electronic data signals from said user devices, said switching signals and said decoded fiber data signal and for selecting at least one output signal from said electronic data signals and said decoded fiber data signal in response to said switching signals.

66. The device of claim 65 further comprising: diagnostic light emitting diode means for indicating the current state of operation of said fiber optic interface device.

67. The device of claim 65 further comprising: receive fiber means for transmitting said input optical data signals to said fiber receiver means; transmit fiber means for receiving said output optical data signals from said fiber transmitter means; fiber optic cable means for simultaneously bi-directionally transmitting said input and output optical data signals; combined coupler/connector means for connecting and axially and angularly aligning said transmit and receive fiber means with said fiber optic cable means to allow simultaneous bi-directional coupling of said input and output data signals between said transmit and receive fiber means and said fiber optic cable means.

68. The device of claim 67 wherein said fiber receiver means comprises: threshold means for distinguishing between optical input signals and reflected optical output signals.

69. The device of claim 65 further comprising: power supply means for deriving power from said data input signal and said ready-in-signals.

70. The device of claim 69 wherein said power supply means comprises: first diode summing means for accumulating a positive voltage supply from said ready-in-signals; second diode summing means for accumulating a positive voltage supply from said data input signals; third diode summing means for accumulating a negative voltage supply from said data input signals.

71. The device of claim 69 further comprising voltage inverter means coupled to said second diode summing means for providing an additional source of negative voltage.

72. The device of claim 70 further comprising: current limiting means for limiting the amount of current supplied by said first and third diode summing means; comparator means for generating a control signal to control said current limiting means.

73. The device of claim 72 further comprising: auxiliary power source means coupled to said positive and negative voltage supplies; power conditioner means coupled to said positive and negative voltage supplies to provide a conditioned voltage source.

74. A fiber optic interface device for connecting a plurality of user devices in a communications network comprising: fiber receiver means for receiving optical input transition encoded data signals which have a data transmission rate indicative of the operational state of an additional fiber optic interface device and for decoding said optical input transition encoded data signals to produce a decoded fiber data signal, and for detecting said data transmission rate of said optical input transition encoded data signals to produce a fiber activity signal, asynchronous combinational logic means for receiving ready-in-signals produced by said user devices and said fiber activity signal and for addressing a series of gates with said ready-in-signals and said fiber activity signal to produce switching signals, ready-out-signals and state signals; line driver means for transmitting said ready-in-signals and data-out-signals over one of a plurality of electronic serial data ports; fiber transmitter means for transmitting an optical output transion encoded data signal over a single fiber optic link cable; data steering means for receiving electronic data signals from said user devices, said switching signals and said decoded fiber data signal and for selecting at least one output signal from said electronic data signals and said decoded fiber data signal in response to said switching signals.

75. A lightguide sub-assembly device comprising: lightguide means for transmitting and receiving optical data; recladding formed over end portions of said lightguide means for decreasing light divergence and leakage; heat shrink tube means disposed over said recladding to hold said lightguide means in a closely spaced configuration; ferrule means for positioning said lightguide means in a combined coupler connector device; adhesive means for securing said lightguide means in said ferrule means; insert means for providing strain relief for said lightguide means; shrink tube means for securing said lightguide means to said insert means and said ferrule means.

76. The device of claim 75 further comprising: enclosure means having an opening adapted to secure said insert means to said enclosure means.

77. The device of claim 76 wherein said enclosure means further comprises: slot means formed in said enclosure means for retaining a fiber optic link cable in a curved configuration having a predetermined radius; fiber optic link cable locking means disposed in said slot means for securing said fiber optic link cable in said enclosure means and providing strain relief for said fiber optic link cable.

78. The device of claim 77 wherein said predetermined radius is sufficiently small to secure said fiber optic link cable to said enclosure means and sufficiently large to allow transmission of optical sigrals through said fiber optic link cable without significant attenuation.

79. The method of forming a sub-assembly receive and transmit lightguide assembly for use in a combined coupler/connector means for simultaneously bi-directionally coupling optical information in a link cable connected to said sub-assembly in said combined coupler/connector means comprising the steps of: stripping buffer and cladding from end portions of receive lightguide means and transmit lightguide means; applying recladding to said end portions of said receive lightguide means and said transmit lightguide means such that said cladding has a thickness of less than 30% of the diameter of the fiber optic core of said receive lightguide means and said transmit lightguide means; securing said end portions together in a closely spaced triangular configuration with fluoropolymer heat shrink tubing.

80. The method of claim 79 further comprising: positioning said end portions in ferrule means of said combined coupler/connector means; securing said end portions in said ferrule means of said combined coupler/connector means; removing protruding portions of said end portions by air abrasive cutting.

81. The method of claim 80 further comprising: cleaving opposite end portions of said receive lightguides and said transmit lightguides to a desired length to produce flat opposite end surfaces; optically coupling said opposite end surface of said receive lightguide means to an optical detector means; optically coupling said opposite end surface of said transmit lightguide means to an optical transmitter means.

82. The method of claim 81 further comprising: threading said receive lightguide means and said transmit lightguide means through a first optical cable sleeving; securing said first optical cable sleeving to said segment of said combined coupler/connector means and a strain relief device adapted to be attached to an enclosure device.

83. The method of claim 81 wherein said step of optically coupling said receive lightguide means to said optical detector means comprises: aligning said receive lightguide means with said optical detector means to produce a maximum output signal; securing said receive lightguide means to said optical detector means with an adhesive.

84. The method of claim 81 wherein said step of optically coupling said transmit lightguide means to said optical transmitter means comprises: aligning said transmit lightguide means to maximize transmitted light through said transmit lightguide means while maintaining detection levels of said optical detector means as a result of reflections of said transmitted light below a predetermined level.

85. The method of claim 82 comprising the further steps of: threading said receive lightguide means through a receive optical cable sleeving; threading said transmit lightguide means through a transmit optical cable sleeving; securing said receive optical cable sleeving and said transmit optical cable sleeving to said first optical cable sleeving with heat shrink tubing; adhesively securing said receive optical cable sleeving to said optical detector means; adhesively securing said transmit optical cable sleeving to said optical transmitter means.

86. A method of preparing the end portion of a single fiber optic link cable used to simultaneously bi-directionally transmit optical signals which minimizes both internal and external reflections comprising the steps of: stripping outer portions of said link cable to expose fiber optic cladding means; removing said cladding means to expose fiber optic core means; applying a recladding material to said fiber optic core means; securing fluoropolymer heat shrink tube means over said recladding material.

87. The method of claim 86 further comprising the steps of: securing said end portion in a ferrule means having a tapered surface for aligning said link cable; removing protruding portions of said end portions from said ferrule means by air abrasive cutting; rough polishing said end portions with abrasive means to reduce reflections.

88. The method of claim 87 wherein said step of rough polishing said end portions comprises the step of: rough polishing said end portions with abrasive means to produce a surface which is sufficiently rough to induce high order modes of reflected radiation in said link cable.

89. The method of claim 88 wherein said step of securing said fluoropolymer heat shrink tube means over said recladding material comprises the steps of: heat crimping said fluoropolymer heat shrink tube means to a buffer portion of said link cable; heat shrinking said fluoropolymer heat shrink tube means over said end portions of said link cable.

90. The method of claim 89 comprising the further steps of: attaching heat shrink tube means to said ferrule means and said outer portions of said link cable to provide strain relief.

91. A bi-directional optical fiber transmission system capable of simultaneous bi-directional transmission of optical signals comprising: first lightguide means for transmitting and receiving data from a first fiber optic interface device; second lightguide means for transmitting and receiving data from a second fiber optic interface device; first lightguide alignment means for retaining said first lightguide means in a closely spaced triangular configuration; second lightguide alignment means for retaining said second lightguide means in a closely spaced triangular configuration; single fiber optic link cable means having a fiber optic link core diameter sufficiently large to substantially overlap fiber optic lightguide cores of said first and second lightguide means disposed in said closely spaced triangular configuration in said first and second retention means for simultaneously bi-directionally transmitting said optical signals between said first and second lightguide means; first link cable alignment means disposed on a first end of said single fiber optic link cable means; second link cable alignment means disposed on a second end of said single fiber optic link cable means; first connector means for axially and angularly aligning said first lightguide alignment means with said first link cable alignment means to simultaneously bi-directionally couple said optical signals between said first lightguide means and said single fiber optic link cable means; second connector means for axially and angularly aligning said second lightguide alignment means with said second link cable alignment means to simultaneously bi-directionally couple said optical signals between said second lightguide means and said single fiber optic link cable means.

92. The system of claim 91 further comprising: cladding means disposed on end portions of said first and second lightguide means, said cladding means having a thickness sufficient to cause lower order modes of said optical signals to propagate through said first and second lightguide means and cause higher order modes of said optical signals to leak through said cladding means; optical absorbing means surrounding said cladding means for absorbing said higher order modes of said optical signals which have leaked through said cladding means.

93. The system of claim 92 wherein said optical absorbing means comprises a black adhesive compound for securing said first and second lightguide means in said first and second lightguide alignment means.

94. The system of claim 92 wherein the length and thickness of said cladding means can be adjusted to strip higher order modes of propagation in a manner equivalent to link cable means greater than a predetermined minimum length.

95. The system of claim 91 wherein said single fiber. optic link cable means have end surfaces which are sufficiently rough to substantially reduce reflection of said optical signals within said link cable means from said end surfaces.

96. The system of claim 95 wherein said end surfaces cause a substantial portion of reflected optical signals within said link cable means to be reflected as higher order mode radiation.

97. The system of claim 91 wherein said first and second connector means cause said first and second lightguide means to be separated from said first and second ends of said single fiber optic link cable by a distance which is approximately one quarter but no more than one half of the diameter of the. smallest of said fiber optic lightguide cores.

98. The system of claim 91 further comprising: refractive index matching means disposed between said first lightguide alignment means and said first link cable alignment means, and said second lightguide alignment means and said second link cable alignment means to reduce reflection.

99. The system of claim 91 wherein said single fiber optic link cable means has a predetermined minimum attenuation to maintain the magnitude of an optical signal which has been reflected in said link cable means from said first and second end of said link cable means below a predetermined level.

100. The system of claim 92 wherein said single fiber optic link cable means has a predetermined minimum attenuation to maintain the magnitude of an optical signal which has been reflected in said link cable means from said first and second end of said link cable means below a predetermined level.

101. The system of claim 95 wherein said single fiber optic link cable means has a predetermined minimum attenuation to maintain the magnitude of an optical signal which has been reflected in said link cable means from said first and second end of said link cable means below a predetermined level.

102. The system of claim 99 wherein said predetermined minimum attenuation is provided by use of link cable means having a predetermined minimum length.

103. The system of claim 99 wherein said predetermined minimum attenuation is provided by use of a material for said fiber optic link core having a predetermined minimum attenuation per unit of length.

104. The system of claim 99 wherein said predetermined minimum attenuation is provided by use of mode stripping means in said fiber optic link cable.

105. The system of claim 91 wherein said lightguide means comprises: receive lightguide means for receiving optical input signals from said link cable means; transmit lightguide means for transmitting optical output signals to said link cable means.

106. The system of claim 105 further comprising: receiver assembly means coupled to said receive lightguide means for detecting said optical input signals; transmitter assembly means coupled to said transmit lightguide means for producing said optical output signals.

107. The device of claim 106 wherein said receiver assembly means comprises: detector means for detecting said optical input signals; optical coupling means for increasing optical coupling efficiency between said detector means and said receive lightguide means; adhesive means for securing said receive lightguide means in optical alignment with said detector means.

108. The device of claim 107 wherein said receiver assembly means further comprises: heat shrink means disposed around said receive lightguide means for holding said receive lightguide means in a closely spaced configuration.

109. The device of claim 108 further comprising: receive lightguide cable sleeving means surrounding said receive lightguide means and adhesively secured to said adhesive means so as to provide strain relief to said receive lightguide means.

110. The device of claim 106 wherein said transmitter assembly means comprises: transmitter means for generating said optical output signals in response to said electrical output signals; optical coupling means for increasing optical coupling efficiency between said transmit means and said transmit lightguide means; adhesive means for securing said transmit lightguide means in optical alignment with said transmitter means.

111. The device of claim 110 further comprising: transmit lightguide cable sleeving means surrounding said transmit lightguide means and adhesively secured to said adhesive means so as to provide strain relief to said transmit lightguide means.

112. The device of claim 106 wherein said transmitter assembly means comprises: transmitter means for generating said optical output signal in response to said electrical output signal; adhesive means for securing said transmit lightguide means in optical alignment with said transmitter means and for increasing optical coupling efficiency between said transmitter means and said transmit lightguide means by providing retractive index matching.

113. The system of claim 106 further comprising: threshold means connected to said receiver assembly means for distinguishing between said optical input signals and reflections of said optical output signals.

114. A method of reducing reflections in an asymmetric Y-coupler/connector device for bi- directionally coupling optical signals from a plurality of transmit/receive lightguides to a single fiber optic link cable comprising the steps of: angularly aligning end portions of said transmit/receive lightguides with said link cable so that end surfaces of said transmit/receive lightguides and the end surface of said link cable are substantially parallel and substantially perpendicular to a common axis of said transmit/receive lightguides and said link cable; longitudinally aligning said transmit/receive lightguides and said link cable such that said end surfaces of said transmit/receive lightguides are separated from said end surface of said, link cable by a distance which is approximately one quarter but no more than one half of the diameter of the fiber optic core of the smallest of said transmit/receive lightguides.

115. A method of reducing reflections in a fiber optic link cable used to bi-directionally couple optical signals between fiber optic interface devices comprising the steps of: abrasively polishing said fiber optic link cable to produce end surfaces which cause a substantial portion of said optical signals reflected within said link cable from said end surfaces to be reflected as higher order modes of radiation which attenuate in said link cable; providing a link cable having a predetermined minimum attenuation.

116. The method of claim 114 wherein said step of providing a link cable having a predetermined minimum attenuation comprises: providing a link cable having a predetermined minimum length; using a fiber optic core material in said link cable to produce said predetermined minimum attenuation for said predetermined minimum length.

117. A method of reducing reflections in combined optical coupler/connector for optically coupling and mechanically connecting optical fibers by removing higher order modes of radiation comprising the steps of: providing a cladding material on said optical fibers which allows higher order modes of radiation to leak through said cladding material; surrounding said cladding material with a light absorbing medium for a length sufficient to remove said higher order modes of radiation.

118. A method of reducing optical losses in a bidirectional asymmetric Y-coupler/connector by increasing the ratio of active surface area to loss area in said coupler/connector comprising the steps of: providing transmit/receive lightguides having a cladding surface which has a thickness of approximately 4% to 15% of the thickness of the fiber optic core diameter of said transmit/receive lightguides; arranging said transmit/receive lightguides in a closely spaced configuration; providing link cable means having a fiber optic core means which substantially overlaps the fiber optic cores of said transmit/receive light- guides when said transmit/receiver lightguides are arranged in said closely spaced configuration.

119. The device of claim 36 further comprising: means for continuously monitoring a fiber optic link cable coupled between said fiber optic interface device and said additional fiber optic interface device to detect a failure of transmission of data indicative of a disruption in said fiber optic link cable.