WO2001016639A1

WO2001016639A1 - Automatic alignment system for coupling multiple light sources

Info

Publication number: WO2001016639A1
Application number: PCT/US2000/024247
Authority: WO
Inventors: Stephen C. Yetso; Quan Nguyen; Timothy Andrews
Original assignee: Bio-Rad Laboratories, Inc.
Priority date: 1999-08-31
Filing date: 2000-08-31
Publication date: 2001-03-08
Also published as: AU7109900A; CA2382565A1; WO2001016639A9

Abstract

A system for coupling up one or more light sources to one or more destinations is provided. Under the present invention, the transmission efficiency from a light source to a destination is optimized regularly on an automatic basis by monitoring the intensity of the light transmitted. In a preferred embodiment, the system includes a source fiberoptic cable for bundling up light emitted from a multitude of light sources, a destination fiberoptic cable for receiving light transmitted from the source fiberoptic cable, a motorized positioning stage for aligning the source and the destination fiberoptic cables, and a feedback servo control for adjusting the motorized positioning stage to accurately align the source and the destination fiberoptic cables based on the intensity of the light transmitted by the source fiberoptic cable. In operation, the intensity of the light transmitted by the source fiberoptic cable is detected by the feedback servo control. Based on the intensity reading, the feedback servo control selectively directs the motorized positioning stage to align the source and the destination fiberoptic cables in an optimal position to improve transmission efficiency.

Description

AUTOMATIC ALIGNMENT SYSTEM FOR COUPLING MULTIPLE

LIGHT SOURCES

CROSS-REFERENCES TO RELATED APPLICATIONS This application claims the benefit of priority under 35 U.S.C. § 119 from

U.S. Provisional Patent Application Serial No. 60/151,704 filed on August 31, 1999, the disclosure of which is hereby incorporated by reference in its entirety for all purposes.

BACKGROUND OF THE INVENTION Research and development efforts over the past couple of decades have led to the commercial realization of relatively low-cost, low-loss optical fibers. In many industries, such as biomedical instrumentation and telecommunications, optical fibers have become the preferred choice of transmission medium.

A variety of equipment exploiting the benefits of optical fibers have been developed over the years. For example, due to their small size, optical fibers are now commonly utilized in various types of medical instruments to help reduce the invasive nature of surgical or other medical procedures. In the telecommunications field, a number of telephone companies are revamping or otherwise rebuilding their communication systems and networks to take advantage of the benefits, such as compact size and high transmission speed and capacity, offered by optical fibers.

Generally, optical fibers are used to transmit light emitted from a light source to a destination. Optical fibers are usually encapsulated in a fiberoptic cable. The light emitted from the light source represents one or more signals. The transmitted light is received at the destination and then deciphered to identify the intended signals. For a relatively short distance, one integral segment of fiberoptic cable can be used to transmit the light from the light source to the destination. However, for a number of practical considerations, such as signal strength degradation, scalability, and maintainability, etc., disjoint pieces of fiberoptic cables coupled together by optical couplers are typically used to transmit the light from the light source to the destination. Inevitably, a certain amount of coupling loss is incurred when optical couplers are used to couple disjoint segments of fiberoptic cables.

Despite the advances made in the fiber optics field, coupling losses or coupling efficiency in fiberoptic cables have remained a major topic of interests for engineers and researchers alike. Coupling losses may be caused by alignment errors, as well as a number of other factors including reflections at glass-air interfaces, poor fiber- end quality, and mismatches between the parameters of the fibers being coupled.

Coupling losses resulting from alignment errors are a particularly acute problem for fiberoptic cables due to the minuscule size of the individual optical fibers. The diameter of an optical fiber is generally in the range of 10-200 microns. To put it in a more tangible context, this quantity is usually no greater than the diameter of a strand of human hair. Due to this minuscule size, it is self-evident that the problem of aligning fiberoptic cables, in particular, the optical fibers, to achieve optimal transmission efficiency is a particularly challenging one.

Alignment errors are generally caused by mechanical imperfections in the jointing techniques. Such imperfections include separation between the fiber ends, relative lateral displacement of the core axes, and angular misalignment of the fiber axes. On a conceptual level, these errors can be easily identified. The apparent solution appears deceptively simple and straightforward ~ all that is required seems to be the accurate mechanical alignment of the optical fibers. However, due to the microscopic size of the optical fibers and the mechanical nature of alignment, these errors in most cases are actually immensely difficult to correct. Thus, it would be desirable to provide a system that is capable of optimizing the coupling efficiency and conversely minimizing the coupling loss of connected fiberoptic cables.

Moreover, for new and old equipment alike, calibration or alignment of the fiberoptic cables need to be performed initially before use and periodically thereafter to ensure that the accuracy of the equipment stays within tolerable levels. Under most of the currently existing industry practices, the mechanical alignment is manually performed by a field technician with the aid of certain calibration equipment. Consequently, this manual approach often requires a substantial amount of time for the technician to complete the necessary procedures. Hence, it would be desirable to provide a system that is capable of correcting alignment errors without human intervention and in a time efficient manner. Furthermore, as a consequence of the difficult nature in resolving the alignment problem, the cost of remedying such problem has become proportionally expensive. As previously mentioned, in order to correctly align two optical fibers (to within tolerable levels of accuracy), current conventional practices require a field technician to be present on site to perform the mechanical alignment manually. Needless to say, this necessarily incurs substantial expenses.

In addition, since mechanical alignment has a very narrow margin for error, the use of precision equipment are almost always mandatory and necessary. Incidentally, these precision equipment are also quite expensive. Therefore, the cost of having a mechanical alignment performed on fiberoptic cables can often reach the range of thousands of dollars. Consequently, it would also be desirable to provide a system that is capable of correcting alignment errors in a cost effective manner.

Perhaps, due to the alignment problem often experienced in coupling two disjoint segments of fiberoptic cables, there is a dearth of equipment capable of providing the ability to efficiently couple up multiple light sources to one or more destinations. Therefore, it would be desirable to provide a system that is capable of coupling multiple light sources to one or more destinations.

SUMMARY OF THE INVENTION

The present invention relates to the efficient transmission of light along connected cables. More specifically, the present invention relates to a system for coupling up multiple light sources to one or more destination and/or applications. Under the present invention, the transmission efficiency from a light source to a destination is optimized regularly on an automatic basis by monitoring the intensity of the light transmitted.

In an exemplary embodiment, the system includes a source fiberoptic cable for bundling up light emitted from a multitude of light sources, a destination fiberoptic cable for receiving light transmitted from the source fiberoptic cable, a motorized positioning stage for aligning the source and the destination cables, and a feedback servo control for adjusting the motorized positioning stage to accurately align the source and the destination fiberoptic cables based on the intensity of the light transmitted by the source fiberoptic cable.

In a preferred embodiment, the source fiberoptic cable and the destination fiberoptic cable both contain one or more constituent optical fibers. With this design, one of a multitude of light sources can be selectively directed to one of a number of destinations. The feedback servo control comprises a light sensor for detecting the intensity of the light transmitted by the source fiberoptic cable, an A D converter for converting the intensity signal, in analog form, into digital electrical signals, and control logic for controlling the motorized positioning stage to properly align the source and the destination cables based on the digital electrical signals. Preferably, the light sensor is a photomultiplier tube and the control logic includes a control circuitry and a software program. In operation, light from one of the optical fibers within the source fiberoptic cable is selected for transmission. The intensity of the selected light transmitted by the source fiberoptic cable is detected by the feedback servo control. Based on the intensity reading, the feedback servo control then selectively directs the motorized positioning stage to align the source and the destination fiberoptic cables in an optimal position to improve transmission efficiency.

In particular, the light sensor, for example, the photomultiplier tube, detects the intensity of the selected light transmitted by the source fiberoptic cable. The detected intensity signal is then converted by the A/D converter into digital form. Using the digital signal, the control logic then directs the motorized positioning stage to align the source and the destination fiberoptic cables to achieve optimal transmission efficiency.

Reference to the remaining portions of the specification, including the drawings and claims, will realize other features and advantages of the present invention. Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with respect to accompanying drawings, like reference numbers indicate identical or functionally similar elements.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a simplified schematic diagram showing the various elements of a preferred embodiment of the present invention;

Fig. 2 is a simplified cross-sectional view of a preferred embodiment of a source cable in accordance with the present invention;

Fig. 3 is a simplified schematic diagram showing the various elements of a second preferred embodiment of the present invention; and

Fig. 4 is a simplified schematic diagram showing a preferred embodiment of the present invention as incorporated into another device. DESCRIPTION OF THE SPECIFIC EMBODIMENTS The present invention will now be described. An exemplary system for coupling up multiple light sources into one or more destinations, embodying the principles and concepts of the present invention is generally shown in Fig. 1. Referring to Fig. 1, in an exemplary embodiment, the system 10 includes a source fiberoptic cable 12, a destination fiberoptic cable 16, a motorized positioning stage 14, and feedback servo control 18 designed to control the motorized positioning stage 14.

Preferably, the source fiberoptic cable 12 is made up of a series of individual multimode optical fibers that are conveniently terminated into one common endpoint. Alternatively, the various optical fibers can be terminated into multiple endpoints. The function of the source fiberoptic cable 12 is to carry light emanating from a number of different sources 20.

Fig. 2 shows a simplified cross-sectional view of the source fiberoptic cable 12. As shown in Fig. 2, the source fiberoptic cable 12 comprises three individual optical fibers 24, 26, 28. Each of these individual optical fibers 24, 26, 28, in turn, is connected to a light source 20. As a result, the source fiberoptic cable 12 is capable of carrying light originating from one or more different light sources 20. It should be understood that, depending on the design requirements, the source fiberoptic cable 12 may comprise any number of individual optical fibers to accommodate the desired number of light sources 20, subject to the physical limitation of the source fiberoptic cable 12. Further, it should also be noted that, to the extent that the source fiberoptic cable 12 allows, additional optical fibers may be inserted into the source fiberoptic cable 12 at a subsequent time to accommodate for an increase in the number of light sources 20. The light sources 20 may emit light of various wavelengths along the spectrum including infrared, ultraviolet, and light from the visible spectrum. A light source 20 that is commonly used in a typical application is a laser. By its very nature, the laser may be controlled to emit monochromatic and coherent light of specific wavelengths for purposes dependent on the particular application.

In a preferred embodiment, the multitude of light sources 20 is a group of three lasers each capable of emitting light at a different wavelength, for example, red (~ 635nm), green (~ 535nm) and blue (~ 488nm). The emitted light from each laser is directed into an individual optical fiber for relay and transmission over extended distances. Lasers are particularly suited for relay over a fiberoptic cable because they produce focused monochromatic and coherent light which makes for relatively easy transmission and reception.

Likewise, the destination fiberoptic cable 16 contains one or more individual optical fibers (not shown). These individual optical fibers are then appropriately and respectively coupled to a number of destinations and/or applications 22. The number of optical fibers contained within the destination fiberoptic cable 16 is similarly adjustable, depending on the practical and design considerations. As will be more fully described below, one of these optical fibers within the destination fiberoptic cable 16 is selectively positioned to receive light transmitted from one of the light sources 20.

In a preferred embodiment, the motorized positioning stage 14 is a mechanical device having a couple of screw drives driven by their respective motors. The motorized positioning stage 14 is capable of providing highly accurate and repeatable position control. Alternatively, the motorized positioning stage 14 can be implemented using piezoelectric motors. As will be described further below, the motorized positioning stage 14 is controlled by the feedback servo control 18 to align the source and destination fiberoptic cables 12, 16.

The source and destination fiberoptic cables 12, 16 are movably coupled to one another via the motorized positioning stage 14. The motorized positioning stage 14 mechanically aligns the source and the destination fiberoptic cables 12, 16 to ensure optimal coupling between the cables 12, 16. More specifically, the motorized positioning stage 14 is capable of aligning an individual optical fiber 24, 26, 28 in the source fiberoptic cable 12 with the desired corresponding optical fiber in the destination fiberoptic cable 16. In one preferred embodiment, the destination fiberoptic cable 16 contains one optical fiber. This permits light from any one of the multiple light sources 20 to be selectively transmitted to a single destination or application 22.

In an alternative embodiment, the destination fiberoptic cable 16 contains more than one optical fiber, thereby allowing light from any one of the multiple light sources 20 to be selectively transmitted to multiple destinations or applications 22. With multiple optical fibers in both the source and the destination fiberoptic cables 12, 16, a multiplexing scheme may be implemented. The alignment process is performed based on the feedback servo control 18 and this process will be more fully described later. The physical connections between the motorized positioning stage 14 and the source and the destination fiberoptic cables 12, 16 will be described next. In one preferred embodiment, the terminated end of the source fiberoptic cable 12 is maintained at a fixed reference position relative to the terminated end of the destination fiberoptic cable 16. Consequently, the motorized positioning stage 14 only need to adjust the destination fiberoptic cable 16 to achieve the proper alignment. Alternatively, the destination fiberoptic cable 16 may be maintained at a fixed reference position relative to the source fiberoptic cable 12 to serve the same purpose.

The optimal alignment of the source and the destination fiberoptic cables 12, 16 is achieved via the feedback servo control 18. The function of the feedback servo control 18 is to ensure that the source and destination fiberoptic cables 12, 16 are optimally aligned so as to improve transmission efficiency. The feedback servo control 18 performs this function by monitoring the intensity of light transmitted by the source fiberoptic cable 12. Referring to Fig. 3, in an exemplary embodiment, the feedback servo control 18 comprises the following components, namely, a light sensor 32 for detecting the intensity of the light transmitted by the source fiberoptic cable 12, an A/D converter 34 for converting the detected intensity into digital electrical signals, and control circuitry 36 for controlling the motorized positioning stage 14 to adjust the alignment of the source and the destination fiberoptic cables 12, 16 in accordance with the digital electrical signals.

In a preferred embodiment, the light sensor 32 for detecting the intensity of the light transmitted by the source fiberoptic cable 12 is a photomultiplier tube. The photomultiplier tube is a type of photodetector which detects the presence of photons by their intensity and then subsequently amplifies the detected intensity, thereby facilitating any needed analyses. Alternative devices which may be used as light sensors to detect the intensity of light include CCD's (charge coupled devices), photodiodes, and other photon counting devices.

Once the light transmitted by the source fiberoptic cable 12 is detected, the analog signal captured by the photomultiplier tube is then converted by the A/D converter 34 into digital electrical signals. Various A/D devices commonly used in the art to convert analog light signal into digital electrical signals are available including, for example, a device manufactured by Advanced Micro Devices with model number P/N AD976A. The digital electrical signals are then used to adjust the alignment of the source and destination fiberoptic cables 12, 16 to achieve an optimal transmission efficiency. In one preferred embodiment, the control circuitry 36 for interpreting the digital electrical signals to control the alignment is a controller integrated circuit (controller IC) and a software program. The controller IC is programmed by the software program to scan an area at a certain acceleration and velocity to detect the intensity of the light transmitted. A commercially available product which may be used as the controller IC for this purpose is a device manufactured by National Semiconductor with model number LM629M. The software program used to control the controller IC may be implemented as a separate program resident outside of the controller IC or as firmware embedded inside the controller IC.

The intensity of the light is detected and scanned in the following basic manner. Various scanning mechanisms and devices are commonly known in the art for detecting and scanning the intensity of light. In one preferred embodiment, light transmitted from the source fiberoptic cable 12 is directed to hit a film having an area of about ten (10) square millimeters. For scanning purposes, the film is divided into a grid of rows and columns. The scanning mechanism is initially calibrated to home in on an initial starting scan position, generally located at one of the lower or upper corners of the grid. This initial starting scan position is needed to provide a fixed reference position for all subsequent measurements to be taken. The scanning then starts from the initial starting scan position and examines each column from top to bottom (or vice versa), i.e., row by row, and then sequentially from column to column until all the desired rows and columns are scanned. A second or any desired number of subsequent scans may be performed iteratively to ensure the accuracy of the readings. The maximum readings are recorded based on a dual coordinate system by position of the rows and columns. These maximum readings represent the location of the detected light on the film. Using these readings, the software program then directs the motorized positioning stage 14 to adjust the position of the source fiberoptic cable 12 relative to the destination fiberoptic cable 16 to obtain the optimal alignment thus improving the transmission efficiency. In the foregoing arrangement, it is assumed that the destination fiberoptic cable 16 is maintained at a fixed reference position relative to the source fiberoptic cable 12. Alternatively, the source fiberoptic cable 12 can be maintained as a reference instead.

To compensate for any loss in efficiency due to subsequent changes, such as movement in the source or destination fiberoptic cables 12, 16 or other components, the scanning process may be re-initiated periodically to verify the location of the maximum readings and remedial adjustment may be made by the motorized positioning stage 14 accordingly.

There are other ways to perform the column-by-column scan. For example, instead of scanning all the columns and rows one by one as described above, a divide-and-conquer strategy, similar to a binary search, may be used. Using this strategy, only a selected number of columns are initially examined. The coordinates of the area, i.e., the delimiting columns and rows, containing the maximum readings are recorded. Another selected number of columns and/or rows within this area is then scanned a second time to further constrict the area containing the precise location of the maximum readings. This process is then iterated until the desired resolution for the area containing the maximum readings is reached. In general, as the area is iteratively constricted, the selected number of columns and/or rows used for scanning is proportionally increased to better identify where the maximum readings appear. The following is the sequence of events which generally take place when a preferred embodiment of the present invention is in operation. When the system 10 is first turned on, the feedback servo control 18 engages a self-calibrating mode identifying the initial starting scan position. Light from one of the multiple light sources 20 is then transmitted via its designated optical fiber 24, 26, 28 within the source fiberoptic cable 12 to a film for scanning. The intensity of the light as received on the film is then detected by the photomultiplier tube and converted by the A/D converter 34 into digital electrical signals. The scanning process iterates itself, as previously described above, to identify the location of the maximum readings on the film. After having identified the maximum readings, the controller IC controlled by the software program then directs the motorized positioning stage 14 to make the necessary adjustments to achieve optimal alignment between the source and the destination fiberoptic cables 12, 16. The controller IC under the control of the software program periodically performs the scanning process to verify the location of the maximum readings, and if necessary, directs the motorized positioning stage 14 to make any remedial adjustments. Referring to Fig. 4, an exemplary embodiment of the present invention is shown incorporated into another device 38. This device 38 can be any device that requires light to be transmitted from one or more light sources 20 to a destination or application 22. For example, this device 38 can be a scanner. As shown therein, the system 10 permits multiple light sources 20 to be selectively transmitted to a destination 22, in this case, a scan head. In another application, the present invention can be used to provide proper alignment for telecommunication connections along telecommunication lines spanning extended distances. Each telecommunication connection can be periodically monitored or adjusted after occurrence of a triggering event, such as an earth quake, by the present invention to ensure optimal signal transmission. Based on the disclosure provided herein, a person reasonably skilled in the art will know of other ways and methods to apply the present invention to other applications.

It is understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and scope of the appended claims. All publications, patents, and patent applications cited herein are hereby incorporated by reference for all purposes in their entirety.

Claims

WHAT IS CLAIMED IS:

1. A system for coupling a light source to a destination, comprising: a source cable for transmitting light from said light source; a destination cable for receiving said light transmitted from said source cable; a positioning stage for movably aligning said source cable and said destination cable; and a feedback servo control configured to generate a control signal to control said positioning stage; wherein said control signal generated by said feedback servo control is based on intensity and location of said light transmitted from said source cable.

2. The system according to claim 1, wherein transmission efficiency between said source cable and said destination cable is optimized by aligning said source cable and said destination cable.

3. The system according to claim 1, wherein said source cable is a fiberoptic cable.

4. The system according to claim 1, wherein said destination cable is a fiberoptic cable.

5. The system according to claim 1 , wherein said positioning stage comprises a piezoelectric motor.

6. The system according to claim 1 , wherein said feedback servo control further comprises: a light sensor for detecting said intensity and location of said light transmitted from said source cable; an A/D converter configured to convert said detected intensity and location to digital signals; and a control circuit configured to use said digital signals to control said positioning stage.

7. The system according to claim 6, wherein said light sensor is a photomultiplier tube.

8. The system according to claim 6, further comprising: a software program designed to direct said control circuit to use said digital signals to control said positioning stage.

9. A system for coupling two connecting cables, comprising: a source cable capable of transmitting light from a plurality of light sources; a destination cable for receiving light transmitted from said source cable; a positioning stage for aligning said source cable and said destination cable so as to optimize transmission efficiency therebetween; and a feedback servo control configured to control said positioning stage by detecting and using intensity and associated location of said light transmitted via said source cable.

10. The system according to claim 9, wherein said source cable is a first fiberoptic cable having a plurality of optical fibers contained therein; wherein light from each of said plurality of light sources is transmitted via a corresponding optical fiber within said first fiberoptic cable; and wherein said destination cable is a second fiberoptic cable having one or more optical fibers contained therein.

11. The system according to claim 10, wherein an optical fiber within said first fiberoptic cable is aligned with an optical fiber within said second fiberoptic cable.

12. The system according to claim 9, wherein said destination cable is coupled to one or more applications.

13 . The system according to claim 9, wherein said feedback servo control further comprises: a light sensor for detecting said intensity and associated location of said light transmitted from said source cable; an A/D converter configured to convert said detected intensity and associated location to digital signals; and a control circuit configured to use said digital signals to control said positioning stage.

14. An apparatus for transmitting light from a plurality of light sources, comprising: a first fiberoptic cable having a plurality of optical fibers contained therein; a second fiberoptic cable having a plurality of optical fibers contained therein; a positioning stage for aligning said first fiberoptic cable with said second fiberoptic cable; a light sensor for detecting intensity and location of light transmitted from said first fiberoptic cable; an A/D converter for converting said detected intensity and location to digital signals; and a control circuit configured to receive said digital signals and control said positioning stage in accordance therewith.

15. The apparatus according to claim 14, wherein each of said plurality of light sources is coupled to a corresponding optical fiber within said first fiberoptic cable; and wherein each of said plurality of optical fibers within said second fiberoptic cable is coupled to a corresponding application.

16. The apparatus according to claim 14, wherein light from one of said plurality of light sources is selectively transmitted via said first fiberoptic cable to one of said plurality of optical fibers within said second fiberoptic cable.

17. The apparatus according to claim 16, wherein one of said plurality of optical fibers within said first fiberoptic cable is selectively aligned by said positioning stage with one of said plurality of optical fibers within said second fiberoptic cable.

18. The apparatus according to claim 17, wherein said selective alignment is periodically adjusted by said positioning stage based on said digital signals.

19. The apparatus according to claim 17, wherein said selective alignment is performed to optimize transmission efficiency between said first fiberoptic cable and said second fiberoptic cable.

20. A method for coupling a plurality of light sources to a destination, comprising steps of: selectively transmitting light from one of said plurality of light sources via a source cable; detecting intensity and location of said light; adjusting position of said source cable based on said detected intensity and location so as to align said source cable with a destination cable thereby optimizing transmission efficiency between said source cable and said destination cable; and transmitting said light to said destination cable.

21. The method according to claim 20, further comprising steps of: coupling an application to said destination cable; and performing said adjusting step on a periodic basis.