CA1282831C - Optical signal regenerator - Google Patents
Optical signal regeneratorInfo
- Publication number
- CA1282831C CA1282831C CA000538088A CA538088A CA1282831C CA 1282831 C CA1282831 C CA 1282831C CA 000538088 A CA000538088 A CA 000538088A CA 538088 A CA538088 A CA 538088A CA 1282831 C CA1282831 C CA 1282831C
- Authority
- CA
- Canada
- Prior art keywords
- optical
- amplifier
- signal
- input
- output
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/29—Repeaters
- H04B10/291—Repeaters in which processing or amplification is carried out without conversion of the main signal from optical form
- H04B10/299—Signal waveform processing, e.g. reshaping or retiming
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/50—Amplifier structures not provided for in groups H01S5/02 - H01S5/30
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/29—Repeaters
- H04B10/291—Repeaters in which processing or amplification is carried out without conversion of the main signal from optical form
- H04B10/2912—Repeaters in which processing or amplification is carried out without conversion of the main signal from optical form characterised by the medium used for amplification or processing
- H04B10/2914—Repeaters in which processing or amplification is carried out without conversion of the main signal from optical form characterised by the medium used for amplification or processing using lumped semiconductor optical amplifiers [SOA]
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L7/00—Arrangements for synchronising receiver with transmitter
- H04L7/0075—Arrangements for synchronising receiver with transmitter with photonic or optical means
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L7/00—Arrangements for synchronising receiver with transmitter
- H04L7/02—Speed or phase control by the received code signals, the signals containing no special synchronisation information
- H04L7/027—Speed or phase control by the received code signals, the signals containing no special synchronisation information extracting the synchronising or clock signal from the received signal spectrum, e.g. by using a resonant or bandpass circuit
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
- H01S5/0607—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying physical parameters other than the potential of the electrodes, e.g. by an electric or magnetic field, mechanical deformation, pressure, light, temperature
- H01S5/0608—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying physical parameters other than the potential of the electrodes, e.g. by an electric or magnetic field, mechanical deformation, pressure, light, temperature controlled by light, e.g. optical switch
Abstract
ABSTRACT
OPTICAL SIGNAL REGENERATOR
An optical signal regenerator comprises an optical coupler (1) having a first input (2) for an optical information signal, a second input (3) for optical clock pulses and an output (4) for a combined signal, and a resonant laser amplifier (5) downstream of the output (4) of the coupler (1) and arranged to receive the combined signal and, in use, output a regenerated optical information signal. The bias current applied to the laser amplifier (5), in use; biases the amplifier (5) to a level below its lasing threshold, and the power of the optical clock pulses is just below the bistable threshold of the amplifier, so that, when an optical information signal is fed into the first input (2) during the application of an optical clock pulse to the second input (3), the bistable threshold of the amplifier (5) is exceeded causing a sudden jump in the power of the optical output of the amplifier to provide a regenerated optical information signal.
OPTICAL SIGNAL REGENERATOR
An optical signal regenerator comprises an optical coupler (1) having a first input (2) for an optical information signal, a second input (3) for optical clock pulses and an output (4) for a combined signal, and a resonant laser amplifier (5) downstream of the output (4) of the coupler (1) and arranged to receive the combined signal and, in use, output a regenerated optical information signal. The bias current applied to the laser amplifier (5), in use; biases the amplifier (5) to a level below its lasing threshold, and the power of the optical clock pulses is just below the bistable threshold of the amplifier, so that, when an optical information signal is fed into the first input (2) during the application of an optical clock pulse to the second input (3), the bistable threshold of the amplifier (5) is exceeded causing a sudden jump in the power of the optical output of the amplifier to provide a regenerated optical information signal.
Description
0268P ~ 83~
OPTICAL SIGNAL REGENERATOR
Communications and data transmission systems which transmit in~ormation signals in the form of optical pulses over a dielectric waveguide such as an optical ~ibre are now commonplace. Whilst improvements in the sources of the optical pulses and in the optical fibre waveguides have increased the range over which such signals can be transmitted to between 100 and 200 kilometers it is still necessary to regenerate the sisnals when they are o transmitted over greater distances and when their power is reduced by beam splitting or being switched or otherwise handled. In a conventional regenerator, the optical signal is received by a photodiode and converted to an electrical signal. This electrical signal is then amplified and reshaped in an electronic regenerator circuit hefore being converted by an optical source into an optical pulse once again for onward transmission along the next optical fibre transmission line.
In this specification9 the term optical is intended to re~er to the visible region of the electromagnetic spectrum together with those parts of the in~rared and ultraviolet regions at each end o~ the visible region which are capable of being transmitted by dielectric optical waveguides such as optical fibres.
According to this invention an optical signal regenerator comprises an optical coupler having a first input for an optical information signal~ a second input ~or optical clock pulses and an output ~or a combined signal, and a resonant laser ampli~ier downstream of the output o~ the coupler and arranged to recei~e the combined signal and, in use, output a regenerated optical information signal. The bias current applied to the laser amplifier, in use, biases the ampli~ier to a level below ~k q~
83~
its lasing threshold, and the power of the optical clock -- pulses is just below the bistable threshold of the amplifier, so that~ when an optical in~ormation signal is fed into the first input during the application of an s optical clock pulse to the second input, the bistable threshold of the amplifier is exceeded causing a sudden jump in the power o~ the optical output of the amplifier to provide a regenerated optical information signal.
It should be noted that the lasing threshold and the bistable threshold apply to distinct phenomena. In the optical regeneratcr, the e1ectrical bias applied to the laser amplifier is below the lasing threshold bias current and cnnsequently the amplifier does not lase. The sudden amplification occurs because the optical power of an input optical signal is made to exceed an optical power bistable threshold for the ampli~ier.
When the optical power input to a semiconductor laser amplifier is increased, the extra stimulated emission raises the recombination rate. The carrier density is correspondingly reduced. As a result9 th~
ef~ective re~ractive index o~ the active region of a resonant laser amplifier increases with the optical power passing through it. The amplifier resonances are thereby tuned to longer wavelengths, and the gain at a given wavelength therefore varies. The puwer transfer characteristios o~ such an ampli~ier are consequently non-linear and, at appropriate input wavelengths, bistable operation is made possible.
Regeneratinn is achieved by combining an input signal with an optical clock signal and coupling them both into the resonant optical amplifier.
The clock signal consists of a train of optical pulses at the desired regeneration rate and with a wavelength at which the amplifier is ~istable. The peak 2~331 power of the clock signal is held marginally below the bistable threshold optical power level at which the amplifier will jump into a higher gain state.
With a low level input signal the output of the amplifier is in a lower gain state and its output comprises the slightly amplified clock signal. When the input signal increases to a high enough level such that the extra power in the combined input and clock signals is sufficient to exceed the bistable threshold then suddenly lo the resonant wavelength of the laser amplifier is matched to that of the light passing through it and the amplifier jumps into the higher gain state. It remains in this state, even if the input signal level again falls, until the end of the current clock pulse. The output of the amplifier for that period then includes a highly ampli~ied clock pulse.
The complete regenerated signal comprises a train of return-to-zero pulses with the timing and wavelength of the clock signal.
The input signal need not be at the same wavelength as the clock signal, so long as the amplifier has adequate gain at the input signal wavelength to trigger the bistable operation. Therefore, for example, the wavelength may be shifted between input and output by multiples of the amplifier mode spacing.
The optical signal regenerator may include an optical clock pulse generator which generates optical clock pulses in synchronism with a standard clock such as a system clock or, alternatively, it may be arranged to recover ti~ing information from the input optical information signal and generate the clock pulses in accordance with this recovered timing information.
The optical signal regenerator may also include biasing means such as a constant current source to provide a bias current which biases the laser amplifier to a level just below its lasing threshold. When the regenerator includes an optical clock pulse generator preferably it also includes power control means which control the power of the optical clock pulses to a level just below the bistable threshold o~ the laser amplifier. For example, the control means may monitor the output of the laser ampli~ier at a time that the regenerated output signal is not being emitted and control the power o~ the clock o pulses in accordance with the monitored output.
The resonant laser amplifier is preferably formed by a semiconductor laser amplifier and this may have the form of a resonant Fabry-Perot ampli~ier or a distributed feedback laser.
Pre~erably the clock pulses do not have the same wavelength as the input optical information signal and preferably the clock pulses have a wavelength slightly longer than that of the input information signal.
However, the clock pulses may be removed from the input information signal by multiples of the mode spacing in either direction when the laser amplifier is of the Fabry Perot type. Typically the clock pulses would be of the order o~ ten or tens of nanometers longer or shorter than that of the input information signal. In this way the regeneratPd optical information output signal which has the same wavelength as the clock pulses has its wavelength shifted from that of the input in~ormation signal and this can be an advantage in scme applications.
Indeed the regenerator can be used as a wavelength shifter.
Filtering means suoh as a mon~chromator or narrow bandpass ~ilter may be located downstream of the resonant laser amplifier to separate the regenerated information signal from the slightly amplified input information signal and any spontaneous emission generated by the 3~L
laser. However, filtering means are unnecessary when equipment which receives the regenerated information signal downstream from the laser is only responsive to light of the regererated signal wavelength.
A particular example of a signal regenerator in accordance with this invention together with an experiment to demonstrate its operation will now be described with reference to the accompanying drawings in which:-Figure 1 is a graph illustrating the output power -o input power characteristics o~ an amplifier for light of different wavelengths;
Figure 2 is a graph of output power against input power illustrating the typical operating range for the laser amplifier;
Figure 3 is a diagram of a regenerator together with equipment to demonstrate its operation; and, Figures 4, 5, 6 and 7 are oscillographs showing the output of the regenerator with data low, and with data high9 an input data stream, and a corresponding regenerated output data stream, respectively.
Referring first to Figure 3, the illustrated optical signal regenerator in accordance with this invention includes an optical coupler 1 having an optical signal input 2, a clock pulse input 3 and an output 4 for the combined signal, and a laser amplifier 5 coupled to receive the combined signal ~rom the output 4. The laser amplifier 5 is a double channel planar buried heterostructure semiconductor laser such as that described in an article in Electronics Letters 23 May 1985, Vol.21, No.ll, pages 493-494, entitled "High Performance DC-PBH
Lasers at 1.52 micrometres by a Hybrid MOVPE/LPE Process", by Nelson A W, Wong S, Regnault J C9 Hobbs R E, Murrel D
L, and Walling R H. The facet reflectivies of the laser are reduced to 3% by the application o~ anti-reflection coating.
d8~33~3L
In an experiment to demonstrate the effectiveness of the regenerator an input signal to the first input 2 ls produced by a distributed feedback laser 7 having a wavelength of 1526 nm which is driven from a 140 Mb/second pattern generator 8. This provides a continuous stream of optical pulses representing a stream of cptical information. The pattern generator B is also used to drive a clock source formed by an external cavity tuneable laser 9 having a wavelength of 1514 nm. The output of the laser amplifier 5 passes through an optical bandpass filter 10 centred on 1514 nm and the output from this is received by a photodiode 11 connected to an input of an oscilloscope 12. The combined optical signal input to the amplifier can be monitored at the output 13 of the coupler 1 using a receiver and oscilloscope arrangement analogous to that illustrated for monitoring the ampli~ier output. Alternatively the output 13 may be conventionally terminated in a non-reflectihg manner.
Figure 1 shows typical theoretical characteristics of the amplifier 5 for light input of four different wavelengths A, B, C, D at 0, C.l, 0.15 and 0~2 nm longer respectively than a resonant wavelength for the amplifier at zero input power. For light having a wavelength which is dif~erent from the resonant wavelength of the amplifier at zero input power the characteristic curve is generally S-shaped. In this case, where the input wavelength exceeds the zero power resonance by O.lnm or less, as shown by curves A and 8, the characteristic is not bistable. The S-shaped curves C and D illustrate the bistable nature of the laser amplifier when the input wavelength is slightly longer. Under these conditions, as the input power increases the output power gradually increases until it approaches the first knee of the curve which defines the bistable threshold o~ the laser - ~7~
amplifier for the jump to the higher amplification level for that input wavelength. As soon as the input power reaches this bistable threshold there is a sudden jump as the output power increases to that shown by the upper part of the curve.
Figure 2 shows one such curve. From this Figure, it is clear ~hat i~ the power of the clock signals passing through the laser 5 is arranged to be close to the bis~able threshold then a slight increase in the optical o power, for example that provided by the optical information in an input optical signal, is just su~ficient to exceed the bistable threshold. This results in an immediate jump in output power of the amplifier to the upper part of the curve shown in Figure 2. During any subsequent reduction of the optical input information signal the output power returns along the upper part o~
the curve. The regenerated output signal therefore remains high for the remainder of the duration o~ the clock pulse irrespective of a subsequent fall in the optical information signal. Thus, with both the clock signal and a information signal being applied to the laser amplifier 5, -For example, the output of the amplifier follows the hysteresis loop shown in Figure 2 moving between the high and low amplification levels to provide a regenerated signal which consists o~ large and small pulses at the clock frequency corresponding to '70nes" and 'zeroes" in the input signal. The low level amplification of the clock signal during the input signal lows therefore means that the extinction ratio is finite.
As shown in Figure 4, initially with the lase~ 9 providing a string of clock pulses but with the laser 7 not providing any optical in~ormation signals the clock pulses are slightly amplified in passage through the laser amplifier 5 with a resultant low level output at 1514 ~m.
~82~3~
In the present e~ample, with the laser 7 producing a - signal with a continuous high level o~ around 1 microwatt at the input to the ampli~ier the bistable threshold was reached and the output clock pulses abruptly jumped to a high level at 1514 nm as shown in Figure 5. Figure 6 illustrates a typical optical data stream input to the amplifier when the distributed feedback laser 7 is modulated by the pattern generator 8 with a non-return-to-zero data stream at 140 mb/second. The o corresponding output of the laser amplifier 5 is a regenerated pattern in a return-to-zero form at 1514 nm as shown in Figure 7.
2~)
OPTICAL SIGNAL REGENERATOR
Communications and data transmission systems which transmit in~ormation signals in the form of optical pulses over a dielectric waveguide such as an optical ~ibre are now commonplace. Whilst improvements in the sources of the optical pulses and in the optical fibre waveguides have increased the range over which such signals can be transmitted to between 100 and 200 kilometers it is still necessary to regenerate the sisnals when they are o transmitted over greater distances and when their power is reduced by beam splitting or being switched or otherwise handled. In a conventional regenerator, the optical signal is received by a photodiode and converted to an electrical signal. This electrical signal is then amplified and reshaped in an electronic regenerator circuit hefore being converted by an optical source into an optical pulse once again for onward transmission along the next optical fibre transmission line.
In this specification9 the term optical is intended to re~er to the visible region of the electromagnetic spectrum together with those parts of the in~rared and ultraviolet regions at each end o~ the visible region which are capable of being transmitted by dielectric optical waveguides such as optical fibres.
According to this invention an optical signal regenerator comprises an optical coupler having a first input for an optical information signal~ a second input ~or optical clock pulses and an output ~or a combined signal, and a resonant laser ampli~ier downstream of the output o~ the coupler and arranged to recei~e the combined signal and, in use, output a regenerated optical information signal. The bias current applied to the laser amplifier, in use, biases the ampli~ier to a level below ~k q~
83~
its lasing threshold, and the power of the optical clock -- pulses is just below the bistable threshold of the amplifier, so that~ when an optical in~ormation signal is fed into the first input during the application of an s optical clock pulse to the second input, the bistable threshold of the amplifier is exceeded causing a sudden jump in the power o~ the optical output of the amplifier to provide a regenerated optical information signal.
It should be noted that the lasing threshold and the bistable threshold apply to distinct phenomena. In the optical regeneratcr, the e1ectrical bias applied to the laser amplifier is below the lasing threshold bias current and cnnsequently the amplifier does not lase. The sudden amplification occurs because the optical power of an input optical signal is made to exceed an optical power bistable threshold for the ampli~ier.
When the optical power input to a semiconductor laser amplifier is increased, the extra stimulated emission raises the recombination rate. The carrier density is correspondingly reduced. As a result9 th~
ef~ective re~ractive index o~ the active region of a resonant laser amplifier increases with the optical power passing through it. The amplifier resonances are thereby tuned to longer wavelengths, and the gain at a given wavelength therefore varies. The puwer transfer characteristios o~ such an ampli~ier are consequently non-linear and, at appropriate input wavelengths, bistable operation is made possible.
Regeneratinn is achieved by combining an input signal with an optical clock signal and coupling them both into the resonant optical amplifier.
The clock signal consists of a train of optical pulses at the desired regeneration rate and with a wavelength at which the amplifier is ~istable. The peak 2~331 power of the clock signal is held marginally below the bistable threshold optical power level at which the amplifier will jump into a higher gain state.
With a low level input signal the output of the amplifier is in a lower gain state and its output comprises the slightly amplified clock signal. When the input signal increases to a high enough level such that the extra power in the combined input and clock signals is sufficient to exceed the bistable threshold then suddenly lo the resonant wavelength of the laser amplifier is matched to that of the light passing through it and the amplifier jumps into the higher gain state. It remains in this state, even if the input signal level again falls, until the end of the current clock pulse. The output of the amplifier for that period then includes a highly ampli~ied clock pulse.
The complete regenerated signal comprises a train of return-to-zero pulses with the timing and wavelength of the clock signal.
The input signal need not be at the same wavelength as the clock signal, so long as the amplifier has adequate gain at the input signal wavelength to trigger the bistable operation. Therefore, for example, the wavelength may be shifted between input and output by multiples of the amplifier mode spacing.
The optical signal regenerator may include an optical clock pulse generator which generates optical clock pulses in synchronism with a standard clock such as a system clock or, alternatively, it may be arranged to recover ti~ing information from the input optical information signal and generate the clock pulses in accordance with this recovered timing information.
The optical signal regenerator may also include biasing means such as a constant current source to provide a bias current which biases the laser amplifier to a level just below its lasing threshold. When the regenerator includes an optical clock pulse generator preferably it also includes power control means which control the power of the optical clock pulses to a level just below the bistable threshold o~ the laser amplifier. For example, the control means may monitor the output of the laser ampli~ier at a time that the regenerated output signal is not being emitted and control the power o~ the clock o pulses in accordance with the monitored output.
The resonant laser amplifier is preferably formed by a semiconductor laser amplifier and this may have the form of a resonant Fabry-Perot ampli~ier or a distributed feedback laser.
Pre~erably the clock pulses do not have the same wavelength as the input optical information signal and preferably the clock pulses have a wavelength slightly longer than that of the input information signal.
However, the clock pulses may be removed from the input information signal by multiples of the mode spacing in either direction when the laser amplifier is of the Fabry Perot type. Typically the clock pulses would be of the order o~ ten or tens of nanometers longer or shorter than that of the input information signal. In this way the regeneratPd optical information output signal which has the same wavelength as the clock pulses has its wavelength shifted from that of the input in~ormation signal and this can be an advantage in scme applications.
Indeed the regenerator can be used as a wavelength shifter.
Filtering means suoh as a mon~chromator or narrow bandpass ~ilter may be located downstream of the resonant laser amplifier to separate the regenerated information signal from the slightly amplified input information signal and any spontaneous emission generated by the 3~L
laser. However, filtering means are unnecessary when equipment which receives the regenerated information signal downstream from the laser is only responsive to light of the regererated signal wavelength.
A particular example of a signal regenerator in accordance with this invention together with an experiment to demonstrate its operation will now be described with reference to the accompanying drawings in which:-Figure 1 is a graph illustrating the output power -o input power characteristics o~ an amplifier for light of different wavelengths;
Figure 2 is a graph of output power against input power illustrating the typical operating range for the laser amplifier;
Figure 3 is a diagram of a regenerator together with equipment to demonstrate its operation; and, Figures 4, 5, 6 and 7 are oscillographs showing the output of the regenerator with data low, and with data high9 an input data stream, and a corresponding regenerated output data stream, respectively.
Referring first to Figure 3, the illustrated optical signal regenerator in accordance with this invention includes an optical coupler 1 having an optical signal input 2, a clock pulse input 3 and an output 4 for the combined signal, and a laser amplifier 5 coupled to receive the combined signal ~rom the output 4. The laser amplifier 5 is a double channel planar buried heterostructure semiconductor laser such as that described in an article in Electronics Letters 23 May 1985, Vol.21, No.ll, pages 493-494, entitled "High Performance DC-PBH
Lasers at 1.52 micrometres by a Hybrid MOVPE/LPE Process", by Nelson A W, Wong S, Regnault J C9 Hobbs R E, Murrel D
L, and Walling R H. The facet reflectivies of the laser are reduced to 3% by the application o~ anti-reflection coating.
d8~33~3L
In an experiment to demonstrate the effectiveness of the regenerator an input signal to the first input 2 ls produced by a distributed feedback laser 7 having a wavelength of 1526 nm which is driven from a 140 Mb/second pattern generator 8. This provides a continuous stream of optical pulses representing a stream of cptical information. The pattern generator B is also used to drive a clock source formed by an external cavity tuneable laser 9 having a wavelength of 1514 nm. The output of the laser amplifier 5 passes through an optical bandpass filter 10 centred on 1514 nm and the output from this is received by a photodiode 11 connected to an input of an oscilloscope 12. The combined optical signal input to the amplifier can be monitored at the output 13 of the coupler 1 using a receiver and oscilloscope arrangement analogous to that illustrated for monitoring the ampli~ier output. Alternatively the output 13 may be conventionally terminated in a non-reflectihg manner.
Figure 1 shows typical theoretical characteristics of the amplifier 5 for light input of four different wavelengths A, B, C, D at 0, C.l, 0.15 and 0~2 nm longer respectively than a resonant wavelength for the amplifier at zero input power. For light having a wavelength which is dif~erent from the resonant wavelength of the amplifier at zero input power the characteristic curve is generally S-shaped. In this case, where the input wavelength exceeds the zero power resonance by O.lnm or less, as shown by curves A and 8, the characteristic is not bistable. The S-shaped curves C and D illustrate the bistable nature of the laser amplifier when the input wavelength is slightly longer. Under these conditions, as the input power increases the output power gradually increases until it approaches the first knee of the curve which defines the bistable threshold o~ the laser - ~7~
amplifier for the jump to the higher amplification level for that input wavelength. As soon as the input power reaches this bistable threshold there is a sudden jump as the output power increases to that shown by the upper part of the curve.
Figure 2 shows one such curve. From this Figure, it is clear ~hat i~ the power of the clock signals passing through the laser 5 is arranged to be close to the bis~able threshold then a slight increase in the optical o power, for example that provided by the optical information in an input optical signal, is just su~ficient to exceed the bistable threshold. This results in an immediate jump in output power of the amplifier to the upper part of the curve shown in Figure 2. During any subsequent reduction of the optical input information signal the output power returns along the upper part o~
the curve. The regenerated output signal therefore remains high for the remainder of the duration o~ the clock pulse irrespective of a subsequent fall in the optical information signal. Thus, with both the clock signal and a information signal being applied to the laser amplifier 5, -For example, the output of the amplifier follows the hysteresis loop shown in Figure 2 moving between the high and low amplification levels to provide a regenerated signal which consists o~ large and small pulses at the clock frequency corresponding to '70nes" and 'zeroes" in the input signal. The low level amplification of the clock signal during the input signal lows therefore means that the extinction ratio is finite.
As shown in Figure 4, initially with the lase~ 9 providing a string of clock pulses but with the laser 7 not providing any optical in~ormation signals the clock pulses are slightly amplified in passage through the laser amplifier 5 with a resultant low level output at 1514 ~m.
~82~3~
In the present e~ample, with the laser 7 producing a - signal with a continuous high level o~ around 1 microwatt at the input to the ampli~ier the bistable threshold was reached and the output clock pulses abruptly jumped to a high level at 1514 nm as shown in Figure 5. Figure 6 illustrates a typical optical data stream input to the amplifier when the distributed feedback laser 7 is modulated by the pattern generator 8 with a non-return-to-zero data stream at 140 mb/second. The o corresponding output of the laser amplifier 5 is a regenerated pattern in a return-to-zero form at 1514 nm as shown in Figure 7.
2~)
Claims (9)
1. An optical signal regenerator comprising an optical coupler having a first input for an optical information signal, a second input for optical clock pulses and an output for a combined signal, and a resonant laser amplifier downstream of the output of the coupler and arranged to receive the combined signal and, in use, output a regenerated optical information signal; the bias current applied to the laser amplifier, in use, biasing the amplifier to a level below its lasing threshold and the power of the optical clock pulses being just below the bistable threshold of the amplifier, so that, when an optical information signal is fed into the first input during the application of an optical clock pulse to the second input the bistable threshold of the amplifier is exceeded causing a sudden jump in the power of the optical output of the amplifier to provide a regenerated optical information signal.
2. An optical signal regenerator according to claim 1, which also includes an optical clock signal generator which generates the optical clock pulses and applies them to the second input.
3. An optical signal regenerator according to claim 2, in which the optical clock signal generator includes power control means which control the power of the optical clock pulses to a level just below the bistable threshold of the laser amplifier.
4. An optical signal regenerator according to claim which also includes biasing means for providing a bias current to bias the laser amplifier to a level below its lasing threshold.
5. An optical signal regenerator according to claim 1, in which the resonant laser amplifier is formed by a semiconductor laser amplifier.
6. An optical signal regenerator according to claim 5, in which the semiconductor laser amplifier is a resonant Fabry-Perot amplifier.
7. An optical signal regenerator according to claim 5, in which the semiconductor laser amplifier is a distributed feedback laser.
8. An optical signal regenerator according to claim 1, which also includes filter means located downstream of the resonant laser amplifier to separate the regenerated information signal from the slightly amplified input information signal and any spontaneous emission generated by the laser.
9. An information transmission system including an optical signal regenerator according to claim 1, 5 or 8.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB868612956A GB8612956D0 (en) | 1986-05-28 | 1986-05-28 | Optical signal regenerator |
| GB8612956 | 1986-05-28 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1282831C true CA1282831C (en) | 1991-04-09 |
Family
ID=10598558
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000538088A Expired - Fee Related CA1282831C (en) | 1986-05-28 | 1987-05-27 | Optical signal regenerator |
Country Status (9)
| Country | Link |
|---|---|
| US (1) | US4879761A (en) |
| EP (1) | EP0247834B1 (en) |
| JP (1) | JPH0683143B2 (en) |
| AT (1) | ATE83346T1 (en) |
| CA (1) | CA1282831C (en) |
| DE (1) | DE3782974T2 (en) |
| ES (1) | ES2036574T3 (en) |
| GB (1) | GB8612956D0 (en) |
| WO (1) | WO1987007458A1 (en) |
Families Citing this family (23)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB8709073D0 (en) * | 1987-04-15 | 1987-05-20 | British Telecomm | Coherent optical systems |
| EP0325374B1 (en) * | 1988-01-22 | 1995-04-05 | AT&T Corp. | Optical communication by injection-locking to a signal which modulates an optical carrier |
| US5073981A (en) * | 1988-01-22 | 1991-12-17 | At&T Bell Laboratories | Optical communication by injection-locking to a signal which modulates an optical carrier |
| IT1219324B (en) * | 1988-05-24 | 1990-05-03 | Cselt Centro Studi Lab Telecom | PROCEDURE FOR THE CHARACTERIZATION OF RESTABLE SEMICONDUCTOR LASERS |
| DE69019846T2 (en) * | 1989-03-09 | 1995-12-07 | Canon Kk | Optical transmission system. |
| GB9010242D0 (en) * | 1990-05-08 | 1990-06-27 | British Telecomm | Optical signal regenerator and optical communications system incorporating same |
| DE4038503C2 (en) * | 1990-12-03 | 1997-04-17 | Kommunikations Elektronik | Network for the transmission of optical information signals |
| US5119039A (en) * | 1990-12-31 | 1992-06-02 | Gte Laboratories Incorporated | Semiconductor optical amplifier with wideband electrical response |
| CA2068975C (en) * | 1991-05-20 | 2002-03-26 | Kazunori Nakamura | Optical amplification system |
| US5194979A (en) * | 1991-06-07 | 1993-03-16 | Gte Laboratories Incorporated | Wideband optical amplifier-receiver system |
| US5264960A (en) * | 1992-05-08 | 1993-11-23 | At&T Bell Laboratories | Optical wavelength shifter |
| JPH05347449A (en) * | 1992-06-12 | 1993-12-27 | Ando Electric Co Ltd | Optical amplifier amplifying signal light and continuous light having wavelength different from signal light |
| US5359450A (en) * | 1992-06-25 | 1994-10-25 | Synchronous Communications, Inc. | Optical transmission system |
| US5535968A (en) * | 1992-07-27 | 1996-07-16 | Union Switch & Signal Inc. | Vital railway signal link |
| US5463488A (en) * | 1992-07-31 | 1995-10-31 | At&T Ipm Corp. | Distribution of clock signals by pump power modulation in an optically amplified network |
| US5532863A (en) * | 1994-07-27 | 1996-07-02 | U.S. Philips Corporation | Optical signal-regenerating unit and transmission system comprising such a unit |
| EP0717482A1 (en) * | 1994-12-14 | 1996-06-19 | AT&T Corp. | Semiconductor interferometric optical wavelength conversion device |
| US5880866A (en) * | 1996-11-13 | 1999-03-09 | At&T Corp | Time division demultiplexing using selective Raman amplification |
| NL1004806C2 (en) * | 1996-12-17 | 1998-06-18 | Nederland Ptt | Optical long-range signal transmission with optical amplification. |
| US6463113B1 (en) * | 1997-06-05 | 2002-10-08 | Compaq Information Technologies Group, L.P. | External signal attenuator for a single-ended transmission line |
| JP4689008B2 (en) | 2000-07-04 | 2011-05-25 | 富士通株式会社 | Method and apparatus for waveform shaping of signal light |
| US20040066550A1 (en) * | 2002-10-02 | 2004-04-08 | Jay Paul R. | Optical pulse reshaping system |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2248372C2 (en) * | 1972-10-03 | 1984-09-20 | Siemens AG, 1000 Berlin und 8000 München | Repeater for an optical communication system |
| DE2248211C3 (en) * | 1972-10-02 | 1980-01-03 | Allgemeine Elektricitaets-Gesellschaft Aeg-Telefunken, 1000 Berlin Und 6000 Frankfurt | Fiber line communication system |
| DE2418981B2 (en) * | 1974-04-19 | 1976-10-28 | Max-Planck-Gesellschaft zur Förderung der Wissenschaften e.V., 3400 Göttingen | PROCESS AND EQUIPMENT FOR OPTICAL DOUBLE EXCITATION OF A STIMULABLE MEDIUM TO REDUCE THE TEMPORARY FLUCTUATIONS OF THE LASER PULSE IN PULSE MODE WITH PASSIVE PHASE-COUPLED GUITCHING |
| US4475201A (en) * | 1981-06-11 | 1984-10-02 | Photochemical Research Associates Inc. | Longitudinally pumped dye laser arrangement |
| US4608682A (en) * | 1982-11-29 | 1986-08-26 | Nec Corporation | Optical time-division switching system employing optical bistable devices |
| US4562582A (en) * | 1983-04-18 | 1985-12-31 | Nippon Telegraph & Telephone Public Corporation | Burst signal receiving apparatus |
| US4674830A (en) * | 1983-11-25 | 1987-06-23 | The Board Of Trustees Of The Leland Stanford Junior University | Fiber optic amplifier |
| JPH0632332B2 (en) * | 1984-08-24 | 1994-04-27 | 日本電気株式会社 | Semiconductor laser device |
-
1986
- 1986-05-28 GB GB868612956A patent/GB8612956D0/en active Pending
-
1987
- 1987-05-26 JP JP62503119A patent/JPH0683143B2/en not_active Expired - Lifetime
- 1987-05-26 US US07/143,857 patent/US4879761A/en not_active Expired - Lifetime
- 1987-05-26 ES ES198787304657T patent/ES2036574T3/en not_active Expired - Lifetime
- 1987-05-26 WO PCT/GB1987/000360 patent/WO1987007458A1/en unknown
- 1987-05-26 EP EP87304657A patent/EP0247834B1/en not_active Expired - Lifetime
- 1987-05-26 AT AT87304657T patent/ATE83346T1/en not_active IP Right Cessation
- 1987-05-26 DE DE8787304657T patent/DE3782974T2/en not_active Expired - Lifetime
- 1987-05-27 CA CA000538088A patent/CA1282831C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| EP0247834B1 (en) | 1992-12-09 |
| DE3782974D1 (en) | 1993-01-21 |
| EP0247834A1 (en) | 1987-12-02 |
| ATE83346T1 (en) | 1992-12-15 |
| US4879761A (en) | 1989-11-07 |
| DE3782974T2 (en) | 1993-04-08 |
| WO1987007458A1 (en) | 1987-12-03 |
| ES2036574T3 (en) | 1993-06-01 |
| GB8612956D0 (en) | 1986-07-02 |
| JPH0683143B2 (en) | 1994-10-19 |
| JPS63503430A (en) | 1988-12-08 |
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