CA2402974A1 - Pump monitoring and control in a fiber raman amplifier - Google Patents
Pump monitoring and control in a fiber raman amplifier Download PDFInfo
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- CA2402974A1 CA2402974A1 CA002402974A CA2402974A CA2402974A1 CA 2402974 A1 CA2402974 A1 CA 2402974A1 CA 002402974 A CA002402974 A CA 002402974A CA 2402974 A CA2402974 A CA 2402974A CA 2402974 A1 CA2402974 A1 CA 2402974A1
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- 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
- H04B10/2916—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 Raman or Brillouin amplifiers
-
- 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
- H04B10/07—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems
- H04B10/075—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal
- H04B10/077—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal using a supervisory or additional signal
- H04B10/0779—Monitoring line transmitter or line receiver equipment
-
- 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
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/09—Processes or apparatus for excitation, e.g. pumping
- H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
- H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
- H01S3/094003—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light the pumped medium being a fibre
-
- 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
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
- H01S3/13—Stabilisation of laser output parameters, e.g. frequency or amplitude
- H01S3/131—Stabilisation of laser output parameters, e.g. frequency or amplitude by controlling the active medium, e.g. by controlling the processes or apparatus for excitation
- H01S3/1312—Stabilisation of laser output parameters, e.g. frequency or amplitude by controlling the active medium, e.g. by controlling the processes or apparatus for excitation by controlling the optical pumping
-
- 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
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/30—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range using scattering effects, e.g. stimulated Brillouin or Raman effects
- H01S3/302—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range using scattering effects, e.g. stimulated Brillouin or Raman effects in an optical fibre
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B2210/00—Indexing scheme relating to optical transmission systems
- H04B2210/07—Monitoring an optical transmission system using a supervisory signal
- H04B2210/074—Monitoring an optical transmission system using a supervisory signal using a superposed, over-modulated signal
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- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Optical Communication System (AREA)
- Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
- Lasers (AREA)
Abstract
An arrangement for monitoring the performance of each pump source in a fiber Raman amplifier arrangement utilizes a set of unique "signature"
signals, each signature signal impressed on a different pump input signal. At the receiver, the signature signals are extracted from the received, amplified signal. If a particular signature signal is missing at the receiver, this is indicative of failure of its associated pump source at the transmitter. If a particular signature signal is noticeable weaker than other received signature signals (as evidenced by, for example a low SNR
or high BER), this is indicative of a power loss in its associated pump source.
Since each signature signal is chosen to be unique, the identity of each pump source can be easily ascertained. In one embodiment, a low data rate signal is impressed on an RF
signal used to modulate the pump prior to be applied to the transmission fiber.
Alternatively, the RF modulation signal associated with each pump source can be offset by a predetermined frequency and the frequency offset used as the signature.
signals, each signature signal impressed on a different pump input signal. At the receiver, the signature signals are extracted from the received, amplified signal. If a particular signature signal is missing at the receiver, this is indicative of failure of its associated pump source at the transmitter. If a particular signature signal is noticeable weaker than other received signature signals (as evidenced by, for example a low SNR
or high BER), this is indicative of a power loss in its associated pump source.
Since each signature signal is chosen to be unique, the identity of each pump source can be easily ascertained. In one embodiment, a low data rate signal is impressed on an RF
signal used to modulate the pump prior to be applied to the transmission fiber.
Alternatively, the RF modulation signal associated with each pump source can be offset by a predetermined frequency and the frequency offset used as the signature.
Description
CA 02402974 2002-09-12 ' _1, Gehlot 29 PUMP MONITORING AND CONTROL IN A FIBER RAMAN AMPLIFIER
Technical Field The present invention relates to fiber Raman amplifiers and, more particularly, to the use of monitoring information on an applied Raman pump signal to analyze the performance of the amplifier.
Background of the Invention Optical amplification by stimulated Rarnan scattering in a single mode fiber is l « of interest for applications in optical communication systems. In particular, the use of Raman amplification in wavelength division multiplexed (WDM) optical communication systems is particularly attractive, since the bandwidth of the Raman amplifier can be large enaugh to accommodate two or more WDM channels. The performance of intensity-modulated WDM systems using Raman amplifiers, however, 1 ~ may be limited by the cross talk between the information channels and the amount of power actually coupled from the Raman pump into the information channels (as well as fiber nonlinearity-related penalties):
The cross talk in Raman amplifiers is mediated by the pump source. That is, cach modulated channel causes pattern-dependent pump depletion that is subsequently superimposed on all other channels during the amplification process.
The cross talk has been found to be dependent on the modulation frequency of the channels, as well as the relative speed between the channels and the pump. For this reason, the amount of cross talk present in co- and counter-propagating pump configurations has been found to differ significantly.
Regarding the issue of pattern dependence, if one channel is transmitting a song stream of "1's" or "0's", the power in the adjacent channel will change.
Thus, optical amplifiers would perform best in situations where the data pattern is random.
The pattern-dependence problem, which leads 1:0 "power stealing" between channels leas been addressed in co-pending Application '.~lo. - , which discloses the use of a radio frequency (RF) modulation signal impressed on a conventional continuous wave (CW) pump signal. In our co-pending application, the modulation frequency and depth are controlled to introduce a slight fluctuation to the input power level of the pump signal, resulting in introducing a sufficient degree of randomness to overcome the cross talk problem, and increase the amount of power coupled from the Gehlot Z9 -.a -Kaman pump into the information-bearing signals. Modifying the modulation index of the RF signal applied to the pump has been found to control any non-linearities present in the amplified output signal.
While this arrangement is helpful, a need remains to monitor the performance of the fiber Kaman amplifier system Existing methods in the prior art may use a separate communication channel as a "monitoring" channel, observing and analyzing a transmitted monitoring signal at a receiver. Although useful, this method decreases the efficiency of the system by requiring the dedication of a channel to the monitoring process. Another method utilizes "monitoring tones" impressed on a transmitted data l~ signal. This method results in introducing a penalty in terms of the recovered information from this data signal.
Thus, a need remains in the art for an arrangement which can monitor the performance of a fiber Kaman amplifier withoua incurring penalties on the transmitted data signals.
i Summary of the Invention The need remaining in the art is addressed by the present invention, which relates to fiber Kaman amplifiers and, more particularly, to the use of monitoring information on an applied pump signal to analyze the performance of the amplifier.
i In accordance with the present invention, the RF signal used to modulate the pump is itself modulated with a low data rate "signature" signal, chosen to be-unique for that particular pump. At the receiver end., a filter and demodulator are used to separate the pump from the amplified information signal and recover the unique signature signal. Problems with a given pump source can be presumed, therefore. i f os associated, recovered unique signature signal is absent, exhibits a low signal-to-noise ratio (SNR), or an excessive bit error rate (BER). In systems which utilize multiple pump sources, the use of a unique signature signal for each pump source allows for the receiver to distinguish between the pumps and monitor each source.
In an alternative embodiment of the present invention, the unique signature s~~ may comprise a frequency offset applied to the RF modulation signal at the pump source, where this offset is then be used at the receiver to identify each separate punch source. Once detected, an appropr2ate mechanism can be utilized to correct tic defective pump source (e.g., replace optic device, increase power, etc,.).
Gehlot 29 _3 _ Brief Description of the Drawings Referring now to the drawings, FIG. I illustrates an exemplary optical transmitter including a fiber Raman amplifier and utilizing a pair of pump sources including a monitoring arrangement formed in accordance with the present invention;
FIG. 2 is an exemplary ontic;~l receiver for recovering the pump monitoring signal utilized in the arrangement of FIG. l; and FIG. 3 illustrates an alternative optical transmitter formed in accordance with the present invention, utilizing different, unique frequency offsets with the RF pump l ~~ modulation signal to provide the monitoring function of the present invention.
Detailed Description An exemplary WDM optical communication system 10, utilizing fiber Raman amplification in accordance with the principles of the present invention, is illustrated in FIG. 1. As shown, a transmitter 12 is included and used to provide a plurality of'.~1 optical input signals, each occupying a different channel and operating at a different ~ avelength, denoted ~,, - ~.N in FIG. I . It is to be understood that transmitter 12 may comprise, in fact, a plurality of separate transmitting sources (i.e., lasers), and include a wavelength division multiplexer (WDM) and/or other suitable devices, used to combine all of the optical input signals onto a single optical transmission fiber 14. In an exemplary system that utilizes fiber Raman amplification, the plurality of input signals may utilize wavelengths in the range of, for example, 1520nm to 1620nm.
In the arrangement as shown in FICi. ';, both a co-propagating pump signal, denoted P,, and a counter-propagating pump signal, denoted Pz, are used to provide amplification of the input signals along transmission fiber 14. A first pump source I O
is used to generate pump signal P, and a first wavelength division multiplexer 1 S is used couple Raman pump signal P, (as a co-propagating pump signal) onto transmission fiber 14. h~ a similar fashion, a second pump source 20 is used to generate pump signal PZ and a second wavelength division multiplexer 22 is used to couple Raman pump signal P, (as <3 cou.nter-propagating pump signal) onto transmission fiber 14 In accordance with the present invention, a unique pump signature is impressed on each pump signal, where the sie;nature signal will thereafter propa~~.nc _4 _ Gehlot 29 through the transmission system and can later be captured by an optical receiver (as shown in FIG. 2), and used to monitor and control the various pump sources at an optical transmitter. Refernng in particular to hIG. l, first pump source 16 includes a CW pump element 24, used to provide the continuous wave optical pump input signal (operating at a wavelength of, for example 1420nm). The CW output from element 24 is then applied as the optical input to a modulator 26 (which may comprise an clectroabsorption modulator (EAM), or alternatively be an integral external modulator coupled directly to the pump element). The electrical signal input to modulator 26 comprises an RF signal, as supplied by an Rh generator 28, where the RF signal is 1 a itself modulated with a predetermined, unique signature sognal S,. As shown in FIG.
l, the RF signal and signature signal S, are applied as separate inputs to a multiplier ~0, where the output of multiplier 30 is used as the electrical input to modulator 26.
In accordance with the present inversion, unique signature signal S, may comprise a low data rate (i.e., a few kilobytes,'second) signal having a predetermined 1 ~ binary pattern. As long as the data rate is sufficiently low, the amplification process within fiber 14 will not be adversely affected. Moreover, the presence of the low data rate signal as modulating the pump input will allow for this data to pass through the transmission system and be recovered at the receiver without incurring any penalty on the input information signals (as was the case in the prior art arrangements).
~(! In a similar fashion as described above, second pump source 20 comprises a pump element 32, modulator 34, RF signal generator 36, and a multiplier 38. In this case, a different signature signal, denoted Sz, is applied as an input to multiplier 38 with the RF signal, where this signature Sz will then also be carried on the pump signal as it propagates along the transmission path. Since the amplification process occurs regardless of the propagation direction of the pump signal, second signature signal SZ will also appear at the output of transmitter 10, and can thereafter be recovered in an optical receiver (such as shown in FIG. 2).
In accordance with the present invention, therefore, an optical receiver can he configured to monitor the received signals, filter out the pump signals and look for the presence of the signature signals. If one or both of the signature signals would not be present in the recovered pump signal, this would indicate that the pump is not ~~orking (or at least not operating at a sufficient power level). Since each signature signal is unique, this factor can be used to identify and isolate the defective punch source.
Gehlot 29 FIG. 2 illustrates an exemplary, simplified optical receiver arrangement 40 that can be used to recover the pump monitor signals (i.e., the signature signals) in accordance with the teachings of the present invention. As shown, the incoming amplified optical signals are first filtered in a low pass filter 42 to remove the remaining pump signal from the plurality of optical signals being transmitted.
The recovered pump signal is then passed through a demodulator 44 to remove the impressed RF modulation signal, leaving only the signature signals. In the case where the signature signals comprise low data rate signals, an autocorrelation function can be used to identify each particular signature signal. Therefore, as long as each 1 n~ signature signal is present, it can be assumed that each pump source is operating properly. Various indicators may be used to analyze the recovered signature signals.
For example, if one of the signal signature :>ignals is absent, this is indicative of complete failure of the pump source twhich ca:n then be corrected by replacing one or more components in the failed pump source at transmitter). The SNR or BER of the 1 ~ recovered signature signal can be measured (when a signature signal is present), and used to determine the amount of power being emitted by the associated pump source.
If the SNR is too low (i.e., too much noise on the transmitted signal) or the BER too high (i.e., too many errors in the transmitted signal), the input power level of the associated pump source can be increased until acceptable value for the SNR
and/or BER is obtained..
FIG. 3 illustrates an alternative transmitter 50 that can be used in accordance with the present invention. In this case, a unique frequency offset is imparted to each RF modulation signal applied to the CW pump signal to create an associated unique pump signature. In particular, and with reference to FIG. 3 (where like elements from tl~e arrangement of FIG. 1 carrel like reference numerals), a first pump source ~Z
comprises CW pump element 24 ;and modulator 26, as discussed above. The RF
input is modified, in this case, to utilize an RF signal offset by a first predetermined frequency J,. Similarly, a second pump source 54 comprises CW pump element s~
and modulator 34, where the RF modulation signal input is offset by a different frequency f_~. At the receiver (not shown), these frequency offsets can be recovered.
As with the arrangement described above, various measures can be used to analye the performance of the pump source (as well as its presence/absence), including but not limited to measurements of SNR and B)=;R. Once a problem with a particular pump source has been identified, appropriate corrective measures may be taken at tl~e Gehlot 29 transmitter (such as, for example, replacing one or more components in a pump unit, increasing the pump power, etc.
It is to be understood that the above-described embodiments are considered to be merely illustrative of the principles of the present invention. Numerous and various other arrangements can be made in accordance with these principles and are considered to fall within the spirit and scope or' the invention as defined by the claims appended hereto.
Technical Field The present invention relates to fiber Raman amplifiers and, more particularly, to the use of monitoring information on an applied Raman pump signal to analyze the performance of the amplifier.
Background of the Invention Optical amplification by stimulated Rarnan scattering in a single mode fiber is l « of interest for applications in optical communication systems. In particular, the use of Raman amplification in wavelength division multiplexed (WDM) optical communication systems is particularly attractive, since the bandwidth of the Raman amplifier can be large enaugh to accommodate two or more WDM channels. The performance of intensity-modulated WDM systems using Raman amplifiers, however, 1 ~ may be limited by the cross talk between the information channels and the amount of power actually coupled from the Raman pump into the information channels (as well as fiber nonlinearity-related penalties):
The cross talk in Raman amplifiers is mediated by the pump source. That is, cach modulated channel causes pattern-dependent pump depletion that is subsequently superimposed on all other channels during the amplification process.
The cross talk has been found to be dependent on the modulation frequency of the channels, as well as the relative speed between the channels and the pump. For this reason, the amount of cross talk present in co- and counter-propagating pump configurations has been found to differ significantly.
Regarding the issue of pattern dependence, if one channel is transmitting a song stream of "1's" or "0's", the power in the adjacent channel will change.
Thus, optical amplifiers would perform best in situations where the data pattern is random.
The pattern-dependence problem, which leads 1:0 "power stealing" between channels leas been addressed in co-pending Application '.~lo. - , which discloses the use of a radio frequency (RF) modulation signal impressed on a conventional continuous wave (CW) pump signal. In our co-pending application, the modulation frequency and depth are controlled to introduce a slight fluctuation to the input power level of the pump signal, resulting in introducing a sufficient degree of randomness to overcome the cross talk problem, and increase the amount of power coupled from the Gehlot Z9 -.a -Kaman pump into the information-bearing signals. Modifying the modulation index of the RF signal applied to the pump has been found to control any non-linearities present in the amplified output signal.
While this arrangement is helpful, a need remains to monitor the performance of the fiber Kaman amplifier system Existing methods in the prior art may use a separate communication channel as a "monitoring" channel, observing and analyzing a transmitted monitoring signal at a receiver. Although useful, this method decreases the efficiency of the system by requiring the dedication of a channel to the monitoring process. Another method utilizes "monitoring tones" impressed on a transmitted data l~ signal. This method results in introducing a penalty in terms of the recovered information from this data signal.
Thus, a need remains in the art for an arrangement which can monitor the performance of a fiber Kaman amplifier withoua incurring penalties on the transmitted data signals.
i Summary of the Invention The need remaining in the art is addressed by the present invention, which relates to fiber Kaman amplifiers and, more particularly, to the use of monitoring information on an applied pump signal to analyze the performance of the amplifier.
i In accordance with the present invention, the RF signal used to modulate the pump is itself modulated with a low data rate "signature" signal, chosen to be-unique for that particular pump. At the receiver end., a filter and demodulator are used to separate the pump from the amplified information signal and recover the unique signature signal. Problems with a given pump source can be presumed, therefore. i f os associated, recovered unique signature signal is absent, exhibits a low signal-to-noise ratio (SNR), or an excessive bit error rate (BER). In systems which utilize multiple pump sources, the use of a unique signature signal for each pump source allows for the receiver to distinguish between the pumps and monitor each source.
In an alternative embodiment of the present invention, the unique signature s~~ may comprise a frequency offset applied to the RF modulation signal at the pump source, where this offset is then be used at the receiver to identify each separate punch source. Once detected, an appropr2ate mechanism can be utilized to correct tic defective pump source (e.g., replace optic device, increase power, etc,.).
Gehlot 29 _3 _ Brief Description of the Drawings Referring now to the drawings, FIG. I illustrates an exemplary optical transmitter including a fiber Raman amplifier and utilizing a pair of pump sources including a monitoring arrangement formed in accordance with the present invention;
FIG. 2 is an exemplary ontic;~l receiver for recovering the pump monitoring signal utilized in the arrangement of FIG. l; and FIG. 3 illustrates an alternative optical transmitter formed in accordance with the present invention, utilizing different, unique frequency offsets with the RF pump l ~~ modulation signal to provide the monitoring function of the present invention.
Detailed Description An exemplary WDM optical communication system 10, utilizing fiber Raman amplification in accordance with the principles of the present invention, is illustrated in FIG. 1. As shown, a transmitter 12 is included and used to provide a plurality of'.~1 optical input signals, each occupying a different channel and operating at a different ~ avelength, denoted ~,, - ~.N in FIG. I . It is to be understood that transmitter 12 may comprise, in fact, a plurality of separate transmitting sources (i.e., lasers), and include a wavelength division multiplexer (WDM) and/or other suitable devices, used to combine all of the optical input signals onto a single optical transmission fiber 14. In an exemplary system that utilizes fiber Raman amplification, the plurality of input signals may utilize wavelengths in the range of, for example, 1520nm to 1620nm.
In the arrangement as shown in FICi. ';, both a co-propagating pump signal, denoted P,, and a counter-propagating pump signal, denoted Pz, are used to provide amplification of the input signals along transmission fiber 14. A first pump source I O
is used to generate pump signal P, and a first wavelength division multiplexer 1 S is used couple Raman pump signal P, (as a co-propagating pump signal) onto transmission fiber 14. h~ a similar fashion, a second pump source 20 is used to generate pump signal PZ and a second wavelength division multiplexer 22 is used to couple Raman pump signal P, (as <3 cou.nter-propagating pump signal) onto transmission fiber 14 In accordance with the present invention, a unique pump signature is impressed on each pump signal, where the sie;nature signal will thereafter propa~~.nc _4 _ Gehlot 29 through the transmission system and can later be captured by an optical receiver (as shown in FIG. 2), and used to monitor and control the various pump sources at an optical transmitter. Refernng in particular to hIG. l, first pump source 16 includes a CW pump element 24, used to provide the continuous wave optical pump input signal (operating at a wavelength of, for example 1420nm). The CW output from element 24 is then applied as the optical input to a modulator 26 (which may comprise an clectroabsorption modulator (EAM), or alternatively be an integral external modulator coupled directly to the pump element). The electrical signal input to modulator 26 comprises an RF signal, as supplied by an Rh generator 28, where the RF signal is 1 a itself modulated with a predetermined, unique signature sognal S,. As shown in FIG.
l, the RF signal and signature signal S, are applied as separate inputs to a multiplier ~0, where the output of multiplier 30 is used as the electrical input to modulator 26.
In accordance with the present inversion, unique signature signal S, may comprise a low data rate (i.e., a few kilobytes,'second) signal having a predetermined 1 ~ binary pattern. As long as the data rate is sufficiently low, the amplification process within fiber 14 will not be adversely affected. Moreover, the presence of the low data rate signal as modulating the pump input will allow for this data to pass through the transmission system and be recovered at the receiver without incurring any penalty on the input information signals (as was the case in the prior art arrangements).
~(! In a similar fashion as described above, second pump source 20 comprises a pump element 32, modulator 34, RF signal generator 36, and a multiplier 38. In this case, a different signature signal, denoted Sz, is applied as an input to multiplier 38 with the RF signal, where this signature Sz will then also be carried on the pump signal as it propagates along the transmission path. Since the amplification process occurs regardless of the propagation direction of the pump signal, second signature signal SZ will also appear at the output of transmitter 10, and can thereafter be recovered in an optical receiver (such as shown in FIG. 2).
In accordance with the present invention, therefore, an optical receiver can he configured to monitor the received signals, filter out the pump signals and look for the presence of the signature signals. If one or both of the signature signals would not be present in the recovered pump signal, this would indicate that the pump is not ~~orking (or at least not operating at a sufficient power level). Since each signature signal is unique, this factor can be used to identify and isolate the defective punch source.
Gehlot 29 FIG. 2 illustrates an exemplary, simplified optical receiver arrangement 40 that can be used to recover the pump monitor signals (i.e., the signature signals) in accordance with the teachings of the present invention. As shown, the incoming amplified optical signals are first filtered in a low pass filter 42 to remove the remaining pump signal from the plurality of optical signals being transmitted.
The recovered pump signal is then passed through a demodulator 44 to remove the impressed RF modulation signal, leaving only the signature signals. In the case where the signature signals comprise low data rate signals, an autocorrelation function can be used to identify each particular signature signal. Therefore, as long as each 1 n~ signature signal is present, it can be assumed that each pump source is operating properly. Various indicators may be used to analyze the recovered signature signals.
For example, if one of the signal signature :>ignals is absent, this is indicative of complete failure of the pump source twhich ca:n then be corrected by replacing one or more components in the failed pump source at transmitter). The SNR or BER of the 1 ~ recovered signature signal can be measured (when a signature signal is present), and used to determine the amount of power being emitted by the associated pump source.
If the SNR is too low (i.e., too much noise on the transmitted signal) or the BER too high (i.e., too many errors in the transmitted signal), the input power level of the associated pump source can be increased until acceptable value for the SNR
and/or BER is obtained..
FIG. 3 illustrates an alternative transmitter 50 that can be used in accordance with the present invention. In this case, a unique frequency offset is imparted to each RF modulation signal applied to the CW pump signal to create an associated unique pump signature. In particular, and with reference to FIG. 3 (where like elements from tl~e arrangement of FIG. 1 carrel like reference numerals), a first pump source ~Z
comprises CW pump element 24 ;and modulator 26, as discussed above. The RF
input is modified, in this case, to utilize an RF signal offset by a first predetermined frequency J,. Similarly, a second pump source 54 comprises CW pump element s~
and modulator 34, where the RF modulation signal input is offset by a different frequency f_~. At the receiver (not shown), these frequency offsets can be recovered.
As with the arrangement described above, various measures can be used to analye the performance of the pump source (as well as its presence/absence), including but not limited to measurements of SNR and B)=;R. Once a problem with a particular pump source has been identified, appropriate corrective measures may be taken at tl~e Gehlot 29 transmitter (such as, for example, replacing one or more components in a pump unit, increasing the pump power, etc.
It is to be understood that the above-described embodiments are considered to be merely illustrative of the principles of the present invention. Numerous and various other arrangements can be made in accordance with these principles and are considered to fall within the spirit and scope or' the invention as defined by the claims appended hereto.
Claims (10)
1. An optical transmitter for amplifying a plurality of input signals operating over a predetermined wavelength range of .lambda.1 - .lambda.N , the system comprising at least one optical pump source for supplying at least one RF-signature modulated Raman pump signal; and a transmission optical fiber coupled to both the at least one RF-signature modulated Raman pump signal and the plurality of N input optical signals for providing amplification of said plurality of N input optical signals using said at least one RF-signature-modulated Raman pump signal, whereby the amplified signal carries the signature associated with each pump element in the transmitter.
2. The optical transmitter as defined in claim 1 wherein each optical pump source comprises an element for providing a continuous wave (CW) optical pump signal;
a radio frequency (RF) electrical signal generator;
a modulator; and a unique pump signature element, the unique pump signature element being used with the RF electrical signal output from the RF signal generator and applied as an electrical input to the modulator, wherein the CW optical pump signal is applied as an optical input to the modulator, the output of the modulator comprising the RF-signature-modulated Raman pump signal
a radio frequency (RF) electrical signal generator;
a modulator; and a unique pump signature element, the unique pump signature element being used with the RF electrical signal output from the RF signal generator and applied as an electrical input to the modulator, wherein the CW optical pump signal is applied as an optical input to the modulator, the output of the modulator comprising the RF-signature-modulated Raman pump signal
3. The optical transmitter as defined by claim 1 wherein the at least one optical pump source comprises at least two pump sources, each utilizing a different pump signature signal.
4. The optical transmitter as defined in claim 2 wherein the at least two pump sources comprise a co-propagating pump source and a counter-propagating pump source, each utilizing a different pump signature signal.
5. The optical transmitter as defined in claim 2 wherein at least one unique pump signature element comprises a low data rate signal, each pump signature element utilizing a different, unique low data rate signal.
6. A pump source for providing an input amplifying signal for a Raman fiber amplifier and a control signal for monitoring the pump source performance, said pump source comprising an optical signal source of continuous wave (CW) pump light;
a modulator having an optical input and an electrical, modulating input, and an optical output, the optical output being representative of the optical input as modulated by the electrical, modulating input;
an RF generator for providing an RF electrical signal at a predetermined frequency and modulation depth; and a signature element, coupled to the RF generator, for creating a unique RF
signal input for the external modulator, the signature element thereafter associated with the pump signal input to the fiber Raman amplifier for transmission and later collection at an optical receiver as a monitor signal for the pump source.
a modulator having an optical input and an electrical, modulating input, and an optical output, the optical output being representative of the optical input as modulated by the electrical, modulating input;
an RF generator for providing an RF electrical signal at a predetermined frequency and modulation depth; and a signature element, coupled to the RF generator, for creating a unique RF
signal input for the external modulator, the signature element thereafter associated with the pump signal input to the fiber Raman amplifier for transmission and later collection at an optical receiver as a monitor signal for the pump source.
7. An optical communication system utilizing fiber Raman amplification for a plurality of N input optical signals operating over a predetermined wavelength range of .lambda.1 - .lambda.N and providing monitoring and control of each pump source used in the communication system, the system including an optical transmitter comprising at least one optical pump source including an element for providing a continuous wave (CW) optical pump signal, a radio frequency (RF) electrical signal generator, a modulator and a unique pump signature element, the unique pump signature element being used with the RF signal output from the RF signal generator and applied as an electrical input to the modulator, wherein the CW optical pump signal is applied as an optical input to the modulator, the output of the modulator then comprising an RF/signature-modulated Raman pump signal; a transmission optical fiber coupled to both the at least one optical pump source and the source of the plurality of N input optical signals for providing amplification of the plurality of N
input optical signals using the RF/signature-modulated Raman pump signal, the amplified signal carrying the signature associated with each pump element in the transmitter for later removal and monitoring; and an optical receiver coupled to the output end of the transmission optical fiber and comprising an optical filter for removing each RF/signature-modulated Raman pump signal from the plurality of received, amplified optical signals;
a demodulator for removing the RF modulator signal from the filters Raman pump signal; and a detector for isolating each signature from the demodulated pump signal and determining the performance of each associated pump source based an the presence or absence of each signature.
input optical signals using the RF/signature-modulated Raman pump signal, the amplified signal carrying the signature associated with each pump element in the transmitter for later removal and monitoring; and an optical receiver coupled to the output end of the transmission optical fiber and comprising an optical filter for removing each RF/signature-modulated Raman pump signal from the plurality of received, amplified optical signals;
a demodulator for removing the RF modulator signal from the filters Raman pump signal; and a detector for isolating each signature from the demodulated pump signal and determining the performance of each associated pump source based an the presence or absence of each signature.
8. The optical communication system as defined in claim 7 wherein each signature associated with a pump source comprises a unique low data rate signal such that the detector in the optical receiver can recover each separate low data rate signal and monitor the performance of each pump source.
9. The optical communication system as defined in claim 8 wherein the detector comprises an autocorrelation element that utilizes the known set of unique low data rate signals as an input with the recovered pump signal to determine the presence or absence of each low data rate signal.
10. A method of applying a monitor and control signal to an optical signal passing through a fiber Raman amplifier between an optical transmitter and an optical receiver, the method comprising the steps of:
coupling a plurality of N input optical signals, operating over a predetermined wavelength range of .gamma.~ - .gamma.n, into a transmission fiber;
coupling at least one optical pump signal at a predetermined wavelength.
modulated with an RF signal at a predetermined frequency and modulation depth and including a unique monitoring signal into the transmission fiber for amplifying the plurality of N input optical signals;
transmitting the plurality of N amplified signals along the transmission fiber-to an optical receiver;
filtering the plurality of N received and amplified optical signals to remove the at least one optical pump signal; and detecting each unique monitoring signal present in the filtered pump signal to ascertain the performance of each pump source associated with each unique monitoring signal.
coupling a plurality of N input optical signals, operating over a predetermined wavelength range of .gamma.~ - .gamma.n, into a transmission fiber;
coupling at least one optical pump signal at a predetermined wavelength.
modulated with an RF signal at a predetermined frequency and modulation depth and including a unique monitoring signal into the transmission fiber for amplifying the plurality of N input optical signals;
transmitting the plurality of N amplified signals along the transmission fiber-to an optical receiver;
filtering the plurality of N received and amplified optical signals to remove the at least one optical pump signal; and detecting each unique monitoring signal present in the filtered pump signal to ascertain the performance of each pump source associated with each unique monitoring signal.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US09/990,231 | 2001-11-21 | ||
| US09/990,231 US6731428B2 (en) | 2001-11-21 | 2001-11-21 | Pump monitoring and control in a fiber Raman amplifier |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2402974A1 true CA2402974A1 (en) | 2003-05-21 |
Family
ID=25535928
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002402974A Abandoned CA2402974A1 (en) | 2001-11-21 | 2002-09-12 | Pump monitoring and control in a fiber raman amplifier |
Country Status (3)
| Country | Link |
|---|---|
| US (1) | US6731428B2 (en) |
| JP (1) | JP2003209519A (en) |
| CA (1) | CA2402974A1 (en) |
Families Citing this family (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP3808734B2 (en) * | 2001-08-10 | 2006-08-16 | 富士通株式会社 | Raman amplifier |
| US7289735B2 (en) * | 2004-04-05 | 2007-10-30 | Jds Uniphase Corporation | Apparatus for emitting light with controllable degree of polarization |
| US20060251423A1 (en) * | 2005-05-09 | 2006-11-09 | Evangelides Stephen G Jr | Method and apparatus for identifying pump failures using an optical line interface |
| CN1874193B (en) * | 2005-06-03 | 2012-05-23 | 华为技术有限公司 | Method for realizing laser safety protection, optical amplifier, and identification signal loading method |
| CN100479352C (en) * | 2006-02-21 | 2009-04-15 | 华为技术有限公司 | Optical associated signal loading, monitoring method and apparatus |
| GB2483878B8 (en) * | 2010-09-22 | 2012-11-07 | Univ Southampton | Optical signal processing |
| US9673920B2 (en) | 2012-12-18 | 2017-06-06 | Department 13, LLC | Intrusion detection and radio fingerprint tracking |
| US9762319B1 (en) * | 2015-09-29 | 2017-09-12 | Juniper Networks, Inc. | Real-time Raman gain monitoring |
| IL254803B2 (en) * | 2017-09-29 | 2023-09-01 | Prisma Photonics Ltd | Tailor distributed amplification for fiber sensing |
| CN108692918B (en) * | 2018-07-17 | 2023-12-15 | 中国人民解放军国防科技大学 | Device and method for evaluating time domain stability of high-power fiber laser system |
| JP7466529B2 (en) * | 2018-09-21 | 2024-04-12 | アビオメド インコーポレイテッド | Use of Fiber Optic Sensors as Diagnostic Tools in Catheter-Based Medical Devices |
| US11588295B2 (en) | 2019-11-01 | 2023-02-21 | Ii-Vi Delaware, Inc. | Pump modulation for optical amplifier link communication |
| US11575241B2 (en) | 2020-12-11 | 2023-02-07 | Ii-Vi Delaware, Inc. | Optical amplifier modules |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2245120B (en) * | 1990-06-16 | 1994-03-30 | Stc Plc | Telemetry |
| DE4036327A1 (en) * | 1990-11-15 | 1992-05-21 | Standard Elektrik Lorenz Ag | OPTICAL MESSAGE TRANSMISSION SYSTEM WITH A FIBER OPTICAL AMPLIFIER |
| US5208817A (en) * | 1992-04-10 | 1993-05-04 | At&T Bell Laboratories | Modulator-based lightwave transmitter |
| US5383046A (en) * | 1992-05-29 | 1995-01-17 | Fujitsu Limited | Supervisory and control signal transmitting system for use in optically amplifying repeaters system |
| US5436750A (en) * | 1993-05-07 | 1995-07-25 | Nec Corporation | Optical repeatered transmission with fault locating capability |
| DE4333367A1 (en) * | 1993-09-30 | 1995-04-06 | Ant Nachrichtentech | Sender and receiver for an optical communication system |
| US6191877B1 (en) | 1995-02-17 | 2001-02-20 | Lucent Technologies Inc. | WDM optical fiber system using Raman amplification |
| US5668658A (en) * | 1995-02-28 | 1997-09-16 | Nec Corporation | Transfer of repeater information signals in in-line optical amplifier repeater system |
| JP2748891B2 (en) * | 1995-07-06 | 1998-05-13 | 日本電気株式会社 | Optical amplifier |
| US6122298A (en) | 1996-11-01 | 2000-09-19 | Tyco Submarine Systems Ltd. | Multi-wavelength optical pump |
| US6178025B1 (en) * | 1997-12-03 | 2001-01-23 | Nortel Networks Limited | Optical network loss-of-signal detection |
| US6115174A (en) | 1998-07-21 | 2000-09-05 | Corvis Corporation | Optical signal varying devices |
| US6147794A (en) | 1999-02-04 | 2000-11-14 | Lucent Technologies, Inc. | Raman amplifier with pump source for improved performance |
| US6356383B1 (en) * | 1999-04-02 | 2002-03-12 | Corvis Corporation | Optical transmission systems including optical amplifiers apparatuses and methods |
| EP1312975A1 (en) * | 2000-08-25 | 2003-05-21 | Fujitsu Limited | Optical communication system, method of providing excitation light, and distributed raman amplifier |
| US6452716B1 (en) * | 2000-10-05 | 2002-09-17 | Nortel Networks Limited | Amplitude modulation of a pump laser signal in a distributed raman amplifier |
| JP4487420B2 (en) * | 2000-12-22 | 2010-06-23 | 富士通株式会社 | Optical amplification transmission system |
| US6456426B1 (en) * | 2001-06-28 | 2002-09-24 | Onetta, Inc. | Raman amplifiers with modulated pumps |
-
2001
- 2001-11-21 US US09/990,231 patent/US6731428B2/en not_active Expired - Fee Related
-
2002
- 2002-09-12 CA CA002402974A patent/CA2402974A1/en not_active Abandoned
- 2002-10-21 JP JP2002306028A patent/JP2003209519A/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| US20030095322A1 (en) | 2003-05-22 |
| US6731428B2 (en) | 2004-05-04 |
| JP2003209519A (en) | 2003-07-25 |
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| Date | Code | Title | Description |
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| EEER | Examination request | ||
| FZDE | Discontinued |