WO2016009638A1 - Optical transmission device and optical transmission method - Google Patents

Optical transmission device and optical transmission method Download PDF

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Publication number
WO2016009638A1
WO2016009638A1 PCT/JP2015/003535 JP2015003535W WO2016009638A1 WO 2016009638 A1 WO2016009638 A1 WO 2016009638A1 JP 2015003535 W JP2015003535 W JP 2015003535W WO 2016009638 A1 WO2016009638 A1 WO 2016009638A1
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Prior art keywords
light
optical transmission
optical
signal light
power
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PCT/JP2015/003535
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French (fr)
Japanese (ja)
Inventor
喜久 稲田
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日本電気株式会社
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Publication of WO2016009638A1 publication Critical patent/WO2016009638A1/en

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    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/35—Non-linear optics
    • 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
    • H04B10/25—Arrangements specific to fibre transmission
    • H04B10/2507—Arrangements specific to fibre transmission for the reduction or elimination of distortion or dispersion
    • 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
    • H04B10/293—Signal power control

Definitions

  • the present invention relates to an optical transmission device and an optical transmission method.
  • the present invention particularly relates to an optical transmission device and an optical transmission method used in an optical transmission system in which signal light is distributed and amplified in an optical transmission line.
  • FIG. 11 is a diagram illustrating an example of the relationship between the wavelength of excitation light and the Raman gain spectrum in Raman amplification. Stimulated emission based on Raman scattering occurs due to the strong excitation light incident on the optical fiber.
  • Raman amplification is a phenomenon in which a light amplification effect is obtained in a wavelength range longer by about 100 nm than the wavelength of excitation light.
  • the amplification characteristic of signal light by Raman amplification varies depending on the power and wavelength of pump light and the power and wavelength of signal light.
  • Distributed Raman amplification causes Raman amplification to occur in an optical fiber that is an optical transmission line, and its low noise and low nonlinearity are expected to improve the transmission quality of optical transmission systems and increase the transmission span.
  • Patent Document 1 describes a transmission loss measuring apparatus using an OTDR (optical time domain reflexometer). Further, Patent Document 2 describes a power adjustment device in which the output power of a relay amplifier is adjusted by Raman gain efficiency obtained from the amount of change in noise light power.
  • OTDR optical time domain reflexometer
  • JP 2006-287649 A (paragraph [0048], FIG. 1)
  • the optical transmitter transmits a high output signal light and obtains a high Raman gain by a high output pump light source.
  • a high Raman amplification gain can be obtained, but when the signal light power in the optical fiber is very high, it is caused by the nonlinear optical effect of the optical fiber. This is because the signal light is distorted and the transmission quality of the signal light is deteriorated.
  • FIG. 12 is a diagram showing an example of a change in optical power when the number of wavelengths of WDM (wavelength division multiplexing) signal light changes in an optical transmission system using distributed Raman amplification.
  • a plurality of signal lights having different wavelengths are wavelength-multiplexed with the WDM signal light.
  • the power of the WDM signal light is not sufficiently small with respect to the power of the excitation light, a saturation phenomenon of Raman amplification occurs.
  • the Raman gain changes according to a change in the number of wavelengths of the WDM signal light (that is, a change in the power of the WDM signal light incident on the optical fiber). For example, when the number of wavelengths of WDM signal light decreases, the Raman gain increases.
  • the signal power per wavelength of the WDM signal light in the optical fiber increases from before the decrease in the number of wavelengths (“normal time” in FIG. 12).
  • the transmission quality may deteriorate due to the nonlinear optical effect.
  • An object of this invention is to provide the technique for implement
  • the first optical transmission apparatus includes an optical amplifying unit that amplifies input signal light, an excitation unit that outputs pumping light that causes distributed Raman amplification in an optical transmission line, and an optical amplification unit that amplifies the optical signal.
  • the signal light and the pumping light are combined and sent to the optical transmission line, and the light is generated by scattering of the propagation light propagating through the optical transmission line.
  • the first optical transmission method of the present invention amplifies input signal light, outputs pumping light that causes distributed Raman amplification in the optical transmission line, and combines the amplified signal light and the pumping light. Detecting the scattered light generated by the scattering in the optical transmission path of the propagating light propagating through the optical transmission path and transmitted to the optical transmission path. The power is measured, and the output power of the pumping light and the output power of the optical amplification means are controlled based on the maximum power.
  • the present invention has the effect of suppressing the deterioration of transmission quality due to the nonlinear optical effect and expanding the transmission span.
  • FIG. 1 is a block diagram illustrating a configuration of an optical transmission system 10 according to a first embodiment of this invention.
  • the optical communication system 10 includes an optical transmission device 100, an optical reception device 110, and an optical fiber 7.
  • the optical transmission device 100 outputs signal light to the optical fiber 7.
  • the optical receiver 110 receives the signal light propagated through the optical fiber 7.
  • the optical transmission apparatus 100 includes n (n is a natural number) optical transmitters 11-1n, an optical multiplexer 1, an optical amplifier 2, an excitation light source 3, an OTDR (optical time domain domain reflectometer) 4, an optical multiplexer 5, and a control circuit. 6 is provided.
  • the optical transmitters 11-1n output signal lights having different wavelengths.
  • the optical multiplexer 1 wavelength-multiplexes the signal light output from the optical transmitter 11-1n to generate WDM (wavelength-division-multiplexing) signal light.
  • the optical amplifier 2 amplifies the WDM signal light and outputs it to the optical multiplexer 5.
  • the pumping light source 3 outputs pumping light for generating distributed Raman amplification in the optical fiber 7 to the optical multiplexer 5.
  • OTDR4 is an optical pulse tester.
  • the OTDR 4 detects Rayleigh scattered light generated in the optical fiber 7 by the transmitted optical pulse test light (hereinafter referred to as “OTDR light”).
  • the optical fiber 7 is an optical transmission line on which distributed Raman amplification is performed.
  • the optical multiplexer 5 combines the WDM signal light, the excitation light, and the OTDR light, and sends these lights to the optical fiber 7. Further, the optical multiplexer 5 receives light (hereinafter referred to as “scattered light”) obtained by scattering the OTDR light in the optical fiber 7 and outputs the light to the OTDR 4.
  • the OTDR 4 receives the scattered light and obtains the power distribution of the OTDR light in the length direction of the optical fiber 7 (hereinafter referred to as “OTDR waveform”).
  • the control circuit 6 analyzes the OTDR waveform and controls the output power of the optical amplifier 2 and the excitation light source 3 based on the analysis result.
  • the WDM signal light transmitted to the optical transmission line 7 is received by the optical receiver 110.
  • the optical transmission device 100 may further include a CPU (central processing unit) 91 and a memory 92.
  • the memory 92 is a fixed, non-temporary recording medium composed of, for example, a nonvolatile semiconductor memory. However, the configuration of the memory 92 is not limited to these.
  • the memory 92 stores a program executed by the CPU 91.
  • the CPU 91 may realize the function of the optical transmission device 100 by executing a program stored in the memory 92.
  • the optical transmission apparatus 100 of the first embodiment will be described.
  • the WDM signal light and the pumping light are simultaneously transmitted from the optical transmission apparatus 100 to the optical fiber 7.
  • the WDM signal light is amplified by distributed Raman amplification generated by the pumping light.
  • An example of the relationship between the wavelength of the excitation light and the Raman gain spectrum has already been described with reference to FIG.
  • distributed Raman amplification optical amplification is distributed in the optical fiber 7 that is an amplification medium.
  • FIG. 2 is a diagram showing an example of the power distribution of the WDM signal light in the optical fiber 7 when distributed Raman amplification is used.
  • the output unit of the optical transmission apparatus 100 is described as “transmission end” in FIG.
  • the transmission end is a port on the multiplexing side (optical fiber 7 side) of the optical multiplexer 5 and is a connection portion between the optical transmission device 100 and the optical fiber 7.
  • the power of the WDM signal light is highest at the output section of the optical transmission apparatus 100.
  • the power of the WDM signal light is attenuated along with the propagation of the WDM signal light due to the loss of the optical fiber 7. This is indicated by a broken line in FIG. 2 as “when the excitation light source is OFF”. Therefore, when distributed Raman amplification is not used, in order to reduce the influence of the nonlinear optical effect, which is one of the main causes of signal quality degradation in the optical transmission system 10, a signal is output from the output unit of the optical transmission apparatus 100. It is sufficient to manage the transmission level of light to the optical transmission line.
  • the WDM signal light is amplified in a distributed manner in the optical fiber 7.
  • the power of the WDM signal light is not necessarily the maximum at the output unit of the optical transmission apparatus 100 (the port on the output side of the optical multiplexer 5 in FIG. 1), but is the maximum in the middle of transmission through the optical fiber 7.
  • a solid line in FIG. 2 as “when the excitation light source is ON”.
  • the optical transmission apparatus 100 sends out OTDR light to the optical fiber 7 in addition to the WDM signal light and the pumping light for Raman amplification.
  • the OTDR light is used to monitor the level change in the optical fiber 7 of the distributed Raman amplified signal light.
  • FIG. 3 and 4 are diagrams illustrating examples of wavelength arrangements of the pump light, the WDM signal light, and the OTDR light in the optical transmission apparatus 100.
  • FIG. The OTDR light is used to indirectly monitor the power distribution of the WDM signal light in the longitudinal direction of the optical fiber 7. For this reason, the wavelength of the OTDR light is arranged in a wavelength band where a distributed Raman amplification characteristic substantially similar to that of the WDM signal light can be obtained.
  • the wavelength of the OTDR light is slightly longer than the upper limit wavelength of the wavelength band of the WDM signal light.
  • the wavelength of the OTDR light is slightly shorter than the lower limit wavelength of the wavelength band of the WDM signal light.
  • the wavelength of the OTDR light is preferably set to a wavelength at which the distributed Raman amplification characteristic for the OTDR light is substantially the same as the distributed Raman amplification characteristic for the WDM signal light.
  • the wavelength of the OTDR light is a wavelength that can estimate the characteristic of the distributed Raman amplification for the WDM signal light based on the characteristic of the distributed Raman amplification for the OTDR light.
  • the wavelength of OTDR light is in the vicinity of the wavelength band of WDM signal light.
  • FIG. 5 is a diagram for explaining the operation of the optical transmission apparatus 100. Similar to the WDM signal light, the OTDR light is also lost by the optical fiber 7 and amplified by the pumping light. The OTDR 4 measures the OTDR waveform by receiving the OTDR light that returns to the optical transmission apparatus 100 due to Rayleigh scattering in the optical fiber 7. The OTDR waveform indicates the power distribution in the transmission direction of the OTDR light in the optical fiber 7.
  • the control circuit 6 analyzes the OTDR waveform generated by the OTDR 4 and controls the optical amplifier 2 and the pumping light source 3 so that the maximum power of the WDM signal light in the optical fiber 7 obtained from the OTDR waveform does not exceed a predetermined threshold. Controls output power.
  • the predetermined threshold is determined based on an allowable amount of transmission quality degradation caused by the nonlinear optical effect on the WDM signal light generated in the optical fiber 7. Since the wavelength of the OTDR light is in the vicinity of the WDM signal light, it is easy to estimate the power distribution of the WDM signal light from the OTDR waveform. For example, it may be estimated that the OTDR waveform is similar to the power distribution of the WDM signal light.
  • the difference in power between the OTDR light and the WDM signal light can be corrected, for example, by measuring the power of both at the transmission end.
  • the power distribution of the WDM signal light can be easily estimated from the OTDR waveform by keeping the ratio of the incident power of the OTDR light to the optical transmission line 7 and the power per wavelength of the WDM signal light constant.
  • a difference between an OTDR waveform by OTDR light having the same wavelength as the WDM signal light and an OTDR waveform by OTDR light having a wavelength near the WDM signal light may be acquired.
  • the power distribution of the WDM signal light can be estimated more accurately by correcting the OTDR waveform of the OTDR light having a wavelength in the vicinity of the WDM signal light with the difference acquired at the time of manufacture.
  • FIG. 6 is a flowchart illustrating an example of an operation procedure of the optical transmission device 100 according to the first embodiment.
  • the optical amplifier 2 amplifies the input WDM signal light (step S1 in FIG. 6), and the pumping light source 3 outputs pumping light for causing Raman amplification in the optical fiber 7 (step S2).
  • Step S1 and step S2 may be executed in the reverse order, or may be executed simultaneously.
  • the optical multiplexer 5 combines the amplified WDM signal light, the excitation light, and the OTDR light (step S3).
  • the OTDR 4 measures the power distribution in the optical fiber 7 of the OTDR light transmitted to the optical fiber 7 (step S4).
  • the control circuit 6 controls the output power of the pumping light source 3 and the output power of the optical amplifier 2 based on the power distribution measured by the OTDR 4 (Step S5).
  • the optical transmission device 100 monitors the level change in the transmission direction of the optical transmission line using OTDR light, and controls the optical amplifier 2 and the pumping light source 3 based on the monitoring result.
  • the control circuit 6 controls the output power of the optical amplifier 2 in order to change the power at the transmission end of the WDM signal light.
  • the control circuit 6 controls the output power of the excitation light source 3 in order to control the gain of Raman amplification.
  • Specific control contents for the optical amplifier 2 and the excitation light source 3 corresponding to the OTDR waveform input from the OTDR 4 may be set in the control circuit 6 in advance according to the characteristics of the OTDR waveform.
  • the optical transmission device 100 propagates the OTDR light together with the WDM signal light, and monitors the optical power change in the longitudinal direction of the optical fiber 7 of the OTDR light by the OTDR waveform, thereby indirectly monitoring the power distribution of the WDM signal light. it can. As a result, the optical transmission device 100 can control the output power of the optical amplifier 2 and the pumping light source 3 so that the maximum power of the WDM signal light in the optical fiber 7 does not exceed the threshold at which the influence of nonlinear waveform distortion occurs.
  • the optical transmission device 100 manages the maximum power of the WDM signal light in the transmission direction of the optical fiber 7 by such control, thereby suppressing the deterioration of the transmission quality of the signal light due to the nonlinear optical effect in the optical transmission path.
  • the transmission span can be expanded.
  • the optical transmission device 100 can monitor the power change per wavelength of the WDM signal light by monitoring the OTDR waveform even when the number of wavelengths of the WDM signal light changes. Therefore, the optical transmission device 100 controls the output power of the optical amplifier 2 and the excitation light source 3 based on the power change per wavelength of the WDM signal light, thereby suppressing the level fluctuation for each wavelength of the WDM signal light, The transmission quality of WDM signal light can be maintained.
  • the optical transmission apparatus 100 compensates for the power of the WDM signal light that has decreased due to the increase in the loss of the optical fiber by monitoring the change in the optical power per wavelength of the WDM signal light.
  • the output power of the optical amplifier 2 and the pumping light source 3 can be controlled. That is, the optical transmission device 100 can maintain the optical power per wavelength of the WDM signal light and maintain the transmission quality of the WDM signal light even when the loss of the optical fiber increases.
  • the optical transmission device includes an optical amplifier, an excitation light source, a measurement unit, an optical multiplexer, and a control circuit.
  • the optical amplifier amplifies the input signal light.
  • the pumping light source outputs pumping light that causes distributed Raman amplification in the optical transmission line.
  • the optical multiplexer combines the signal light amplified by the optical amplifier and the pumping light, and sends them to the optical transmission line.
  • the measurement unit measures the maximum power in the optical transmission line of the propagation light by detecting the scattered light generated by the scattering in the optical transmission line of the propagation light propagating through the optical transmission line.
  • the measurement unit notifies the control circuit of the maximum power of the measured propagation light.
  • the control circuit controls the output power of the pumping light and the output power of the optical amplifier based on the maximum power of the propagating light notified from the measurement unit.
  • the optical amplifier, pumping light source, measurement unit, optical multiplexer, and control circuit included in the optical transmission device according to the modification of the first embodiment are the optical amplifier 2, pumping light source included in the optical transmission device 100 illustrated in FIG. 3, OTDR 4, optical multiplexer 5, and control circuit 6.
  • the function of the measurement unit is not limited to the function of OTDR4.
  • the measurement unit only needs to have a function of measuring the maximum power of the propagation light in the optical transmission path by detecting scattered light and notifying the control circuit.
  • the optical transmission device of this modification having such a configuration is configured so that the maximum power of the light propagating in the optical transmission path does not exceed the threshold at which the influence of nonlinear waveform distortion occurs, and the output power of the optical amplifier and the pumping light source. Can be controlled. That is, by managing the maximum power inside the optical transmission line, the optical transmission device according to the modification of the first embodiment suppresses the deterioration of the transmission quality of the signal light due to the nonlinear optical effect in the optical transmission line.
  • the transmission span can be expanded.
  • FIG. 7 is a block diagram illustrating a configuration of the optical transmission system 20 according to the second embodiment.
  • FIG. 8 is a diagram illustrating an example of wavelength arrangement in the second embodiment.
  • the optical transmission system 20 according to the second embodiment includes an optical transmission device 200, an optical fiber 7, and an optical reception device 110.
  • the functions of the optical fiber 7 and the optical receiver 110 are the same as those in the first embodiment shown in FIG.
  • the optical transmission device 200 is different from the optical transmission device 100 according to the first embodiment in that the excitation light source 31 includes two light sources (LD1 and LD2). LD1 and LD2 are laser diodes, and the wavelength of LD1 is different from the wavelength of LD2 as shown in FIG.
  • the configuration and operation of the optical transmission device 200 other than the pumping light source 3 are basically the same as those of the optical transmission device 100.
  • the control circuit 6 independently controls the output power of the two LDs (LD1 and LD2) provided in the excitation light source 3 based on the OTDR waveform. Due to the excitation light source 3 having a plurality of wavelengths, the optical transmission device 200 has a wider Raman amplification band than the optical transmission device 100.
  • the OTDR light may be arranged one wavelength each on the short wavelength side and the long wavelength side of the WDM signal light.
  • the wavelengths of the OTDR light are indicated by upward arrows in FIG. 8 as OTDR wavelength 1 and OTDR wavelength 2.
  • the OTDR 4 outputs a plurality of OTDR lights having different wavelengths.
  • the wavelengths of two OTDR lights among the plurality of OTDR lights are near the upper limit and the lower limit of the wavelength of the WDM signal light, respectively.
  • a level difference between wavelengths of WDM signal light subjected to distributed Raman amplification in the optical fiber 7 (that is, wavelength dependence of distributed Raman gain). Can be estimated.
  • the control circuit 6 may obtain the power of each wavelength of the WDM signal light by interpolating the wavelength characteristics of the OTDR light 1 and the OTDR light 2.
  • the control circuit 6 may independently control the output power of the two LDs (LD1 and LD2) provided in the pumping light source 3 based on the comparison result of the respective OTDR waveforms by the OTDR light of two wavelengths.
  • the optical transmission device 200 suppresses the occurrence of optical power deviation between the wavelengths of the WDM signal light in the optical fiber 7, and the wavelength of the WDM signal light is reduced. There is an effect that a certain transmission quality can be secured over the entire area.
  • 7 and 8 show the case where both the excitation light source 3 and the OTDR light have two wavelengths.
  • the number of wavelengths of the excitation light source and the OTDR light is not limited to two wavelengths. Further, the number of wavelengths of the excitation light source and the number of wavelengths of the OTDR light may not be the same.
  • FIG. 9 is a block diagram illustrating a configuration of an optical transmission system 30 according to the third embodiment of this invention.
  • the optical transmission system 30 according to the third embodiment includes an optical transmission device 300, an optical fiber 7, and an optical reception device 110.
  • the functions of the optical fiber 7 and the optical receiver 110 are the same as those in the first embodiment shown in FIG.
  • the optical transmission device 300 is different from the optical transmission device 100 according to the first embodiment in that a dispersion compensation unit 8 is provided between the optical multiplexer 1 and the optical amplifier 2.
  • the configuration and operation of the optical transmission device 300 other than the control of the dispersion compensation unit 8 and the dispersion compensation unit 8 in the control circuit 6 are the same as those of the optical transmission device 100.
  • the dispersion compensator 8 imparts WDM signal light with an amount of chromatic dispersion that cancels out the chromatic dispersion caused by the optical fiber 7 at a point where the power of the WDM signal light propagating through the optical fiber 7 is maximum.
  • the dispersion compensator 8 adds the WDM signal light to the WDM signal light.
  • the dispersion compensation amount is given by ⁇ D ⁇ L1.
  • the distance L1 can be known from the OTDR waveform.
  • the optical transmission apparatus 300 according to the third embodiment having such a configuration has an effect of suppressing a decrease in transmission quality due to wavelength dispersion of the optical fiber 7 in addition to the effect of the first embodiment.
  • FIG. 10 is a block diagram showing the configuration of the optical transmission system 40 according to the fourth embodiment of the present invention.
  • the optical transmission system 40 according to the fourth embodiment includes an optical transmission device 400, an optical fiber 7, and an optical reception device 110.
  • the functions of the optical fiber 7 and the optical receiver 110 are the same as those in the first embodiment shown in FIG.
  • the optical transmission device 400 is different from the optical transmission device 100 of the first embodiment in that the control circuit 6 further controls the optical transmitter 11-1n.
  • the configuration and operation of other parts of the optical transmission device 400 are the same as those of the optical transmission device 100.
  • the control circuit 6 controls the transmission waveform of the optical transmitter 11-1n so that dispersion and waveform distortion caused by the optical fiber 7 are compensated.
  • These dispersion compensation and waveform distortion compensation in the optical transmission apparatus 400 may be either optical compensation or electrical compensation.
  • the optical transmission apparatus 400 may further include the dispersion compensator 8 described in the third embodiment between the optical multiplexer 1 and the optical amplifier 2.
  • the optical transmission apparatus 400 according to the fourth embodiment having such a configuration has an effect of suppressing a reduction in transmission quality due to chromatic dispersion and waveform distortion in addition to the effects of the first embodiment.
  • Optical amplification means for amplifying the input signal light; Pumping means for outputting pumping light that causes distributed Raman amplification in the optical transmission line; First optical multiplexing means for multiplexing the signal light amplified by the optical amplification means and the pumping light and sending them to the optical transmission line; Measuring means for measuring the maximum power of the propagation light in the optical transmission line by detecting scattered light generated by scattering of the propagation light propagating in the optical transmission line; Control means for controlling the output power of the pumping light and the output power of the optical amplifying means based on the maximum power notified from the measuring means;
  • An optical transmission device comprising:
  • the first optical multiplexing means further combines test light and sends it to the optical transmission line,
  • the measurement means outputs the test light to the first multiplexing means, and measures the maximum power by detecting the test light scattered in the optical transmission path as the scattered light.
  • the optical transmission device according to attachment 1.
  • Appendix 3 The optical transmission apparatus according to appendix 2, wherein the measuring means is an OTDR (optical time domain reflectometer).
  • the control means is configured so that the maximum power does not exceed a threshold value determined based on an allowable amount of deterioration in transmission quality of the signal light due to a nonlinear optical effect in the optical transmission path with respect to the signal light.
  • the optical transmission device according to any one of appendices 1 to 4, wherein the output power of the optical amplifying means is controlled.
  • Appendix 6 The light according to any one of appendices 2 to 5, wherein the wavelength of the test light is a wavelength capable of estimating the characteristic of the distributed Raman amplification with respect to the signal light based on the characteristic of the distributed Raman amplification with respect to the test light.
  • Transmission equipment The wavelength of the test light is a wavelength capable of estimating the characteristic of the distributed Raman amplification with respect to the signal light based on the characteristic of the distributed Raman amplification with respect to the test light.
  • Appendix 7 The optical transmission device according to any one of appendices 2 to 6, wherein the wavelength of the test light is in the vicinity of the wavelength of the signal light.
  • the test means outputs a plurality of the test lights having different wavelengths, and the wavelengths of the two test lights out of the plurality of test lights are in the vicinity of the upper limit and the lower limit of the wavelength multiplexed light, respectively.
  • the optical transmission apparatus according to appendix 8.
  • (Appendix 10) Further comprising dispersion compensation means connected to the input side of the amplification means, The test means measures the distance from the input end of the propagation light of the optical transmission path to a point where the power of the propagation light becomes the maximum power, and notifies the control means, the control means, The light according to any one of appendices 1 to 9, wherein the dispersion compensation unit is controlled based on a distance so as to give the signal light an amount of dispersion that cancels out the amount of dispersion of the optical transmission line generated at the point. Transmission equipment.
  • the excitation unit outputs a plurality of the excitation lights having different wavelengths, and the control unit is configured to output the plurality of excitations so that the wavelength dependence of the power distribution of the propagating light in the optical transmission path falls within a predetermined range.
  • the optical transmission device according to any one of appendices 1 to 10, wherein the light is controlled independently.
  • Appendix 12 The optical transmission apparatus according to any one of appendices 1 to 11, further comprising: an optical transmission unit connected so that the output signal light is input to the optical amplification unit.
  • Appendix 13 An optical transmitter connected so that the output signal light is input to the optical amplifier;
  • the second light is connected so that the light output from the plurality of optical transmission units having different wavelengths is combined, and the combined light output from the optical transmission unit is input to the optical amplification unit.
  • Appendix 15 The optical transmission device according to any one of appendices 1 to 14, An optical transmission path for propagating light output from the optical transmission device; An optical receiver for receiving the signal light output from the optical transmission line; An optical transmission system comprising:
  • (Appendix 16) Amplifies the input signal light, Outputs pumping light that causes distributed Raman amplification in the optical transmission line, The amplified signal light and the excitation light are combined and sent to the optical transmission line, By detecting scattered light generated by scattering in the optical transmission path of propagation light propagating through the optical transmission path, the maximum power in the optical transmission path of the signal light is measured, Controlling the output power of the pumping light and the output power of the optical amplification means based on the maximum power; Control method of optical transmission apparatus.
  • a control program for an optical transmission device for controlling the output power of pumping light that causes Raman amplification in the optical transmission line and the output power of optical amplification means that amplifies signal light and outputs it to the optical transmission line .
  • the OTDR 4 described in the first to fourth embodiments may be a coherent OTDR that uses coherent reception to detect scattered light.
  • the configuration for dispersion compensation and the configuration for waveform distortion compensation described in the third and fourth embodiments may be applied to the optical transmission device 200 of the second embodiment.
  • Optical transmission system 100 200, 300, 400
  • Optical transmission device 110 Optical reception device 1, 5
  • Optical multiplexer 2 Optical amplifier 3, 31 Excitation light source 4
  • OTDR 6 Control Circuit 7
  • Optical Fiber 8 Dispersion Compensator 11-1n
  • Optical Transmitter 91 CPU 92 memory

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Abstract

In order to achieve the suppression of degradation of transmission quality caused by a nonlinear optical effect and the increase of a transmission span, an optical transmission device is provided with: an optical amplification means which amplifies inputted signal light; an excitation means which outputs excitation light that generates distributed Raman amplification in an optical transmission path; a first optical multiplexing means which multiplexes the signal light amplified by the optical amplification means and the excitation light and sends out resultant light to the optical transmission path; a measurement means which detects scattered light generated by scattering of propagation light propagating through the optical transmission path in the optical transmission path to thereby measure the maximum power of the propagation light in the optical transmission path; and a control means which controls the output power of the excitation light and the output power of the optical amplification means on the basis of the maximum power reported from the measurement means.

Description

光伝送装置及び光伝送方法Optical transmission apparatus and optical transmission method
　本発明は、光伝送装置及び光伝送方法に関する。本発明は、特に、光伝送路で信号光が分布的に増幅される光伝送システムで用いられる光伝送装置及び光伝送方法に関する。 The present invention relates to an optical transmission device and an optical transmission method. The present invention particularly relates to an optical transmission device and an optical transmission method used in an optical transmission system in which signal light is distributed and amplified in an optical transmission line.
　伝送路に光ファイバが用いられる光伝送システムにおいて、光ファイバ内で信号光を分布的に増幅する手段の一つとして、分布ラマン増幅が知られている。図１１は、ラマン増幅における励起光の波長とラマン利得スペクトルとの関係の例を示す図である。光ファイバへの強い励起光の入射により、ラマン散乱に基づく誘導放出が起こる。ラマン増幅は、図１１に示すように励起光の波長より約１００ｎｍ長い波長域において光の増幅効果が得られる現象である。ラマン増幅による信号光の増幅特性は、励起光のパワー及び波長、信号光のパワー及び波長により変化する。分布ラマン増幅は、ラマン増幅を光伝送路である光ファイバ内で生じさせるものであり、その低雑音性と低非線形性とにより、光伝送システムの伝送品質改善や、伝送スパンの拡大が期待される。 In an optical transmission system in which an optical fiber is used for a transmission path, distributed Raman amplification is known as one of means for amplifying signal light within the optical fiber in a distributed manner. FIG. 11 is a diagram illustrating an example of the relationship between the wavelength of excitation light and the Raman gain spectrum in Raman amplification. Stimulated emission based on Raman scattering occurs due to the strong excitation light incident on the optical fiber. As shown in FIG. 11, Raman amplification is a phenomenon in which a light amplification effect is obtained in a wavelength range longer by about 100 nm than the wavelength of excitation light. The amplification characteristic of signal light by Raman amplification varies depending on the power and wavelength of pump light and the power and wavelength of signal light. Distributed Raman amplification causes Raman amplification to occur in an optical fiber that is an optical transmission line, and its low noise and low nonlinearity are expected to improve the transmission quality of optical transmission systems and increase the transmission span. The
　本発明に関連して、特許文献１には、ＯＴＤＲ（optical time domain reflectometer）を用いた伝送損失測定装置が記載されている。また、特許文献２には、ノイズ光パワーの変化量から求めたラマン利得効率によって中継増幅器の出力パワーが調整される、パワー調整装置が記載されている。 In connection with the present invention, Patent Document 1 describes a transmission loss measuring apparatus using an OTDR (optical time domain reflexometer). Further, Patent Document 2 describes a power adjustment device in which the output power of a relay amplifier is adjusted by Raman gain efficiency obtained from the amount of change in noise light power.
特開２００５－０８４０４１号公報（段落［００２８］－［００３１］、図１）Japanese Patent Laying-Open No. 2005-084041 (paragraphs [0028]-[0031], FIG. 1) 特開２００６－２８７６４９号公報（段落［００４８］、図１）JP 2006-287649 A (paragraph [0048], FIG. 1)
　伝送スパンの拡大のためには、光送信機が高出力の信号光を送信するとともに、高出力の励起光源によって高いラマン利得を得ることが好ましい。しかしながら、分布ラマン増幅では、光伝送路（光ファイバ）内の信号光パワーの上限を管理する必要がある。なぜならば、ラマン増幅のための励起光のパワーを増大させることで高いラマン増幅利得が得られる一方で、光ファイバ内の信号光パワーが非常に高い場合には、光ファイバの非線形光学効果に起因して信号光に歪みが生じ、信号光の伝送品質が劣化するからである。このため、分布ラマン増幅が用いられる光伝送システムでは、非線形光学効果による伝送品質への影響が少ないパワーの範囲でより高いラマン増幅利得が得られるように、信号光及び励起光の、光ファイバへの入力パワーを制御する必要がある。 In order to expand the transmission span, it is preferable that the optical transmitter transmits a high output signal light and obtains a high Raman gain by a high output pump light source. However, in distributed Raman amplification, it is necessary to manage the upper limit of signal light power in the optical transmission line (optical fiber). This is because, when the power of the pumping light for Raman amplification is increased, a high Raman amplification gain can be obtained, but when the signal light power in the optical fiber is very high, it is caused by the nonlinear optical effect of the optical fiber. This is because the signal light is distorted and the transmission quality of the signal light is deteriorated. For this reason, in an optical transmission system in which distributed Raman amplification is used, signal light and pumping light are transmitted to an optical fiber so that a higher Raman amplification gain can be obtained in a power range with less influence on transmission quality due to nonlinear optical effects. It is necessary to control the input power.
　図１２は、分布ラマン増幅が用いられる光伝送システムにおける、ＷＤＭ（wavelength division multiplexing、波長分割多重）信号光の波長数が変化した場合の光パワーの変化の例を示す図である。ＷＤＭ信号光には、異なる波長を持つ複数の信号光が波長多重される。励起光のパワーに対してＷＤＭ信号光のパワーが充分に小さくない場合、ラマン増幅の飽和現象が発生する。ラマン増幅が飽和した場合、ＷＤＭ信号光の波長数の変化（すなわち、光ファイバへ入射されるＷＤＭ信号光のパワーの変化）に応じて、ラマン利得が変化する。例えば、ＷＤＭ信号光の波長数が減少した場合には、ラマン利得が増加する。すると、図１２に示すように、光ファイバ中でのＷＤＭ信号光の波長当たりの信号パワーが波長数の減少前（図１２の「通常時」）よりも上昇する。信号パワーの最大値が上昇することにより（図１２の破線枠内）、非線形光学効果により伝送品質が低下する可能性がある。 FIG. 12 is a diagram showing an example of a change in optical power when the number of wavelengths of WDM (wavelength division multiplexing) signal light changes in an optical transmission system using distributed Raman amplification. A plurality of signal lights having different wavelengths are wavelength-multiplexed with the WDM signal light. When the power of the WDM signal light is not sufficiently small with respect to the power of the excitation light, a saturation phenomenon of Raman amplification occurs. When the Raman amplification is saturated, the Raman gain changes according to a change in the number of wavelengths of the WDM signal light (that is, a change in the power of the WDM signal light incident on the optical fiber). For example, when the number of wavelengths of WDM signal light decreases, the Raman gain increases. Then, as shown in FIG. 12, the signal power per wavelength of the WDM signal light in the optical fiber increases from before the decrease in the number of wavelengths (“normal time” in FIG. 12). As the maximum value of the signal power increases (within the broken line frame in FIG. 12), the transmission quality may deteriorate due to the nonlinear optical effect.
　逆に、ＷＤＭ信号光の波長数の増加によって光ファイバへ入射するＷＤＭ信号光の総パワーが増加した場合には、ラマン利得が減少し、光ファイバ中のＷＤＭ信号光の１波長当たりの信号光パワーが減少する。このような場合には、ＯＳＮＲ（optical signal to noise ratio、光信号対雑音比）が低下して伝送品質が低下する可能性がある。 Conversely, when the total power of the WDM signal light incident on the optical fiber increases due to an increase in the number of wavelengths of the WDM signal light, the Raman gain decreases, and the signal light per wavelength of the WDM signal light in the optical fiber. Power is reduced. In such a case, there is a possibility that OSNR (optical signal to noise ratio) decreases and transmission quality deteriorates.
　しかしながら、特許文献１及び２に記載された技術は、ラマン増幅による光伝送路内の信号光のパワーの伝送方向の分布を測定するための構成を備えていない。このため、特許文献１及び２に記載された技術は、光伝送路の途中で信号光パワーが増大することに起因する非線形光学効果による伝送品質の悪化を抑制することができない。
（発明の目的）
　本発明は、非線形光学効果に起因する伝送品質の悪化の抑制と伝送スパンの拡大とを実現するための技術を提供することを目的とする。 However, the techniques described in Patent Documents 1 and 2 do not have a configuration for measuring the distribution in the transmission direction of the power of the signal light in the optical transmission line by Raman amplification. For this reason, the techniques described in Patent Documents 1 and 2 cannot suppress deterioration in transmission quality due to the nonlinear optical effect resulting from an increase in signal light power in the middle of the optical transmission path.
(Object of invention)
An object of this invention is to provide the technique for implement | achieving suppression of the deterioration of the transmission quality resulting from a nonlinear optical effect, and the expansion of a transmission span.
　本発明の第１の光伝送装置は、入力された信号光を増幅する光増幅手段と、光伝送路において分布ラマン増幅を生じさせる励起光を出力する励起手段と、前記光増幅手段で増幅された前記信号光と、前記励起光とを合波して前記光伝送路に送出する第１の光合波手段と、前記光伝送路を伝搬する伝搬光の前記光伝送路内の散乱によって発生した散乱光を検出することで前記伝搬光の前記光伝送路内の最大パワーを測定する測定手段と、前記測定手段から通知された前記最大パワーに基づいて前記励起光の出力パワーと前記光増幅手段の出力パワーとを制御する制御手段と、を備える。 The first optical transmission apparatus according to the present invention includes an optical amplifying unit that amplifies input signal light, an excitation unit that outputs pumping light that causes distributed Raman amplification in an optical transmission line, and an optical amplification unit that amplifies the optical signal. The signal light and the pumping light are combined and sent to the optical transmission line, and the light is generated by scattering of the propagation light propagating through the optical transmission line. Measuring means for measuring the maximum power of the propagating light in the optical transmission line by detecting scattered light, output power of the excitation light and the optical amplifying means based on the maximum power notified from the measuring means And a control means for controlling the output power.
　本発明の第１の光伝送方法は、入力された信号光を増幅し、光伝送路において分布ラマン増幅を生じさせる励起光を出力し、増幅された前記信号光と、前記励起光とを合波して前記光伝送路へ送出し、前記光伝送路を伝搬する伝搬光の前記光伝送路内の散乱によって発生した散乱光を検出することで、前記信号光の前記光伝送路内の最大パワーを測定し、前記最大パワーに基づいて前記励起光の出力パワーと前記光増幅手段の出力パワーとを制御する、ことを特徴とする。 The first optical transmission method of the present invention amplifies input signal light, outputs pumping light that causes distributed Raman amplification in the optical transmission line, and combines the amplified signal light and the pumping light. Detecting the scattered light generated by the scattering in the optical transmission path of the propagating light propagating through the optical transmission path and transmitted to the optical transmission path. The power is measured, and the output power of the pumping light and the output power of the optical amplification means are controlled based on the maximum power.
　本発明は、非線形光学効果に起因する伝送品質の悪化の抑制と伝送スパンの拡大とを実現するという効果を奏する。 The present invention has the effect of suppressing the deterioration of transmission quality due to the nonlinear optical effect and expanding the transmission span.
第１の実施形態の光伝送装置の構成を示すブロック図である。It is a block diagram which shows the structure of the optical transmission apparatus of 1st Embodiment. 分布ラマン増幅が用いられた場合の、光ファイバ中のＷＤＭ信号光のパワー分布の例を示す図である。It is a figure which shows the example of the power distribution of the WDM signal light in an optical fiber when distributed Raman amplification is used. 第１の実施形態における波長配置の例を示す図である。It is a figure which shows the example of the wavelength arrangement | positioning in 1st Embodiment. 第１の実施形態における波長配置の例を示す図である。It is a figure which shows the example of the wavelength arrangement | positioning in 1st Embodiment. 第１の実施形態の光伝送装置の動作を説明するための図である。It is a figure for demonstrating operation | movement of the optical transmission apparatus of 1st Embodiment. 第１の実施形態の光伝送装置の動作手順の例を示すフローチャートである。3 is a flowchart illustrating an example of an operation procedure of the optical transmission apparatus according to the first embodiment. 第２の実施形態の光伝送装置の構成を示すブロック図である。It is a block diagram which shows the structure of the optical transmission apparatus of 2nd Embodiment. 第２の実施形態における波長配置の例を示す図である。It is a figure which shows the example of the wavelength arrangement | positioning in 2nd Embodiment. 第３の実施形態の光伝送装置の構成を示すブロック図である。It is a block diagram which shows the structure of the optical transmission apparatus of 3rd Embodiment. 第４の実施形態の光伝送装置の構成を示すブロック図である。It is a block diagram which shows the structure of the optical transmission apparatus of 4th Embodiment. ラマン増幅における励起光の波長とラマン利得スペクトルとの関係の例を示す図である。It is a figure which shows the example of the relationship between the wavelength of the excitation light in a Raman amplification, and a Raman gain spectrum. 分布ラマン増幅が用いられた光伝送システムにおける、波長数変化時のＷＤＭ信号光の光パワー変化の例を示す図である。It is a figure which shows the example of the optical power change of the WDM signal light at the time of the wavelength change in the optical transmission system using distributed Raman amplification.
（第１の実施形態）
　図１は、本発明の第１の実施形態の光伝送システム１０の構成を示すブロック図である。光通信システム１０は、光伝送装置１００、光受信装置１１０及び光ファイバ７を備える。光伝送装置１００は光ファイバ７へ信号光を出力する。光受信装置１１０は、光ファイバ７を伝搬した信号光を受信する。 (First embodiment)
FIG. 1 is a block diagram illustrating a configuration of an optical transmission system 10 according to a first embodiment of this invention. The optical communication system 10 includes an optical transmission device 100, an optical reception device 110, and an optical fiber 7. The optical transmission device 100 outputs signal light to the optical fiber 7. The optical receiver 110 receives the signal light propagated through the optical fiber 7.
　光伝送装置１００は、ｎ台（ｎは自然数）の光送信機１１－１ｎ、光合波器１、光増幅器２、励起光源３、ＯＴＤＲ（optical time domain reflectometer）４、光合波器５及び制御回路６を備える。 The optical transmission apparatus 100 includes n (n is a natural number) optical transmitters 11-1n, an optical multiplexer 1, an optical amplifier 2, an excitation light source 3, an OTDR (optical time domain domain reflectometer) 4, an optical multiplexer 5, and a control circuit. 6 is provided.
　光送信機１１－１ｎは、それぞれ波長が異なる信号光を出力する。光合波器１は、光送信機１１－１ｎから出力される信号光を波長多重して、ＷＤＭ（wavelength division multiplexing、波長分割多重）信号光を生成する。光増幅器２は、ＷＤＭ信号光を増幅して光合波器５へ出力する。 The optical transmitters 11-1n output signal lights having different wavelengths. The optical multiplexer 1 wavelength-multiplexes the signal light output from the optical transmitter 11-1n to generate WDM (wavelength-division-multiplexing) signal light. The optical amplifier 2 amplifies the WDM signal light and outputs it to the optical multiplexer 5.
　励起光源３は、光ファイバ７において分布ラマン増幅を発生させるための励起光を光合波器５へ出力する。ＯＴＤＲ４は光パルス試験器である。ＯＴＤＲ４は、送出された光パルス試験光（以下、「ＯＴＤＲ光」という。）によって光ファイバ７で生成されたレイリー散乱光を検出する。光ファイバ７は、分布ラマン増幅が行われる光伝送路である。 The pumping light source 3 outputs pumping light for generating distributed Raman amplification in the optical fiber 7 to the optical multiplexer 5. OTDR4 is an optical pulse tester. The OTDR 4 detects Rayleigh scattered light generated in the optical fiber 7 by the transmitted optical pulse test light (hereinafter referred to as “OTDR light”). The optical fiber 7 is an optical transmission line on which distributed Raman amplification is performed.
　光合波器５は、ＷＤＭ信号光、励起光及びＯＴＤＲ光を合波して、これらの光を光ファイバ７へ送出する。また、光合波器５は、ＯＴＤＲ光が光ファイバ７内で散乱された光（以下、「散乱光」という。）を受信してＯＴＤＲ４へ出力する。ＯＴＤＲ４は、散乱光を受信して、光ファイバ７の長さ方向のＯＴＤＲ光のパワー分布（以下、「ＯＴＤＲ波形」という。）を求める。制御回路６は、ＯＴＤＲ波形を解析し、解析結果に基づいて光増幅器２及び励起光源３の出力パワーを制御する。光伝送路７に送出されたＷＤＭ信号光は、光受信装置１１０で受信される。 The optical multiplexer 5 combines the WDM signal light, the excitation light, and the OTDR light, and sends these lights to the optical fiber 7. Further, the optical multiplexer 5 receives light (hereinafter referred to as “scattered light”) obtained by scattering the OTDR light in the optical fiber 7 and outputs the light to the OTDR 4. The OTDR 4 receives the scattered light and obtains the power distribution of the OTDR light in the length direction of the optical fiber 7 (hereinafter referred to as “OTDR waveform”). The control circuit 6 analyzes the OTDR waveform and controls the output power of the optical amplifier 2 and the excitation light source 3 based on the analysis result. The WDM signal light transmitted to the optical transmission line 7 is received by the optical receiver 110.
　光伝送装置１００は、さらに、ＣＰＵ（central processing unit、中央処理装置）９１及びメモリ９２を備えていてもよい。メモリ９２は、例えば不揮発性の半導体メモリで構成される、固定された、一時的でない記録媒体である。ただし、メモリ９２の構成はこれらには限定されない。メモリ９２は、ＣＰＵ９１において実行されるプログラムを記憶する。ＣＰＵ９１は、メモリ９２に記憶されたプログラムを実行することで、光伝送装置１００の機能を実現してもよい。 The optical transmission device 100 may further include a CPU (central processing unit) 91 and a memory 92. The memory 92 is a fixed, non-temporary recording medium composed of, for example, a nonvolatile semiconductor memory. However, the configuration of the memory 92 is not limited to these. The memory 92 stores a program executed by the CPU 91. The CPU 91 may realize the function of the optical transmission device 100 by executing a program stored in the memory 92.
　第１の実施形態の光伝送装置１００の動作について説明する。分布ラマン増幅が用いられる光伝送システム１０では、光伝送装置１００から、ＷＤＭ信号光と励起光とが、同時に光ファイバ７へ送出される。光ファイバ７では、励起光により発生する分布ラマン増幅により、ＷＤＭ信号光が増幅される。励起光の波長とラマン利得スペクトルとの関係例は、既に図１１で説明した。分布ラマン増幅においては、増幅媒体である光ファイバ７内で分布的に光増幅が行われる。 The operation of the optical transmission apparatus 100 of the first embodiment will be described. In the optical transmission system 10 in which distributed Raman amplification is used, the WDM signal light and the pumping light are simultaneously transmitted from the optical transmission apparatus 100 to the optical fiber 7. In the optical fiber 7, the WDM signal light is amplified by distributed Raman amplification generated by the pumping light. An example of the relationship between the wavelength of the excitation light and the Raman gain spectrum has already been described with reference to FIG. In distributed Raman amplification, optical amplification is distributed in the optical fiber 7 that is an amplification medium.
　図２は、分布ラマン増幅が用いられた場合の、光ファイバ７中のＷＤＭ信号光のパワー分布の例を示す図である。光伝送装置１００の出力部は、図２では「送信端」と記載される。送信端は、光合波器５の合波側（光ファイバ７側）のポートであり、光伝送装置１００と光ファイバ７との接続部である。 FIG. 2 is a diagram showing an example of the power distribution of the WDM signal light in the optical fiber 7 when distributed Raman amplification is used. The output unit of the optical transmission apparatus 100 is described as “transmission end” in FIG. The transmission end is a port on the multiplexing side (optical fiber 7 side) of the optical multiplexer 5 and is a connection portion between the optical transmission device 100 and the optical fiber 7.
　分布ラマン増幅が用いられない場合、あるいは励起光が光ファイバに供給されていない場合には、ＷＤＭ信号光のパワーは光伝送装置１００の出力部で最も高い。この場合には、ＷＤＭ信号光のパワーは、光ファイバ７の損失により、ＷＤＭ信号光の伝搬とともに減衰する。これは、図２において「励起光源ＯＦＦ時」として破線で示される。このため、分布ラマン増幅が用いられない場合に、光伝送システム１０における信号品質劣化の主要因の１つである非線形光学効果の影響を低減するためには、光伝送装置１００の出力部において信号光の光伝送路への送出レベルを管理すれば充分である。 When distributed Raman amplification is not used, or when pumping light is not supplied to the optical fiber, the power of the WDM signal light is highest at the output section of the optical transmission apparatus 100. In this case, the power of the WDM signal light is attenuated along with the propagation of the WDM signal light due to the loss of the optical fiber 7. This is indicated by a broken line in FIG. 2 as “when the excitation light source is OFF”. Therefore, when distributed Raman amplification is not used, in order to reduce the influence of the nonlinear optical effect, which is one of the main causes of signal quality degradation in the optical transmission system 10, a signal is output from the output unit of the optical transmission apparatus 100. It is sufficient to manage the transmission level of light to the optical transmission line.
　一方、光伝送装置１００を用いて分布ラマン増幅が行われる場合には、ＷＤＭ信号光は、光ファイバ７内で分布的に増幅される。このため、ＷＤＭ信号光のパワーは、光伝送装置１００の出力部（図１では、光合波器５の出力側のポート）で必ずしも最大ではなく、光ファイバ７による伝送の途中で最大となる場合がある。これは、図２において「励起光源ＯＮ時」として実線で例示される。このため、分布ラマン増幅が適用された光伝送システムにおいては、光ファイバ７の長手方向（すなわち、伝送方向）のＷＤＭ信号光のパワーの変化を管理できることが望ましい。このような管理により、光ファイバ７内のＷＤＭ信号光パワーを、非線形光学効果による歪の影響が生じるレベル未満に維持できる。 On the other hand, when distributed Raman amplification is performed using the optical transmission device 100, the WDM signal light is amplified in a distributed manner in the optical fiber 7. For this reason, the power of the WDM signal light is not necessarily the maximum at the output unit of the optical transmission apparatus 100 (the port on the output side of the optical multiplexer 5 in FIG. 1), but is the maximum in the middle of transmission through the optical fiber 7. There is. This is illustrated by a solid line in FIG. 2 as “when the excitation light source is ON”. For this reason, in an optical transmission system to which distributed Raman amplification is applied, it is desirable to be able to manage changes in the power of the WDM signal light in the longitudinal direction of the optical fiber 7 (that is, the transmission direction). With such management, the WDM signal light power in the optical fiber 7 can be maintained below a level at which the influence of distortion due to the nonlinear optical effect occurs.
　光伝送装置１００は、ＷＤＭ信号光及びラマン増幅用の励起光に加えて、ＯＴＤＲ光を光ファイバ７へ送出する。ＯＴＤＲ光は、分布ラマン増幅された信号光の、光ファイバ７内のレベル変化を監視するために用いられる。 The optical transmission apparatus 100 sends out OTDR light to the optical fiber 7 in addition to the WDM signal light and the pumping light for Raman amplification. The OTDR light is used to monitor the level change in the optical fiber 7 of the distributed Raman amplified signal light.
　図３及び図４は、光伝送装置１００における、励起光、ＷＤＭ信号光、ＯＴＤＲ光のそれぞれの波長配置の例を示す図である。ＯＴＤＲ光は、ＷＤＭ信号光の、光ファイバ７の長手方向のパワー分布を間接的に監視するために用いられる。このため、ＯＴＤＲ光の波長は、ＷＤＭ信号光とほぼ同様の分布ラマン増幅特性が得られる波長帯に配置される。例えば、図３では、ＯＴＤＲ光の波長は、ＷＤＭ信号光の波長帯の上限の波長よりもわずかに長い。図４では、ＯＴＤＲ光の波長は、ＷＤＭ信号光の波長帯の下限の波長よりもわずかに短い。このように、ＯＴＤＲ光の波長は、ＯＴＤＲ光に対する分布ラマン増幅特性がＷＤＭ信号光に対する分布ラマン増幅特性とおおむね同一である波長に設定されることが好ましい。いいかえれば、ＯＴＤＲ光の波長は、ＯＴＤＲ光に対する分布ラマン増幅の特性に基づいてＷＤＭ信号光に対する分布ラマン増幅の特性を推定可能な波長である。例えば、ＯＴＤＲ光の波長は、ＷＤＭ信号光の波長帯の近傍にある。 3 and 4 are diagrams illustrating examples of wavelength arrangements of the pump light, the WDM signal light, and the OTDR light in the optical transmission apparatus 100. FIG. The OTDR light is used to indirectly monitor the power distribution of the WDM signal light in the longitudinal direction of the optical fiber 7. For this reason, the wavelength of the OTDR light is arranged in a wavelength band where a distributed Raman amplification characteristic substantially similar to that of the WDM signal light can be obtained. For example, in FIG. 3, the wavelength of the OTDR light is slightly longer than the upper limit wavelength of the wavelength band of the WDM signal light. In FIG. 4, the wavelength of the OTDR light is slightly shorter than the lower limit wavelength of the wavelength band of the WDM signal light. Thus, the wavelength of the OTDR light is preferably set to a wavelength at which the distributed Raman amplification characteristic for the OTDR light is substantially the same as the distributed Raman amplification characteristic for the WDM signal light. In other words, the wavelength of the OTDR light is a wavelength that can estimate the characteristic of the distributed Raman amplification for the WDM signal light based on the characteristic of the distributed Raman amplification for the OTDR light. For example, the wavelength of OTDR light is in the vicinity of the wavelength band of WDM signal light.
　図５は、光伝送装置１００の動作を説明するための図である。ＷＤＭ信号光と同様に、ＯＴＤＲ光も、光ファイバ７による損失を受けるとともに励起光により増幅される。ＯＴＤＲ４は、光ファイバ７におけるレイリー散乱によって光伝送装置１００に戻るＯＴＤＲ光を受信することで、ＯＴＤＲ波形を測定する。ＯＴＤＲ波形は、ＯＴＤＲ光の光ファイバ７内の伝送方向のパワー分布を示す。 FIG. 5 is a diagram for explaining the operation of the optical transmission apparatus 100. Similar to the WDM signal light, the OTDR light is also lost by the optical fiber 7 and amplified by the pumping light. The OTDR 4 measures the OTDR waveform by receiving the OTDR light that returns to the optical transmission apparatus 100 due to Rayleigh scattering in the optical fiber 7. The OTDR waveform indicates the power distribution in the transmission direction of the OTDR light in the optical fiber 7.
　制御回路６は、ＯＴＤＲ４で生成されたＯＴＤＲ波形を解析し、ＯＴＤＲ波形から求められる光ファイバ７内のＷＤＭ信号光の最大パワーが所定の閾値を超えないように、光増幅器２及び励起光源３の出力パワーを制御する。所定の閾値は、光ファイバ７で発生する、ＷＤＭ信号光に対する非線形光学効果に起因する伝送品質の劣化の許容量に基づいて決定される。ＯＴＤＲ光の波長はＷＤＭ信号光の近傍にあるため、ＷＤＭ信号光のパワー分布をＯＴＤＲ波形から推定することは容易である。例えば、ＯＴＤＲ波形がＷＤＭ信号光のパワーの分布と相似であると推定してもよい。ＯＴＤＲ光とＷＤＭ信号光とのパワーの差は、例えば、送信端で両者のパワーを測定することで補正できる。あるいは、ＯＴＤＲ光の光伝送路７への入射パワーと、ＷＤＭ信号光の１波長あたりのパワーとの比を一定にしておくことで、ＯＴＤＲ波形からＷＤＭ信号光のパワー分布を容易に推定できる。 The control circuit 6 analyzes the OTDR waveform generated by the OTDR 4 and controls the optical amplifier 2 and the pumping light source 3 so that the maximum power of the WDM signal light in the optical fiber 7 obtained from the OTDR waveform does not exceed a predetermined threshold. Controls output power. The predetermined threshold is determined based on an allowable amount of transmission quality degradation caused by the nonlinear optical effect on the WDM signal light generated in the optical fiber 7. Since the wavelength of the OTDR light is in the vicinity of the WDM signal light, it is easy to estimate the power distribution of the WDM signal light from the OTDR waveform. For example, it may be estimated that the OTDR waveform is similar to the power distribution of the WDM signal light. The difference in power between the OTDR light and the WDM signal light can be corrected, for example, by measuring the power of both at the transmission end. Alternatively, the power distribution of the WDM signal light can be easily estimated from the OTDR waveform by keeping the ratio of the incident power of the OTDR light to the optical transmission line 7 and the power per wavelength of the WDM signal light constant.
　また、光伝送装置１００の製造時に、ＷＤＭ信号光と同一の波長のＯＴＤＲ光によるＯＴＤＲ波形と、ＷＤＭ信号光の近傍の波長のＯＴＤＲ光によるＯＴＤＲ波形との差分が取得されてもよい。そして、運用時には、ＷＤＭ信号光の近傍の波長のＯＴＤＲ光によるＯＴＤＲ波形を、製造時に取得された差分により補正することで、ＷＤＭ信号光のパワー分布をより正確に推定できる。 Also, at the time of manufacturing the optical transmission apparatus 100, a difference between an OTDR waveform by OTDR light having the same wavelength as the WDM signal light and an OTDR waveform by OTDR light having a wavelength near the WDM signal light may be acquired. At the time of operation, the power distribution of the WDM signal light can be estimated more accurately by correcting the OTDR waveform of the OTDR light having a wavelength in the vicinity of the WDM signal light with the difference acquired at the time of manufacture.
　図６は、第１の実施形態の光伝送装置１００の動作手順の例を示すフローチャートである。光増幅器２は入力されたＷＤＭ信号光を増幅し（図６のステップＳ１）、励起光源３は光ファイバ７にラマン増幅を生じさせるための励起光を出力する（ステップＳ２）。ステップＳ１とステップＳ２とは逆の順序で実行されてもよく、同時に実行されてもよい。 FIG. 6 is a flowchart illustrating an example of an operation procedure of the optical transmission device 100 according to the first embodiment. The optical amplifier 2 amplifies the input WDM signal light (step S1 in FIG. 6), and the pumping light source 3 outputs pumping light for causing Raman amplification in the optical fiber 7 (step S2). Step S1 and step S2 may be executed in the reverse order, or may be executed simultaneously.
　光合波器５は、増幅されたＷＤＭ信号光と、励起光と、ＯＴＤＲ光とを合波する（ステップＳ３）。ＯＴＤＲ４は、光ファイバ７へ送出されたＯＴＤＲ光の、光ファイバ７内のパワー分布を測定する（ステップＳ４）。制御回路６は、ＯＴＤＲ４によって測定されたパワー分布に基づいて、励起光源３の出力パワーと光増幅器２の出力パワーとを制御する（ステップＳ５）。 The optical multiplexer 5 combines the amplified WDM signal light, the excitation light, and the OTDR light (step S3). The OTDR 4 measures the power distribution in the optical fiber 7 of the OTDR light transmitted to the optical fiber 7 (step S4). The control circuit 6 controls the output power of the pumping light source 3 and the output power of the optical amplifier 2 based on the power distribution measured by the OTDR 4 (Step S5).
　第１の実施形態の光伝送装置１００は、ＯＴＤＲ光を用いて光伝送路の伝送方向のレベル変化を監視し、監視結果に基づいて光増幅器２及び励起光源３を制御する。例えば、制御回路６は、ＷＤＭ信号光の送信端におけるパワーを変化させるために光増幅器２の出力パワーを制御する。また、制御回路６は、ラマン増幅の利得を制御するために励起光源３の出力パワーを制御する。ＯＴＤＲ４から入力されたＯＴＤＲ波形に対応する光増幅器２及び励起光源３への具体的な制御内容は、ＯＴＤＲ波形の特徴に応じてあらかじめ制御回路６に設定されていてもよい。 The optical transmission device 100 according to the first embodiment monitors the level change in the transmission direction of the optical transmission line using OTDR light, and controls the optical amplifier 2 and the pumping light source 3 based on the monitoring result. For example, the control circuit 6 controls the output power of the optical amplifier 2 in order to change the power at the transmission end of the WDM signal light. The control circuit 6 controls the output power of the excitation light source 3 in order to control the gain of Raman amplification. Specific control contents for the optical amplifier 2 and the excitation light source 3 corresponding to the OTDR waveform input from the OTDR 4 may be set in the control circuit 6 in advance according to the characteristics of the OTDR waveform.
　光伝送装置１００は、ＷＤＭ信号光とともにＯＴＤＲ光を伝搬させ、ＯＴＤＲ波形によりＯＴＤＲ光の光ファイバ７の長手方向の光パワー変化を監視することで、間接的にＷＤＭ信号光のパワーの分布を監視できる。これにより、光伝送装置１００は、光ファイバ７内のＷＤＭ信号光の最大パワーが非線形波形歪による影響が発生する閾値を超えないように、光増幅器２及び励起光源３の出力パワーを制御できる。 The optical transmission device 100 propagates the OTDR light together with the WDM signal light, and monitors the optical power change in the longitudinal direction of the optical fiber 7 of the OTDR light by the OTDR waveform, thereby indirectly monitoring the power distribution of the WDM signal light. it can. As a result, the optical transmission device 100 can control the output power of the optical amplifier 2 and the pumping light source 3 so that the maximum power of the WDM signal light in the optical fiber 7 does not exceed the threshold at which the influence of nonlinear waveform distortion occurs.
　光伝送装置１００は、このような制御により光ファイバ７の伝送方向のＷＤＭ信号光の最大パワーを管理することで、光伝送路内の非線形光学効果による信号光の伝送品質の悪化を抑制しつつ、伝送スパンを拡大できる。 The optical transmission device 100 manages the maximum power of the WDM signal light in the transmission direction of the optical fiber 7 by such control, thereby suppressing the deterioration of the transmission quality of the signal light due to the nonlinear optical effect in the optical transmission path. The transmission span can be expanded.
　さらに、光伝送装置１００は、ＷＤＭ信号光の波長数が変化した場合においても、ＯＴＤＲ波形を監視することで、ＷＤＭ信号光の１波長当たりのパワー変化を監視できる。従って、光伝送装置１００は、ＷＤＭ信号光の１波長当たりのパワー変化に基づいて光増幅器２及び励起光源３の出力パワーを制御することで、ＷＤＭ信号光の波長ごとのレベル変動を抑制し、ＷＤＭ信号光の伝送品質を維持できる。 Furthermore, the optical transmission device 100 can monitor the power change per wavelength of the WDM signal light by monitoring the OTDR waveform even when the number of wavelengths of the WDM signal light changes. Therefore, the optical transmission device 100 controls the output power of the optical amplifier 2 and the excitation light source 3 based on the power change per wavelength of the WDM signal light, thereby suppressing the level fluctuation for each wavelength of the WDM signal light, The transmission quality of WDM signal light can be maintained.
　分布ラマン増幅は光ファイバを媒体としているため、光ファイバの損失が増加した場合には、光ファイバ内の励起光のパワーが低下し、ラマン利得が減少する。このような光ファイバの損失増加時にも、ＷＤＭ信号光の１波長当たりの光パワー変化を監視することで、光伝送装置１００は、光ファイバの損失増加により低下したＷＤＭ信号光のパワーを補償するように光増幅器２及び励起光源３の出力パワーを制御できる。すなわち、光伝送装置１００は、光ファイバの損失が増加した場合も、ＷＤＭ信号光の１波長あたりの光パワーを維持し、ＷＤＭ信号光の伝送品質を維持できる。 Since distributed Raman amplification uses an optical fiber as a medium, when the loss of the optical fiber increases, the power of the pumping light in the optical fiber decreases and the Raman gain decreases. Even when the loss of such an optical fiber increases, the optical transmission apparatus 100 compensates for the power of the WDM signal light that has decreased due to the increase in the loss of the optical fiber by monitoring the change in the optical power per wavelength of the WDM signal light. Thus, the output power of the optical amplifier 2 and the pumping light source 3 can be controlled. That is, the optical transmission device 100 can maintain the optical power per wavelength of the WDM signal light and maintain the transmission quality of the WDM signal light even when the loss of the optical fiber increases.
　（第１の実施形態の変形例）
　第１の実施形態の変形例について説明する。第１の実施形態の変形例の光伝送装置は、光増幅器、励起光源、測定部、光合波器、制御回路を備える。光増幅器は、入力された信号光を増幅する。励起光源は、光伝送路において分布ラマン増幅を生じさせる励起光を出力する。光合波器は、光増幅器で増幅された信号光と、励起光とを合波して光伝送路に送出する。測定部は、光伝送路を伝搬する伝搬光の光伝送路内の散乱によって発生した散乱光を検出することで、伝搬光の光伝送路内の最大パワーを測定する。測定部は、測定された伝搬光の最大パワーを制御回路へ通知する。制御回路は、測定部から通知された伝搬光の最大パワーに基づいて、励起光の出力パワーと光増幅器の出力パワーとを制御する。 (Modification of the first embodiment)
A modification of the first embodiment will be described. The optical transmission device according to the modification of the first embodiment includes an optical amplifier, an excitation light source, a measurement unit, an optical multiplexer, and a control circuit. The optical amplifier amplifies the input signal light. The pumping light source outputs pumping light that causes distributed Raman amplification in the optical transmission line. The optical multiplexer combines the signal light amplified by the optical amplifier and the pumping light, and sends them to the optical transmission line. The measurement unit measures the maximum power in the optical transmission line of the propagation light by detecting the scattered light generated by the scattering in the optical transmission line of the propagation light propagating through the optical transmission line. The measurement unit notifies the control circuit of the maximum power of the measured propagation light. The control circuit controls the output power of the pumping light and the output power of the optical amplifier based on the maximum power of the propagating light notified from the measurement unit.
　第１の実施形態の変形例の光伝送装置が備える光増幅器、励起光源、測定部、光合波器及び制御回路は、それぞれ、図１に示した光伝送装置１００が備える光増幅器２、励起光源３、ＯＴＤＲ４、光合波器５、制御回路６に対応する。ただし、本変形例においては、測定部の機能はＯＴＤＲ４の機能に限定されない。測定部は、散乱光を検出することで伝搬光の光伝送路内の最大パワーを測定して制御回路へ通知する機能を備えていればよい。 The optical amplifier, pumping light source, measurement unit, optical multiplexer, and control circuit included in the optical transmission device according to the modification of the first embodiment are the optical amplifier 2, pumping light source included in the optical transmission device 100 illustrated in FIG. 3, OTDR 4, optical multiplexer 5, and control circuit 6. However, in the present modification, the function of the measurement unit is not limited to the function of OTDR4. The measurement unit only needs to have a function of measuring the maximum power of the propagation light in the optical transmission path by detecting scattered light and notifying the control circuit.
　このような構成を備える本変形例の光伝送装置は、光伝送路内を伝搬する光の最大パワーが非線形波形歪による影響が発生する閾値を超えないように、光増幅器及び励起光源の出力パワーを制御できる。すなわち、光伝送路の内部の最大パワーを管理することで、第１の実施形態の変形例の光伝送装置は、光伝送路内の非線形光学効果による信号光の伝送品質の悪化を抑制しつつ、伝送スパンを拡大できる。 The optical transmission device of this modification having such a configuration is configured so that the maximum power of the light propagating in the optical transmission path does not exceed the threshold at which the influence of nonlinear waveform distortion occurs, and the output power of the optical amplifier and the pumping light source. Can be controlled. That is, by managing the maximum power inside the optical transmission line, the optical transmission device according to the modification of the first embodiment suppresses the deterioration of the transmission quality of the signal light due to the nonlinear optical effect in the optical transmission line. The transmission span can be expanded.
　（第２の実施形態）
　ＷＤＭ信号光が伝送される光伝送システムでは、広帯域に亘って平坦なラマン増幅特性を確保するため、複数の異なる波長を持つ励起光が励起光源として用いられる場合がある。図７は、第２の実施形態の光伝送システム２０の構成を示すブロック図である。図８は、第２の実施形態における波長配置の例を示す図である。第２の実施形態の光伝送システム２０は、光伝送装置２００、光ファイバ７及び光受信装置１１０を備える。光ファイバ７及び光受信装置１１０の機能は、図１に示した第１の実施形態と同様である。 (Second Embodiment)
In an optical transmission system in which WDM signal light is transmitted, pump light having a plurality of different wavelengths may be used as a pump light source in order to ensure flat Raman amplification characteristics over a wide band. FIG. 7 is a block diagram illustrating a configuration of the optical transmission system 20 according to the second embodiment. FIG. 8 is a diagram illustrating an example of wavelength arrangement in the second embodiment. The optical transmission system 20 according to the second embodiment includes an optical transmission device 200, an optical fiber 7, and an optical reception device 110. The functions of the optical fiber 7 and the optical receiver 110 are the same as those in the first embodiment shown in FIG.
　光伝送装置２００は、第１の実施形態の光伝送装置１００と比較して、励起光源３１が２個の光源（ＬＤ１及びＬＤ２）を備える点で相違する。ＬＤ１及びＬＤ２はレーザダイオード（laser diode）であり、図８に示すようにＬＤ１の波長とＬＤ２の波長とは異なる。励起光源３以外の要素の光伝送装置２００の構成及び動作は、光伝送装置１００と基本的に同様である。制御回路６は、ＯＴＤＲ波形に基づいて、励起光源３が備える２個のＬＤ（ＬＤ１及びＬＤ２）の出力パワーを独立に制御する。複数の波長を持つ励起光源３により、光伝送装置２００は、光伝送装置１００よりも広いラマン増幅帯域を持つ。 The optical transmission device 200 is different from the optical transmission device 100 according to the first embodiment in that the excitation light source 31 includes two light sources (LD1 and LD2). LD1 and LD2 are laser diodes, and the wavelength of LD1 is different from the wavelength of LD2 as shown in FIG. The configuration and operation of the optical transmission device 200 other than the pumping light source 3 are basically the same as those of the optical transmission device 100. The control circuit 6 independently controls the output power of the two LDs (LD1 and LD2) provided in the excitation light source 3 based on the OTDR waveform. Due to the excitation light source 3 having a plurality of wavelengths, the optical transmission device 200 has a wider Raman amplification band than the optical transmission device 100.
　また、図８に示すように、ＯＴＤＲ光はＷＤＭ信号光の短波長側と長波長側に１波長ずつ配置されてもよい。ＯＴＤＲ光の波長はＯＴＤＲ波長１及びＯＴＤＲ波長２として、図８の上向きの矢印で示される。この場合には、ＯＴＤＲ４は波長が異なる複数のＯＴＤＲ光を出力する。例えば、複数のＯＴＤＲ光のうち２つのＯＴＤＲ光の波長は、それぞれＷＤＭ信号光の波長の上限の近傍及び下限の近傍にある。 Further, as shown in FIG. 8, the OTDR light may be arranged one wavelength each on the short wavelength side and the long wavelength side of the WDM signal light. The wavelengths of the OTDR light are indicated by upward arrows in FIG. 8 as OTDR wavelength 1 and OTDR wavelength 2. In this case, the OTDR 4 outputs a plurality of OTDR lights having different wavelengths. For example, the wavelengths of two OTDR lights among the plurality of OTDR lights are near the upper limit and the lower limit of the wavelength of the WDM signal light, respectively.
　波長が異なる複数のＯＴＤＲ光のＯＴＤＲ波形を監視して比較することにより、光ファイバ７内で分布ラマン増幅を受けたＷＤＭ信号光の波長間のレベル差（すなわち、分布ラマン利得の波長依存性）を推定できる。制御回路６は、ＷＤＭ信号光の各波長のパワーを、ＯＴＤＲ光１及びＯＴＤＲ光２の波長特性を補間して求めてもよい。制御回路６は、２波長のＯＴＤＲ光によるそれぞれのＯＴＤＲ波形の比較結果に基づいて、励起光源３が備える２個のＬＤ（ＬＤ１及びＬＤ２）の出力パワーを独立に制御してもよい。 By monitoring and comparing OTDR waveforms of a plurality of OTDR lights having different wavelengths, a level difference between wavelengths of WDM signal light subjected to distributed Raman amplification in the optical fiber 7 (that is, wavelength dependence of distributed Raman gain). Can be estimated. The control circuit 6 may obtain the power of each wavelength of the WDM signal light by interpolating the wavelength characteristics of the OTDR light 1 and the OTDR light 2. The control circuit 6 may independently control the output power of the two LDs (LD1 and LD2) provided in the pumping light source 3 based on the comparison result of the respective OTDR waveforms by the OTDR light of two wavelengths.
　このような制御により、光伝送装置２００は、光伝送装置１００の効果に加えて、光ファイバ７内でのＷＤＭ信号光の波長間の光パワー偏差の発生を抑制し、ＷＤＭ信号光の波長の全域に亘って一定の伝送品質を確保できるという効果を奏する。なお、図７及び図８では、励起光源３及びＯＴＤＲ光がいずれも２波長である場合を示した。しかし、励起光源及びＯＴＤＲ光の波長数はいずれも２波長に限定されない。また、励起光源の波長数とＯＴＤＲ光の波長数とは同一でなくてもよい。 By such control, in addition to the effect of the optical transmission device 100, the optical transmission device 200 suppresses the occurrence of optical power deviation between the wavelengths of the WDM signal light in the optical fiber 7, and the wavelength of the WDM signal light is reduced. There is an effect that a certain transmission quality can be secured over the entire area. 7 and 8 show the case where both the excitation light source 3 and the OTDR light have two wavelengths. However, the number of wavelengths of the excitation light source and the OTDR light is not limited to two wavelengths. Further, the number of wavelengths of the excitation light source and the number of wavelengths of the OTDR light may not be the same.
　（第３の実施形態）
　図９は、本発明の第３の実施形態の光伝送システム３０の構成を示すブロック図である。第３の実施形態の光伝送システム３０は、光伝送装置３００、光ファイバ７及び光受信装置１１０を備える。光ファイバ７及び光受信装置１１０の機能は、図１に示した第１の実施形態と同様である。 (Third embodiment)
FIG. 9 is a block diagram illustrating a configuration of an optical transmission system 30 according to the third embodiment of this invention. The optical transmission system 30 according to the third embodiment includes an optical transmission device 300, an optical fiber 7, and an optical reception device 110. The functions of the optical fiber 7 and the optical receiver 110 are the same as those in the first embodiment shown in FIG.
　光伝送装置３００は、第１の実施形態の光伝送装置１００と比較して、光合波器１と光増幅器２との間に分散補償部８を備える点で相違する。光伝送装置３００の、分散補償部８及び制御回路６における分散補償部８の制御以外の構成及び動作は、光伝送装置１００と同様である。分散補償部８は、光ファイバ７を伝搬するＷＤＭ信号光のパワーが最大となる地点において光ファイバ７によって生じる波長分散を相殺する量の波長分散を、ＷＤＭ信号光に付与する。 The optical transmission device 300 is different from the optical transmission device 100 according to the first embodiment in that a dispersion compensation unit 8 is provided between the optical multiplexer 1 and the optical amplifier 2. The configuration and operation of the optical transmission device 300 other than the control of the dispersion compensation unit 8 and the dispersion compensation unit 8 in the control circuit 6 are the same as those of the optical transmission device 100. The dispersion compensator 8 imparts WDM signal light with an amount of chromatic dispersion that cancels out the chromatic dispersion caused by the optical fiber 7 at a point where the power of the WDM signal light propagating through the optical fiber 7 is maximum.
　伝送特性の観点からは、伝搬中の信号光パワーが最大となる地点において、信号光の分散が補償された状態（すなわち、分散量が０(ps/nm)である状態）に近いほど、信号光の伝送品質が高くなる。光ファイバ７の入力端からＷＤＭ信号光のパワーが最大となる地点までの距離をＬ１、光ファイバの単位長さあたりの分散量をＤとすると、分散補償部８においてＷＤＭ信号光に付加される分散補償量は、－Ｄ×Ｌ１で与えられる。ここで、光ファイバ７の特性が既知であれば、分散量Ｄの値は容易に確認できる。また、距離Ｌ１は、ＯＴＤＲ波形から知ることができる。 From the viewpoint of transmission characteristics, at a point where the signal light power during propagation is maximum, the closer the signal light dispersion is to the compensated state (that is, the state where the dispersion amount is 0 (ps / nm)), the more the signal The transmission quality of light increases. When the distance from the input end of the optical fiber 7 to the point where the power of the WDM signal light is maximum is L1, and the dispersion amount per unit length of the optical fiber is D, the dispersion compensator 8 adds the WDM signal light to the WDM signal light. The dispersion compensation amount is given by −D × L1. Here, if the characteristics of the optical fiber 7 are known, the value of the dispersion amount D can be easily confirmed. The distance L1 can be known from the OTDR waveform.
　このような構成を備える第３の実施形態の光伝送装置３００は、第１の実施形態の効果に加えて、光ファイバ７の波長分散に起因する伝送品質の低下を抑制できるという効果を奏する。 The optical transmission apparatus 300 according to the third embodiment having such a configuration has an effect of suppressing a decrease in transmission quality due to wavelength dispersion of the optical fiber 7 in addition to the effect of the first embodiment.
　（第４の実施形態）
　図１０は、本発明の第４の実施形態の光伝送システム４０の構成を示すブロック図である。第４の実施形態の光伝送システム４０は、光伝送装置４００、光ファイバ７及び光受信装置１１０を備える。光ファイバ７及び光受信装置１１０の機能は、図１に示した第１の実施形態と同様である。 (Fourth embodiment)
FIG. 10 is a block diagram showing the configuration of the optical transmission system 40 according to the fourth embodiment of the present invention. The optical transmission system 40 according to the fourth embodiment includes an optical transmission device 400, an optical fiber 7, and an optical reception device 110. The functions of the optical fiber 7 and the optical receiver 110 are the same as those in the first embodiment shown in FIG.
　光伝送装置４００は、第１の実施形態の光伝送装置１００と比較して、制御回路６が、さらに、光送信機１１－１ｎを制御する点で相違する。光伝送装置４００の他の部分の構成及び動作は、光伝送装置１００と同様である。制御回路６は、ＯＴＤＲ波形に基づいて、光ファイバ７によって生じる分散及び波形歪みが補償されるように、光送信機１１－１ｎの送信波形を制御する。光伝送装置４００におけるこれらの分散補償及び波形歪補償は、光学的な補償及び電気的な補償のいずれでもよい。なお、光伝送装置４００は、さらに、第３の実施形態で説明した分散補償部８を光合波器１と光増幅器２との間に備えていてもよい。 The optical transmission device 400 is different from the optical transmission device 100 of the first embodiment in that the control circuit 6 further controls the optical transmitter 11-1n. The configuration and operation of other parts of the optical transmission device 400 are the same as those of the optical transmission device 100. Based on the OTDR waveform, the control circuit 6 controls the transmission waveform of the optical transmitter 11-1n so that dispersion and waveform distortion caused by the optical fiber 7 are compensated. These dispersion compensation and waveform distortion compensation in the optical transmission apparatus 400 may be either optical compensation or electrical compensation. The optical transmission apparatus 400 may further include the dispersion compensator 8 described in the third embodiment between the optical multiplexer 1 and the optical amplifier 2.
　このような構成を備える第４の実施形態の光伝送装置４００は、第１の実施形態の効果に加えて、波長分散及び波形歪に起因する伝送品質の低下を抑制できるという効果を奏する。 The optical transmission apparatus 400 according to the fourth embodiment having such a configuration has an effect of suppressing a reduction in transmission quality due to chromatic dispersion and waveform distortion in addition to the effects of the first embodiment.
　なお、本発明の実施形態は以下の付記のようにも記載されうるが、これらには限定されない。 In addition, although embodiment of this invention can be described also as the following additional remarks, it is not limited to these.
　（付記１）
　入力された信号光を増幅する光増幅手段と、
　光伝送路において分布ラマン増幅を生じさせる励起光を出力する励起手段と、
　前記光増幅手段で増幅された前記信号光と、前記励起光とを合波して前記光伝送路に送出する第１の光合波手段と、
　前記光伝送路を伝搬する伝搬光の前記光伝送路内の散乱によって発生した散乱光を検出することで前記伝搬光の前記光伝送路内の最大パワーを測定する測定手段と、
　前記測定手段から通知された前記最大パワーに基づいて前記励起光の出力パワーと前記光増幅手段の出力パワーとを制御する制御手段と、
を備える光伝送装置。 (Appendix 1)
Optical amplification means for amplifying the input signal light;
Pumping means for outputting pumping light that causes distributed Raman amplification in the optical transmission line;
First optical multiplexing means for multiplexing the signal light amplified by the optical amplification means and the pumping light and sending them to the optical transmission line;
Measuring means for measuring the maximum power of the propagation light in the optical transmission line by detecting scattered light generated by scattering of the propagation light propagating in the optical transmission line;
Control means for controlling the output power of the pumping light and the output power of the optical amplifying means based on the maximum power notified from the measuring means;
An optical transmission device comprising:
　（付記２）
　前記第１の光合波手段はさらに試験光を合波して前記光伝送路に送出し、
　前記測定手段は前記試験光を前記第１の合波手段に出力し、前記光伝送路内で散乱された前記試験光を前記散乱光として検出することで前記最大パワーを測定する、
　付記１に記載された光伝送装置。 (Appendix 2)
The first optical multiplexing means further combines test light and sends it to the optical transmission line,
The measurement means outputs the test light to the first multiplexing means, and measures the maximum power by detecting the test light scattered in the optical transmission path as the scattered light.
The optical transmission device according to attachment 1.
　（付記３）
　前記測定手段はＯＴＤＲ（optical time domain reflectometer）である、付記２に記載された光伝送装置。 (Appendix 3)
The optical transmission apparatus according to appendix 2, wherein the measuring means is an OTDR (optical time domain reflectometer).
　（付記４）
　前記ＯＴＤＲは、前記散乱光の受信にコヒーレント受信を用いるコヒーレントＯＴＤＲである、付記３に記載された光伝送装置。 (Appendix 4)
The optical transmission apparatus according to attachment 3, wherein the OTDR is a coherent OTDR that uses coherent reception to receive the scattered light.
　（付記５）
　前記制御手段は、前記最大パワーが、前記信号光に対する前記光伝送路内における非線形光学効果による前記信号光の伝送品質の劣化の許容量に基づいて決定された閾値を超えないように前記励起光の出力パワーと前記光増幅手段の出力パワーとを制御する、付記１乃至４のいずれかに記載された光伝送装置。 (Appendix 5)
The control means is configured so that the maximum power does not exceed a threshold value determined based on an allowable amount of deterioration in transmission quality of the signal light due to a nonlinear optical effect in the optical transmission path with respect to the signal light. The optical transmission device according to any one of appendices 1 to 4, wherein the output power of the optical amplifying means is controlled.
　（付記６）
　前記試験光の波長は、前記試験光に対する前記分布ラマン増幅の特性に基づいて前記信号光に対する前記分布ラマン増幅の特性を推定可能な波長である、付記２乃至５のいずれかに記載された光伝送装置。 (Appendix 6)
The light according to any one of appendices 2 to 5, wherein the wavelength of the test light is a wavelength capable of estimating the characteristic of the distributed Raman amplification with respect to the signal light based on the characteristic of the distributed Raman amplification with respect to the test light. Transmission equipment.
　（付記７）
　前記試験光の波長は、前記信号光の波長の近傍にある、付記２乃至６のいずれかに記載された光伝送装置。 (Appendix 7)
The optical transmission device according to any one of appendices 2 to 6, wherein the wavelength of the test light is in the vicinity of the wavelength of the signal light.
　（付記８）
　前記信号光は波長多重された複数の光を含む、付記２乃至７のいずれかに記載された光伝送装置。 (Appendix 8)
8. The optical transmission device according to any one of appendices 2 to 7, wherein the signal light includes a plurality of wavelengths multiplexed light.
　（付記９）
　前記試験手段は波長が異なる複数の前記試験光を出力し、前記複数の試験光のうち２つの前記試験光の波長はそれぞれ前記波長多重された光の波長の上限の近傍及び下限の近傍にある、付記８に記載された光伝送装置。 (Appendix 9)
The test means outputs a plurality of the test lights having different wavelengths, and the wavelengths of the two test lights out of the plurality of test lights are in the vicinity of the upper limit and the lower limit of the wavelength multiplexed light, respectively. The optical transmission apparatus according to appendix 8.
　（付記１０）
　前記増幅手段の入力側に接続された分散補償手段をさらに備え、
　前記試験手段は、前記光伝送路の、前記伝搬光の入力端から前記伝搬光のパワーが前記最大パワーとなる地点までの距離を測定して前記制御手段に通知し、前記制御手段は、前記距離に基づいて、前記地点において生じる前記光伝送路の分散量を相殺する量の分散を前記信号光に与えるように前記分散補償手段を制御する、付記１乃至９のいずれかに記載された光伝送装置。 (Appendix 10)
Further comprising dispersion compensation means connected to the input side of the amplification means,
The test means measures the distance from the input end of the propagation light of the optical transmission path to a point where the power of the propagation light becomes the maximum power, and notifies the control means, the control means, The light according to any one of appendices 1 to 9, wherein the dispersion compensation unit is controlled based on a distance so as to give the signal light an amount of dispersion that cancels out the amount of dispersion of the optical transmission line generated at the point. Transmission equipment.
　（付記１１）
　前記励起手段は相異なる波長を持つ複数の前記励起光を出力し、前記制御手段は前記光伝送路内の前記伝搬光のパワー分布の波長依存性が所定の範囲となるように前記複数の励起光を独立に制御する、付記１乃至１０のいずれかに記載された光伝送装置。 (Appendix 11)
The excitation unit outputs a plurality of the excitation lights having different wavelengths, and the control unit is configured to output the plurality of excitations so that the wavelength dependence of the power distribution of the propagating light in the optical transmission path falls within a predetermined range. The optical transmission device according to any one of appendices 1 to 10, wherein the light is controlled independently.
　（付記１２）
　出力された前記信号光が前記光増幅手段に入力されるように接続された光送信手段をさらに備える、付記１乃至１１のいずれかに記載された光伝送装置。 (Appendix 12)
The optical transmission apparatus according to any one of appendices 1 to 11, further comprising: an optical transmission unit connected so that the output signal light is input to the optical amplification unit.
　（付記１３）
　出力された前記信号光が前記光増幅手段に入力されるように接続された光送信手段をさらに備え、
　前記制御手段は、前記地点において生じる前記光伝送路の分散量及び前記信号光の波形歪の少なくとも一方を相殺するように前記光送信手段を制御する、付記１０に記載された光伝送装置。 (Appendix 13)
An optical transmitter connected so that the output signal light is input to the optical amplifier;
The optical transmission apparatus according to appendix 10, wherein the control unit controls the optical transmission unit so as to cancel at least one of a dispersion amount of the optical transmission path and a waveform distortion of the signal light generated at the point.
　（付記１４）
　波長の異なる複数の前記光送信手段から出力された光を合波して、合波された前記光送信手段から出力された光が前記光増幅手段に入力されるように接続された第２の光合波手段をさらに備える、付記１２又は１３に記載された光伝送装置。 (Appendix 14)
The second light is connected so that the light output from the plurality of optical transmission units having different wavelengths is combined, and the combined light output from the optical transmission unit is input to the optical amplification unit. The optical transmission device according to appendix 12 or 13, further comprising optical multiplexing means.
　（付記１５）
　付記１乃至１４のいずれかに記載された光伝送装置と、
　前記光伝送装置から出力される光を伝搬させる光伝送路と、
　前記光伝送路から出力される前記信号光を受信する光受信装置と、
を備える光伝送システム。 (Appendix 15)
The optical transmission device according to any one of appendices 1 to 14,
An optical transmission path for propagating light output from the optical transmission device;
An optical receiver for receiving the signal light output from the optical transmission line;
An optical transmission system comprising:
　（付記１６）
　入力された信号光を増幅し、
　光伝送路において分布ラマン増幅を生じさせる励起光を出力し、
　増幅された前記信号光と、前記励起光とを合波して前記光伝送路へ送出し、
　前記光伝送路を伝搬する伝搬光の前記光伝送路内の散乱によって発生した散乱光を検出することで、前記信号光の前記光伝送路内の最大パワーを測定し、
　前記最大パワーに基づいて前記励起光の出力パワーと前記光増幅手段の出力パワーとを制御する、
光伝送装置の制御方法。 (Appendix 16)
Amplifies the input signal light,
Outputs pumping light that causes distributed Raman amplification in the optical transmission line,
The amplified signal light and the excitation light are combined and sent to the optical transmission line,
By detecting scattered light generated by scattering in the optical transmission path of propagation light propagating through the optical transmission path, the maximum power in the optical transmission path of the signal light is measured,
Controlling the output power of the pumping light and the output power of the optical amplification means based on the maximum power;
Control method of optical transmission apparatus.
　（付記１７）
　光伝送装置のコンピュータに、
　光伝送路を伝搬する伝搬光の前記光伝送路内の散乱によって発生した散乱光に基づいて測定された、前記伝搬光の前記光伝送路内の最大パワーに基づいて、
　前記光伝送路にラマン増幅を生じさせる励起光の出力パワーと、信号光を増幅して前記光伝送路に出力する光増幅手段の出力パワーと、を制御させるための、光伝送装置の制御プログラム。 (Appendix 17)
In the computer of the optical transmission device,
Based on the maximum power in the optical transmission line of the propagation light measured based on the scattered light generated by scattering in the optical transmission path of the propagation light propagating through the optical transmission line,
A control program for an optical transmission device for controlling the output power of pumping light that causes Raman amplification in the optical transmission line and the output power of optical amplification means that amplifies signal light and outputs it to the optical transmission line .
　以上、実施形態を参照して本願発明を説明したが、本願発明は上記の実施形態に限定されない。本願発明の構成や詳細には、本願発明のスコープ内で当業者が理解し得る様々な変更をすることができる。例えば、第１乃至第４の実施形態に記載されたＯＴＤＲ４は、散乱光の検出にコヒーレント受信を用いるコヒーレントＯＴＤＲであってもよい。また、第３及び第４の実施形態で説明した分散補償のための構成や波形歪み補償のための構成は、第２の実施形態の光伝送装置２００に適用されてもよい。 As mentioned above, although this invention was demonstrated with reference to embodiment, this invention is not limited to said embodiment. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention. For example, the OTDR 4 described in the first to fourth embodiments may be a coherent OTDR that uses coherent reception to detect scattered light. In addition, the configuration for dispersion compensation and the configuration for waveform distortion compensation described in the third and fourth embodiments may be applied to the optical transmission device 200 of the second embodiment.
　この出願は、２０１４年７月１８日に出願された日本出願特願２０１４－１４７４０８を基礎とする優先権を主張し、その開示の全てをここに取り込む。 This application claims priority based on Japanese Patent Application No. 2014-147408 filed on July 18, 2014, the entire disclosure of which is incorporated herein.
　１０、２０、３０、４０　　光伝送システム
　１００、２００、３００、４００　　光伝送装置
　１１０　　光受信装置
　１、５　　光合波器
　２　　光増幅器
　３、３１　　励起光源
　４　　ＯＴＤＲ
　６　　制御回路
　７　　光ファイバ
　８　　分散補償部
　１１－１ｎ　　光送信機
　９１　　ＣＰＵ
　９２　　メモリ 10, 20, 30, 40 Optical transmission system 100, 200, 300, 400 Optical transmission device 110 Optical reception device 1, 5 Optical multiplexer 2 Optical amplifier 3, 31 Excitation light source 4 OTDR
6 Control Circuit 7 Optical Fiber 8 Dispersion Compensator 11-1n Optical Transmitter 91 CPU
92 memory

Claims (10)

  1. 　入力された信号光を増幅する光増幅手段と、
    　光伝送路において分布ラマン増幅を生じさせる励起光を出力する励起手段と、
    　前記光増幅手段で増幅された前記信号光と、前記励起光とを合波して前記光伝送路に送出する第１の光合波手段と、
    　前記光伝送路を伝搬する伝搬光の前記光伝送路内の散乱によって発生した散乱光を検出することで前記伝搬光の前記光伝送路内の最大パワーを測定する測定手段と、
    　前記測定手段から通知された前記最大パワーに基づいて前記励起光の出力パワーと前記光増幅手段の出力パワーとを制御する制御手段と、
    を備える光伝送装置。     Optical amplification means for amplifying the input signal light;
    Pumping means for outputting pumping light that causes distributed Raman amplification in the optical transmission line;
    First optical multiplexing means for multiplexing the signal light amplified by the optical amplification means and the pumping light and sending them to the optical transmission line;
    Measuring means for measuring the maximum power of the propagation light in the optical transmission line by detecting scattered light generated by scattering of the propagation light propagating in the optical transmission line;
    Control means for controlling the output power of the pumping light and the output power of the optical amplifying means based on the maximum power notified from the measuring means;
    An optical transmission device comprising:
  2. 　前記第１の光合波手段はさらに試験光を合波して前記光伝送路に送出し、
    　前記測定手段は前記試験光を前記第１の合波手段に出力し、前記光伝送路内で散乱された前記試験光を前記散乱光として検出することで前記最大パワーを測定する、
    　請求項１に記載された光伝送装置。     The first optical multiplexing means further combines test light and sends it to the optical transmission line,
    The measurement means outputs the test light to the first multiplexing means, and measures the maximum power by detecting the test light scattered in the optical transmission path as the scattered light.
    The optical transmission device according to claim 1.
  3. 　前記制御手段は、前記最大パワーが、前記信号光に対する前記光伝送路内における非線形光学効果による前記信号光の伝送品質の劣化の許容量に基づいて決定された閾値を超えないように前記励起光の出力パワーと前記光増幅手段の出力パワーとを制御する、請求項１又は２に記載された光伝送装置。 The control means is configured so that the maximum power does not exceed a threshold value determined based on an allowable amount of deterioration in transmission quality of the signal light due to a nonlinear optical effect in the optical transmission path with respect to the signal light. The optical transmission apparatus according to claim 1, wherein the output power of the optical amplifying unit and the output power of the optical amplifying unit are controlled.
  4. 　前記試験光の波長は、前記試験光に対する前記分布ラマン増幅の特性に基づいて前記信号光に対する前記分布ラマン増幅の特性を推定可能な波長である、請求項２又は３に記載された光伝送装置。 4. The optical transmission device according to claim 2, wherein the wavelength of the test light is a wavelength capable of estimating the characteristic of the distributed Raman amplification with respect to the signal light based on the characteristic of the distributed Raman amplification with respect to the test light. .
  5. 　前記信号光は波長多重された複数の光を含む、請求項２乃至４のいずれかに記載された光伝送装置。 5. The optical transmission apparatus according to claim 2, wherein the signal light includes a plurality of wavelengths multiplexed light.
  6. 　前記試験手段は波長が異なる複数の前記試験光を出力し、前記複数の試験光のうち２つの前記試験光の波長はそれぞれ前記波長多重された光の波長の上限の近傍及び下限の近傍にある、請求項５に記載された光伝送装置。 The test means outputs a plurality of the test lights having different wavelengths, and the wavelengths of the two test lights out of the plurality of test lights are in the vicinity of the upper limit and the lower limit of the wavelength multiplexed light, respectively. The optical transmission device according to claim 5.
  7. 　前記増幅手段の入力側に接続された分散補償手段をさらに備え、
    　前記試験手段は前記光伝送路の入力端から前記伝搬光のパワーが前記最大パワーとなる地点までの距離を測定して前記制御手段に通知し、前記制御手段は、前記距離に基づいて、前記地点において生じる前記光伝送路の分散量を相殺する量の分散を前記信号光に与えるように前記分散補償手段を制御する、請求項１乃至６のいずれかに記載された光伝送装置。     Further comprising dispersion compensation means connected to the input side of the amplification means,
    The test means measures the distance from the input end of the optical transmission line to the point where the power of the propagating light is the maximum power and notifies the control means, and the control means is based on the distance, The optical transmission apparatus according to claim 1, wherein the dispersion compensation unit is controlled to give the signal light an amount of dispersion that cancels out the amount of dispersion of the optical transmission path that occurs at a point.
  8. 　出力された前記信号光が前記光増幅手段に入力されるように接続された光送信手段をさらに備える、請求項１乃至７のいずれかに記載された光伝送装置。 The optical transmission device according to any one of claims 1 to 7, further comprising an optical transmission unit connected so that the output signal light is input to the optical amplification unit.
  9. 　波長の異なる複数の前記光送信手段から出力された光を合波して、合波された前記光送信手段から出力された光が前記光増幅手段に入力されるように接続された第２の光合波手段をさらに備える、請求項８に記載された光伝送装置。 The second light is connected so that the light output from the plurality of optical transmission units having different wavelengths is combined, and the combined light output from the optical transmission unit is input to the optical amplification unit. The optical transmission device according to claim 8, further comprising optical multiplexing means.
  10. 　入力された信号光を増幅し、
    　光伝送路において分布ラマン増幅を生じさせる励起光を出力し、
    　増幅された前記信号光と、前記励起光とを合波して前記光伝送路へ送出し、
    　前記光伝送路を伝搬する伝搬光の前記光伝送路内の散乱によって発生した散乱光を検出することで、前記信号光の前記光伝送路内の最大パワーを測定し、
    　前記最大パワーに基づいて前記励起光の出力パワーと前記光増幅手段の出力パワーとを制御する、
    光伝送装置の制御方法。     Amplifies the input signal light,
    Outputs pumping light that causes distributed Raman amplification in the optical transmission line,
    The amplified signal light and the excitation light are combined and sent to the optical transmission line,
    By detecting scattered light generated by scattering in the optical transmission path of propagation light propagating through the optical transmission path, the maximum power in the optical transmission path of the signal light is measured,
    Controlling the output power of the pumping light and the output power of the optical amplification means based on the maximum power;
    Control method of optical transmission apparatus.
PCT/JP2015/003535 2014-07-18 2015-07-13 Optical transmission device and optical transmission method WO2016009638A1 (en)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2856435B2 (en) * 1989-06-12 1999-02-10 日本電信電話株式会社 Stabilization method of optical fiber active transmission line
JP2001235772A (en) * 2000-02-22 2001-08-31 Sumitomo Electric Ind Ltd Raman amplification control device and optical transmission system
JP2005084041A (en) * 2003-09-11 2005-03-31 Nippon Telegr & Teleph Corp <Ntt> Transmission loss measuring device of optical transmission system, and its method
JP2006279610A (en) * 2005-03-29 2006-10-12 Fujitsu Ltd Optical transmission apparatus
JP2006287649A (en) * 2005-03-31 2006-10-19 Nec Corp Optical signal transmission power adjusting device in optical transmission system and optical signal transmission power adjusting method
WO2007111797A2 (en) * 2006-03-23 2007-10-04 Xtera Communications, Inc. System and method for implementing a boosterless optical communication system
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Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2856435B2 (en) * 1989-06-12 1999-02-10 日本電信電話株式会社 Stabilization method of optical fiber active transmission line
JP2001235772A (en) * 2000-02-22 2001-08-31 Sumitomo Electric Ind Ltd Raman amplification control device and optical transmission system
JP2005084041A (en) * 2003-09-11 2005-03-31 Nippon Telegr & Teleph Corp <Ntt> Transmission loss measuring device of optical transmission system, and its method
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