JP2014170085A - Raman amplifier, optical repeater, optical communication system, raman amplification control metho, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Raman amplifier capable of obtaining wavelength characteristics of a desired gain by a simple configuration.SOLUTION: A part of light which is transmitted on a transmission line optical fiber 20 and is subjected to Raman amplification is branched by a first branching device 33 and a second branching device 34, and only noise light in a prescribed wavelength band is transmitted by a noise light transmission filter 35. Power of the noise light outputted from the noise light transmission filter 35 is detected by a noise light power detection unit 37. A change rate of excitation light power is determined so that a decibel value of a change rate of the noise light power detected by the noise light power detection unit 37 and a decibel value of the change rate of the excitation light power have the same absolute value and opposite signs, and a driving current value is determined so that the excitation light power changed at this change rate is determined.

Description

  The present invention relates to a Raman amplifier that amplifies signal light propagating through an optical fiber by a Raman amplification effect, an optical repeater using the Raman amplifier, an optical communication system, a Raman amplification control method, and a program.

  In order to transmit wavelength-multiplexed signal light over a long distance, a system that amplifies and repeats light in a number of repeaters has been put into practical use. In such a system, when a Raman amplifier is used for optical amplification, the optical SNR (Signal to Noise Ratio) of signal light can be improved, which is effective in extending the transmission distance. Expected.

  If the number of optical amplification repeaters increases as the transmission distance increases, the wavelength characteristics of the gain of each optical amplifier within the wavelength band of the signal light are flattened to maintain the signal quality, and the power of the signal light at each wavelength It is necessary to reduce the wavelength dependence of the optical SNR.

  Here, the gain of the Raman amplifier is defined as the ratio of the power of the output signal light to the presence or absence of the excitation light. In order to flatten the wavelength characteristic of the gain of the Raman amplifier, it is conceivable to insert a gain equalizer having a loss wavelength characteristic that compensates for the wavelength characteristic of the gain of Raman amplification into the signal light transmission line. However, since the wavelength characteristic of the Raman amplification gain changes according to the average gain, there is a problem that the wavelength characteristic cannot be sufficiently compensated by the gain equalizer depending on the average gain.

  To solve this problem, there is a technique for making the average gain of Raman amplification constant (for example, Patent Document 1). The optical repeater transmission system described in Patent Document 1 transmits signal light obtained by multiplexing signal light having a plurality of wavelengths and reference light not subjected to Raman amplification from the transmission side through a fiber. In the Raman amplifier, the signal light and the reference light are demultiplexed from a part of the signal light transmitted through the optical fiber, the signal light level and the reference light level are detected, and the Raman amplification is performed based on the detected reference light level. A signal light level control target value for maintaining the average gain of the signal at a predetermined value is calculated. The output of the excitation light is controlled so that the detected signal light level matches the calculated signal light level control target value.

JP 2004-193640 A

  Since the optical repeater transmission system described in Patent Document 1 transmits the reference light through a fiber and controls the gain of Raman amplification based on the reference light level in the Raman amplifier, it is used as the reference light on the transmission side or transmission path. When a failure occurs, there is a problem that gain control cannot be performed normally. As a result, the gain control cannot be normally performed, so that the gain cannot be compensated by the gain equalizer or the like, and the wavelength characteristic of the desired gain cannot be obtained.

  In addition, in order to superimpose the reference light on the signal light, it is necessary to prepare a light emitting element for reference light separately on the transmission device side, and a configuration for detecting the reference light level is required on the relay device side, which makes the configuration complicated. There was a negative effect of cost reduction.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a Raman amplifier or the like that can obtain a desired gain wavelength characteristic with a simple configuration.

  To achieve the above object, the Raman amplifier according to the present invention transmits optical signals having a plurality of wavelengths and Raman-amplifies light including signal light, and excitation for Raman-amplifying light including signal light. A pumping light source for injecting light into the optical fiber, a noise light extracting unit for extracting noise light in a wavelength band not including the wavelength of the signal light from the light amplified by Raman transmission through the optical fiber, and the power of the noise light And a noise light power detector for detecting. Based on the rate of change of the power of the noise light detected by the noise light power detector, the rate of change of the power of the pump light is determined, and the pump light source is controlled so that the power of the pump light changes at the rate of change.

  According to the present invention, it is possible to obtain a desired gain wavelength characteristic with a simple configuration.

1 is a block diagram showing an optical communication system according to an embodiment of the present invention. It is a figure which shows the wavelength characteristic of signal light power and noise light power. It is a flowchart of an excitation light source drive process. (A) is a table | surface which showed the change of the gain when not performing feedback control. (B) is a table showing changes in gain when control for making the noise light power constant is performed. (C) is a table | surface which showed the change of the gain at the time of performing control which concerns on embodiment. It is a block diagram which shows the other structure of the optical communication system which concerns on embodiment.

Embodiment.
Embodiments of the present invention will be described in detail with reference to the drawings.

  As shown in FIG. 1, the optical communication system 1 according to the present embodiment includes a transmission device 10, a transmission line optical fiber 20, a relay device 30, and a reception device 50. Although only one relay device 30 is illustrated in FIG. 1, an arbitrary number of relay devices 30 are connected between the transmission device 10 and the reception device 50. The arbitrary number of relay apparatuses 30 have substantially the same configuration.

  The transmission apparatus 10 generates optical signals of a plurality of wavelengths that are optically modulated with a transmission electrical signal using an arbitrary modulation method, and transmits a wavelength-multiplexed signal light obtained by wavelength-multiplexing them to the transmission line optical fiber 20.

  The transmission line optical fiber 20 is a transmission line that transmits wavelength multiplexed signal light, and is also an amplification medium that obtains a Raman amplification effect by entering excitation light. In the present embodiment, since the excitation light is incident from the receiving device 50 side of the transmission line optical fiber 20, that is, from behind the transmission line optical fiber 20, Raman amplification by so-called backward excitation is performed.

  The relay device 30 has a function of controlling Raman amplification in the transmission line optical fiber 20 on the transmission device 10 side, that is, the upstream transmission line optical fiber 20, and the wavelength amplified by the upstream transmission line optical fiber 20. The multiplexed signal light is transmitted to the transmission line optical fiber 20 on the receiving device 50 side, that is, the downstream transmission line optical fiber 20.

  The receiving device 50 receives the wavelength-division multiplexed signal light transmitted through the transmission line optical fiber 20, demodulates it with a demodulation method corresponding to the modulation method of the transmitting device 10, and acquires a received electrical signal.

  The repeater 30 includes a multiplexer / demultiplexer 31, an excitation light source 32, a first branching device 33, a second branching device 34, a noise light transmission filter 35, a signal light power detection unit 36, a noise light power detection unit 37, and a storage unit. 38, an arithmetic circuit 39, and a gain equalizer (GEQ) 40 are provided. The upstream transmission line optical fiber 20, the multiplexer / demultiplexer 31, the pumping light source 32, the first branching device 33, the second branching device 34, the noise light transmission filter 35, and the signal light power detection unit 36 in the relay device 30. The noise light power detection unit 37, the storage unit 38, and the arithmetic circuit 39 constitute a Raman amplifier 60.

  The multiplexer / demultiplexer 31 is an multiplexer / demultiplexer for guiding the pumping light output from the pumping light source 32 to the upstream transmission line optical fiber 20, and pumping light and signal light having different wavelength bands in a predetermined direction. It consists of a wavelength filter to pass through and a circulator having a directional coupling function. The multiplexer / demultiplexer 31 outputs the signal light input from the upstream transmission line optical fiber 20 side to the first branching unit 33 side, and the excitation light input from the excitation light source 32 is converted to the upstream transmission line optical fiber. Output to the 20 side.

  The excitation light source 32 is a light source that generates excitation light incident from behind the transmission line optical fiber 20 in order to perform Raman amplification with the transmission line optical fiber 20, and has a high output with a wavelength of 1.4 to 1.5 μm, for example. It is a laser. By controlling the drive current value of the excitation light source 32, the excitation light power output from the excitation light source 32 is controlled. The excitation light source 32 may be a light source provided with a depolarizer in order to reduce the polarization dependence of the Raman gain.

  The first splitter 33 is a 1-input / 2-output optical splitter that splits the light output from the multiplexer / demultiplexer 31 into two, and includes, for example, a 10 dB coupler, a 15 dB coupler, a 20 dB coupler, and the like. The first branching device 33 branches light input from the input port 331 on the multiplexer / demultiplexer 31 side, and outputs it from the main signal port 332 on the signal transmission path side and the sub signal port 333 for optical power detection. To do. When the first branching device 33 is a 10 dB coupler, light having a power of −10 dB with respect to the input light is output from the sub signal port 333.

  The second branching unit 34 is a 1-input 2-output branching unit that splits the light output from the sub-signal port 333 of the first branching unit 33 into two, and is composed of, for example, a 3 dB coupler. The second branching device 34 branches the light input from the input port 341 on the first branching device 33 side, from the first port 342 for signal light power detection and the second port 343 for noise light power detection. Output. When the second splitter 34 is a 3 dB coupler, light having a power of −3 dB is output from the first port 342 and the second port 343 with respect to the input light.

  The noise light transmission filter 35 includes a wavelength filter that transmits only light in a specific wavelength band, and is connected to the second port 343 of the second branching device 34. The noise light transmission filter 35 transmits noise light in a wavelength band that does not include the wavelength of the signal light among the light output from the second port 343 of the second branching device 34 and outputs the noise light to the noise light power detection unit 37 side. .

  The input / output of the noise light transmission filter 35 will be described with reference to FIG. The light input to the noise light transmission filter 35 from the second port 343 of the second branching device 34 is, as shown in FIG. 2A, signal light obtained by multiplexing light having wavelengths arranged at equal intervals, and Contains noisy light. The light output from the noise light transmission filter 35 is a part of noise light in a band that does not include signal light within the Raman amplification band. The band to be transmitted may be, for example, a band having a longer wavelength than the signal light or a band having a shorter wavelength than the signal light, as indicated by a solid line in FIG.

  As described above, the first branching device 33, the second branching device 34, and the noise light transmission filter 35 connected in series include the wavelength of the signal light from the light transmitted through the transmission line optical fiber 20 and Raman amplified. It has a function to extract noise light in no wavelength band.

  The signal light power detector 36 is connected to the first port 342 of the second branching device 34 and outputs a signal light power signal that is a voltage signal corresponding to the power of light output from the first port 342. The signal light power detection unit 36 includes, for example, a photodiode that photoelectrically converts input light and outputs a current corresponding to the input light power, and a current-voltage conversion amplifier that converts the output current of the photodiode into a voltage signal. .

  The light detected by the signal light power detector 36 is light output from the first port 342 of the second branching device 34, and is substantially the same as the light input to the noise light transmission filter 35. FIG. As shown in (), signal light and noise light are included. However, since the power of the noise light is sufficiently smaller than the power of the signal light, the power of the signal light is substantially detected.

  The noise light power detection unit 37 is connected to the side opposite to the second branching device 34 side of the noise light transmission filter 35 and is a noise light power signal that is a voltage signal corresponding to the light power output from the noise light transmission filter 35. Is output. The noise light power detection unit 37 includes, for example, a photodiode and a current-voltage conversion amplifier, like the signal light power detection unit 36.

  Since the light detected by the noise light power detection unit 37 is light after passing through the noise light transmission filter 35, it is noise light within a specific band as shown in FIG. That is, the noise light power detector 37 detects the power of noise light within a specific band.

  Here, since the power of the noise light transmitted through the noise light transmission filter 35 is a parameter used for control to keep the Raman amplification gain constant, it is desirable to detect the noise light power generated by the Raman amplification. The main element of noise generated by Raman amplification is ASE (Amplified spontaneous emission) noise that is output after amplification of spontaneous emission light. For this reason, in order to eliminate the shot noise etc. which generate | occur | produces in the light emission part of the transmitter 10, the optical output part of the transmitter 10 is equipped with the filter which removes the noise light of the wavelength band permeate | transmitted with the noise light transmission filter 35. Also good.

  The storage unit 38 is composed of a nonvolatile memory such as a flash memory. The storage unit 38 stores an initial value of the drive current of the excitation light source 32, data indicating the relationship between the drive current of the excitation light source 32 and the excitation light power, a program executed by the arithmetic circuit 39, and the like.

  The data indicating the relationship between the driving current of the pumping light source 32 and the pumping light power stored in the storage unit 38 is, for example, when the pumping light source 32 is connected to the multiplexer / demultiplexer 31 when the Raman amplifier 60 is assembled. 6 is a table data showing measurement results obtained by measuring the relationship between the drive current of the excitation light source 32 and the excitation light power output from the port on the transmission line optical fiber 20 side of the multiplexer / demultiplexer 31.

  The arithmetic circuit 39 executes a program stored in the storage unit 38 to execute an excitation light source driving process for driving and controlling the excitation light source 32 so that the gain of the Raman amplifier 60 becomes constant.

  Further, the arithmetic circuit 39 monitors the occurrence of the transmission signal output abnormality based on the signal light power signal output from the signal light power detection unit 36, and gives a warning when there is an abnormality, Processes such as sending information.

  The excitation light source driving process executed by the arithmetic circuit 39 periodically reads the noise light power signal output from the noise light power detection unit 37 and determines the change rate of the excitation light power based on the change rate of the noise light power. . Then, the drive current is determined so that the pumping light power changes at the determined change rate. The excitation light source driving process will be described in detail along the flowchart shown in FIG.

  When the excitation light source driving process is started, the timer is first reset and then started (step S101). The arithmetic circuit 39 reads the initial value of the drive current of the excitation light source 32 from the storage unit 38 and outputs it to the excitation light source 32 (step S102). The excitation light source 32 is driven based on the initial value information of the drive current input from the arithmetic circuit 39.

Next, the arithmetic circuit 39 acquires the noise light power detected by the noise light power detection unit 37 (step S103). That is, the noise light power in the initial state is acquired and temporarily stored in the internal memory of the arithmetic circuit 39. Then monitors the timer and wait timer time t to over noise light power detection interval _{t 0} (step S104: No). If the timer time t exceeds the noise light power detection interval t ₀ (step S104: Yes), the noise light power is reacquired (step S105).

  A change rate of the noise light power is calculated from the noise light power acquired in step S105 (step S106). In the present embodiment, the noise light power acquired in step S105 is divided by the previously acquired noise light power temporarily stored in the internal memory of the arithmetic circuit 39 to be converted into a decibel value.

  Thereafter, the noise light power acquired in step S105 is temporarily stored in the internal memory of the arithmetic circuit 39 (step S107). This temporary storage in the internal memory is for use in calculating the next change rate.

  Next, the pump light power change rate is determined based on the noise light power change rate calculated in step S106 (step S108). In the present embodiment, the pump light power change rate is obtained so that the decibel value of the change rate of the noise light power and the decibel value of the pump light power change rate have the same absolute value and opposite signs. In other words, the pump light power change rate is obtained so that the sum of the decibel value of the change rate of the noise light power and the decibel value of the pump light power change rate becomes 0 dB.

  Next, the arithmetic circuit 39 refers to the table data in the storage unit 38 and calculates the change rate of the drive current corresponding to the change rate of the pumping light power determined in step S108. Then, the drive current of the excitation light source changed by the calculated change rate of the drive current with respect to the current drive current is determined, and information on the drive current is output to the excitation light source 32 (step S109).

  Thereafter, it is determined whether or not there is an instruction to end the excitation light source driving process such as power OFF (step S110). If there is no instruction to end (step S110: No), the timer is reset (step S111). ), The process returns to step S104. If there is an instruction to end (step S110: Yes), this process ends.

  The results when the excitation light source driving process according to the present embodiment described above is executed are compared with the case where feedback control based on the noise light power is not performed and the case where control for making the noise light power constant is performed. To do.

  The table shown in FIG. 4 shows a case where a loss increase of 1 dB occurs at a position (near the transmission end) of the transmission line optical fiber 20 near the transmitting device 10 or the preceding relay device 30, and the multiplexer / demultiplexer of the relay device 30. When the loss increase of 1 dB occurs at a position close to 31 (near the receiving end), the result of estimating the change rate of each optical power and the gain of Raman amplification is shown.

  Note that the gain of Raman amplification here is a substantial amplification gain in the transmission line optical fiber 20, and unlike the gain of the entire Raman amplifier, the loss at the receiving end, the multiplexer / demultiplexer 31, and the first gain. The insertion loss of the branching device 33 or the like is not taken into consideration. That is, the gain of Raman amplification that affects the wavelength characteristics of the gain.

  The table in FIG. 4A shows the rate of change of each optical power and gain when the excitation light source 32 is not subjected to feedback control.

  First, a case where a 1 dB loss increase occurs near the transmission end will be described. In the vicinity of the transmission end, the pumping light power is weakly attenuated, and the noise light power is hardly affected by the increase in loss, so the change rate of the noise light power is ± 0 dB. The rate of change of pumping light power is ± 0 dB because feedback control is not performed. Therefore, the sum of the change rate of the noise light power and the change rate of the excitation light power is ± 0 dB. On the other hand, the rate of change in signal light power is -1.0 dB due to the influence of loss. The gain of Raman amplification is ± 0 dB because the pumping light power does not change and the gain does not change.

  Next, a case where a 1 dB loss increase occurs near the receiving end will be described. Since the pumping light power not subjected to feedback control is reduced by 1 dB when propagating through the transmission line optical fiber 20, the gain of Raman amplification is reduced. The amount of gain reduction depends on various conditions, but here the amount of gain reduction due to a 1 dB reduction in pumping light power at the time of transmission line optical fiber 20 input is 1.5 dB. In this case, the noise light power generated in the transmission path is also reduced by 1.5 dB, and further, a 1 dB loss near the receiving end is added, and the noise light power detected by the noise light power detector 37 is reduced by a total of 2.5 dB. Also for the signal light power, the signal light power detected by the signal light power detector 36 is lowered by a total of 2.5 dB due to a gain drop of 1.5 dB and a loss of 1 dB near the receiving end. At this time, the rate of change of the pumping light power output from the pumping light source 32 is ± 0 dB, and the sum of the rate of change of the noise light power and the rate of change of the pumping light power is −2.5 dB.

  In other words, when feedback control based on the noise light power is not performed, there is almost no effect if there is a loss near the transmitting end, but if there is a loss near the receiving end, the substantial Raman amplification gain is large. The wavelength characteristic of gain changes.

  The table in FIG. 4B shows the change rate of each optical power and gain when control for making the noise light power constant is performed.

  First, a case where a 1 dB loss increase occurs near the transmission end will be described. In the vicinity of the transmission end, the pumping light power is weakly attenuated, and the noise light power is hardly affected by the loss. Therefore, the change rate of the noise light power is ± 0 dB. The rate of change of the excitation light power is ± 0 dB because the noise light power has not changed. Therefore, the sum of the change rate of the noise light power and the change rate of the excitation light power is ± 0 dB. On the other hand, the rate of change in signal light power is -1.0 dB due to the influence of loss. The gain of Raman amplification is ± 0 dB with almost no change in the pump light power because the pump light power has not changed.

  Next, a case where a 1 dB loss increase occurs near the receiving end will be described. Since the pumping light power is controlled so as to compensate for the change rate of the noise light power due to the increase in loss, as a result, the noise light power and the signal light power become the same power (± 0 dB) as before the loss increase. . In this state, the noise light power and the signal light power propagating through the transmission line optical fiber on the transmission device 10 side from the loss increase point should be 1 dB higher than before the loss increase. That would be 1 dB higher. Note that the pumping light power required to increase the gain by 1 dB depends on various conditions. However, considering 1 dB, the rate of change of the pumping light power is +2.0 dB in consideration of the increase in loss. Further, the sum of the change rate of the noise light power and the change rate of the excitation light power is +2.0 dB.

  In other words, when control is performed to keep the noise light power constant, there is almost no effect if there is a loss near the transmitting end, but if there is a loss near the receiving end, the substantial Raman amplification gain is increased. The wavelength characteristic of gain changes.

  The table in FIG. 4C shows the rate of change of each optical power and gain when the control according to the present embodiment is performed. First, a case where a 1 dB loss increase occurs near the transmission end will be described. In the vicinity of the transmission end, the pumping light power is weakly attenuated, and the noise light power is hardly affected by the loss. Therefore, the change rate of the noise light power is ± 0 dB. The rate of change of the excitation light power is ± 0 dB because the noise light power has not changed. Therefore, the sum of the change rate of the noise light power and the change rate of the excitation light power is ± 0 dB. On the other hand, the rate of change in signal light power is -1.0 dB due to the influence of loss. The gain of Raman amplification is ± 0 dB with almost no change in the pump light power because the pump light power has not changed.

  Next, a case where a 1 dB loss increase occurs near the receiving end will be described. When a loss increase of 1 dB occurs near the receiving end, the rate of change between the signal light power and the noise light power is -1.0 dB. The change rate of the pumping light power is controlled to be +1.0 dB, which has the same absolute value and the opposite sign as the change rate of the noise light power. Therefore, the sum of the change rate of the noise light power and the change rate of the excitation light power is ± 0 dB. In this state, the increase in pumping light power just compensates for the loss (1 dB). As a result, the gain of Raman amplification becomes the same as before loss increase (± 0 dB).

  That is, when the control according to this embodiment is performed, the substantial Raman amplification gain can be kept constant not only when there is a loss near the transmission end but also when there is a loss near the reception end. it can. As a result, the wavelength characteristic of gain does not change.

  Thus, the Raman amplifier 60 of this embodiment can Raman-amplify the signal light with a constant gain. The signal light Raman-amplified with a constant gain is input to the gain equalizer 40 inserted on the optical output side of the repeater 30. The gain equalizer 40 includes a filter having a loss wavelength characteristic that compensates for the wavelength characteristic of the gain of Raman amplification. The output power of the light that has passed through the gain equalizer has a wavelength characteristic substantially equal to the power of the light before Raman amplification. That is, the flatness of the gain of the transmission line optical fiber 20 and the relay device 30 as a whole can be ensured.

  As described above, according to the present embodiment, a part of the light transmitted through the transmission line optical fiber 20 in the Raman amplifier 60 is branched by the first branching device 33 and the second branching device 34 to transmit noise light. The power of the noise light transmitted through the filter 35 is detected by the noise light power detector 37, and the decibel value of the change rate of the noise light power and the decibel value of the change rate of the excitation light power have the same absolute value and the opposite sign. The change rate of the excitation light power is obtained so that the drive current value of the excitation light source 32 is controlled so that the excitation light power changes at the change rate. Thereby, the substantial Raman amplification gain can be kept constant, and the flatness of the gain of the transmission line optical fiber 20 and the repeater 30 as a whole can be ensured.

  As described above, in the Raman amplifier that makes the pump light output from the pump light source incident on the transmission line optical fiber and Raman-amplifies the signal light, the wavelength of the signal light is transmitted from the Raman-amplified light transmitted through the optical fiber. Extract noise light in a wavelength band not included, detect the noise light power, determine the pump light source change rate based on the detected noise light power change rate, and use the pump light power at the determined change rate The excitation light source was controlled so as to change. Thereby, a desired gain wavelength characteristic can be obtained with a simple configuration.

  In addition, this invention is not limited to the said embodiment, Of course, the various change in the range which does not deviate from the summary of this invention is possible.

  For example, in the above embodiment, the optical communication system 1 has been described with respect to the configuration in which the transmission device 10, an arbitrary number of relay devices 30 and the reception device 50 are connected in series. Alternatively, a tree-like configuration may be adopted by further including a 1-input / multi-output optical branching device.

  Moreover, in the said embodiment, although the structure which consists of only one excitation light source 32 was demonstrated, what provided the plurality of excitation light sources 32 and combined the excitation light of several excitation light sources 32 with the multiplexer / demultiplexer 31. FIG. The light may enter the transmission line optical fiber 20. In this case, the storage unit 38 stores table data indicating the relationship between the drive current of each pumping light source 32 and the pumping light power, and the arithmetic circuit 39 changes the rate of change determined by the pumping light power of each pumping light source 32. The drive currents of the respective excitation light sources 32 are determined so as to change respectively. By providing a plurality of pumping light sources 32 having different wavelengths, it is possible to expand the amplification band and improve the flatness of the gain. Or the reliability of the relay apparatus 30 is securable by making the structure which made the excitation light source 32 of the same wavelength redundant.

  In the above embodiment, the first branching device 33, the second branching device 34, and the noise light transmitting filter 35 are connected in series to extract noise light. However, noise light in a predetermined wavelength band is used. If it can extract, it will not be restricted to this structure. For example, a single optical component generated by inserting a wavelength filter into a waveguide having an optical branching function may be used.

  In the above embodiment, the configuration in which the gain equalizer 40 is inserted in the output stage of the relay device 30 has been described. However, when a non-flat gain is desired in the relay by the relay device 30, the gain of Raman amplification is desired. And a gain equalizer 40 may be inserted in place of the gain equalizer 40 so as to obtain a desired gain.

  Further, the gain equalizer 40 may be omitted depending on the desired gain wavelength characteristic.

  In the above-described embodiment, the change rate of the noise light power is converted into a decibel value in step S106 of the excitation light source driving process executed by the arithmetic circuit 39, and the decibel value of the change rate of the noise light power is calculated in step S107. Although the decibel value of the rate of change of pumping light power is the same in absolute value and the sign is reversed, the rate of change of pumping light power is calculated, but the rate of change is not limited to the decibel value, but converted to logarithm Any value is acceptable. This is because the logarithm of the rate of change of the noise light power and the logarithm of the rate of change of the pumping light power and the absolute value are only compared. .

  In step S106 of the excitation light source driving process, the change rate of the noise light power is not converted into a decibel value, and the product of the change rate (real number) of the noise light power and the change rate (real number) of the excitation light power is 1. The rate of change (real number) of pumping light power may be obtained as follows. Thereby, when the increase amount of the loss of the transmission line optical fiber 20 is small, the gain can be kept constant with high accuracy. In addition, the processing amount of the arithmetic circuit 39 can be reduced.

  In the above embodiment, the outputs of the signal light power detector 36 and the noise light power detector 37 are directly input to the arithmetic circuit 39, and the arithmetic circuit 39 outputs the noise light power signal output by the noise light power detector 37. As shown in FIG. 5, the input voltage is logarithmically converted between the signal light power detector 36, the noise light power detector 37, and the arithmetic circuit 39, as shown in FIG. Log amplifiers 41 and 42 that output the signal may be inserted. In this case, the arithmetic circuit 39 determines the drive current of the excitation light source 32 based on the voltage value obtained by logarithmically converting the voltage indicating the noise light power output from the noise light power detection unit 37 by the Log amplifier 42. Specifically, the noise light power acquired in steps S103 and S105 in the flowchart of FIG. 3 is a logarithmically converted value, and the change rate of the noise light power calculated in step S106 is the noise light acquired in step S105. It is calculated by subtracting the previously acquired noise light power from the power. The rate of change (logarithm) of the pumping light power is obtained so that the change rate of the noise light power and the rate of change of the pumping light power calculated in step S106 have the same absolute value and opposite signs. Thereby, the processing amount of the arithmetic circuit 39 can be reduced.

  In the relay device 30, an erbium doped fiber amplifier (EDFA) may be connected to the subsequent stage of the Raman amplifier 60 or the gain equalizer 40. A decrease in signal light power due to the constant gain of substantial Raman amplification in the Raman amplifier 60 can be compensated by constant output control of the EDFA.

  In addition, by applying a program executed by the arithmetic circuit 39 to an existing arithmetic processing device, the Raman amplifier 60 including the arithmetic processing device can be configured.

  Such a program distribution method is arbitrary, for example, a computer-readable recording medium such as a CD-ROM (Compact Disk Read-Only Memory), a DVD (Digital Versatile Disk), an MO (Magneto Optical Disk), or a memory card. It may be stored and distributed in the network, or distributed via a communication network such as the Internet.

  DESCRIPTION OF SYMBOLS 1 Optical communication system, 10 Transmitter, 20 Transmission line optical fiber, 30 Repeater, 31 Multiplexer / demultiplexer, 32 Excitation light source, 33 1st branching device, 331 Input port, 332 Main signal port, 333 Sub signal port, 34 Second branching unit, 341 input port, 342 first port, 343 second port, 35 noise light transmission filter, 36 signal light power detection unit, 37 noise light power detection unit, 38 storage unit, 39 arithmetic circuit, 40 gain, etc. , 41, 42 Log amplifier, 50 receiver

Claims (11)

An optical fiber that transmits signal light of a plurality of wavelengths and Raman-amplifies the light including the signal light;
An excitation light source that makes excitation light for Raman amplification of the light including the signal light incident on the optical fiber;
A noise light extraction unit that extracts noise light in a wavelength band that does not include the wavelength of the signal light from light that has been Raman-amplified through the optical fiber;
A noise light power detection unit for detecting the power of the noise light extracted by the noise light extraction unit;
Based on the rate of change of the power of the noise light detected by the noise light power detector, the rate of change of the power of the pump light is determined, and the excitation light source changes so that the power of the pump light changes at the rate of change. An excitation light source control unit for controlling
A Raman amplifier comprising: The excitation light source control unit is configured such that the rate of change of the logarithm of the power of the noise light detected by the noise light power detection unit and the rate of change of the logarithm of the power of the pump light have substantially the same absolute value and opposite signs. Determining the rate of change of the power of the pumping light so as to control the pumping light source so that the power of the pumping light changes at the rate of change,
The Raman amplifier according to claim 1. A logarithmic conversion unit for logarithmically converting the power of the noise light detected by the noise light power detection unit;
The excitation light source control unit is configured such that the logarithmic change rate of the noise light power logarithmically converted by the logarithmic conversion unit and the logarithmic change rate of the excitation light power have substantially the same absolute value and opposite signs. Determining the rate of change of the power of the excitation light, and controlling the excitation light source so that the power of the excitation light changes at the rate of change,
The Raman amplifier according to claim 1. The excitation light source controller is configured so that a product of a change rate of the real number of the noise light detected by the noise light power detection unit and a change rate of the real number of the power of the excitation light is about 1. Determining the rate of change of the power of the light, and controlling the excitation light source so that the power of the excitation light changes at the rate of change,
The Raman amplifier according to claim 1. A storage unit that stores the excitation light power and the control value of the excitation light source in association with each other when the excitation light source enters the optical fiber with excitation light having a predetermined power;
The excitation light source control unit refers to the storage unit so that the excitation light power changes at the excitation light power change rate determined based on the noise light power change rate. Determining a control value of the light source, and controlling to drive the excitation light source with the control value;
The Raman amplifier according to any one of claims 1 to 4.   An optical repeater having the Raman amplifier according to claim 1. A gain equalizer having a wavelength characteristic of loss for compensating the wavelength characteristic of the gain of the Raman amplifier, and connecting the Raman amplifier and the gain equalizer in series;
The optical repeater according to claim 6. Further comprising an erbium-doped fiber amplifier, wherein the Raman amplifier and the erbium-doped fiber amplifier are connected in series;
The optical repeater according to claim 6 or 7.   An optical communication system comprising the optical repeater according to any one of claims 6 to 8. A Raman amplification control method performed by a Raman amplifier that makes pump light from a pump light source incident on an optical fiber that transmits signal light having a plurality of wavelengths and Raman-amplifies the light including the signal light. A noise light extraction step of extracting noise light in a wavelength band not including the wavelength of the signal light from the amplified light;
A noise light power detection step for detecting the power of the noise light extracted in the noise light extraction step;
Based on the rate of change of the power of the noise light detected in the noise light power detection step, the rate of change of the power of the pump light is determined, and the pump light source is changed so that the power of the pump light changes at the rate of change. An excitation light source control step for controlling
A Raman amplification control method comprising: A program for causing a computer to execute control of a pumping light source in a Raman amplifier that makes pumping light from a pumping light source enter an optical fiber that transmits signal light having a plurality of wavelengths and Raman-amplifies light including the signal light. ,
A noise light power acquisition procedure for acquiring the power of the noise light when extracting the noise light in a wavelength band not including the wavelength of the signal light from the light that has been Raman-amplified through the optical fiber;
Based on the rate of change of the power of the noise light acquired in the noise light power acquisition procedure, the rate of change of the power of the pump light is determined, and the pump light source so that the power of the pump light changes at the rate of change An excitation light source control procedure for controlling
A program that executes

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