JP2014072283A - Optical amplifier system, and optical amplification method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress level fluctuation width of output optical signals when the number of input optical signals (the number of wavelengths) having mutually different wavelengths fluctuates.SOLUTION: An optical amplification system includes: a plurality of photoexcitation optical amplifiers; a single semiconductor laser for outputting excitation light; and a splitter for distributing the excitation light output from the semiconductor laser to a gain medium of each of the plurality of optical amplifiers. The optical amplification system performs feedforward control for: monitoring light power of an input optical signal of each of the plurality of optical amplifiers; calculating such an output level of the semiconductor laser that an intermediate value of the maximum value and the minimum value of deviation of light power of the excitation light distributed to each of the plurality of optical amplifiers and light power of the excitation light with which desired gain can be obtained, becomes smaller than a predetermined value on the basis of a monitor value after fluctuation and a value of a branch ratio of the splitter in the case that any of monitor values has fluctuated; and setting the output level of the semiconductor laser to the calculated value.

Description

  The present invention relates to an optical amplification system used in an optical communication system. The present invention relates to an optical amplification system capable of high-speed adaptation to fluctuations in the wavelength number of an optical signal incident on an optical amplifier.

  In recent years, research and development of highly functional optical nodes such as CDC-less (Colorless / Directionless / Contention-less) ROADM (Reconfigurable Optical Add / Drop Multiplexer) has been actively promoted. FIG. 1 shows a configuration example of a CDC-less ROADM node.

  The CDC-less function improves the operability such that an optical signal having an arbitrary wavelength can be set in an arbitrary path, but the loss in the optical node increases, so that the transmission distance is limited. Therefore, in CDC-less ROADM and the like, a small and integrated optical amplifier has been developed in order to relax the transmission distance limitation (for example, Non-Patent Document 1). Non-patent document 1 describes that a plurality of optical devices such as a VOA (Variable Optical Attenuator) are integrated in a PLC (Planar Lightwave Circuit) by sharing a plurality of EDFA (Erbium Doped Fiber Amplifier) pumping semiconductor lasers. ing.

  The optical amplifier (EDFA) required for the CDC-less ROADM does not require large pumping light as compared with the optical amplifier for WDM, so it is possible to share an expensive pumping semiconductor laser and increase the device price. Can be suppressed. Further, since the optical amplifier required for the CDC-less ROADM is required for each transmitter / receiver, the number of apparatuses becomes enormous. However, as described in Non-Patent Document 1, a plurality of optical devices are integrated and a plurality of optical devices are integrated. By integrating the optical amplifier, the entire apparatus can be reduced. When multiple optical amplifiers are integrated using a PLC, the gain can be adjusted by adjusting the pumping light by changing the branching ratio of the VOA or optical coupler made on the PLC. Since the operation speed of the utilized silica-based waveguide is on the order of milliseconds, there is a problem that it cannot follow a steep signal level fluctuation of milliseconds or less. Therefore, when the number of wavelengths incident on any of the integrated optical amplifiers changes abruptly, it is difficult to immediately optimize the excess or deficiency of the gain. Here, the number of wavelengths refers to the number of signals of different wavelengths of the WDM signal.

M.M. Bolshtysky et al. , “Planar Waveguide Integrated EDFA”, PDP17 OFC / NFOEC2008. M.M. Fukutoku et al. , “Pump power reduction of optical fedback controlled EDFA using electrical fedforward control,” Optical Amplifiers and Tiler Applications. Dig. , Vail, CO, 1998, pp. 32-35.

In the optical amplification system that simultaneously pumps a plurality of optically pumped optical amplifiers using a single semiconductor laser as described above, the conventional technique optimizes the gain at a high speed in response to a sudden change in the number of wavelengths. This is difficult because of the speed limit of the PLC switch.
The present invention solves such a problem, and an object of the present invention is to suppress the level fluctuation width of the output optical signal when the number of input optical signals having different wavelengths (number of wavelengths) varies.

  To achieve the above object, an optical amplifier system according to the present invention includes a plurality of optically pumped optical amplifiers, a single semiconductor laser that outputs pumping light, and a plurality of optical amplifiers that emit pumping light output from the semiconductor laser. In an optical amplification system comprising a splitter that distributes to each gain medium, the optical power of the input optical signal of each of a plurality of optical amplifiers is monitored, and when any of the monitored values changes, the changed monitor is monitored. The maximum value and the minimum value of the deviations between the optical power of the pumping light distributed to each of the plurality of optical amplifiers and the optical power of the pumping light that obtains a desired gain based on the value of the splitter and the branching ratio of the splitter The semiconductor laser output level is calculated so that the intermediate value becomes smaller than a predetermined value, and feedforward control is performed to set the output level of the semiconductor laser to the calculated value.

  Specifically, the optical amplifier system of the present invention is an optical amplification system that amplifies a plurality of optical signals, and a plurality of optical amplifiers that amplify each optical signal, and the wavelength of each optical signal before passing through the optical amplifier. A plurality of wavelength measuring units for measuring the number, an excitation light source for generating excitation light for amplifying an optical signal in each optical amplifier, an optical splitter for branching the excitation light from the excitation light source to each optical amplifier, and an optical signal When there is a change in the number of wavelengths, the pump light power and the desired gain that are actually distributed to each optical amplifier are obtained based on the number of wavelengths after the change and the branching ratio value of the optical splitter before the change. The output level of the excitation light source is calculated so that the intermediate value between the maximum value and the minimum value of the set of deviation values from the excitation light power is smaller than a preset value. Perform feedforward control to be set to the calculated value Comprising an excitation light control unit.

  In the optical amplifier system of the present invention, the branching ratio of the optical splitter is variable, and the pumping light control unit determines the branching ratio of the optical splitter from the ratio of the number of wavelengths of the incident signal to each optical amplifier after the change. And the feedforward control may be performed in which the value of the branching ratio of the optical splitter is set to the calculated value.

  In the optical amplifier system of the present invention, the pumping light control unit adjusts the output level of the pumping light source until the power of the pumping light supplied to each optical amplifier reaches a value at which the desired gain is obtained. It may be changed to the same degree.

  In the optical amplifier system of the present invention, the optical amplifier system includes a variable optical attenuator that adjusts the power of each pumping light branched by the optical splitter, and the pumping light control unit includes the power of the optical signal incident on each optical amplifier and each power By monitoring the power of the optical signal emitted from the optical amplifier, the deviation of the gain of each optical amplifier from the desired gain is detected, and the attenuation of the variable optical attenuator is controlled so that the deviation becomes small May be.

  Specifically, the optical amplifier method of the present invention is an optical amplification method for amplifying a plurality of optical signals using individual optical amplifiers, and includes a measurement procedure for measuring the number of wavelengths of each optical signal, When the number of wavelengths varies, the power and desired gain of the pumping light actually distributed to each optical amplifier based on the number of wavelengths after the variation and the branching ratio value of the pumping light supplied to each optical amplifier Setting procedure for setting the output level of the pumping light source so that the intermediate value between the maximum and minimum values of the set of deviation values from the pumping light power obtained is smaller than the preset value, and setting And an optical amplification procedure for generating the excitation light of the output level with the excitation light source, branching the excitation light to each optical amplifier, and amplifying each optical signal using the branched excitation light. Here, the value set in advance is preferably as small as possible in order to set the power of pumping light as accurately as possible. Ideally 0.

  In the optical amplification method of the present invention, in the setting procedure, the branching ratio value of the optical splitter that branches the pumping light is calculated from the ratio of the number of wavelengths of the incident signals to the optical amplifiers after the change. May be set to the calculated value, and in the optical amplification procedure, the excitation light may be branched by an optical splitter having a set branching ratio.

  In the optical amplification method of the present invention, in the setting procedure, the output level of the pumping light source is made equal to the operation speed of the optical splitter until the power of the pumping light supplied to each optical amplifier reaches a value at which the desired gain is obtained. It may be changed depending on the degree.

  In the optical amplification method of the present invention, in the measurement procedure, the power of the optical signal incident on each optical amplifier and the power of the optical signal emitted from each optical amplifier are measured, and in the setting procedure, the gain of each optical amplifier is A deviation from the desired gain is detected, the attenuation amount of each pumping light is set so that the deviation becomes small, and the power of the pumping light incident on each optical amplifier is set in the optical amplification procedure. It may be attenuated only.

  The above inventions can be combined as much as possible.

  According to the present invention, it is possible to suppress the level fluctuation range of the output optical signal when the number of input optical signals having different wavelengths (the number of wavelengths) varies.

An example of a CDC-less ROADM node configuration is shown. An example of the 1st Embodiment of this invention is shown. An example of operation | movement in 1st Embodiment is shown. An example of the relationship between the number of wavelengths and pumping light power in FIG. 3 is shown. FIG. 4B shows an example when the control amount of the excitation light power is changed. An example of the operation in the case of the control in FIG. An example of a control flow is shown. An example of a control flow in the case of adding an operation for controlling the pumping light power with a time constant is shown. An example of the operation when controlling the excitation light in consideration of the time constant of the branching variable splitter will be described. An example of the 2nd Embodiment of this invention is shown. An example of the 3rd Embodiment of this invention is shown. An example of the 4th embodiment of the present invention is shown. An example of the 5th Embodiment of this invention is shown.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components.

(Embodiment 1)
FIG. 2 shows a first embodiment of the present invention. The optical fiber amplifier system according to the present embodiment has a configuration in which a plurality of EDFs 11 are integrated by sharing the pumping light with a splitter 19 (optical branch circuit) having a variable branching ratio, as in Non-Patent Document 1. The configuration differs in that the input light is monitored and the pumping light power is feedforward controlled. In order to share the pumping light of the plurality of EDFs 11, the pumping light power to each erbium-doped fiber: EDF11 (# 1 to #n) is adjusted by using the pumping semiconductor laser 14 and the branching ratio variable optical splitter 19 in combination. Since the variable branching ratio optical splitter 19 is assumed to be integrated on the PLC, the operation speed is about several milliseconds, and the control is slower than that of the pumping semiconductor laser 14.

  Specifically, the optical fiber amplifier system according to the present embodiment includes an EDF 11 as an optical amplifier, a PD 13 as a wavelength measuring unit, an optical splitter 19, a pumping semiconductor laser 14 as a pumping light source, and a pumping light control unit. And an FF control unit 17. The optical fiber amplification method according to the present embodiment includes a measurement procedure, a setting procedure, and an optical amplification procedure in this order.

In the measurement procedure, the number of wavelengths of each optical signal is measured using the PD 13. Thereby, the fluctuation | variation of the wavelength number of an optical signal is detected.
In the setting procedure, the FF (Feedforward) control unit 17 sets the output level of the excitation light source when the number of wavelengths of the optical signal varies. At this time, the FF control unit 17 obtains the power and desired gain of the pumping light actually distributed to each EDF 11 based on the number of wavelengths after the change and the branching ratio value of the pumping light supplied to each EDF 11. The output level of the excitation light source is set so that the intermediate value between the maximum value and the minimum value in the set of deviation values from the excitation light power is smaller than a preset value.
In the optical amplification procedure, pumping light of a set output level is generated by the pumping semiconductor laser 14, the pumping light is branched to each EDF 11, and each optical signal is amplified using the branched pumping light.

In FIG. 2, the operation when the number of input wavelengths changes only for EDF # 1 (multiple wavelength input → one wavelength input) will be described.
When controlling the actual pumping light power, it is only necessary to determine the pumping light power from the relationship between the input light power and the pumping light power under the constant gain condition, but in the following description, under the constant gain condition, It is assumed that the input light power and the pump light power are proportional. That is, when the pumping light is constant and the input light power (= number of input wavelengths) changes, the gain per wavelength changes.

First, a case where the amount of change in pumping light power is determined only by the number of input wavelengths will be described.
At the moment when the number of input wavelengths of EDF # 1 decreases to 1, the pumping light power does not change, and therefore, the surviving 1 channel gain of EDF # 1 becomes excessive.
Thereafter, when the input monitor 13 detects a decrease in the number of input wavelengths, the FF control unit 17 controls to reduce the pumping light power in proportion to the total number of wavelengths. At this time, the FF control unit 17 changes the branching ratio of the branching ratio variable optical splitter 19 simultaneously with the pumping light power of the pumping semiconductor laser 14, but the operation of the branching ratio variable optical splitter 19 is slow, so that the EDFs # 2 to #n. The excitation light of is once decreased.
Thereafter, the branching ratio of the branching ratio variable optical splitter 19 changes, and the pumping light power that should be originally supplied to the EDFs # 2 to #n is distributed. For this reason, the output levels of EDFs # 2 to #n once decrease, and then return to the original level in the time equivalent to the time constant of the branching ratio variable optical splitter 19 (at the operating speed of the branching ratio variable optical splitter 19). become.

  Here, the branching ratio of the variable branching ratio optical splitter 19 is the ratio of the number of input wavelengths to each EDF after the change. For example, if the number of EDFs is 3 and the number of input wavelengths to EDFs # 1 to # 3 is 5, 10, and 15, 5: 10: 15 = 1: 2: 3.

  FIG. 3 shows a summary of the above operations with respect to time. By the feedforward control of the pumping light power, the level fluctuation range of the EDF # 1 is suppressed as compared with the case where the pumping light power is not controlled. However, since the operation of the variable branching ratio optical splitter 19 is slower than the pumping light power, The level fluctuation of #n continues for the time constant of the branching ratio variable optical splitter 19. Here, when the output level fluctuation of each EDF 11 when the number of wavelengths changes does not fall within the reception level range of the transponder (Rx in FIG. 1), a reception error occurs.

  FIG. 4 shows a summary of the contents shown in FIG. 3 while focusing on the relationship between the number of wavelengths in each EDF 11 and the pumping light power. As shown in FIG. 4B, the number of input wavelengths of each EDF 11 is detected until the change in the number of wavelengths is detected, the excitation light is adjusted, and the setting of the branching ratio of the variable branching ratio optical splitter 19 is completed. Since an error occurs in the pumping light power, the output of each EDF 11 varies.

  Next, a case where the target value of the control amount of the pump light power is determined in consideration of the output fluctuation width of all EDFs will be described. FIG. 5 shows the change in the number of wavelengths shown in FIG. 4B, adjusts the pumping light, and changes the number of wavelengths and the pumping light power at the timing until the branching ratio setting change of the branching ratio variable optical splitter 19 is completed. The schematic diagram when the relationship is increased when the control amount of the excitation light power is reduced and increased is shown.

  When the control amount of the pump light control power is reduced as shown in FIG. 5A, the instantaneous level error (Err # 1) of EDF # 1 is larger than that in FIG. The level errors (Err # 2 to Err # n) of the EDFs # 2 to #n are small, and the level fluctuation range of the EDFs # 2 to #n at the moment when the excitation light is changed can be suppressed. However, since the excitation light becomes excessive, the level when the adjustment of the branching ratio ends and returns to the steady state slightly increases for all EDFs. FIG. 6 shows a time change of each EDF in the case of the control of FIG.

  When the control amount of the excitation light power shown in FIG. 5B is increased, the instantaneous level error (Err # 1) of EDF # 1 becomes smaller than that in FIG. The level error (Err # 2 to Err # n) of # 2 to #n is large, and the level fluctuation range of EDF # 2 to #n at the moment when the excitation light is changed becomes large.

Here, the control amount of the excitation light power is determined as follows.
The number of wavelengths is detected using the PD 13 (S101), and the provisional pumping light power control amount is calculated from the amount of wavelength number fluctuation (S102). The branching ratio of the variable branching ratio optical splitter 19 is the same as that before the change in the number of wavelengths, and when the pumping light power is changed, the level deviation amount in each EDF 11 is calculated (S103 to S108). Here, the level error is calculated as a positive value error when the pumping light power supplied is larger than the necessary pumping light power calculated from the number of input wavelengths of each EDF # i (i = 1 to n). If the supplied pumping light power is small, it is calculated as a negative error.
Next, the maximum value and the minimum value of the level error of each EDF 11 are calculated (S104), and the control amount of the excitation light power is determined so that the intermediate value between the maximum value and the minimum value becomes 0 (S105 to S107).

  Specifically, in FIG. 5, the level error (Err # 1) of EDF # 1 corresponds to the maximum value (> 0), and the level error of EDF # 2 (# 3 to #n in FIG.5 is also acceptable) ( Err # 2) corresponds to the minimum value (<0). Therefore, in FIG. 5, the control amount of the pumping light power may be determined so that the value of (Err # 1 + Err # 2) / 2 becomes zero. As a result, the level errors of all the EDFs 11 are averaged, and it is possible to suppress level fluctuations only with a specific EDF 11. A series of the above control flow is shown in FIG.

  As described above, when the control amount of the pumping light power is determined so as to suppress the level fluctuation range, an error occurs in the level in the steady state. For this reason, the control amount of the pumping light power at the moment when the wavelength number change occurs is determined as shown in FIG. 7, and the level fluctuation width is suppressed, and then the pumping light power change amount according to the wavelength number changing amount. The pumping light power is changed with the same time constant as that of the branching ratio variable optical splitter 19. The control flow in this case is shown in FIG. 8, and the operation is shown in FIG.

  The difference between the control flow shown in FIG. 8 and the control flow shown in FIG. 7 is that the pump light power is changed with the same time constant as that of the branching ratio variable optical splitter 19 so that the pump light power change amount according to the wavelength number change amount. Step S109 to be changed is added at the end, and the other control is the same as in FIG.

  The control amount indicated by ΔP1 in FIG. 9 is the control amount in step S107 shown in FIG. 7, and the control amount indicated by ΔP2 in FIG. 9 is the control amount in the last step S109 in FIG. As a result, the output level fluctuation range when the number of wavelengths changes can be suppressed, and the output level in the steady state can also be set to the same value as before the change in the number of wavelengths.

  The present invention integrates a plurality of optically pumped optical amplifiers such as an EDFA using a PLC, and pumps the optical amplifiers with a common pumping semiconductor laser 14 to be incident on each optical amplifier. Even if the number of wavelengths of the optical signal fluctuates abruptly, it becomes possible to realize an optimum excitation state at high speed.

(Embodiment 2)
FIG. 10 shows a second embodiment of the present invention. In addition to the configuration of the first embodiment, the optical amplifier system according to the present embodiment includes a variable optical attenuator 23 that adjusts the power of each pump light, a PD 22 that measures the optical signal power after passing through each EDF 11, and an FB ( And a feedback control unit 18.

  In the present embodiment, the FB control unit 18 detects the deviation of the gain of each EDF 11 from the desired gain by monitoring the power of the optical signal incident on each EDF 11 and the power of the optical signal emitted from each EDF 11. The attenuation amount of the variable optical attenuator 23 is feedback-controlled so that the deviation becomes small.

  In the present embodiment, the pumping light power to each EDF 11 can be adjusted by the variable optical attenuator 23, and the input / output level of the optical signal can be monitored for each EDF 11. Therefore, even if the branching ratio of the splitter 20 is fixed, the difference in gain obtained by monitoring the input / output signal level of each EDF 11 is fed back to the variable optical attenuator 23, so that the pump light power has a desired gain. It can be optimized to the value obtained. When the branching ratio is fixed, this embodiment is useful because optimization cannot be performed only by setting the output of the pumping semiconductor laser.

(Embodiment 3)
FIG. 11 shows a third embodiment of the present invention. In addition to the configuration of the first embodiment, the optical amplifier system according to the present embodiment includes a variable optical attenuator 23 that adjusts the power of each pump light, a PD 22 that measures the optical signal power after passing through each EDF 11, and FB control. And a unit 18.

  In the present embodiment, the FF control unit 17 calculates the output level of the pumping semiconductor laser 14 and then calculates the branching ratio of the branching ratio variable optical splitter 19. Then, the pumping semiconductor laser 14 and the branching ratio variable optical splitter 19 are set to these calculation result values. Further, the variable optical attenuator 23 is feedback controlled using the gain deviation as in the third embodiment.

  Here, the branching ratio of the variable branching ratio optical splitter 19 is the ratio of the number of input wavelengths to each EDF after the change. For example, if the number of EDFs is 3 and the number of input wavelengths to EDFs # 1 to # 3 is 5, 10, and 15, 5: 10: 15 = 1: 2: 3.

  In the present embodiment, after setting the branching ratio of the branching ratio variable splitter 19, the FB control unit 18 performs the above feedback control, and the output of the pumping semiconductor laser 14 is set to a value calculated from the wavelength number fluctuation. Although the time constant of the branching ratio variable optical splitter 19 is changed, by using the variable optical attenuator 23 and the variable function of the branching ratio variable splitter 19 together, the output level before the wavelength fluctuation is reached in a shorter time than in the first embodiment. It becomes possible.

(Embodiment 4)
FIG. 12 shows a fourth embodiment of the present invention. In this embodiment, the branching ratio variable optical splitter 19 is configured by connecting the variable coupler 24 to the cascade using only one branching direction for each branching. By adopting this configuration, it is possible to select that the excitation light is not incident on any EDF 11 with a single optical splitter (selection for emitting the excitation light only from the off-port).

(Embodiment 5)
FIG. 13 shows a fifth embodiment of the present invention. A variable branching ratio optical splitter 19 is configured by using the variable coupler 24 in either branch direction for each branch. By adopting this configuration, the number of 1 × 2 branching ratio variable couplers can be reduced.

  As described above, the present invention integrates a plurality of optical amplifiers using a PLC, and affects the gain of the fluctuation of the number of wavelengths of incident signals in an optical amplifier system that excites each optical amplifier with a common semiconductor laser. It relaxes at high speed and is useful for the operation of optical communication systems.

11: EDF
12, 15, 21: Optical coupler 13, 22: PD
14: pumping semiconductor laser 15: pumping light coupling unit 17: FF control unit 18: FB control unit 19: branching ratio variable optical splitter 20: branching ratio fixed splitter 23: variable optical attenuator 24: variable couplers 51, 66: for WDM Optical amplifiers 52 and 64: couplers 53 and 65: WSS
54, 63: CDC optical amplifier 55, 62: CDC-less optical switch 56: Receiver 61: Transmitter

Claims (8)

An optical amplification system for amplifying a plurality of optical signals,
A plurality of optical amplifiers for amplifying each optical signal;
A plurality of wavelength measuring units for measuring the number of wavelengths of each optical signal before passing through the optical amplifier;
An excitation light source that generates excitation light for amplifying an optical signal in each optical amplifier;
An optical splitter for branching the pumping light from the pumping light source to each optical amplifier;
When there are fluctuations in the number of wavelengths of the optical signal, the power and desired gain of the pumping light actually distributed to each optical amplifier based on the number of wavelengths after fluctuation and the branching ratio value of the optical splitter before fluctuation The output level of the excitation light source is calculated by calculating the output level of the excitation light source so that the intermediate value between the maximum value and the minimum value of the set of deviation values from the excitation light power obtained is smaller than the preset value. An excitation light control unit that performs feedforward control to set the calculated value to the calculated value;
An optical amplifier system comprising: The branching ratio of the optical splitter is variable,
The pumping light control unit calculates the value of the branching ratio of the optical splitter from the ratio of the number of wavelengths of the incident signal to each optical amplifier after the change, and sets the value of the branching ratio of the optical splitter to the calculated value. 2. The optical amplifier system according to claim 1, wherein forward control is performed.   The pumping light controller changes the output level of the pumping light source at the same level as the operation speed of the optical splitter until the power of the pumping light supplied to each optical amplifier reaches a value at which the desired gain is obtained. The optical amplifier system according to claim 2, wherein: A variable optical attenuator for adjusting the power of each pumping light branched by the optical splitter;
The pumping light control unit detects a deviation of the gain of each optical amplifier from the desired gain by monitoring the power of the optical signal incident on each optical amplifier and the power of the optical signal emitted from each optical amplifier. 4. The optical amplifier system according to claim 1, wherein an attenuation amount of the variable optical attenuator is controlled so that the deviation becomes small. An optical amplification method for amplifying a plurality of optical signals using individual optical amplifiers,
A measurement procedure for measuring the number of wavelengths of each optical signal;
When there is a change in the number of wavelengths of the optical signal, the power of the pumping light actually distributed to each optical amplifier based on the number of changed wavelengths and the branching ratio of the pumping light supplied to each optical amplifier Setting procedure for setting the output level of the pumping light source so that the intermediate value between the maximum value and the minimum value among the set of deviation values from the pumping light power at which a desired gain can be obtained is smaller than a preset value. When,
An optical amplification procedure for generating excitation light of a set output level with an excitation light source, branching the excitation light to each optical amplifier, and amplifying each optical signal using the branched excitation light;
An optical amplification method comprising: In the setting procedure, the branching ratio value is calculated from the ratio of the number of wavelengths of the incident signals to the optical amplifiers after the change, and the branching ratio value of the optical splitter that branches the pumping light is set to the calculated value. ,
6. The optical amplification method according to claim 5, wherein in the optical amplification procedure, the excitation light is branched by an optical splitter having a set branching ratio. In the setting procedure, the output level of the pumping light source is changed at the same level as the operation speed of the optical splitter until the power of the pumping light supplied to each optical amplifier reaches a value at which the desired gain is obtained. The optical amplification method according to claim 5 or 6. In the measurement procedure, the power of the optical signal incident on each optical amplifier and the power of the optical signal emitted from each optical amplifier are measured,
In the setting procedure, a deviation of the gain of each optical amplifier from the desired gain is detected, and an attenuation amount of each pumping light is set so that the deviation becomes small,
The optical amplification method according to any one of claims 5 to 7, wherein in the optical amplification procedure, the power of pumping light incident on each optical amplifier is attenuated by a set attenuation amount.

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