JP5841517B2 - Optical fiber amplifier system and optical fiber amplification method - Google Patents

Description

  The present invention relates to an L-band optical fiber amplifier system capable of high-speed gain control and a high-speed gain control method for the L-band optical fiber amplifier system.

  In recent years, research and development of high-function optical nodes such as CDC-less (colorless / directionless / contentionless) ROADM (Reconfigurable Optical Add / Drop Multiplexing) 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 system 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 are integrated in a PLC (Planar Lightwave Circuit) by sharing a plurality of EDFA excitation LDs.

  The optical amplifier required for the CDC-less ROADM does not require large pumping light as compared with the optical amplifier for WDM. Therefore, it is possible to share an expensive pumping LD, and suppress an increase in the device price. It becomes possible. In addition, since an optical amplifier required for CDC-less ROADM is required for each transceiver, 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 a plurality of 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 operating speed of the utilized silica-based waveguide is on the order of msec, there is a problem that it cannot follow a steep signal level fluctuation of less than msec.

  Non-Patent Document 2 describes that feedforward control (FF control) of an excitation LD is effective for high-speed gain control of an EDFA. In the case of feedforward control, the input optical power to the optical amplifier is monitored, and the pumping LD is controlled so that the output optical power becomes the target value. Therefore, the relationship between the input optical power and the output optical power is related to the pumping current. Must be uniquely determined. On the other hand, in the L-band EDFA, the C-band ASE (Amplified Spontaneous Emission) light generated by the 0.98 μm or 1.48 μm pump light becomes the L-band excitation light, so that the input signal light wavelength is shorter than the L-band side. The excitation conditions differ depending on whether the wavelength is on the long wavelength side.

  FIG. 2 shows the result of measuring the relationship between the input signal light power and the excitation current at a signal light wavelength of 1570 nm and 1607 nm under a constant gain (15.5 dB) in an L-band EDFA of 0.98 μm forward pumping. It can be seen that the required excitation current value varies greatly depending on the signal light wavelength when the input signal light power is −30 dBm or more. In the case of feed forward control of the excitation LD current, the target value of the excitation current differs depending on the signal light wavelength, so that high speed feed forward control cannot be performed. In the case of feedback control of the excitation current, the output power to be controlled is always monitored, so that it is not affected by the signal light wavelength dependency, but the control speed is slow.

  FIG. 3 shows a configuration in which the C-band ASE light that propagates backward to the incident side of the EDFA is returned to the EDF by a Faraday mirror in the 0.98 μm forward-excited L-band EDFA. FIG. 4 is a measurement result of the relationship between the input signal light power and the pumping current under the constant gain condition obtained in the case of the configuration of FIG. It can be seen that up to about -5 dBm of input light power, the pumping currents are almost the same regardless of the signal light wavelength. It can also be seen that the difference due to the signal light wavelength is smaller than the result of FIG. 2 even in the case of an input of −5 dBm or more. FIG. 4 shows the same 15.5 dB gain condition as FIG. 2, but the excitation current value is small. This is because the excitation efficiency is improved by returning the C-band ASE that propagates back to the incident side. Patent Documents 1 and 2 describe methods for returning C-band ASE to EDF in order to improve the excitation efficiency of L-band EDFA. However, there is no description that the signal wavelength dependency under the same gain condition is eliminated. Also, the relationship with high-speed gain control is not shown.

Japanese Patent No. 04179662 JP 2009-117720 A

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 order to solve the above-described problems, an object of the present invention is to suppress the level fluctuation width of an output optical signal when the number of input optical signals having different wavelengths (number of wavelengths) varies in an L-band EDFA. .

  In order to achieve the above object, the present invention relates to an erbium-doped optical fiber amplifier (EDFA) that amplifies an L-band (wavelength 1565 to 1625 nm) optical signal. Means for making light incident at a wavelength of 1530 to 1565 nm, and the gain is adjusted by feedforward control of the optical power of the pumping light using the monitor value of the optical power of the input optical signal.

Specifically, the optical fiber amplifier system according to the present invention is arranged in parallel, each provided with a plurality of amplification optical fibers for amplifying an input signal of L-band light , and each of the amplification optical fibers, A plurality of L-band optical branching units that branch the input signal of the L-band light that is input to the amplification optical fiber, and the L-band optical branching unit are provided for each of the L-band optical branching units. A plurality of L-band optical power measuring units that measure the input signal power of the L-band light, a pumping light source that emits pumping light for amplifying the L-band light, and each of the amplification optical fibers, excitation light the amplification optical multiple pumping light supply section supplying the fiber, provided for each of the amplification optical fiber, incident C-band light to the input side of the amplifying optical fiber, respectively A plurality of C-band optical incident portion that, the plurality of said measured at L-band optical power measurement unit in accordance with the input signal power of the L-band optical, the excitation light power incident on the plurality of amplifying optical fiber A pumping light power control unit for feedforward control of the pumping light, and a branching ratio is variable, and the pumping light emitted from the pumping light source is supplied to the plurality of pumping light supply units according to an instruction from the pumping light power control unit The pumping light power control unit includes a variable branching ratio optical coupler based on the input signal power of the L-band light measured by the plurality of L-band light power measuring units. It is characterized by changing the branching ratio .

In the optical fiber amplifier system according to the present invention, when the pumping light power control unit starts to increase the pumping light power necessary to obtain the same gain with respect to the change in the input signal power of the L-band light. , increased control the power of the excitation light, the L when the input signal power is changed power required excitation light even if the band light does not change, the power of the excitation light may be controlled constant value .

  In the optical fiber amplifier system according to the present invention, the input signal is a WDM signal, and the excitation light power control unit supplies the excitation light power and the excitation light power necessary for amplification of an optical signal having the number of wavelengths of the WDM signal. The output level error in each amplification optical fiber is obtained using the power of the pumping light supplied to the amplification optical fiber from the unit, and the intermediate between the maximum value and the minimum value of the output level errors in each amplification optical fiber The control amount of the pump light power may be determined so that becomes zero.

In the optical fiber amplifier system according to the present invention, the C-band light entrance portion, said by fiber grating which is inserted into an optical fiber connected to the input side of the amplifying optical fiber, C-band generated in the amplification optical fiber The ASE may be returned to the amplification optical fiber.
In the optical fiber amplifier system according to the present invention, the C-band light entrance portion, the Faraday mirror inserted in the optical fiber connected to the input side of the amplifying optical fiber, C-band generated in the amplification optical fiber The ASE may be returned to the amplification optical fiber.
In the optical fiber amplifier system according to the present invention, the C-band light entrance portion by the inserted AR coating the outgoing end of the excitation light source, an ASE of the C-band generated in the amplification optical fiber, the amplifying optical It may be returned to the fiber.

  An optical fiber amplifier system according to the present invention includes a C-band light source that generates C-band light, and the C-band light incident unit connects output light from the C-band light source to an input side of the amplification optical fiber. The optical fiber may be coupled to the optical fiber.

Specifically, the optical fiber amplifying method according to the present invention is an optical fiber amplifying method in the optical fiber amplifier system according to the present invention, wherein the plurality of pumping light power control units respectively input the L-band light. and L-band optical power measurement procedure for measuring signal power, the pump light power control unit, in response to the input signal power of the measured at a plurality of L-band optical power measurement section the L-band optical, the plurality of amplification and pumping light power control procedure for feed-forward control of the power of the excitation light incident on the use optical fiber, and type the Symbol excitation light and the C-band light to the plurality of amplifying optical fibers, the amplification optical fiber And an amplification procedure for amplifying the input signal of the L-band light input to.

  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 example is shown. An example of the input optical power vs. pumping current characteristic (gain = 15.5 dB constant) of a 0.98 um forward pumped EDFA is shown. An example of a configuration for returning ASE that propagates back to the incident side to EDF is shown. An example of the relationship between input optical power and pumping current obtained in the configuration of FIG. 3 is shown. An example of 1st embodiment of this invention is shown. The 1st example of 2nd embodiment of this invention is shown. The 2nd example of the input conditions to EDFA is shown. An example of the operation when the number of wavelengths varies will be shown. An example of 3rd embodiment of this invention is shown. An example of 3rd embodiment of this invention is shown. An example of 4th embodiment of this invention is shown. An example of the operation in the fourth embodiment will be shown. An example of the relationship between the number of wavelengths and pumping light power in the fourth embodiment is shown. FIG. 12B 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.

  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)
A first embodiment for solving the problem is shown in FIG. The optical fiber amplifier system according to this embodiment inputs an L-band optical signal and pumping light to the EDF 11, outputs an L-band optical signal amplified by the EDF 11, and converts C-band ASE light that does not contribute to signal amplification to EDFA. To the incident side. At this time, it has a mechanism for monitoring the input optical power of the L-band optical signal and feedforward controlling the excitation current. On the incident side of the EDF 11, there is a mechanism for making the C-band light incident on the EDF 11. It has become the composition.

  Specifically, the optical fiber amplifier system according to the present embodiment includes an EDF 11 as an amplification optical fiber, an optical coupler 12 that taps part of signal light, a PD 13 as an L-band optical power measurement unit, and a pump. A light source LD 14, an optical coupler 15 as a pumping light supply unit, a C-band light incident unit 16, and an FF control unit 17 as a pumping light power control unit are provided. The optical fiber amplification method according to the present embodiment includes an L-band optical power measurement procedure, a pumping light power control procedure, and an amplification procedure.

In the L-band light power measurement procedure, the PD 13 measures the power of the L-band light. Thereby, the fluctuation | variation of the wavelength number of L band light is detectable.
In the pumping light power control procedure, the FF control unit 17 performs feedforward control of the power of the pumping light incident on the EDF 11 according to the power of the L band light.
In the amplification procedure, the EDF 11 inputs the L band light and the excitation light to the EDF 11 and amplifies the L band light. At this time, the C-band light incident unit 16 inputs the C-band light to the EDF 11.

  The C-band light incident unit 16 makes C-band light incident on the input side of the EDF 11. Since it has a mechanism for making the C-band light incident on the EDF 11, the wavelength dependency of the gain is sufficiently small as shown in FIG. 4, and the target value of the feedforward control does not depend on the signal wavelength. Therefore, high-speed gain control can be performed by monitoring only the input optical power. Therefore, the FF control unit 17 controls the power of the excitation light incident on the EDF 11 according to the power of the L band light measured by the PD 13.

  The FF control unit 17 controls the power of the excitation light according to the change in the power of the L band light. Specifically, the pump light power to be set is determined from the monitored input light power with reference to the relationship between the input light power and the pump light power under the constant gain condition shown in FIG.

  The C-band light incident unit 16 reflects the C-band ASE light propagating back to the incident side as shown in FIG. 3 or outputs from an LD light source as a C-band light source that generates C-band light. May be incident. Arbitrary means can be applied as the means for returning the C-band ASE light. For example, a fiber grating or a Faraday mirror is used. Further, the insertion position of the C-band light incident portion 16 is not limited to the position shown in FIG. 5 and may be the means (Faraday mirror) and position shown in FIG.

(Embodiment 2)
A second embodiment of the present invention is shown in FIG. FIG. 6A shows a case where a WDM signal is input to the L-band EDFA 100 of the present invention. Here, it is assumed that the number of wavelengths input to the EDFA varies due to a failure such as fiber breakage. Here, the number of wavelengths refers to the number of signals of different wavelengths of the WDM signal.

  FIG. 6B shows the result of the relationship between the input power and the excitation current in the present invention shown in FIG. In the case of the input conditions as shown in FIG. 6B, when the number of wavelengths changes from a plurality of wavelengths to one wavelength, the total input power to the EDFA changes according to the number of wavelengths, but the excitation current remains constant. The gain is constant. That is, when the number of wavelengths is reduced by the input monitor, the level of the remaining channels can be kept constant only by controlling the excitation current value to be constant. FIG. 7 shows the operation when the number of wavelengths is changed.

  On the other hand, from the operating point shown in FIG. 6B, when the number of wavelengths increases and the input power increases, it is necessary to increase the pumping light power in order to keep the gain constant. In the case of an increase, a plurality of channels are added at a time instead of being added at a time, so the pumping light power may be changed based on information from the input monitor.

  The WDM EDFA shown in the CDC-less ROADM configuration example shown in FIG. 1 receives, for example, an 80-channel signal, but the CDC optical amplifier has a limited number of wavelengths of about 10 channels. become.

(Embodiment 3)
FIG. 8 shows a third embodiment of the present invention. FIG. 3 shows a form using a Faraday mirror, but FIG. 8 uses a fiber grating. Here, the reflectivity of the C band ASE by the fiber grating is about 5%. Further, an ASE reflection coating applied to the excitation LD as shown in Patent Document 2 may be used.

  FIG. 9 shows a configuration in which the output from the C-band LD light source 16-2a is incident on the EDF 11 instead of returning the ASE light propagating back to the incident side. In the case of FIG. 9, the C-band ASE light collected on the incident side of the EDF 11 is used to amplify the light from the C-band LD light source 16-2a, and the amplified C-band light is the longitudinal length of the EDF 11. Since the light is absorbed in the direction and used to amplify the L-band signal light, the configuration of FIG. 9 also improves the excitation efficiency as in the case of FIG.

(Embodiment 4)
FIG. 10 shows a fourth embodiment of the present invention. Similar to Non-Patent Document 1, a plurality of EDFAs are integrated by sharing excitation light with a splitter with variable branching ratio. The configuration is different in that it has means for eliminating the wavelength dependence of the L-band EDFA and feed-forward control of pumping light power by monitoring input light. In order to share the excitation light of a plurality of EDFAs, the excitation light power to each EDF (# 1 to #n) is adjusted using both the excitation LD and the branching ratio variable splitter. Since the variable branching ratio splitter is assumed to be integrated on the PLC, the operation speed is about several msec, which is slower than the excitation LD.

  In FIG. 10, 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 pump light power, as described in the first embodiment, the pump light power may be determined from the relationship between the input light power and the pump light power under a constant gain condition. In the description, it is assumed that the input light power and the pumping light power are proportional to each other under the condition that the gain is constant. 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 a decrease in the number of input wavelengths is detected by the input monitor, control is performed to reduce the pumping light power in proportion to the total number of wavelengths. Although the branching ratio of the variable branching ratio splitter is changed simultaneously with the pumping light power, since the operation of the variable branching ratio splitter is slow, the pumping light to EDFs # 2 to #n once decreases.
Thereafter, the branching ratio of the variable branching ratio splitter is changed, and the pumping light power that should be originally supplied to 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 a time equivalent to the time constant of the branching ratio variable splitter.

  FIG. 11 shows a summary of the above operations with respect to time changes. 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 splitter is slower than the pumping light power, the EDF # 1 to #n. This level variation continues for the time constant of the branching ratio variable splitter. 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. 12 summarizes the contents shown in FIG. 11 while focusing on the relationship between the number of wavelengths in each EDF 11 and the pumping light power. As shown in FIG. 12 (b), the input of each EDF # 1 to #n is detected until the change in the number of wavelengths is detected, the excitation light is adjusted, and the branching ratio setting change of the branching ratio variable splitter is completed. Since errors occur in the number of wavelengths and pumping light power, fluctuations occur in each EDF output.

  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 the EDFs 11 will be described. FIG. 13 shows the relationship between the number of wavelengths and the pumping light power at the timing until the change in the number of wavelengths shown in FIG. 12B is detected, the pumping light is adjusted, and the setting of the branching ratio of the branching ratio variable splitter is completed. The schematic diagram when the control amount of pumping light power is made small and large is shown.

  When the control amount of the excitation light control power shown in FIG. 13A is reduced, the instantaneous level error (Err # 1) of EDF # 1 becomes larger than that in FIG. The level errors (Err # 2 to Err # n) of 2 to #n are small, and the level fluctuation range of 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 in all the EDFs 11. FIG. 14 shows the time change of each EDF 11 in the case of the control of FIG.

  When the control amount of the pumping light power shown in FIG. 13B 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 pumping light power is determined as follows.
The branching ratio of the branching ratio variable splitter is the same as that before the change in the number of wavelengths, and the level error in each EDF 11 is calculated when the pumping light power is changed. 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, 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 zero.

  Specifically, in FIG. 13, 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.13 is also acceptable) ( Err # 2) corresponds to the minimum value (<0). Therefore, in FIG. 13, the control amount of the excitation 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.
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).

  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. Therefore, the control amount of the pumping light power at the moment when the change in the number of wavelengths occurs is determined as shown in FIG. 15 so as to suppress the level fluctuation range, and thereafter, the amount of change in the pumping light power according to the change in the number of wavelengths. The pumping light power is changed with the same time constant as that of the variable splitting ratio splitter. The control flow in this case is shown in FIG. 16, and the operation is shown in FIG.

  The difference from the control flow shown in FIG. 15 is that the step of changing the pumping light power with the same time constant as the branching ratio variable splitter is added at the end so that the pumping light power changes according to the wavelength number changing amount. Otherwise, the control is the same as in FIG. The control amount indicated by ΔP1 in FIG. 17 is the control amount in the last step S107 in FIG. 15 (= second step from the end in FIG. 16), and the control amount indicated by ΔP2 in FIG. 17 is the last step S109 in FIG. Control amount. As a result, the level fluctuation width when the number of wavelengths varies can be suppressed, and the level in the steady state can also be set to the same value as before the change in the number of wavelengths.

  As described above, the present invention simply realizes high-speed gain control of an L-band EDFA, and is useful for the operation of an optical communication system.

11: EDF
12: L-band optical branching unit 13: PD (L-band optical power measuring unit)
14: Excitation light source 15: Excitation light coupling unit (excitation light supply unit)
16: C-band light incident section 16-1: Fiber grating 16-2a: C-band light source 16-2b: C-band light coupling section 16-3: Faraday mirror 17: Excitation light power control section 18: Isolator 19: Variable branching ratio Splitter 51, 66: WDM optical amplifier 52, 64: coupler 53, 65: WSS
54, 63: CDC optical amplifier 55, 62: CDC-less optical switch 56: Receiver 61: Transmitter 81: Faraday mirror 82: Mirror controller 83, 84: Isolator 100: EDFA

Claims (6)

A plurality of amplification optical fibers arranged in parallel and each amplifying an input signal of L-band light;
A plurality of L-band optical branching units that are provided for each of the amplification optical fibers and branch the input signals of the L-band light respectively input to the amplification optical fiber ;
A plurality of L-band optical power measuring units provided for each of the L-band optical branching units, each of which measures the input signal power of the L-band light branched by the L-band optical branching unit ;
An excitation light source that emits excitation light for amplifying the L-band light;
A plurality of pumping light supply units that are provided for each of the amplification optical fibers and supply the pumping light to the amplification optical fiber;
A plurality of C-band light incident portions that are provided for each of the amplification optical fibers and respectively enter the C-band light on the input side of the amplification optical fiber;
Depending on the input signal power of the L-band light measured by said plurality of L-band optical power measuring unit, the pumping light power control unit for power feed-forward control of the excitation light incident on the plurality of amplifying optical fiber When,
The branching ratio is variable, and in accordance with an instruction from the pumping light power control unit, the branching ratio variable optical coupler that supplies the pumping light emitted from the pumping light source to the plurality of pumping light supply units,
Equipped with a,
The pumping light power control unit changes the branching ratio of the variable branching ratio optical coupler based on the input signal power of the L band light measured by the plurality of L band optical power measuring units.
An optical fiber amplifier system. The excitation light power control unit is
When the power of the excitation light required to obtain the same gain for a change in the input signal power of the L band optical began to increase, increased control the power of the excitation light,
2. The optical fiber amplifier according to claim 1, wherein if the required pumping light power does not change even if the input signal power of the L-band light changes, the power of the pumping light is controlled to a constant value. system. The input signal is a WDM signal;
The pumping light power control unit uses each of the pumping light power necessary for amplification of the optical signal having the number of wavelengths of the WDM signal and the pumping light power supplied from the pumping light supply unit to the amplification optical fiber. The output level error in the amplification optical fiber is obtained, and the control amount of the pumping light power is determined so that the midpoint between the maximum value and the minimum value of the output level error in each amplification optical fiber is zero. The optical fiber amplifier system according to claim 1 or 2 . The C-band light incident part is:
The inserted fiber grating or a Faraday mirror optical fiber connected to the input side of the amplifying optical fiber, or,
The inserted AR coating the outgoing end of the excitation light source,
Optical fiber amplifier system according to any one of claims 1 to 3, wherein the ASE C-band generated in the amplification optical fiber, and returning to said amplification optical fiber. A C-band light source for generating C-band light;
The C-band optical incident portion, wherein the output light from the C-band light source, to claim 1, wherein 3 of the be coupled to an optical fiber connected to the input side of the amplifying optical fiber Fiber optic amplifier system. An optical fiber amplification method in an optical fiber amplifier system according to any one of claims 1 to 5,
An L-band optical power measurement procedure in which the plurality of pumping light power controllers respectively measure the input signal power of the L-band light;
The excitation light power control unit, in response to the input signal power was measured at the plurality of L-band optical power measurement section the L-band optical feed the power of the excitation light incident on the plurality of amplifying optical fiber A pump light power control procedure for forward control;
Enter the previous SL excitation light and the C-band light to the plurality of amplifying optical fiber, and amplification procedure for amplifying an input signal of the L-band light input to the amplification optical fiber,
An optical fiber amplification method comprising:

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