JP2009081473A - Wavelength multiplex optical amplifier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wavelength multiplex optical amplifier capable of solving problems of "oscillation" and "output variation due to ASE" in case of abrupt change in the number of input wavelengths. <P>SOLUTION: The wavelength multiplex optical amplifier (3) having a first-stage optical amplification unit (10) and a second-stage optical amplification unit (20), and a common AGC circuit (18) performing AGC control over the first-and second-stage optical amplification units (10, 20) in common is further provided with an exciting light distributing means (30) of applying exciting light to the first-and second-stage optical amplification units (10, 20) at a predetermined distribution ratio. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a WDM optical amplifier that can be used in, for example, an inline amplifier, a preamplifier, or a postamplifier in a wavelength division multiplexing optical communication network.

  In recent years, optical communication networks are required to further improve the correspondence to multimedia. For this reason, the capacity of information transmission by wavelength multiplexing is increasing more and more. For this purpose, the above-described wavelength multiplexing optical amplifier (hereinafter also simply referred to as an optical amplifier) is indispensable and widely used, but further improvements are also required.

  In the present invention, for example, the above-described improvement can be added to an optical amplifier for a metro network whose market is rapidly rising in recent years. The points of improvement are mainly “output fluctuation due to ASE (Amplified Spontaneous Emission)” and “oscillation”.

  As will be described later with reference to the drawings, as a general optical amplifier, a two-stage configuration including a front-stage optical amplifying section and a rear-stage optical amplifying section is widely used, and thereby the wavelength dependence of gain. Is realized.

  In this general two-stage optical amplifier, as shown later in FIG. 1, the front-stage optical amplifying unit individually performs the front-stage AGC control, and the rear-stage optical amplifying section also individually performs the rear-stage AGC control. Yes. Such front-stage / back-stage individual AGC control type optical amplifiers are disclosed in, for example, the following [Patent Document 1] to [Patent Document 3].

  However, such pre-stage / post-stage individual AGC control is not suitable for the above-described optical amplifier for a metro network. This is because such an optical amplifier based on the two-stage individual AGC control is difficult to control at high speed, and cannot follow a rapid change in the number of input wavelengths, for example, 40 waves → 1 wave, which frequently occurs in a metro network. Because.

  Therefore, recently, it has been proposed that, for such an optical amplifier having a two-stage configuration with a sudden change in the number of input wavelengths, the two-stage common AGC control is performed instead of the above-described two-stage individual AGC control. Being offered.

  However, according to the two-stage common AGC control type optical amplifier, although high-speed control is satisfactory, the problems such as “output fluctuation due to ASE” and “oscillation” (described later in detail) occur, and the improvement Will be required.

JP-A-8-248455

JP 2002-368698 A

JP 2003-174421 A

  An object of the present invention is to provide a common AGC-controlled wavelength division multiplexing optical amplifier capable of solving problems such as “output fluctuation due to ASE” and “oscillation”.

  In order to achieve the above object, a wavelength division multiplexing optical amplifier according to the present invention receives a control signal from a common AGC circuit, and at a predetermined distribution ratio to each of the first-stage optical amplifier and the second-stage optical amplifier. Excitation light distribution means for applying excitation light is provided.

  As will be described in detail later, according to the present invention, there is provided a common AGC-type wavelength division multiplexing optical amplifier that does not oscillate even when the number of input wavelengths of signal light changes suddenly and can suppress output fluctuation due to ASE. Can be realized.

It is a figure which shows the basic composition of a general 2 step | paragraph structure optical amplifier. It is a figure for demonstrating the characteristic of EDF (11,21) and LD (12,22) of a front | former stage and a back | latter stage. It is a graph which shows the drive control of front | former stage and back | latter stage LD (12, 22). It is a figure which shows the basic composition of the wavelength division multiplexing optical amplifier to which this invention is applied. It is a figure which shows the basic composition of the wavelength division multiplexing optical amplifier based on this invention. It is a figure which shows the wavelength division multiplexing optical amplifier which concerns on Example 1 of this invention. It is a figure which shows the wavelength division multiplexing optical amplifier which concerns on Example 2 of this invention. It is a figure which shows the wavelength multiplexing optical amplifier which concerns on Example 3 of this invention. It is a figure which shows the wavelength division multiplexing optical amplifier which concerns on Example 4-1 of this invention. It is a figure which shows the wavelength multiplexing optical amplifier which concerns on Example 4-2 of this invention. It is a graph which shows the output fluctuation by ASE graphically. It is a figure which shows the detailed example of the wavelength division multiplexing optical amplifier based on this invention.

  In order to clarify the effects brought about by the present invention, first, a general wavelength division multiplexing optical amplifier will be described with reference to the drawings.

  FIG. 1 is a diagram showing a basic configuration of a general two-stage optical amplifier.

  Basically, as the wavelength multiplexing optical amplifier having the configuration as shown in this figure, for example, the above-mentioned [1] JP-A-8-248455, [2] JP-A-2002-368698, [3] JP-A-2003-174421 It is disclosed in No. etc.

  In FIG. 1, reference numeral 1 indicates a general wavelength division multiplexing optical amplifier. This optical amplifier 1 has a two-stage configuration. In other words, it is composed of the front-stage optical amplification section 10 and the rear-stage optical amplification section 20.

  The front-stage optical amplification unit 10 includes a front-stage rare earth doped fiber 11 (for example, Erbium Doped Fiber: EDF) and a front-stage pumping light source 12 (for example, Laser Diode: LD), and includes a front-stage individual AGC loop.

  This front-stage individual AGC loop has an input-side optical detector (PD) 13, an output-side optical detector (PD) 14, and output signals from the input-side and output-side PDs 13 and 14 as inputs, and the front-stage optical amplification. An AGC circuit 15 that performs AGC control of the unit 10 via the LD 12 is configured.

  Similarly to the above, the post-stage optical amplifying unit 20 includes the post-stage EDF 21 and the post-stage LD 22 and includes a post-stage individual AGC loop.

  This latter-stage individual AGC loop also has an input-side PD 23, an output-side PD 24, and an AGC circuit 25 that performs AGC control of the latter-stage optical amplifying unit 20 through the LD 22 with each output signal from these PDs as input. Consists of

  Further, it is a general configuration that a variable optical attenuator (VOA) 17 is provided between the front-stage and rear-stage optical amplification units 10 and 20.

  As shown in FIG. 1, in general, AGC control is performed in the front-stage and rear-stage optical amplifiers 10 and 20, respectively. By performing such AGC control, the front-stage and rear-stage optical amplification sections 10 are independent of the number of input wavelengths of the signal applied to the input end (IN) side of the front-stage optical amplification section 10 and the input dynamic range. And 20 can be kept constant, and further, the wavelength of the optical output signal transmitted from the output end (OUT) side of the post-stage optical amplifying unit 20 can be flattened by appropriately adjusting the loss in the VOA 17. Can keep sex. The characteristics and operation of the optical amplifier 1 having such a configuration will be described with reference to FIGS.

FIG. 2 is a diagram for explaining the characteristics of the EDF (11, 21) and the LD (12, 22) in the former stage and the latter stage in FIG.
FIG. 3 is a graph showing drive control of the front and rear LDs (12, 22) in FIG. Throughout the drawings, similar components are denoted by the same reference numerals or symbols.

  Reference is first made to FIG. In general, the wavelength division multiplexing optical amplifier 1 employs “forward pumping” as shown in FIG. This is to keep the noise figure NF (Noise Figure) of the optical amplifier 1 low (low NF).

  Since the contribution of the front EDF 11 is particularly large for this reduction in NF, 0.98 μm is generally adopted as the optimum excitation wavelength for realizing the reduction in NF. On the other hand, 1.48 μm is generally adopted as the excitation wavelength of the post-stage EDF 21 in order to optimize the gain efficiency.

  The excitation light of the front-stage LD 12 and the rear-stage LD 22 having the characteristics as described in FIG. 2 is generally driven and controlled as shown in the graph of FIG. In this graph, the horizontal axis indicates the power of the input signal applied to the input terminal IN in FIG. 1, and the vertical axis indicates the pumping light power of the front-stage LD 12 and the rear-stage LD 22.

  As shown in this graph, in general, the pumping light power is increased in the order of forward pumping of the front EDF 11 (LD12) → forward pumping of the rear EDF 21 (LD22).

  In the general wavelength division multiplexing optical amplifier 1 (FIGS. 1 to 3) described above, that is, the front-stage / back-stage individual AGC control type optical amplifier 1, as described above, high-speed control is difficult. For this reason, it has been proposed to use a common AGC-controlled wavelength division multiplexing optical amplifier when high speed control is required, such as the wavelength division multiplexing optical amplifier for a metro network described above. This is shown in FIG.

  FIG. 4 is a diagram showing a basic configuration of a wavelength division multiplexing optical amplifier to which the present invention is applied.

  What should be noted in the optical amplifier 2 shown in the figure is that a common AGC circuit 18 common to the front and rear optical amplifiers 10 and 20 is introduced in place of the front / back individual AGC circuits 15 and 25 in FIG. Is a point. As a result, a high-speed control optical amplifier that can be used for, for example, a metro network can be realized.

  However, since the individual AGC control (FIG. 1) is changed to the common AGC control (FIG. 2), a new problem arises. This is the problem of “output fluctuation due to ASE” and the problem of “oscillation”.

  First, consider the former “output fluctuation due to ASE”. When the pre-stage EDF 11 and the post-stage EDF 21 are excited by the control method shown in FIG. 3 and the common AGC control is performed for the entire optical amplifier as shown in FIG. 4, the maximum number of input wavelengths is changed from 40 waves to 1 wave, for example. Suppose that it suddenly decreased.

  In this case, the gain ratio of the front EDF 11 that is the excitation (LD12) of 0.98 μm is increased, while the gain ratio of the rear EDF 21 that is the excitation (LD22) of 1.48 μm is decreased. Then, the fluctuation due to the sudden decrease in the number of wavelengths with respect to the ASE in the short wavelength band in the signal wavelength band generated from the post-stage EDF 21 eventually appears as a large output fluctuation of the signal light at the output terminal OUT. This phenomenon appears remarkably in the L-band band.

  The output fluctuation of the signal light (OUT) described above must be suppressed due to the desired performance of the optical amplifier 2, but when the suppression of the output fluctuation is to be realized, the latter “oscillation” described above. Cause problems. This will be described in more detail below.

  As a method for realizing the suppression of the output fluctuation, first, it is considered that the former stage EDF 11 is excited from the rear of the former stage EDF 11 (see the LD ′ in the dotted line in FIG. 2), for example, at an excitation wavelength of 1.48 μm, and the former stage EDF 11 is set as bidirectional excitation. In this method, the gain of the front EDF 11 is increased, and the gain of the rear EDF 21 is decreased accordingly.

  However, when the drive control shown in FIG. 3 is performed under such a method, the pumping light power does not change when the input wavelength suddenly decreases, for example, 40 waves → 1 wave as described above. Becomes too big. This excessive gain causes oscillation between the front EDF 11 and peripheral optical components such as an optical isolator. This is the above-mentioned “oscillation” problem.

  Therefore, the present invention proposes wavelength multiplexing optical amplifiers (3,4, 5, 6, 7-1 and 7-2) described in detail below.

  The specific idea of the present invention is that in order to suppress “output fluctuation due to ASE” and prevent “oscillation”, backward excitation (LD ′) for the front EDF 11 and forward excitation (LD ′) for the rear EDF 22 shown in FIG. 22) and at the same time, the excitation ratio of the two is set to a predetermined value in accordance with conditions such as the input level of the input signal. More specifically, this pumping ratio is such that the pumping power of the rear pumping light having such a magnitude that the above-described low NF can be achieved in the preceding EDF 11 is prevented from being generated in the preceding EDF 11. A value that can be given.

  Hereinafter, the present invention will be described in detail with reference to the drawings.

  FIG. 5 is a diagram showing a basic configuration of a wavelength division multiplexing optical amplifier according to the present invention.

  The wavelength division multiplexing optical amplifier 3 shown in this figure is similar to the wavelength division multiplexing optical amplifier 2 shown in FIG. 4. The first stage optical amplification unit 10 and the second stage light are arranged in series with respect to the signal light OS (Optical Signal). This is an optical amplifier having an amplifying unit 20 and a common AGC circuit 18 that performs AGC control by the signal light OS at the input terminal IN and the output terminal OUT of the first and second stage optical amplifying units 10 and 20.

  The feature of the present invention is that the excitation light distribution means 30 is introduced. The pumping light distributing means 30 receives the control signal from the common AGC circuit 18 and pumps the first stage optical amplifying unit 10 and the second stage optical amplifying unit 20 at a predetermined distribution ratio (a: b). Light is applied.

  The basic configuration of the present invention shown in FIG. 5 can be embodied by the following Example 1, Example 2, Example 3, and the like.

  FIG. 6 is a diagram illustrating the wavelength division multiplexing optical amplifier according to the first embodiment of the present invention. Throughout the drawings, the same components are denoted by the same reference numerals or symbols.

  The wavelength division multiplexing optical amplifier 4 according to the first embodiment is characterized in that the pumping light distributing unit 30 is realized using an optical coupler.

  That is, as shown in FIG. 6, the excitation light distribution means 30 in the first embodiment includes a single excitation light source (LD) 31 and the predetermined distribution ratio a: b of the excitation light from the single excitation light source 31 described above. And an optical coupler 32 that is branched and applied to the first-stage optical amplifying unit 10 and the second-stage optical amplifying unit 20. In addition, about the component which attached | subjected the reference numbers 11, 12, 13, 17, 21, and 24, it is as having shown in FIG.

  FIG. 7 is a diagram showing a wavelength division multiplexing optical amplifier according to Embodiment 2 of the present invention.

  The wavelength division multiplexing optical amplifier 5 according to the second embodiment is characterized in that the pumping light distributing unit 30 is realized by using individual pumping light sources and driving units that individually drive these pumping light sources. is there.

  That is, as shown in FIG. 7, the pumping light distribution unit 30 in the second embodiment includes a first pumping light source 33 that pumps the first stage optical amplification unit 10 and a second pumping light source 34 that pumps the second stage optical amplification unit 20. And a drive unit 35 that drives the first and second excitation light sources 33 and 34 to meet the predetermined distribution ratio (a: b) described above.

  FIG. 8 is a diagram illustrating a wavelength division multiplexing optical amplifier according to Embodiment 3 of the present invention.

  The wavelength division multiplexing optical amplifier 6 according to the third embodiment is characterized by further comprising a distribution ratio control means 40 that makes the predetermined distribution ratio (a: b) variable (a ′: b ′). is there. The distribution ratio control means 40 can be applied to any of the first embodiment (FIG. 6) and the second embodiment (FIG. 7), but FIG. 8 shows a case where the distribution ratio control means 40 is applied to the former first embodiment.

As a specific example of the distribution ratio control means 40, FIG. 8 shows a case where the first optical attenuator 41 and the second optical attenuator 42 that make the intensity of the pumping light variable are used.
[Example 4-1]

  Example 4-1 and Example 4-2, which will be described later, are modifications that can be applied to any of Examples 1, 2, and 3 described above. In addition, at least three stages of optical amplifying sections are added, and two of these optical amplifying sections are the first-stage optical amplifying section and the second-stage optical amplifying section described above. .

  FIG. 9 is a diagram illustrating the wavelength division multiplexing optical amplifier 7-1 according to the embodiment 4-1 of the present invention.

  The above-described “further optical amplification unit” refers to the middle stage optical amplification unit 19 in FIG. 9. The optical amplifier 7-1 includes the optical amplifiers 10 ', 19 and 20 having a three-stage configuration in addition to the intermediate optical amplifier 19. Similarly, a configuration with four or more stages may be used, but it is not illustrated.

In the case of FIG. 9, the middle-stage optical amplifying unit 19 functions as the first-stage optical amplifying unit 10 shown in FIGS. The optical amplifying unit 19 includes a middle EDF 11 ′. Further, a variable optical attenuator 17 'similar to the variable optical attenuator (VOA) described above is added.
[Example 4-2]

  Example 4-2 shown in FIG. 10 is a modification of Example 4-1 (FIG. 9). That is, the middle stage optical amplifying unit 19 (10) in FIG. 9 corresponds to a forward pump type and the variable optical attenuator 17 ′ in FIG. 9 is removed.

  The circuit configurations of the various embodiments have been mainly described with reference to the drawings. Specific items of these embodiments will be further described below.

  As is well known, the pumping modes of the rare earth doped fiber (11, 11'21) include forward pumping, back pumping and bi-directional pumping. As a preferable pumping mode of the present invention, Example 1 (FIG. 6) is used. ) And Example 2 (FIG. 7), the first-stage optical amplifying unit 10 is added with backward pumping from the pumping light distributing unit 30 to be bi-directionally pumped. This is the forward pumping for the second stage optical amplification unit 20.

  In this case, a wavelength of 1.48 μm is selected as the backward pumping light (a) and forward pumping light (b) from the pumping light distributing means 30, while the wavelength of the forward pumping light (12) to the fiber 11 is selected. It is preferable to select 0.98 μm. Therefore, the bidirectional excitation described above is excitation with a wavelength of 0.98 μm and a wavelength of 1.48 μm.

  Here, the “predetermined distribution ratio” (a: b) of the backward pumping light (a) and the forward pumping light (b) has already been described in detail, but is defined again as follows.

  (I) The predetermined distribution ratio (a: b) is a value capable of obtaining a gain increased to the vicinity of the upper limit at which oscillation occurs in the first stage optical amplifying unit 10 in order to obtain a low noise figure (NF). .

  (Ii) Further, the predetermined distribution ratio (a: b) is a value that can suppress the output fluctuation at the output terminal OUT due to ASE when the number of input wavelengths of the signal light OS received at the input terminal IN rapidly decreases. It is. This will be discussed in more detail with reference to the figure.

  FIG. 11 is a graph illustrating the output fluctuation due to ASE.

  In the graphs (A) and (B) of this figure, the wavelength of the input light is taken on the horizontal axis, and the power of the light is taken on the vertical axis.

  A graph (A) represents a case where 40 waves (1, 2, 3,... 39, 40) are processed as the signal light OS. Here, it is assumed that the signal light OS suddenly decreases from 40 waves to 1 wave (for example, 20). This is graph (B).

  On the other hand, looking at the ASE in the graphs (A) and (B), the amount of ASE substantially corresponds to the excitation light, so that the excitation light is almost constant even if there is a large fluctuation (40 → 1) in the signal light. In order to maintain power, this ASE does not change between (A) and (B).

  Then, the amount of ASE with respect to the signal light OS greatly increases from (A) to (B), and this appears as the output fluctuation.

  Thus, the predetermined distribution ratio (a: b) needs to satisfy at least one of the above values (i) and (ii). Preferably, both of the above (i) and (ii) are satisfied. It is a satisfactory value. In the detailed example of the present invention described later, a: b = 1: 20.

  In the above description, a rare earth doped fiber (EDF) is taken as an example of an optical amplifying medium constituting each amplifying section (10, 19, 20), but the present invention is not limited to this, and an optical waveguide may be used.

  Finally, a detailed example of the present invention is shown in the figure.

  FIG. 12 is a diagram showing a detailed example of a wavelength division multiplexing optical amplifier according to the present invention.

  The wavelength division multiplexing optical amplifier 8 of this figure is based on the configuration of FIG. 6, and the components in FIG. 12 corresponding to the components shown in FIG. 6 are denoted by the same reference numerals and symbols.

  CN at the left end of FIG. 12 is an optical connector from which signal light is input. The input signal light is branched into two by the beam splitter BS, and applied to the isolator ISO and the input side photodetector (PD) 13 with BPF.

  The signal light exiting the isolator ISO is input to the optical amplifying unit 10 via the multiplexer / demultiplexer WDM. Excitation light from the pre-stage excitation light source (LD) 12 is applied to the optical amplification unit 10 via this WDM. The LD 12 is provided with a wavelength lock unit LC.

  The signal light from the optical amplifying unit 10 reaches the variable optical attenuator (VOA) 17 via the coupler CP. The above-described branched pumping light (a) from the optical coupler 32 performs the above-described backward pumping on the amplifier 10 via this coupler CP.

  The signal light that has passed through the coupler CP reaches the VOA 17 via the gain equalizer GEQ. Furthermore, the optical signal reaches the isolator ISO and the coupler CP via the tap PD and is input to the optical amplifying unit 20. The above-described branched pumping light (b) from the optical coupler 32 performs the forward pumping described above on the optical amplifying unit 20 through the coupler CP. The optical amplifying unit 20 in the figure is backward pumped by LD ′ through the coupler CP on the output side, but is not related to the present invention.

  The output signal light from the optical amplifying unit 20 is output from the output end (OUT) side optical connector CN (output port) via the beam splitter BS, and is output to the beam splitter BS ′ on the other side.

  The signal light that has passed through the beam splitter BS ′ is guided on the one hand to the monitoring optical connector CN ′, and on the other hand to the aforementioned output-side photodetector (PD) 24.

  Preferred embodiments of the present invention described above are as follows.

(Supplementary note 1) a first stage optical amplification unit and a second stage optical amplification unit arranged in series with respect to the signal light;
A common AGC circuit that performs AGC control by each signal light at the input end and the output end of the first and second stage optical amplifying units;
Pumping light distribution means for receiving a control signal from the common AGC circuit and applying pumping light to the first stage optical amplification section and the second stage optical amplification section at a predetermined distribution ratio;
A wavelength division multiplexing optical amplifier.
(Additional remark 2) The said excitation light distribution means branches the excitation light from this single excitation light source and this single excitation light source by the said predetermined distribution ratio, and the said 1st stage optical amplification part and 2nd stage light The wavelength division multiplexing optical amplifier according to appendix 1, comprising an optical coupler applied to the amplifying unit.

  (Additional remark 3) The said excitation light distribution means is a 1st excitation light source which excites the said 1st stage optical amplification part, a 2nd excitation light source which excites the said 2nd stage optical amplification part, and this 1st and 2nd excitation The wavelength division multiplexing optical amplifier according to claim 1, further comprising: a drive unit that drives a light source so as to meet the predetermined distribution ratio.

  (Supplementary Note 4) The first stage optical amplifying unit is added with backward pumping from the pumping light distributing unit to provide bidirectional pumping, and the pumping light distributing unit forward pumps the second stage optical amplifying unit. The wavelength multiplexing optical amplifier according to appendix 1.

  (Supplementary Note 5) The wavelength according to Supplementary Note 1, wherein the predetermined distribution ratio is a value capable of obtaining a gain increased to near an upper limit at which oscillation occurs in the first-stage optical amplification unit so as to have a low noise figure. Multiplex optical amplifier.

  (Additional remark 6) The said predetermined distribution ratio is set as the value which can suppress the output fluctuation in the said output end by ASE, when the number of input wavelengths of the signal light received at the said input end falls rapidly. The wavelength division multiplexing optical amplifier described.

  (Supplementary note 7) An additional optical amplification unit arranged in series with respect to the signal light is added to provide at least three stages of optical amplification units, and two of these optical amplification units are connected to the first stage optical amplification unit and 2. The wavelength division multiplexing optical amplifier according to appendix 1, wherein the second stage optical amplification unit is used.

  (Supplementary note 8) The wavelength division multiplexing optical amplifier according to supplementary note 1, further comprising distribution ratio control means for making the predetermined distribution ratio variable.

  (Supplementary note 9) The wavelength division multiplexing optical amplifier according to supplementary note 8, wherein the distribution ratio control means is an optical attenuator that makes the intensity of the excitation light variable.

  (Supplementary note 10) The wavelength division multiplexing optical amplifier according to supplementary note 1 or 7, wherein the optical amplification medium constituting each of the optical amplification units is a rare earth doped fiber or an optical waveguide.

  The present invention can be applied to general wavelength division multiplexing optical amplifiers that are required to follow and amplify the input light accompanied by frequent fluctuations in the number of input wavelengths.

3, 4, 5, 6, 7-1, 7-2 Wavelength division multiplexing optical amplifier 10 Pre-stage optical amplifier 11 Pre-stage rare earth doped fiber (pre-stage EDF)
11 'Middle stage rare earth doped fiber (middle stage EDF)
12 Front-stage excitation light source (front-stage LD)
13 Input side photodetector (input side PD)
17, 17 'Variable attenuator (VOA)
18 AGC circuit 19 Middle optical amplifier 20 Rear optical amplifier 21 Rear rare earth doped fiber (second EDF)
24 Output side photo detector (Output side PD)
DESCRIPTION OF SYMBOLS 30 Excitation light distribution means 31 Excitation light source 32 Optical coupler 33 1st excitation light source 34 2nd excitation light source 35 Drive part 40 Distribution ratio control means 41 1st optical attenuator 42 2nd optical attenuator

Claims (1)

A first stage optical amplifying unit and a second stage optical amplifying unit arranged in series with respect to the signal light;
A common AGC circuit that performs AGC control by each signal light at the input end and the output end of the first and second stage optical amplifying units;
Pumping light distribution means for receiving a control signal from the common AGC circuit and applying pumping light to the first stage optical amplification unit and the second stage optical amplification unit at a predetermined distribution ratio;
A wavelength division multiplexing optical amplifier.

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