JP4026458B2 - Gain equalizer and WDM optical repeater system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gain equalization apparatus that equalizes gain characteristics of wavelength division multiplexing (WDM) signals, and a WDM optical repeater system that uses the gain equalization apparatus.
[0002]
[Prior art]
Conventionally, in a WDM optical repeater system, the gain characteristic differs from transmission line to transmission line or transmission section due to characteristic variation at the time of manufacturing a repeater or characteristic variation at the time of manufacturing a cable. In particular, in a submarine optical cable system, the gain characteristics of the system fluctuate due to changes in characteristics of repeaters and cables due to temperature changes at the bottom of the sea and changes in characteristics due to aging. In order to cope with this, the fluctuations in the gain characteristics have been dealt with by managing these characteristics to be uniform or by using a fixed gain equalizer with a design that allows for a system margin. In order to cope with this, there is a gain equalizer that controls a light source that excites the optical amplifier so that the gain flatness of the output WDM signal light does not change. (For example, see Patent Document 1)
[Patent Document 1]
JP 2001-268014 A (page 3-4, FIG. 1)
[0003]
[Problems to be solved by the invention]
In such a method of dealing with fluctuations in gain characteristics using a fixed gain equalizer with a system margin in mind, it is difficult to design a transmission line because the margin is sufficient, and the economics of the transmission line Has the problem of lacking.
[0004]
Further, the gain equalizer disclosed in Japanese Patent Laid-Open No. 2001-268014 is for monitoring the two wavelengths on the output side of the optical amplifier to obtain a gain slope, and performing feedback control so as to eliminate the gain slope. There is a problem that further simplification of control is desired.
[0005]
An object of the present invention is to provide a technique for changing and optimizing the gain characteristic of a WDM optical repeater system by simple automatic control in order to solve such a conventional problem.
[0006]
[Means for Solving the Problems]
A gain equalization apparatus for a WDM optical repeater system according to the present invention is a gain equalizer for a WDM optical repeater system that optically amplifies a WDM optical signal using an optical amplifier and relays it.
A gain tilt amount detecting means for detecting a gain tilt amount from an input WDM optical signal;
Variable gain equalizing means for changing the input WDM optical signal to a WDM optical signal having the same value as the gain tilt amount detected by the gain tilt amount detecting means and having an inverted gain tilt amount of the opposite sign. And
[0007]
A gain equalization apparatus for a WDM optical repeater system according to the present invention is a gain equalization apparatus for a WDM optical repeater system that optically amplifies a WDM optical signal using an optical amplifier and relays it.
A gain tilt amount detecting means for detecting a gain tilt amount from an input WDM optical signal;
A gain tilt change amount detecting means for detecting a gain tilt change amount of an optical amplifier connected to a subsequent stage from the input WDM optical signal;
The input WDM optical signal has the same value as the gain tilt amount detected by the gain tilt amount detecting means and the reverse gain tilt amount having the opposite sign and the same value as the gain tilt change amount detected by the gain tilt change amount detecting means. In addition, it has variable gain equalization means for changing to a WDM optical signal having a gain tilt amount that is the sum of the canceling gain tilt change amount having the opposite sign.
[0008]
Furthermore, a gain equalization apparatus for a WDM optical repeater system according to the present invention is a gain equalization apparatus for a WDM optical repeater system that optically amplifies a WDM optical signal with an optical amplifier and relays it.
Average optical power detection means for detecting average optical power per wavelength from an input WDM optical signal multiplexed with a plurality of wavelengths input from an optical transmission line;
Monitoring wavelength optical power detection means for detecting a monitoring wavelength optical power of light having a predetermined monitoring wavelength from the input WDM optical signal;
The difference between the monitoring wavelength optical power detected by the monitoring wavelength optical power detection means and the average optical power detected by the average optical power detection means is taken, and the gain tilt amount of the input WDM optical signal is detected from this difference. Means for detecting the amount of gain tilt;
The difference between the average optical power detected by the average optical power detector and the standard average optical power that gives the standard gain tilt amount of the optical amplifier, and the gain tilt change amount that is the change amount from the standard gain tilt amount of the optical amplifier. An optical amplifier gain tilt change amount table indicating the relationship is stored, and the difference between the average optical power and the standard average optical power is obtained, and based on this difference, the optical amplifier is based on the optical amplifier gain tilt change amount table. Gain tilt change amount detecting means for detecting the gain tilt change amount of
The input WDM optical signal has the same value as the gain tilt amount detected by the gain tilt amount detecting means and the reverse gain tilt amount having the opposite sign and the same value as the gain tilt change amount detected by the gain tilt change amount detecting means. In addition, it has variable gain equalization means for changing to a WDM optical signal having a gain tilt amount that is the sum of the canceling gain tilt change amount having the opposite sign.
[0009]
A gain equalization apparatus for a WDM optical repeater system according to the present invention is a gain equalizer for a WDM optical repeater system that optically amplifies a WDM optical signal using an optical amplifier and relays the signal using an optical transmission line.
With a variable gain equalizer,
A first optical branching coupler for branching a monitor WDM optical signal from an input WDM optical signal multiplexed with a plurality of wavelengths input from an optical transmission line and sending the input WDM optical signal to the variable gain equalizer;
A second optical branching coupler for branching the monitor WDM optical signal from the first optical branching coupler into two;
A first photodiode that receives one of the monitor WDM optical signals branched into two by the second optical branching coupler, converts the monitor WDM optical signal into an electrical signal, and obtains the total optical power of all of a plurality of wavelengths; An average optical power detector having an average optical power calculator that calculates the average optical power by dividing the total optical power from the photodiode by the number of wavelengths;
The other one of the monitor WDM optical signals branched by the second optical branching coupler is received, and only the light having a predetermined monitoring wavelength is selected from the light of a plurality of wavelengths included in the monitor WDM optical signal. Monitoring wavelength light having a wavelength filter that transmits, and a second photodiode that receives the monitoring wavelength light selected and transmitted by the wavelength filter and converts the monitoring wavelength light into an electrical signal to obtain the monitoring wavelength light power A power detector;
The difference between the monitoring wavelength optical power detected by the monitoring wavelength optical power detection unit and the average optical power detected by the average optical power detection unit is taken, and the gain tilt amount of the input WDM optical signal is detected from this difference. A gain tilt amount detection unit;
The difference between the average optical power detected by the average optical power detector and the standard average optical power that gives the standard gain tilt amount of the optical amplifier connected in the subsequent stage is taken, and from this difference, the standard gain of this optical amplifier is determined. A gain inclination change amount detection unit for detecting a gain inclination change amount that is a change amount from the inclination amount;
The variable gain equalizer has an inverting gain tilt amount equal to a gain tilt amount detected by the gain tilt amount detecting unit and having an opposite sign to the input WDM optical signal from the first optical branch coupler and the gain. Change to a WDM optical signal having a gain tilt amount equal to the gain tilt change amount detected by the tilt change amount detecting unit and the sum of the offset gain tilt change amount having the opposite sign, and connect this WDM optical signal to the subsequent stage Output to an optical amplifier.
[0010]
Further, the gain equalization apparatus of the WDM optical repeater system according to the present invention is a gain equalization apparatus of a WDM optical repeater system that optically amplifies a WDM optical signal by an optical amplifier and relays it by an optical transmission line,
With a variable gain equalizer,
A first optical branching coupler for branching a monitor WDM optical signal from an input WDM optical signal multiplexed with a plurality of wavelengths input from an optical transmission line and sending the input WDM optical signal to the variable gain equalizer;
A second optical branching coupler for branching the monitor WDM optical signal from the first optical branching coupler into two;
A first photodiode that receives one of the monitor WDM optical signals branched into two by the second optical branching coupler, converts the monitor WDM optical signal into an electrical signal, and obtains the total optical power of all of a plurality of wavelengths; An average optical power detector having an average optical power calculator that calculates the average optical power by dividing the total optical power from the photodiode by the number of wavelengths;
The other one of the monitor WDM optical signals branched by the second optical branching coupler is received, and only the light having a predetermined monitoring wavelength is selected from the light of a plurality of wavelengths included in the monitor WDM optical signal. Monitoring wavelength light having a wavelength filter that transmits, and a second photodiode that receives the monitoring wavelength light selected and transmitted by the wavelength filter and converts the monitoring wavelength light into an electrical signal to obtain the monitoring wavelength light power A power detector;
The difference between the monitoring wavelength optical power detected by the monitoring wavelength optical power detection unit and the average optical power detected by the average optical power detection unit is taken, and the gain tilt amount of the input WDM optical signal is detected from this difference. A gain tilt amount detection unit;
The difference between the average optical power detected by the average optical power detection unit and the standard optical average power that gives the standard gain tilt amount of the optical amplifier connected in the subsequent stage is taken, and from this difference, the standard gain of the optical amplifier is determined. A gain tilt change amount detection unit for detecting a gain tilt change amount that is a change amount from the tilt amount;
The gain tilt amount detected by the gain tilt amount detection unit is multiplied by an inversion coefficient -2, the gain tilt change amount detected by the gain tilt change amount detection unit is multiplied by an offset coefficient -1, and both are added. And an equalizer inclination amount determination unit for determining an equalizer inclination amount,
The variable gain equalizer changes the attenuation amount for each wavelength so as to obtain an equalizer inclination amount determined by the equalizer inclination amount determination unit, thereby providing an input from the first optical branching coupler. The WDM optical signal has the same value as the gain tilt amount detected by the gain tilt amount detecting unit and the same value as the inverted gain tilt amount having the opposite sign and the gain tilt change amount detected by the gain tilt change amount detecting unit. The WDM optical signal is changed to a WDM optical signal having a gain tilt amount that is the sum of the canceling gain tilt change amount having the opposite sign, and the WDM optical signal is output to an optical amplifier connected in a subsequent stage.
[0011]
Further, in the gain equalization apparatus for a WDM optical repeater system according to the present invention, the gain tilt change amount detection unit provides a standard average that gives an average optical power detected by the average optical power detection unit and a standard gain tilt amount of the optical amplifier. An optical amplifier gain tilt change amount table indicating a relationship between a difference between the optical power and a gain tilt change amount that is a change amount from the standard gain tilt amount of the optical amplifier is stored, and the average optical power and the standard average are stored. It is characterized in that a difference from the optical power is taken, and from this difference, the gain inclination change amount of the optical amplifier is detected based on the optical amplifier gain inclination change amount table.
[0012]
Furthermore, the gain equalization apparatus of the WDM optical repeater system according to the present invention is characterized in that the wavelength filter is a transmissive wavelength selective grating.
[0013]
The WDM optical repeater system according to the present invention is a WDM optical repeater system configured by connecting an input optical transmission line, a gain equalization device, an optical amplifier, and an output optical transmission line in cascade,
The gain equalization device comprises:
With a variable gain equalizer,
A first optical branching coupler for branching a monitor WDM optical signal from an input WDM optical signal multiplexed with a plurality of wavelengths input from an input optical transmission line and sending the input WDM optical signal to the variable gain equalizer;
A second optical branching coupler for branching the monitor WDM optical signal from the first optical branching coupler into two;
A first photodiode that receives one of the monitor WDM optical signals branched into two by the second optical branching coupler, converts the monitor WDM optical signal into an electrical signal, and obtains the total optical power of all of a plurality of wavelengths; An average optical power detector having an average optical power calculator that calculates the average optical power by dividing the total optical power from the photodiode by the number of wavelengths;
The other one of the monitor WDM optical signals branched by the second optical branching coupler is received, and only the light having a predetermined monitoring wavelength is selected from the light of a plurality of wavelengths included in the monitor WDM optical signal. Monitoring wavelength light having a wavelength filter that transmits, and a second photodiode that receives the monitoring wavelength light selected and transmitted by the wavelength filter and converts the monitoring wavelength light into an electrical signal to obtain the monitoring wavelength light power A power detector;
The difference between the monitoring wavelength optical power detected by the monitoring wavelength optical power detection unit and the average optical power detected by the average optical power detection unit is taken, and the gain tilt amount of the input WDM optical signal is detected from this difference. A gain tilt amount detection unit;
The difference between the average optical power detected by the average optical power detector and the standard average optical power giving the standard gain tilt amount of the optical amplifier connected in the subsequent stage, and the amount of change from the standard gain tilt amount of the optical amplifier An optical amplifier gain inclination change amount table showing a relationship with a certain gain inclination change amount is stored, and a difference between the average optical power and the standard average optical power is obtained, and from this difference, the optical amplifier gain inclination change is obtained. A gain tilt change amount detecting unit for detecting a gain tilt change amount of the optical amplifier based on a quantity table;
The gain tilt amount detected by the gain tilt amount detection unit is multiplied by an inversion coefficient -2, the gain tilt change amount detected by the gain tilt change amount detection unit is multiplied by an offset coefficient -1, and both are added. And an equalizer inclination amount determination unit for determining an equalizer inclination amount,
The variable gain equalizer changes the attenuation amount for each wavelength so as to obtain an equalizer inclination amount determined by the equalizer inclination amount determination unit, thereby providing an input from the first optical branching coupler. The WDM optical signal has the same value as the gain tilt amount detected by the gain tilt amount detecting unit and the same value as the inverted gain tilt amount having the opposite sign and the gain tilt change amount detected by the gain tilt change amount detecting unit. Change to a WDM optical signal having a gain tilt amount that is the sum of the offset gain tilt change amount having the opposite sign, and send this WDM optical signal to the optical amplifier connected to the subsequent stage,
The optical amplifier receives a WDM optical signal whose gain tilt amount has been changed from the gain equalizer, amplifies the WDM optical signal, and outputs the amplified WDM optical signal to an output transmission line.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described in detail with reference to the drawings.
[0015]
FIG. 1 is a block diagram showing the configuration of an embodiment of a gain equalization apparatus according to the present invention and a WDM optical repeater system using the gain equalization apparatus.
[0016]
Referring to FIG. 1, a WDM optical repeater system according to an embodiment of the present invention includes an optical transmission line 200, and a wavelength-multiplexed optical signal in which wavelengths λ1,. (Hereinafter referred to as WDM optical signal), gain equalization apparatus 1 for gain equalization and output of the WDM optical signal, optical transmission line 201 for transmitting the WDM optical signal from gain equalization apparatus 1, and optical transmission line 201 The optical amplifier 2 that amplifies and outputs the WDM optical signal from the optical amplifier 2 and the optical transmission line 202 that transmits the WDM optical signal from the optical amplifier 2 are provided.
[0017]
The gain equalizing apparatus 1 includes a first optical branching coupler 10, a second optical branching coupler 20, an average optical power detection unit 30, a monitoring wavelength optical power detection unit 40, a tilt amount detection unit 50, and a tilt change amount. The detection unit 60, the comparison circuit 70, the gate 80, the equalizer tilt amount determination unit 90, the control circuit 100, and the variable gain equalizer 110 are configured.
[0018]
The first optical branching coupler 10 branches and monitors a part of the WDM optical signal when the WDM optical signal in which the wavelengths λ1 to λn of n wavelengths are multiplexed is input from the optical transmission line 200. While being sent to the second optical branching coupler 20 as a WDM optical signal, most of the WDM optical signal is sent to the variable gain equalizer 110.
[0019]
The second optical branching coupler 20 splits the monitor WDM optical signal from the first optical branching coupler 10 into two branches, sends one of the two split monitor WDM optical signals to the average optical power detection unit 30, and sends the other to the monitoring wavelength. This is sent to the optical power detector 40.
[0020]
The average optical power detection unit 30 includes a first photodiode 31 and an average optical power calculation unit 32.
[0021]
The first photodiode 31 receives one of the monitor WDM optical signals branched into two by the second optical branching coupler 20, converts the monitor WDM optical signal into an electric signal, and has wavelengths λ1,. The total optical power value obtained by combining the respective optical power values is obtained, and this total optical power value is sent to the average optical power calculation unit 32.
[0022]
The average optical power calculation unit 32 obtains an average optical power value Pav by dividing the total optical power value from the first photodiode 31 by the number of wavelengths n, and the average optical power value Pav is changed between the inclination amount detection unit 50 and the inclination change. This is sent to the quantity detection unit 60 and the comparison circuit 70.
[0023]
The monitoring wavelength light power detection unit 40 includes a wavelength filter 41 and a second photodiode 42.
[0024]
The wavelength filter 41 receives the other of the monitor WDM optical signals branched into two by the second optical branching coupler 20, and is determined in advance from light of wavelengths λ1 to λn included in the monitor WDM optical signal. Only the light having the monitoring wavelength λs is selected and transmitted and sent to the second photodiode 42. The wavelength filter 41 is, for example, a transmissive wavelength selection grating.
[0025]
The second photodiode 42 receives the light of the monitoring wavelength λs selected by the wavelength filter 41, converts the light of the monitoring wavelength λs into an electrical signal, and outputs the optical power value Ps of the monitoring wavelength λs (hereinafter, the monitoring wavelength optical power). The monitoring wavelength light power value Ps is sent to the tilt amount detection unit 50.
[0026]
The tilt amount detection unit 50 includes a first difference circuit 51 and a tilt amount calculation unit 52.
[0027]
The first difference circuit 51 of the inclination amount detection unit 50 calculates the difference between the monitoring wavelength light power value Ps from the monitoring wavelength light power detection unit 40 and the average light power value Pav from the average light power detection unit 30 to calculate the first difference circuit 51. The difference value ΔPsav (= Ps−Pav) is obtained, and the first difference value ΔPsav is sent to the tilt amount calculation unit 52.
[0028]
The tilt amount calculation unit 52 calculates the gain tilt amount KI with respect to the wavelength of the WDM optical signal based on the first difference value ΔPsav from the first difference circuit 51, and this gain tilt amount KI is used as the equalizer tilt amount determination unit 90. Send to.
[0029]
The inclination change amount detection unit 60 includes a second difference circuit 61 and an inclination change amount calculation unit 62.
The second difference circuit 61 of the inclination change amount detection unit 60 calculates a difference between the average optical power value Pav from the average optical power detection unit 30 and a predetermined standard average optical power value Pr for reference. A difference value ΔPavr (= Pav−Pr) is obtained, and this second difference value ΔPavr is sent to the inclination change amount calculation unit 62. Here, the standard average optical power value Pr is a reference standard for the average optical power value Pav of the WDM optical signal input to the optical amplifier 2.
[0030]
The inclination change amount calculation unit 62 stores an optical amplifier gain inclination change amount table to be described later. When receiving the second difference value ΔPavr from the second difference circuit 61, the inclination change amount calculating unit 62 refers to the optical amplifier gain inclination change amount table. Thus, the optical amplifier gain tilt change amount Δkr is obtained, and this optical amplifier gain tilt change amount Δkr is sent to the gate 80.
[0031]
The comparison circuit 70 compares the average optical power value Pav from the average optical power detection unit 30 with the standard average optical power value Pr, and generates an open signal for opening the gate 80 when the two do not coincide with each other. At the same time, when the two match, a close signal for closing the gate 80 is generated and sent to the gate 80.
[0032]
The gate 80 opens the gate according to the open signal from the comparison circuit 70, and sends the optical amplifier gain tilt change amount Δkr from the tilt change amount calculation unit 62 to the equalizer tilt amount determination unit 90. Further, the gate 80 is closed by the closing signal from the comparison circuit 70, and the input to the equalizer inclination amount determination unit 90 from the inclination change amount calculation unit 62 is prohibited.
[0033]
The equalizer tilt amount determination unit 90 receives only the gain tilt amount KI from the tilt amount calculation unit 51 when both the average optical power value Pav and the standard average optical power value Pr match, and this gain tilt amount KI. From this, the equalizer loss inclination amount KE set in the variable gain equalizer 110 is obtained, and the equalizer loss inclination amount KE is sent to the control circuit 100, and the average optical power value Pav and the standard average optical power value Pr. Are received, the gain tilt amount KI from the tilt amount calculation unit 51 and the optical amplifier gain tilt change amount Δkr from the tilt change amount calculation unit 62 are received, and the gain tilt amount KI and the optical amplifier gain tilt change amount Δkr are received. Thus, the equalizer loss slope KE set in the variable gain equalizer 110 is obtained, and this equalizer loss slope KE is sent to the control circuit 100.
[0034]
The control circuit 100 sends a control signal for controlling the variable gain equalizer 110 to the variable gain equalizer 110 based on the equalizer loss inclination amount KE from the equalizer inclination amount determining unit 90.
[0035]
The variable gain equalizer 110 varies the optical attenuation amount for each wavelength of the WDM optical signal input from the first optical branching coupler 10 based on the control signal from the control circuit 100, and changes the loss slope characteristic with respect to the wavelength. . Then, the variable gain equalizer 110 sends the WDM optical signal whose loss slope characteristic is changed to the optical amplifier 2.
[0036]
The optical amplifier 2 amplifies the WDM optical signal, amplifies the WDM optical signal whose loss slope characteristic has been changed by the variable gain equalizer 110, and transmits the amplified WDM optical signal to the transmission path 202. The optical amplifier 2 is composed of, for example, a rare earth-doped optical fiber amplifier. As shown in FIG. 4A, this optical amplifier has a gain tilt characteristic that depends on the average optical power value Pav of the input WDM optical signal. That is, when the average optical power value Pav changes from the standard average optical power value Pr by ΔPavr, the gain inclination amount KA of the optical amplifier changes from kr to kr + Δkr. Here, kr is a standard gain tilt amount of the optical amplifier when a WDM optical signal having a standard average optical power value Pr is input to the optical amplifier, and Δkr is a change amount of the gain tilt amount of the amplifier (hereinafter referred to as gain tilt). Change amount).
FIG. 4B is a diagram illustrating the optical amplifier gain tilt change characteristic. The gain tilt change amount Δkr of the amplifier and the second difference value ΔPavr (which is the difference between the standard average optical power value Pr and the average optical power value Pav). = Pav-Pr). The optical amplifier gain inclination change amount table of the inclination change amount calculation unit 62 is a table of the optical amplifier gain inclination change characteristics.
[0037]
Next, the operation of the embodiment of the present invention will be described in detail with reference to the drawings.
[0038]
First, the WDM optical signal input to the gain equalization apparatus 1 and the monitoring wavelength λs will be described.
[0039]
For convenience of explanation, it is assumed that the input WDM optical signal is an optical signal in which the wavelengths λ1,..., Λn of n wavelengths are multiplexed, and the wavelengths increase in the order of the subscripts of the wavelengths λ1,. The monitoring wavelength λs may be any of the wavelengths λ1 to λn, but is set in advance to be the wavelength λn here. Therefore, the bandwidth of the filter 41 is set so as to pass only the monitoring wavelength λs = λn.
[0040]
Next, the operation will be described with reference to FIG. 2 and FIG.
[0041]
FIG. 2 is a diagram for explaining the operation, and FIG. 3 is a diagram showing the inclination characteristics of each part.
[0042]
The operation will be described separately for the case where the average optical power value Pav of the WDM optical signal matches the standard average optical power value Pr and the case where they do not match.
[0043]
<When Average Optical Power Value Pav and Standard Average Optical Power Value Pr>
A WDM optical signal in which the wavelengths λ1 to λn are multiplexed is input to the gain equalization apparatus 1 as indicated by the characteristic (1) -1 in FIG. The average optical power value Pav of the WDM optical signal matches the standard average optical power value Pr.
[0044]
When this WDM optical signal is input, the first optical branching coupler 10 branches a part of the WDM optical signal and sends it to the second optical branching coupler 20 as a monitor WDM optical signal. Part to the variable gain equalizer 110.
[0045]
The second optical branching coupler 20 splits the monitor WDM optical signal from the first optical branching coupler 10 into two branches, sends one of the two split monitor WDM optical signals to the average optical power detection unit 30, and sends the other to the monitoring wavelength. This is sent to the optical power detector 40.
[0046]
The first photodiode 31 of the average optical power detection unit 30 receives one of the monitor WDM optical signals branched by the second optical branching coupler 20, converts the monitor WDM optical signal into an electrical signal, and has a wavelength number n. The total optical power values obtained by combining the optical power values of the wavelengths λ1 to λ1n are obtained, and the total optical power values are sent to the average optical power calculation unit 32.
[0047]
The average optical power calculation unit 32 obtains an average optical power value Pav by dividing the total optical power value from the first photodiode 31 by the number of wavelengths n, and the average optical power value Pav is changed between the inclination amount detection unit 50 and the inclination change. This is sent to the quantity detection unit 60 and the comparison circuit 70.
[0048]
On the other hand, the wavelength filter 41 of the monitoring wavelength optical power detector 40 receives the other of the monitor WDM optical signals branched into two by the second optical branching coupler 20, and receives the wavelengths λ1,..., Λn included in the monitor WDM optical signal. The light having the wavelength λn, that is, the light having the monitoring wavelength λs = λn is selected and transmitted to the second photodiode 42.
[0049]
The second photodiode 42 receives the light of the monitoring wavelength λs = λn selected by the wavelength filter 41, converts the light of the monitoring wavelength λs into an electric signal, and obtains the monitoring wavelength light power value Ps of the monitoring wavelength λs, The monitoring wavelength light power value Ps is sent to the tilt amount detection unit 50.
[0050]
The first difference circuit 51 of the inclination amount detection unit 50 calculates the difference between the monitoring wavelength light power value Ps from the monitoring wavelength light power detection unit 40 and the average light power value Pav from the average light power detection unit 30 to calculate the first difference circuit 51. The difference value ΔPsav (= Ps−Pav) is obtained, and the first difference value ΔPsav is sent to the tilt amount calculation unit 52.
[0051]
The tilt amount calculation unit 52 uses the first difference value ΔPsav from the first difference circuit 50 to calculate the gain tilt amount KI = k with respect to the wavelength of the WDM optical signal, and this gain tilt amount KI = k is an equalizer. This is sent to the tilt amount determination unit 90. Here, the tilt amount calculation unit 52 calculates an accurate gain tilt amount when the gain wavelength characteristic of the WDM optical signal changes linearly as the wavelength increases, and on the other hand, the WDM optical signal When the gain wavelength characteristic changes approximately linearly with the increase in wavelength, the approximate gain tilt amount is calculated.
[0052]
The comparison circuit 70 compares the average optical power value Pav from the average optical power detection unit 30 with the standard average optical power value Pr. As a result of the comparison, the two match here, so a close signal for closing the gate 80 is generated and sent to the gate 80.
[0053]
The gate 80 is closed by the closing signal from the comparison circuit 70, and the input to the equalizer inclination amount determination unit 90 from the inclination change amount calculation unit 62 is prohibited.
[0054]
Since there is no input from the inclination change amount calculation unit 62, the equalizer inclination amount determination unit 90 receives only the gain inclination amount KI = k from the inclination amount calculation unit 52, and the gain inclination amount KI = k is set in advance. By multiplying the determined slope inversion coefficient C = −2, an equalizer loss slope amount KE = −2 × k set in the variable gain equalizer 110 is obtained, and this equalizer loss slope amount KE = −2. Send xk to the control circuit 100.
[0055]
The control circuit 100 receives the equalizer loss inclination amount KE = −2 × k from the equalizer inclination amount determination unit 90, and the variable gain equalizer 110 has the equalizer loss inclination amount KE = −2 × k. A control signal for changing the optical attenuation for each wavelength is generated so as to cause the variable gain equalizer 110 to transmit the control signal.
[0056]
The variable gain equalizer 110 changes the loss wavelength characteristic by changing the optical attenuation amount for each wavelength based on the control signal from the control circuit 100. At this time, the variable gain equalizer 110 is controlled to have a loss wavelength characteristic of an equalizer loss inclination amount KE = −2 × k, as indicated by characteristic (2) -1 in FIG. The Then, the variable gain equalizer 110 receives the WDM optical signal having the gain tilt amount KI = k from the first optical branching coupler 10, changes the gain tilt amount KI = k, and changes the gain tilt amount KI = k as shown in FIG. A WDM optical signal having a gain tilt amount KEO = −k as indicated by the characteristic (3) -1 is output and sent to the optical amplifier 2. Here, the gain inclination amount KEO is a value obtained by adding the equalizer loss inclination amount KE = −2 × k of the variable gain equalizer 110 to the gain inclination amount KI = k of the input WDM optical signal = −k. It is. Therefore, the variable gain equalizer 110 outputs a WDM optical signal having a gain tilt amount KEO = −k obtained by inverting the gain tilt amount KI = k of the input WDM optical signal.
[0057]
That is, the variable gain equalizer 110 outputs a WDM optical signal having a gain tilt amount that is the same as the gain tilt amount of the input WDM optical signal and has the opposite sign.
[0058]
The optical amplifier 2 receives the WDM optical signal with the gain tilt amount KEO = −k from the variable gain equalizer 110, optically amplifies it, and outputs it to the transmission line. At this time, since the average power value Pav of the WDM optical signal input to the optical amplifier 2 matches the standard average optical power value Pr of the optical amplifier 2, the gain inclination amount KA of the optical amplifier 2 is as shown in FIG. ) Is the standard gain tilt amount kr when the WDM light having the standard average optical power value Pr is input to the optical amplifier 2 as indicated by the characteristic (4) -1. Therefore, the optical amplifier 2 optically amplifies the input WDM optical signal with the gain tilt amount KEO = −k, and the gain tilt amount KO = − as shown by the characteristic (5) -1 in FIG. A k + kr WDM optical signal is output to the transmission line.
[0059]
<When Average Optical Power Value Pav and Standard Average Optical Power Value Pr Do Not Match>
A WDM optical signal in which wavelengths λ1 to λn are multiplexed is input to the gain equalization apparatus 1 as indicated by the characteristic (1) -2 in FIG. 3B. The average optical power value Pav of this WDM optical signal does not match the standard average optical power value Pr.
[0060]
When this WDM optical signal is input, the first optical branching coupler 10 branches a part of the WDM optical signal and sends it to the second optical branching coupler 20 as a monitor WDM optical signal. Part to the variable gain equalizer 110.
[0061]
The second optical branching coupler 20 splits the monitor WDM optical signal from the first optical branching coupler 10 into two branches, sends one of the two split monitor WDM optical signals to the average optical power detection unit 30, and sends the other to the monitoring wavelength. This is sent to the optical power detector 40.
[0062]
The first photodiode 31 of the average optical power detection unit 30 receives one of the monitor WDM optical signals branched by the second optical branching coupler 20, converts the monitor WDM optical signal into an electrical signal, and has a wavelength number n. The total optical power values obtained by combining the optical power values of the wavelengths λ1 to λ1n are obtained, and the total optical power values are sent to the average optical power calculation unit 32.
[0063]
The average optical power calculation unit 32 obtains an average optical power value Pav by dividing the total optical power value from the first photodiode 31 by the number of wavelengths n, and the average optical power value Pav is changed between the inclination amount detection unit 50 and the inclination change. This is sent to the quantity detection unit 60 and the comparison circuit 70.
[0064]
On the other hand, the wavelength filter 41 of the monitoring wavelength optical power detector 40 receives the other of the monitor WDM optical signals branched into two by the second optical branching coupler 20, and receives the wavelengths λ1,..., Λn included in the monitor WDM optical signal. Then, only the light having the monitoring wavelength λs = λn is selected and transmitted and sent to the second photodiode 42.
[0065]
The second photodiode 42 receives the light of the monitoring wavelength λs = λn selected by the wavelength filter 41, converts the light of the monitoring wavelength λs into an electric signal, and obtains the monitoring wavelength light power value Ps of the monitoring wavelength λs, The monitoring wavelength light power value Ps is sent to the tilt amount detection unit 50.
[0066]
The first difference circuit 51 of the inclination amount detection unit 50 calculates the difference between the monitoring wavelength light power value Ps from the monitoring wavelength light power detection unit 40 and the average light power value Pav from the average light power detection unit 30 to calculate the first difference circuit 51. The difference value ΔPsav (= Ps−Pav) is obtained, and the first difference value ΔPsav is sent to the tilt amount calculation unit 52.
[0067]
The tilt amount calculation unit 52 uses the first difference value ΔPsav from the first difference circuit 51 to calculate the gain tilt amount KI = k with respect to the wavelength of the WDM optical signal, and equalizes the gain tilt amount KI = k. This is sent to the tilt amount determination unit 90.
[0068]
The comparison circuit 70 compares the average optical power value Pav from the average optical power detection unit 30 with the standard average optical power value Pr, and since they do not match, generates an open signal for opening the gate 80 to generate the gate 80. Send to.
[0069]
The second difference circuit 61 of the inclination change amount detection unit 60 calculates a difference between the average optical power value Pav from the average optical power detection unit 30 and the standard average optical power value Pr, and calculates a second difference value ΔPavr (= Pav−Pr). ) And the second difference value Pavr is sent to the inclination change amount calculation unit 62.
[0070]
Upon receiving the second difference value ΔPavr from the second difference circuit 61, the tilt change amount calculation unit 62 refers to the optical amplifier gain tilt change amount table to obtain the optical amplifier gain tilt change amount Δkr, and this optical amplifier gain tilt The change amount Δkr is sent to the gate 80.
[0071]
The gate 80 opens the gate according to the open signal from the comparison circuit 70, and sends the optical amplifier gain tilt change amount Δkr from the tilt change amount calculation unit 62 to the equalizer tilt amount determination unit 90.
[0072]
When the equalizer tilt amount determination unit 90 receives the gain tilt amount KI = k from the tilt amount calculation unit 52 and receives the optical amplifier gain tilt change amount Δkr from the tilt change amount calculation unit 62, the gain tilt amount KI = k is multiplied by the inclination inversion coefficient C = −2 to obtain −2 × k, and the optical amplifier gain inclination change amount Δkr is multiplied by a predetermined inclination change amount cancellation coefficient CR = −1 to −1 ×. Δkr is obtained, and both are added to obtain an equalizer loss slope amount KE = −2 × k + (− 1 × Δkr) set in the variable gain equalizer 110, and this equalizer loss slope amount KE = −. 2 × k + (− 1 × Δkr) is sent to the control circuit 100.
[0073]
The control circuit 100 receives the equalizer loss inclination amount KE = −2 × k + (− 1 × Δkr) from the equalizer inclination amount determination unit 90 and supplies the equalizer gain inclination amount KE = to the variable gain equalizer 110. A control signal for changing the optical attenuation for each wavelength is generated so as to have −2 × k + (− 1 × Δkr), and this control signal is sent to the variable gain equalizer 110.
[0074]
The variable gain equalizer 110 changes the loss wavelength characteristic by changing the optical attenuation amount for each wavelength based on the control signal from the control circuit 100. At this time, the variable gain equalizer 110 has a loss wavelength of the equalizer loss inclination amount KE = −2 × k + (− 1 × Δkr) as shown by the characteristic (2) -2 in FIG. Controlled to have characteristics. The variable gain equalizer 110 receives the WDM optical signal with the gain tilt amount KI = k from the first optical branching coupler 10, changes the gain tilt amount KI = k, and changes the gain tilt amount KI = k as shown in FIG. A WDM optical signal having a gain tilt amount KEO = −k−Δkr as indicated by characteristic (3) -2 is output and sent to the optical amplifier 2. Here, as the gain tilt amount KEO, the gain tilt amount KI = −2 × k + (− 1 × Δkr) of the variable gain equalizer 110 is set to the gain tilt amount KI = k of the input WDM optical signal. The added value = −k−Δkr.
[0075]
The optical amplifier 2 receives the WDM optical signal with the gain tilt amount KEO = −k−Δkr from the variable gain equalizer 110, optically amplifies it, and outputs it to the transmission line 202. At this time, since the average power value Pav of the WDM optical signal input to the optical amplifier 2 is larger than the standard average optical power value Pr of the optical amplifier 2 by ΔPavr, the gain inclination amount KA of the optical amplifier 2 is shown in FIG. As shown in characteristic (4) -2, the optical amplifier gain inclination change amount Δkr due to ΔPavr is added to the standard gain inclination amount kr when the WDM light having the standard average optical power value Pr is input to the optical amplifier 2. The value kr + Δkr.
Accordingly, the optical amplifier 2 optically amplifies the input main WDM optical signal with the gain tilt amount KEO = −k−Δkr, and the gain tilt amount as shown by the characteristic (5) -2 in FIG. A WDM optical signal of KO = −k + kr is output to the transmission line 202. This gain tilt amount KO = −k + kr is the same value as the gain tilt amount KO of the WDM optical signal output from the optical amplifier 2 when the average optical power value Pav of the WDM optical signal matches the standard average optical power value Pr. .
[0076]
Thus, the variable gain equalizer 110 inverts the gain tilt amount of the input main WDM optical signal and cancels the optical amplifier gain tilt change amount.
[0077]
As described above, the gain equalization apparatus 1 does not depend on whether or not the average optical power value Pav of the input WDM optical signal matches the standard average optical power value Pr, that is, the gain inclination change of the optical amplifier at the subsequent stage. The loss tilt amount of the variable gain equalizer 11 is controlled so that a WDM optical signal having a constant gain tilt amount is always output from the optical amplifier.
[0078]
【The invention's effect】
As described above, the present invention is configured to detect a gain tilt amount of an input WDM optical signal and output a WDM optical signal having a gain tilt amount that is the same value as the detected gain tilt amount and has the opposite sign. Therefore, there is an effect that it is possible to realize a WDM optical repeater system in which the optical power for each wavelength is always kept constant and the transmission characteristics for each wavelength are uniform.
[0079]
Further, the present invention is configured to detect the gain tilt change amount of the optical amplifier and cancel the detected gain tilt change amount, so that the gain tilt change due to the optical power of the WDM light input to the optical amplifier is reduced. The transmission characteristics can be made uniform regardless of the optical power.
[0080]
[Brief description of the drawings]
FIG. 1 is a configuration block diagram of an embodiment according to the present invention.
FIG. 2 is a diagram for explaining an operation;
FIG. 3 is a diagram showing a slope characteristic of each part.
FIG. 4 is a diagram illustrating gain characteristics of an optical optical amplifier.
[Explanation of symbols]
1 Gain equalizer
10 First optical branching coupler
20 Second optical branching coupler
30 Average optical power detector
31 First photodiode
32 Average optical power calculator
40 Monitoring wavelength optical power detector
41 Wavelength filter
42 Second photodiode
50 Inclination amount detector
51 First difference circuit
52 Inclination amount calculator
60 Inclination change detection unit
61 Second difference circuit
62 Inclination change calculation unit
70 Comparison circuit
80 gate
90 Equalizer inclination amount determination unit
100 Control circuit
110 Variable Gain Equalizer
2 Optical amplifier

Claims (8)

A gain equalization apparatus of a WDM optical repeater system for optically amplifying and relaying a WDM optical signal by an optical amplifier,
A gain tilt amount detecting means for detecting a gain tilt amount from an input WDM optical signal;
Variable gain equalizing means for changing the input WDM optical signal to a WDM optical signal having the same value as the gain tilt amount detected by the gain tilt amount detecting means and having an inverted gain tilt amount of the opposite sign. A gain equalization apparatus for a WDM optical repeater system. A gain equalization apparatus of a WDM optical repeater system for optically amplifying and relaying a WDM optical signal by an optical amplifier,
A gain tilt amount detecting means for detecting a gain tilt amount from an input WDM optical signal;
A gain tilt change amount detecting means for detecting a gain tilt change amount of an optical amplifier connected to a subsequent stage from the input WDM optical signal;
The input WDM optical signal has the same value as the gain tilt amount detected by the gain tilt amount detecting means and the reverse gain tilt amount having the opposite sign and the same value as the gain tilt change amount detected by the gain tilt change amount detecting means. A gain equalization apparatus for a WDM optical repeater system, comprising: variable gain equalization means for changing to a WDM optical signal having a gain tilt amount that is the sum of cancellation gain tilt change amounts having opposite signs. A gain equalization apparatus for a WDM optical repeater system for optically amplifying a WDM optical signal by an optical amplifier and relaying the optical signal through an optical transmission line,
Average optical power detection means for detecting average optical power per wavelength from an input WDM optical signal multiplexed with a plurality of wavelengths input from an optical transmission line;
Monitoring wavelength optical power detection means for detecting a monitoring wavelength optical power of light having a predetermined monitoring wavelength from the input WDM optical signal;
The difference between the monitoring wavelength optical power detected by the monitoring wavelength optical power detection means and the average optical power detected by the average optical power detection means is taken, and the gain tilt amount of the input WDM optical signal is detected from this difference. Means for detecting the amount of gain tilt;
The difference between the average optical power detected by the average optical power detector and the standard average optical power that gives the standard gain tilt amount of the optical amplifier, and the gain tilt change amount that is the change amount from the standard gain tilt amount of the optical amplifier. An optical amplifier gain tilt change amount table indicating the relationship is stored, and the difference between the average optical power and the standard average optical power is obtained, and based on this difference, the optical amplifier is based on the optical amplifier gain tilt change amount table. Gain tilt change amount detecting means for detecting the gain tilt change amount of
The input WDM optical signal has the same value as the gain tilt amount detected by the gain tilt amount detecting means and the reverse gain tilt amount having the opposite sign and the same value as the gain tilt change amount detected by the gain tilt change amount detecting means. A gain equalization apparatus for a WDM optical repeater system, comprising: variable gain equalization means for changing to a WDM optical signal having a gain tilt amount that is the sum of cancellation gain tilt change amounts having opposite signs. A gain equalization apparatus for a WDM optical repeater system for optically amplifying a WDM optical signal by an optical amplifier and relaying the optical signal through an optical transmission line,
With a variable gain equalizer,
A first optical branching coupler for branching a monitor WDM optical signal from an input WDM optical signal multiplexed with a plurality of wavelengths input from an optical transmission line and sending the input WDM optical signal to the variable gain equalizer;
A second optical branching coupler for branching the monitor WDM optical signal from the first optical branching coupler into two;
A first photodiode that receives one of the monitor WDM optical signals branched into two by the second optical branching coupler, converts the monitor WDM optical signal into an electrical signal, and obtains the total optical power of all of a plurality of wavelengths; An average optical power detector having an average optical power calculator that calculates the average optical power by dividing the total optical power from the photodiode by the number of wavelengths;
The other one of the monitor WDM optical signals branched by the second optical branching coupler is received, and only the light having a predetermined monitoring wavelength is selected from the light of a plurality of wavelengths included in the monitor WDM optical signal. Monitoring wavelength light having a wavelength filter that transmits, and a second photodiode that receives the monitoring wavelength light selected and transmitted by the wavelength filter and converts the monitoring wavelength light into an electrical signal to obtain the monitoring wavelength light power A power detector;
The difference between the monitoring wavelength optical power detected by the monitoring wavelength optical power detection unit and the average optical power detected by the average optical power detection unit is taken, and the gain tilt amount of the input WDM optical signal is detected from this difference. A gain tilt amount detection unit;
The difference between the average optical power detected by the average optical power detector and the standard average optical power that gives the standard gain tilt amount of the optical amplifier connected in the subsequent stage is taken, and from this difference, the standard gain of this optical amplifier is determined. A gain inclination change amount detection unit for detecting a gain inclination change amount that is a change amount from the inclination amount;
The variable gain equalizer has an inverting gain tilt amount equal to a gain tilt amount detected by the gain tilt amount detecting unit and having an opposite sign to the input WDM optical signal from the first optical branch coupler and the gain. Change to a WDM optical signal having a gain tilt amount equal to the gain tilt change amount detected by the tilt change amount detecting unit and the sum of the offset gain tilt change amount having the opposite sign, and connect this WDM optical signal to the subsequent stage A gain equalization apparatus for a WDM optical repeater system, characterized in that the output is output to an optical amplifier. A gain equalization apparatus for a WDM optical repeater system for optically amplifying a WDM optical signal by an optical amplifier and relaying the optical signal through an optical transmission line,
With a variable gain equalizer,
A first optical branching coupler for branching a monitor WDM optical signal from an input WDM optical signal multiplexed with a plurality of wavelengths input from an optical transmission line and sending the input WDM optical signal to the variable gain equalizer;
A second optical branching coupler for branching the monitor WDM optical signal from the first optical branching coupler into two;
A first photodiode that receives one of the monitor WDM optical signals branched into two by the second optical branching coupler, converts the monitor WDM optical signal into an electrical signal, and obtains the total optical power of all of a plurality of wavelengths; An average optical power detector having an average optical power calculator that calculates the average optical power by dividing the total optical power from the photodiode by the number of wavelengths;
The other one of the monitor WDM optical signals branched by the second optical branching coupler is received, and only the light having a predetermined monitoring wavelength is selected from the light of a plurality of wavelengths included in the monitor WDM optical signal. Monitoring wavelength light having a wavelength filter that transmits, and a second photodiode that receives the monitoring wavelength light selected and transmitted by the wavelength filter and converts the monitoring wavelength light into an electrical signal to obtain the monitoring wavelength light power A power detector;
The difference between the monitoring wavelength optical power detected by the monitoring wavelength optical power detection unit and the average optical power detected by the average optical power detection unit is taken, and the gain tilt amount of the input WDM optical signal is detected from this difference. A gain tilt amount detection unit;
The difference between the average optical power detected by the average optical power detection unit and the standard optical average power that gives the standard gain tilt amount of the optical amplifier connected in the subsequent stage is taken, and from this difference, the standard gain of the optical amplifier is determined. A gain tilt change amount detection unit for detecting a gain tilt change amount that is a change amount from the tilt amount;
The gain tilt amount detected by the gain tilt amount detection unit is multiplied by an inversion coefficient -2, the gain tilt change amount detected by the gain tilt change amount detection unit is multiplied by an offset coefficient -1, and both are added. And an equalizer inclination amount determination unit for determining an equalizer inclination amount,
The variable gain equalizer changes the attenuation amount for each wavelength so as to obtain an equalizer inclination amount determined by the equalizer inclination amount determination unit, thereby providing an input from the first optical branching coupler. The WDM optical signal has the same value as the gain tilt amount detected by the gain tilt amount detecting unit and the same value as the inverted gain tilt amount having the opposite sign and the gain tilt change amount detected by the gain tilt change amount detecting unit. A WDM optical repeater system characterized by changing to a WDM optical signal having a gain tilt amount that is the sum of cancellation gain tilt change amounts having opposite signs, and outputting the WDM optical signal to an optical amplifier connected in a subsequent stage. Gain equalizer. The gain tilt change amount detection unit includes a difference between the average optical power detected by the average optical power detection unit and a standard average optical power giving a standard gain tilt amount of the optical amplifier, and a change from the standard gain tilt amount of the optical amplifier. An optical amplifier gain inclination change amount table showing a relationship with a gain inclination change amount that is a quantity is stored, and a difference between the average optical power and the standard average optical power is obtained, and from this difference, the optical amplifier gain is obtained. 6. The gain equalization apparatus for a WDM optical repeater system according to claim 4, wherein a gain tilt change amount of the optical amplifier is detected based on a tilt change table. 6. The gain equalization apparatus for a WDM optical repeater system according to claim 5, wherein the wavelength filter is a transmission type wavelength selective grating. A WDM optical repeater system in which an input optical transmission line, a gain equalizer, an optical amplifier, and an output optical transmission line are connected in cascade,
The gain equalizer is
With a variable gain equalizer,
A first optical branching coupler for branching a monitor WDM optical signal from an input WDM optical signal multiplexed with a plurality of wavelengths input from an input optical transmission line and sending the input WDM optical signal to the variable gain equalizer;
A second optical branching coupler for branching the monitor WDM optical signal from the first optical branching coupler into two;
A first photodiode that receives one of the monitor WDM optical signals branched into two by the second optical branching coupler, converts the monitor WDM optical signal into an electrical signal, and obtains the total optical power of all of a plurality of wavelengths; An average optical power detector having an average optical power calculator that calculates the average optical power by dividing the total optical power from the photodiode by the number of wavelengths;
The other one of the monitor WDM optical signals branched by the second optical branching coupler is received, and only the light having a predetermined monitoring wavelength is selected from the light of a plurality of wavelengths included in the monitor WDM optical signal. Monitoring wavelength light having a wavelength filter that transmits, and a second photodiode that receives the monitoring wavelength light selected and transmitted by the wavelength filter and converts the monitoring wavelength light into an electrical signal to obtain the monitoring wavelength light power A power detector;
The difference between the monitoring wavelength optical power detected by the monitoring wavelength optical power detection unit and the average optical power detected by the average optical power detection unit is taken, and the gain tilt amount of the input WDM optical signal is detected from this difference. A gain tilt amount detection unit;
The difference between the average optical power detected by the average optical power detector and the standard average optical power giving the standard gain tilt amount of the optical amplifier connected in the subsequent stage, and the amount of change from the standard gain tilt amount of the optical amplifier An optical amplifier gain inclination change amount table showing a relationship with a certain gain inclination change amount is stored, and a difference between the average optical power and the standard average optical power is obtained, and from this difference, the optical amplifier gain inclination change is obtained. A gain tilt change amount detecting unit for detecting a gain tilt change amount of the optical amplifier based on a quantity table;
The gain tilt amount detected by the gain tilt amount detection unit is multiplied by an inversion coefficient -2, the gain tilt change amount detected by the gain tilt change amount detection unit is multiplied by an offset coefficient -1, and both are added. And an equalizer inclination amount determination unit for determining an equalizer inclination amount,
The variable gain equalizer changes the attenuation amount for each wavelength so as to obtain an equalizer inclination amount determined by the equalizer inclination amount determination unit, thereby providing an input from the first optical branching coupler. The WDM optical signal has the same value as the gain tilt amount detected by the gain tilt amount detecting unit and the same value as the inverted gain tilt amount having the opposite sign and the gain tilt change amount detected by the gain tilt change amount detecting unit. Change to a WDM optical signal having a gain tilt amount that is the sum of the offset gain tilt change amount having the opposite sign, and send this WDM optical signal to the optical amplifier connected to the subsequent stage,
The WDM optical repeater system, wherein the optical amplifier receives a WDM optical signal whose gain tilt amount has been changed from the gain equalizer, amplifies the WDM optical signal, and outputs the amplified WDM optical signal to an output transmission line.

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