JPH1168204A - Optical amplifier - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To reduce the wavelength dependence of gain in a predetermined signal wavelength band and, even if the input signal light power changes, output signal light of each wavelength of the wavelength multiplexed signal light according to the change. Control so that the power is constant. SOLUTION: A plurality of types of rare-earth-doped optical fibers having different compositions are cascaded to amplify, and the wavelength dependence of the gain of each amplifying unit is canceled out, and the gain of the entire optical amplifier in which the gains of all the amplifying units are combined is reduced. The gain of each amplifying unit is controlled so as to be a predetermined value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber comprising a plurality of optical fiber transmission lines for multiplexing and transmitting a plurality of optical signals having different wavelengths and an optical amplifier for compensating the loss thereof, which are alternately connected in multiple stages. The present invention relates to an optical amplifier used in an amplification relay wavelength division multiplex communication system.

In particular, an optical amplifier for controlling the output signal light power of each wavelength to be constant with respect to the variation or fluctuation of the input signal light power to the optical amplifier caused by a difference in loss or a change in loss in each optical fiber transmission line. About.

[0003]

FIG. 8 shows a configuration example of a conventional optical amplifier. In the figure, a wavelength multiplexed signal light input from an input terminal 1 is input to a multiplexer 7 via an optical isolator 4-1. The multiplexer 7 multiplexes the pump light and the signal light output from the pump light source 8 and inputs the multiplexed light to the amplifier 5 using a rare-earth-doped optical fiber. The output light of the amplifying unit 5 is
-2, output from the output terminal 2 via the optical coupler 3.
Light partially branched by the optical coupler 3 is inputted to the optical band-pass filter 9, where the signal light of the selected wavelength lambda _i is inputted to the light receiver 10 and converted into an electric signal. The electrical signal indicates a voltage proportional to the output signal light power of the wavelength lambda _i. The control circuit 12 controls the output power of the pump light source 8 so that the output of the light receiver 10 is always constant.

Here, the control principle and operation of the optical amplifier shown in FIG. 8 will be briefly described. First, the gain of the rare earth-doped optical fiber amplifier and its wavelength dependence will be described.
The logarithmic gain G (λ) of the signal light of wavelength λ of the rare-earth-doped optical fiber amplifier is represented by σ _e (λ), σ _a (λ) at the emission cross section and absorption cross section at the wavelength λ, ρ at the rare earth ion density, The confinement coefficient is Γ, the normalized ion density excited to the upper level of the laser at the energy level of the rare earth ion is N ₂ , and the average value of the rare earth-doped optical fiber in the longitudinal direction (hereinafter referred to as the average upper level ion density) <N _2>, when the fiber length of the rare-earth doped optical fiber and L, G (λ) = { σ e (λ) + σ a (λ)} ρΓ <N 2> L-σ a (λ) ρΓL (9) It is represented by

In equation (9), σ _e (λ), σ _a (λ), ρ, and 係数 are coefficients uniquely determined by the optical fiber. Therefore, when the fiber length L is fixed, the logarithmic gain G (λ ) Is uniquely determined only by the upper level ion density <N ₂ >.

[0006] In the configuration of FIG. 8, when the loss fluctuation of the optical fiber transmission line input signal light power per one wavelength changes, and controls the excitation light source 8, the output signal light power of the wavelength lambda _i is constant The gain of the amplifying unit 5 is changed so as to be as follows.
When the gain is changed in this way, the upper-level ion density <N ₂ > uniquely related by the equation (9) changes, and the emission cross section σ _e (λ) and the absorption cross section σ _a (λ) also change. Since it has wavelength dependence, the wavelength dependence of the gain changes. For this reason, when wavelength multiplexed signal light is input, FIG.
When the output signal light power of a specific wavelength is controlled to be constant as described above, the output signal light power of another wavelength changes due to a change in the wavelength dependence of the gain.

FIG. 9 shows a calculation example of output characteristics of the conventional optical amplifier shown in FIG. Here, the amplification unit 5 is 1550 nm
An Al co-doped Er ³⁺ optical fiber capable of realizing a flat gain characteristic in the vicinity was used. To this optical amplifier, 11 wavelength multiplexed signal lights having a wavelength range of 1548 to 1558 nm and a channel interval of 1 nm are input, and the output power of the reference light (wavelength 1553 nm) is always 10 dB.
m. The output signal light power of each wavelength when the input signal light power per wave at this time is used as a parameter is shown. However, the difference between the output signal light powers of the respective wavelengths when the input signal light power per wave is -15 dBm / ch is set to be the smallest.

As shown in FIG. 9, when the power of the input signal light changes, the power of the output signal light other than the reference light (wavelength: 1553 nm) greatly changes. It can be seen that when the input signal light power is in the range of -30 dBm / ch to 0 dBm / ch, which is 30 dB, the change in output signal light power is about 3 dB at 1558 nm at the maximum.

As described above, if the gain of the optical amplifier has wavelength dependence, the output signal light power increases at a wavelength where the gain is large, and nonlinear phenomena such as four-wave mixing and self-phase modulation occur in the optical fiber transmission line. Signal is degraded. Also, at a wavelength where the gain is small, the output signal light power becomes small, and in the optical amplifier at the next stage, the influence of spontaneous emission light becomes large and the signal is degraded.

Further, as an optical amplifier capable of controlling the output power of the wavelength division multiplexed signal light to a constant value, a rare earth-doped optical fiber as an amplifier is cascaded with an optical attenuator, and the gain of the amplifier and the attenuation of the optical attenuator are reduced. A controlled optical amplifier has been proposed (S. Kinoshita et al., "Low-Noise and Wide-Dynamic-R
ange Erbium-Doped Fiber Amplifiers with AutomaticL
evel Control for WDM transmission Systems ", Optica
l Amplifiers and their Applications, Technical Dig
est, pp. 211-214, 1996).

In order to control the gain of the amplifying unit so as to have a small wavelength dependency and to be a constant value irrespective of the input signal light power, and to further control the output signal light power of the entire optical amplifier to be constant, The optical attenuator provides an attenuation proportional to the input signal light power. However, in this configuration, the signal light amplified by using the optical attenuator causes a loss, so that there is a problem that the power consumption of the pump light source increases.

In addition, as an optical amplifier in which the wavelength dependence of the gain is reduced, a configuration has been reported in which two types of rare earth-doped optical fibers having different compositions are connected to compensate for the wavelength dependence of the gain of each other (CGGiles). et al., "Dynamic Gain Equal
ization in Two-Stage FiberAmplifiers ", IEEE Photon
ics Technology Letters, vol.2, no.12, pp.866-868,
1990).

In this analysis, when signal light of two wavelengths (λ ₁ , λ ₂ ) is inputted, the gain deviation of each wavelength is compensated. However, signal light of three or more waves is inputted. It is not clear how to control the case.

[0014]

The power of the signal light input to the optical amplifier changes due to loss fluctuations and loss fluctuations in the optical fiber transmission line. In order to keep the output signal light power constant when the input signal light power changes, it is necessary to change the gain of the optical amplifier according to the change in the input signal light power. However, if the output signal light power is controlled to be constant by adjusting the gain of one kind of rare-earth-doped optical fiber as in the conventional configuration, the wavelength dependence of the gain changes with a change in the gain.

According to the present invention, the wavelength dependence of the gain in a predetermined signal wavelength band is reduced, and even if the input signal light power changes, the output signal light power of each wavelength of the wavelength multiplexed signal light is changed according to the change. It is an object to provide an optical amplifier that can be controlled to be constant.

[0016]

SUMMARY OF THE INVENTION An optical amplifier according to the present invention has a cascade connection of amplifying sections composed of a plurality of types of rare-earth-doped optical fibers having different compositions, cancels the wavelength dependence of the gain of each amplifying section, and eliminates all amplification. The gain of each amplifying unit is controlled so that the gain of the entire optical amplifier with the gain of the unit becomes a predetermined value.

(Configuration Using Two Kinds of Rare-Earth Doped Optical Fibers with Different Compositions) First, in an optical amplifier in which a first and a second amplifying section using two kinds of rare-earth-doped optical fibers having different compositions are cascaded, A method of controlling the gain of the unit will be described.

For the gain characteristic of the rare-earth-doped optical fiber shown in equation (9), a first-order approximation of the wavelength near the reference wavelength λ ₀ gives: G (λ) = ｛σ _e (λ) + σ _a (λ)｝ ρΓ <N ₂ > L−σ _a (λ) ρΓL ≒ (αG ₀ + β) (λ−λ ₀ ) + G ₀ (10) Here, G ₀ , α, β are

[0019]

(Equation 5)

## EQU1 ## From the equation (10), when the gain is approximated by a linear function of the wavelength, the linear coefficient part of the wavelength, that is, the slope of the gain can be represented by a linear function of the gain G ₀ at the reference wavelength λ ₀ . Gain G of first and second amplifying units
₁ (λ) and G ₂ (λ) are given by the following equation (10): G ₁ (λ) ≒ (α ₁ G ₀₁ + β ₁ ) (λ−λ ₀ ) + G ₀₁ (15) G ₂ ( λ) ≒ (α ₂ G ₀₂ + β ₂ ) (λ−λ ₀ ) + G ₀₂ (16) Here, the subscripts 1 and 2 correspond to the first and second amplifying units, respectively.

The gain G _t (λ) of the entire optical amplifier in which the gains of the first and second amplifying sections are combined is the sum of the gains of the first and second amplifying sections shown in equations (15) and (16). G _t (λ) = G ₁ (λ) + G ₂ (λ) ≒ ｛(α ₁ G ₀₁ + β ₁ ) + (α ₂ G ₀₂ + β ₂ )｝ (λ−λ ₀ ) + G ₀₁ + G ₀₂ (17) It is expressed as

Flat gain characteristics without gain wavelength dependence
Obtained, and in order to obtain a predetermined gain, the expression shown in equation (17)
Gain G of the whole optical amplifier_t(λ) Coefficient part of wavelength λ
Should always be 0. The condition is (α₁G₀₁+ Β₁) + (Α_TwoG₀₂+ Β_Two) = 0 (18), and then the gain G of the entire optical amplifier is_tIs G_t= G₀₁+ G₀₂ (19) In the parentheses on the left side of equation (18),
And the slope of the gain of the second amplifier. Equation (1)
8) Coefficient α₁, Β₁, Α_Two, Β_TwoIs the reference wavelength λ ₀Interest
Experimentally measuring the wavelength dependence of gain on gain
Can be obtained by using rare earth doped optical fiber
It is a coefficient uniquely determined.

On the other hand, when the input signal light power of the signal light having the reference wavelength λ ₀ is Pin ₀ and the output signal light power is controlled to be constant at Pout ₀ , the gain G _t required for the entire optical amplifier is obtained. Is expressed as G _t = log [Pout ₀ / Pin ₀ ] (20).

Therefore, the gains G ₀₁ , G ₀₂ of the first and second amplifying sections are given by the following equations when the coefficients α ₁ , β ₁ , α ₂ , β ₂ and the output signal light power Pout ₀ of the control target are given. 18)-(20)
From

[0025]

(Equation 6)

Can be obtained as follows. It can be seen that this depends only on the input signal light power Pin ₀ . That is, according to the equations (21) and (22), the input signal light power Pin ₀
By adjusting the gains of the first and second amplifiers according to the above, it is possible to realize an optical amplifier in which the change in the output signal light power with respect to the change in the input signal light power is small.

In summary, by controlling the gains of the first and second amplifying units according to the equations (21) and (22),
The slope of the gain generated in the first amplifying section can be canceled by the second amplifying sections having different gain characteristics, and the combined gain of the first and second amplifying sections can be controlled to a predetermined value. Thereby, even when the input signal light power of the wavelength multiplexed signal light changes, the change in the output signal light power of the wavelength multiplexed signal light can be suppressed.

(Configuration Using n Kinds of Rare-Earth Doped Optical Fibers with Different Compositions) A method for controlling an optical amplifier in which the first and second amplifiers are cascaded by the two kinds of rare-earth-doped optical fibers having different compositions described above. Generalized n with different composition
A method of controlling the gain of each amplifier will be described for an optical amplifier in which first to n-th amplifiers are connected in cascade using various kinds of rare earth doped optical fibers.

When the wavelength dependence of the gain of the j-th amplifier is expanded by the power of the wavelength λ in the first to n-th amplifiers, G _j (λ) = G _0j + (α _1j G _0j + Β _1j ) (λ−λ ₀ ) + (α _2j G _0j + β _2j ) (λ−λ ₀ ) ² + ... + (α _ij G _0j + β _ij ) (λ−λ ₀ ) ⁱ + ... + (α _{(n -1) j} G _0j + β _{(n-1) j} ) (λ−λ ₀ ) ⁽ⁿ⁻¹⁾ (23) Here, G _0j is the gain at the reference wavelength λ ₀ of the j-th amplification unit, and α _ij and β _ij are λ when the wavelength dependence of the gain of the j-th amplification unit is developed as a power of the wavelength λ. the coefficient of ⁱ

[0030]

(Equation 7)

## EQU1 ## Gain G _t of the entire optical amplifier combined gain of the amplifier of the first to n-th

[0032]

(Equation 8)

## EQU1 ## The gain G _{t of the} entire optical amplifier
There to no wavelength dependence, it is necessary to sum of the coefficients of the amplification portion of lambda ¹ to [lambda] ⁿ of the first to n is always 0. The condition is that i in the equation (23) is in the range of 1 to (n-1).

[0034]

(Equation 9)

At this time, the gain G _{t of the} entire optical amplifier is obtained.
Is

[0036]

(Equation 10)

Is as follows. Here, rewriting equations (29) and (30) into a matrix form,

[0038]

[Equation 11]

Can be expressed as follows. Therefore, the first to first
From the equation (31), the gain of the n-th amplifier is

[0040]

(Equation 12)

Can be obtained as follows. This equation (34)
By adjusting the gains of the first to n-th amplifying units according to the input signal light power Pin ₀ , there is no deviation of the output signal light power, and the change of the output signal light power with respect to the change of the input signal light power. , An optical amplifier with less noise can be realized.

(Corresponding to the case where there is a deviation in the signal light power of each wavelength of the wavelength multiplexed signal light) While keeping the deviation of the signal light power of each wavelength of the wavelength multiplexed signal light constant, the output with respect to the change of the input signal light power is maintained. In order to suppress the change in the signal light power, the coefficient obtained by expanding the gain of the entire amplifying unit of Expression (30) by a power of the wavelength λ may be a constant value δ instead of 0.
That is, equation (34) is

[0043]

(Equation 13)

Is as follows. By controlling the gain of each amplifying unit according to this equation (35), it is possible to realize an optical amplifier in which the output signal light power of each wavelength does not change even if the input signal light power changes, although the wavelength dependence of the gain exists. Can be. If the input signal light power has wavelength dependency,
By setting δ to have the opposite characteristic in (35), it is possible to suppress the deviation of the output signal light power of each wavelength.

As described above, the deviation of the signal light power of each wavelength of the wavelength-division multiplexed signal light can be suppressed by controlling the gains of the plurality of amplifying units constituting the optical amplifier according to the equation (35). A wavelength division multiplexing transmission system in which signal degradation due to a nonlinear optical effect or the like is suppressed can be configured.

[0046]

FIG. 1 shows an embodiment of an optical amplifier according to the present invention. In the present embodiment, a first and a second amplifying section using two kinds of rare earth-doped optical fibers having different compositions are connected in cascade.

In the figure, a wavelength multiplexed signal light input from an input terminal 1 is converted into an optical coupler 3-1 and an optical isolator 4-.
1 is input to the multiplexer 7. The multiplexer 7-1 multiplexes the pump light and the signal light output from the pump light source 8-1, and inputs the multiplexed light to the first amplifier 5. The output light of the first amplifier 5 is input to the second amplifier 6 via the optical coupler 3-2 and the optical isolator 4-2.

The light partially branched by the optical coupler 3-1 is input to the optical band-pass filter 9-1, where the signal light of the selected reference wavelength λ ₀ is input to the optical receiver 10-1 and converted into an electric signal. Is converted. The light partially branched by the optical coupler 3-2 is input to the optical bandpass filter 9-2, where the signal light of the selected reference wavelength λ ₀ is converted to the light receiving device 10-2.
And converted into an electric signal. Each electric signal indicates a voltage proportional to the output signal light power of the reference wavelength λ ₀ . The control circuit 11 receives the electric signals output from the light receivers 10-1 and 10-2, and controls the output power of the pump light source 8-1 according to the equation (21). Specifically, the input signal light power of the reference wavelength λ ₀ (the output of the optical receiver 10-1)
And the logarithmic gain of the reference wavelength λ ₀ (the output ratio of the photodetectors 10-1 and 10-2) in the first amplification unit 5,
The control target of the logarithmic gain of the first amplifying unit 5 is obtained according to 5), and the output power of the pump light source 8-1 is controlled so that the error between the two becomes small.

The output light from the second amplifying section 6 is supplied to a multiplexer 7-
2, via optical isolator 4-3, optical coupler 3-3
Output from the input terminal 2. The multiplexer 7-2 includes the excitation light source 8
-2 is input to the second amplifier 6
You. The light partially branched by the optical coupler 3-3 is an optical bandpass.
The reference wavelength input to the filter 9-3 and selected there
λ ₀Is input to the photodetector 10-3 and converted into an electric signal.
Is converted. This electrical signal has a wavelength λ₀Output signal light
Indicates a voltage proportional to the power. The control circuit 12
Pump light source 8- so that the output of the device 10-3 is always constant.
2 is controlled.

Here, the gain of the first amplifier 5 is controlled in accordance with the equation (21), and the second amplifier 6 is controlled to keep the output signal light power of the reference wavelength λ ₀ constant in accordance with the equations (19) and (22). Control
A flat gain characteristic can be obtained. The gain of the second amplifying unit 6 may be controlled similarly to the first amplifying unit 5.

Hereinafter, a simulation in which the same Al co-doped Er ^{3 +} -doped optical fiber as the conventional example is used as the first amplifying section 5 and the Ge co-doped Er ^{3 +} -doped optical fiber is used as the second amplifying section 6. The results will be described.

First, coefficients α and β required for control are obtained according to the equations (21) and (22). The coefficients α and β are represented by the absorption / emission cross-section and its wavelength derivative as shown in equations (12) and (13). However, when actually obtaining it experimentally, the coefficients α and β are obtained from the slope of the wavelength dependence of the gain shown in the equation (10), instead of measuring the absorption / emission cross section. The method will be described below.

FIGS. 2 and 3 show gain characteristics per unit length of the first amplifier 5 and the second amplifier 6 in the wavelength range of 1548 nm to 1558 nm. Here, the upper-level ion density <N ₂ > is used as a parameter. That is, the slope of the wavelength dependence of the gain differs according to the upper-level ion density.

FIGS. 4 and 5 show the first amplifier 5 and the second amplifier 6 obtained from the wavelength dependence of the gain shown in FIGS.
5 shows the slope of the gain with respect to the gain of FIG. Here, the reference wavelength
The gain per unit length at 1553 nm and its slope are shown. As shown in FIGS. 4 and 5, the first amplifying unit 5 and the second amplifying unit 5
It can be seen that the slope of the gain is expressed by a linear function of the gain at the reference wavelength, as shown in equation (10), for both of the amplifying units 6 of FIG. The coefficients α and β can be determined from the slope and the intercept.

The coefficients α and β obtained from FIGS. 4 and 5 are as follows. First amplification unit 5 (Al co-doped Er ³⁺ doped optical fiber) α ₁ = −0.0180 [1 / nm] β ₁ = 0.0315 [dB / m / nm] Second amplification unit 6 (Ge co-doped Er ³ + ⁺ doped optical _{fiber) α 2 = -0.0781 [1 /} nm] β 2 = 0.0192 [dB / m / nm]

Using these coefficients α and β, equations (21) and (22)
FIG. 6 shows the gains of the first and second amplifying units for obtaining a flat gain characteristic with respect to the gain of the entire optical amplifier required to keep the output signal light power constant.
The fiber length of each of the first and second amplifying units is 18 m,
5 m. The solid line indicates the gain of the first amplifier, and the broken line indicates the gain of the second amplifier. By controlling each amplifier in accordance with the values shown in FIG. 6, flat gain characteristics can be realized.

FIG. 7 shows a calculation example of the output characteristics of the optical amplifier according to the embodiment. Here, 11 wavelength-multiplexed signal lights having a wavelength range of 1548 to 1558 nm and a channel interval of 1 nm are input to the optical amplifier, and the output power of the reference light (wavelength 1553 nm) is always constant.
Control to be 10dBm. The output signal light power of each wavelength when the input signal light power per wave at this time is used as a parameter is shown.

As shown in FIG. 7, the input signal light power is-
In the range of 30 dBm / ch to 30 dBm / ch, the wavelength dependence of the gain is within 0.9 dB, and the change of the output signal light power is about 0.7 dB at 1558 nm at the maximum. Compared with the conventional optical amplifier shown in FIG. 9, it can be seen that flat output characteristics are maintained for a wide range of input signal light power.

In the description of the present embodiment, the first and second amplifying sections are made of Al-codoped Er ³⁺ -doped optical fiber and G
e An example using co-doped Er ³⁺ -doped optical fiber is shown.
Any other composition may be used as long as the composition is different between the first and second amplification sections and the rare-earth-doped optical fiber has different wavelength dependence of the gain. Also, even when there are three or more types of amplifying units, a constant output signal light power can be obtained as in the present embodiment.

[0060]

As described above, the optical amplifier of the present invention cascade-connects amplifying sections composed of a plurality of types of rare-earth-doped optical fibers having different compositions, cancels the wavelength dependence of the gain of each amplifying section, and furthermore, The gain of each amplifying unit is controlled so that the gain of the entire optical amplifier obtained by combining the gains of the amplifying units becomes a predetermined value. Thereby, even when the input signal light power of the wavelength multiplexed signal light changes, the change in the output signal light power of the wavelength multiplexed signal light can be suppressed.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of an optical amplifier of the present invention.

FIG. 2 is a diagram showing a gain characteristic per unit length of a first amplification unit 5;

FIG. 3 is a diagram showing gain characteristics per unit length of a second amplification unit 6;

FIG. 4 is a diagram showing a slope of a gain with respect to a gain of a first amplification unit 5;

FIG. 5 is a diagram showing a slope of a gain with respect to a gain of a second amplification unit 6;

FIG. 6 is a diagram illustrating gains of first and second amplifying units with respect to a gain of the entire optical amplifier.

FIG. 7 is a diagram showing a calculation example of output characteristics of the optical amplifier according to the embodiment.

FIG. 8 is a diagram showing a configuration example of a conventional optical amplifier.

FIG. 9 is a diagram showing a calculation example of output characteristics of a conventional optical amplifier.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 input terminal 2 output terminal 3 optical coupler 4 optical isolator 5 first amplifier 6 second amplifier 7 multiplexer 8 excitation light source 9 optical bandpass filter 10 optical receiver 11, 12 control circuit

Claims (4)

[Claims] 1. A first to n-th amplifying section made of n kinds (n is an integer of 2 or more) of rare-earth-doped optical fibers having different compositions, and pump lights for exciting the first to n-th amplifying sections, respectively. The first to n-th excitation light sources to be generated, and excitation light input means for inputting the respective excitation lights to the first to n-th amplification units, respectively, wherein the first to n-th amplification units are cascaded. In the optical amplifier configured by connection, the logarithmic gain G _j (λ) of the j-th amplification unit is developed as a power of the wavelength λ, and G _j (λ) = G _0j + (α _1j G _0j + β _1j ) (λ−λ ₀ ) + (α _2j G _0j + β _2j ) (λ−λ ₀ ) ² + ... + (α _ij G _0j + β _ij ) (λ−λ ₀ ) ⁱ + ... + (α _{(n−1) j} G _0j + β _{(n-1) j} ) (λ−λ ₀ ) ⁽ⁿ⁻¹⁾ (1), where G _0j is the logarithmic gain of the j-th amplifier at the reference wavelength λ ₀ , α _ij and β _ij Is the coefficient of λ ⁱ , Further, the input signal light power of the signal light of the reference wavelength λ ₀ is Pin ₀ , the output signal light power is Pout _0, and the logarithmic gain G _{t of the} entire optical amplifier is G _t = log [Pout ₀ / Pin ₀ ] ( 4), the logarithmic gain G _{01 of the} first to n-th amplification units
~ G _0n is An optical amplifier comprising control means for controlling the first to n-th pumping light sources so as to have a value given by: 2. The method according to claim 1, wherein when the constants δ ₁ to δ _(n−1) are set for each of the amplifying sections according to the wavelength dependence of the gain of the optical amplifier according to claim 1, Logarithmic gain G _{01 of} amplifying section
G _0n is given by An optical amplifier comprising control means for controlling the first to n-th pumping light sources so as to have a value given by: 3. The optical amplifier according to claim 1, wherein the control means includes an input signal light power Pin having a reference wavelength λ _0.
0 and the log-gain G ₀₁ ~G _0n of the amplifier of the first to n monitors, optical amplifier which is a configuration for controlling the first to excitation light source of the n accordingly. 4. The optical amplifier according to claim 1, wherein when n = 2, the input signal light power Pin ₀ of the reference wavelength λ ₀ and the logarithmic gains G ₀₁ , G ₀₁ , of the first and second amplifying units. G
₀₂ , and the logarithmic gains G ₀₁ , G _{02 of} the first and second amplifying sections are calculated accordingly. An optical amplifier comprising control means for controlling the first and second pumping light sources so as to obtain a value given by: