JPH10335730A - Light amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To cancel the intensity deviation between the channels of wavelength multiplied signal light. SOLUTION: A light circulator 4 is inserted halfway on a light amplifying fiber 2 while this light circulator 4 is provided with a reflecting means 8, so that the wavelength of the wavelength multiplied light inputted in the light amplifying fibers 2 may be selected by the rectifying means 8 to be properly attenuated for amplification, by the reflectance of the reflecting means 8 set up per wavelength so as to be outputted as the signal light in no intensity deviation from the light amplifying fibers 2 to the channels.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplifier for amplifying an optical signal in various optical communication systems, and is particularly suitable for use in wavelength division multiplexing optical communication.

[0002]

2. Description of the Related Art In an optical fiber communication system, a regenerative repeater is used which converts an optical signal into an electric signal, amplifies the signal, and then outputs the signal again as an optical signal. Amplifying optical fiber amplifiers, particularly those called erbium-doped optical fiber optical amplifiers (EDFAs), have been rapidly commercialized. The application range of the EDFA is expanding, and it also extends to wavelength division multiplexing optical communication (WDM), which has attracted attention as high-capacity optical communication. Wavelength division multiplexing optical communication uses signal light of a plurality of different wavelengths, carries information on each light, multiplexes these by a wavelength division multiplexer, and transmits them as an optical fiber as wavelength multiplexed signal light. The communication capacity per fiber can be greatly increased as compared with the conventional optical communication using only one light.

The EDFA can amplify WDM wavelength multiplexed signal light at a time, and is expected to be a simple linear repeater replacing a conventional regenerative repeater in a WDM system. There are also problems that need to be solved in order to use in a WDM system. EDFA
Is to excite erbium ions in the EDF by passing excitation light of a predetermined wavelength through an erbium-doped fiber (EDF), to create a population inversion state of electrons in the EDF, and to pass a signal light through the EDF in the population inversion state, The light having the same wavelength as that of the signal light is stimulated to be emitted to amplify the passing signal light. In this case, the gain characteristic of each wavelength (channel) causes a deviation in gain between channels due to the EDF absorption coefficient, stimulated emission coefficient, inversion distribution state, and the like.
Also, a gain deviation between channels is caused by a change in the inversion distribution state due to a change in the intensity of the input signal light.
Even if the signal light is input to A, the signal light output from the EDFA may have an intensity difference depending on the wavelength. That is,
EDFA gain has wavelength dependence. EDFA
When multi-stages are connected as a linear repeater, the gain difference between wavelengths is integrated and increased, which causes a larger problem, and limits the transmission characteristics of the system.

As a method for solving such a problem, a method has been proposed in which a correction filter for flattening a gain spectrum is inserted into an EDFA. A typical one is disclosed in US Pat. No. 5,260,823. No. (US5, 26
0, 823). According to the present invention, E
It is shown that a flat gain spectrum can be obtained in a wide band by reducing a gain peak near 1530 nm characteristic of an EDFA by a filter inserted in the DFA.

On the other hand, as a correction filter used for eliminating the level variation between the wavelength lights of the wavelength multiplexed signal light, a transmission filter combining a fiber grating and an optical circulator as disclosed in JP-A-7-336327 is used. There is a type filter. This filter vertically connects a plurality of fiber gratings B1, B2,... Bn to a second port of an optical circulator A having three ports as shown in FIG. Wavelength λ at B2,... Bn
1, λ2... Λn are selectively reflected, and the light input to the first port of the optical circulator A and reflected by the fiber gratings B1, B2,. Things.

[0006] Japanese Patent Application Laid-Open No. 7-226560 discloses an optical amplifier suitable for wavelength division multiplexing communication in which an optical circulator and wavelength selective reflection means are combined. This optical amplifier has three ports, as shown in FIG. 9, and an optical amplifier fiber C which is pumped with pump light from a pump light source (not shown) at a second port of an optical circulator A.
And a wavelength-selective reflection means D for reflecting signal light is inserted in the longitudinal direction of the fiber C, and is input from the signal light input port E and amplified by the optical amplification fiber C. The signal light reflected by the selective reflection means is output from the signal light output port F.
In this case, a deviation corresponding to the wavelength occurs in the gain of each signal light amplified by the optical amplification fiber C. Therefore, the reflection means D is provided independently for each signal light, and these reflection means D are provided by the optical amplification fiber C. Are distributed in the longitudinal direction, and the amplification distances of the respective signal lights are made different so as to eliminate the difference in gain, so that the gains of the signal lights output from the signal light output ports F are made uniform. You can do it.

[0007]

Among the techniques disclosed for eliminating the level deviation of wavelength multiplexed signal light in an optical amplifier, US Pat. No. 5,260,823 discloses a gain peak near 1530 nm characteristic of an EDFA. Therefore, it is difficult to perform accurate level adjustment to each signal light, and in a wavelength division multiplexing system in which optical amplifiers are connected in multiple stages and transmitted over long distances, the final output has a level deviation. May occur.

Further, the optical amplifier shown in FIG. 9 comprises fiber gratings B1, B distributed in an optical amplification fiber C.
By changing the position of 2,... Bn, the final output level can be made uniform by changing the propagation distance of each signal light in the optical amplification fiber C. However, the fiber grating B1 is provided in the optical amplification fiber C. , B2,..., And Bn have a number of reflection points in the amplification fiber, so that noise characteristics may be degraded due to multiple reflection of signal light or the like.

In addition, in order to eliminate the intensity deviation between signal lights by inserting a correction filter (wavelength selective filter) for flattening the gain spectrum in an optical fiber amplifier such as an EDFA, the gain of the optical amplification fiber must be increased. It is necessary to properly set the characteristics (reflection characteristics and transmission characteristics) of the correction filter according to the characteristics. In this case, it is necessary to adjust the length of the optical amplification fiber and replace parts such as the optical amplification fiber and fiber grating. Therefore, a great deal of time is required for setting during the production of the optical amplifier, maintenance after production, and setting change.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide an EDF.
Correcting the wavelength existence of an optical fiber amplifier such as A, and eliminating wavelength-dependent gain or output light intensity deviation;
It is an object of the present invention to provide an optical amplifier which can easily adjust the wavelength dependency of an optical fiber amplifier such as a DFA when obtaining an output without gain deviation.

[0011] The optical amplifier according to claim 1 of the present invention comprises:
The signal light input to the signal light input port 1 is input to the optical amplification fiber 2, is excited by the pump light, and is optically amplified in the optical amplification fiber 2 having the optical amplification effect by stimulated emission, and the signal light output port 3 In the optical amplifier, the optical circulator 4 having at least three ports is provided between the signal light input port 1 and the signal light output port 3, and the light input to the first port 5 is transmitted to the second port. Light output from the port 6 and input to the second port 6 is inserted so as to be output from the third port 7, and light emitted from the port 6 is reflected by the second port 6 of the optical circulator 4. The reflection means 8 is connected, and the reflection means 8 selectively reflects each of two or more signal lights having different wavelengths input from the signal light input port 1, and outputs the light from the signal light output port 3. Output, and Is characterized in that with the reflective properties of light intensity deviation between two or more of the signal light power is reflected so as to be smaller.

The optical amplifier according to the second aspect of the present invention comprises:
The optical circulator 4 to which the reflection means 8 is connected is inserted before, after, or in the middle of the optical amplification fiber 2.

An optical amplifier according to a third aspect of the present invention comprises:
The optical circulator 4 and the reflection means 8 are connected by an optical connector 12 so as to be detachable.

An optical amplifier according to a fourth aspect of the present invention comprises:
The second port 6 of the optical circulator 4 has at least one input port 9 and two or more output ports 10, and light incident on the input port 9 is switched to a desired one of the two or more output ports 10. Switching means 1 capable of emitting light
1 and each output port 10 of the switching means 11
Are connected to reflecting means 8 having different characteristics for reflecting the signal light input to the signal light input port 1, and each reflecting means 8 reflects a predetermined signal light and outputs it from the signal light output port 3. Further, it has a reflection characteristic such that a light intensity deviation between two or more output signal lights is reduced.

According to a fifth aspect of the present invention, there is provided an optical amplifier comprising:
From the signal light input to the signal light input port 1 or the signal light propagated between the signal light input port 1 and the signal light output port 3, the signal light is monitored to determine the wavelength arrangement, the light intensity for each wavelength, and the like. The signal light monitor 18 to be detected and the signal light monitor 1
Switching means 1 for controlling the switching of output port 10 of switching means 11 based on the information of the signal light detected at 8
9 is provided.

The optical amplifier according to claim 6 of the present invention comprises:
The optical circulator 4 and the switching means 11 are connected by an optical connector 12 and are detachable.

According to a seventh aspect of the present invention, there is provided an optical amplifier comprising:
At least one of the reflection means 8 connected to each output port 10 of the switching means 11 is characterized in that a combination of selective reflection wavelengths is different from a combination of selection wavelengths of other reflection means.

An optical amplifier according to claim 8 of the present invention comprises:
The reflection means 8 includes a fiber grating.

[0019]

FIG. 1 shows a first embodiment of an optical amplifier according to the present invention.
1 is an embodiment of the present invention. The optical amplifier (ED
FA) is a signal light input port 1, an optical isolator 13
a, 13b, wavelength multi-wavers 14a, 14b, pump light sources 15a, 15b, erbium-doped optical fiber (optical amplification fiber) 2 (2a, 2b), optical circulator 4 having three ports 5, 6, 7; fiber When the excitation light sources 15a and 15b are driven to inject the excitation light into the erbium-doped optical fibers 2a and 2b, the optical fibers 2a and 2b Has an optical amplifying function, and converts the wavelength-multiplexed signal light input to the signal light input port 1 and output from the signal light output port 3 into the optical amplification fibers 2a and 2b.
Optical amplification. The wavelength multiplexed signal light input to the signal light input port 1 is composed of a plurality of signal lights having different wavelengths (the wavelength of each signal light is λn (hereinafter, n is n = 1, 2,...)
..)) are multiplexed, and the signal light that has been individually amplified is output from the signal light output port 3 as a wavelength multiplexed signal light. If the optical amplification fiber used is an erbium-doped fiber, the wavelength multiplexed signal light is in the amplification band of 1.53 to 1.61 μm.
For example, 1.5485, 1.5501, 1.5517,
It is obtained by multiplexing light of each wavelength of 1.5533 μm.
As the two pumping lights output from the pumping light sources 15a and 15b, light having a wavelength of 0.98 μm band or 1.48 μm band is generally used.

The erbium-doped optical fibers 2a, 2b
The optical circulator 4 inserted therebetween propagates the erbium-doped optical fiber 2a and outputs light input to the first port 5 from the second port 6, and outputs light input to the second port 6 to the second port 6. The light is output from the three ports 7 and can be propagated to the erbium-doped optical fiber 2b. Further, the light output from the second port 6 is reflected by the fiber grating 8 and returned to the second port 6. Thus, the light propagating in the erbium-doped optical fiber 2a can be reflected by the fiber grating 8 and propagated to the erbium-doped optical fiber 2b.

The fiber grating 8 can selectively reflect only two or more light beams having a desired wavelength, and can set a desired reflectance Rn for each light beam. Only the desired wavelength light can be selected from the light propagated to the erbium-doped optical fiber 2b, and the light intensity of each wavelength light propagated to the erbium-doped optical fiber 2b can be individually adjusted. It is like that. The specific wavelength light refers to an optical signal relayed by the present optical amplifier, the desired reflectance Rn is the reflectance for each signal light to be relayed, and in the present invention, the intensity deviation at the signal light output port 3 is defined as It is set to be canceled. An example of a method for setting the reflectance Rn will be described below.

The light intensity of each channel (signal light of wavelength λn) incident on the signal light input port 1 is represented by Pn (d
B) The gain received by the two erbium-doped optical fibers 2a and 2b is Gn (dB), the optical loss in the optical fiber amplifier is In (dB), and the intensity emitted from the signal light output port 3 is P'n ( dBm), P'n
= Pn + Gn + Rn -In
By setting Rn so that n = -Pn-Gn + P'm + In (m is a certain channel number), P'1
= P'2 = P'3 =... = P'm, and an output having no output intensity deviation between channels can be obtained at the signal light output port 3. Although m may be any channel number, the output from the output port 3 is the smallest before the intensity deviation is eliminated, that is, P′n ≧ P′m (n
= 1, 2,...).

[0023]

FIG. 2 shows a second embodiment of the optical amplifier according to the present invention.
In this embodiment, the fiber gratings 8 (8a, 8a,
8b, 8c, 8d), and fiber gratings 8a, 8b, 8 connected to the second port 6 of the optical circulator 4 by the optical switching means 11.
c and 8d can be easily switched. The optical switching means 11 has one input port (also an output port) 9 on the side connected to the second port 6 of the optical circulator 4, and four output ports (also an input port) 10a on the opposite side. , 10b, 10c, 10
d, input ports 9 and four output ports 10a, 10b, 10
c and 10d can be optically connected to a desired one. In the optical switching means 11, the signal light output from the second port 6 of the optical circulator 4 is input, and the fiber gratings 8a, 8b, 8c, 8
d can be output to a desired one of the ports 10a to 10d to which the fiber gratings 8a, 8b, 8c, 8d are output.
The signal light reflected and input by the optical circulator 4 can be input to the second port 6 of the optical circulator 4.

The individual fiber gratings 8a, 8b, 8c, 8d connected to the optical switching means 11
Have different reflection characteristics, so that the signal light input to the signal input port 1 is reflected by one of these fiber gratings 8a, 8b, 8c, 8d and output from the signal output port 3. It is. FIG. 7 shows a specific example of the reflection characteristics of the fiber gratings 8a, 8b, 8c and 8d. In this case, the fiber grating 8a has a high reflectance on the short wavelength side and a low reflectance on the long wavelength side. The fiber grating 8d has such a characteristic that the reflectance is low on the short wavelength side and the reflectance is high on the long wavelength side, and the fiber gratings 8b and 8c have intermediate reflection characteristics. The selection from these fiber gratings 8a, 8b, 8c, 8d depends on the characteristics of the input wavelength multiplexed signal light (the intensity of each input signal channel, the total intensity thereof, the wavelength arrangement,
The number of channels may be selected based on a predetermined criterion, for example, according to the intensity of each wavelength light of the input wavelength multiplexed signal light, or a combination of channel wavelengths of the wavelength multiplexed signal light. May be selected based on a predetermined determination criterion in accordance with the change of. In the former example, when the wavelength light on the short wavelength side is at a high level and the wavelength light on the long wavelength side is at a low level, the fiber grating 8d shown in FIG. 7 can be selected to reduce the level deviation.
The number of fiber gratings 8 and the number of output ports 10 in the optical switching means 11 are not limited to the example of the present embodiment, and according to the present configuration example, if a plurality of fiber gratings 8 are provided in advance, there is no replacement of parts. Can change the characteristics of the amplifier.

The switching means 11 can be used to switch between combinations of channel wavelengths and changes in the wavelength arrangement.
A fiber grating 8 having a different combination of selective reflection wavelengths may be attached to each of the output ports 10 described above. For example, fiber gratings 8a, 8b, 8 shown in FIG.
A fiber grating 8e corresponding to the signal light of 8 channels may be attached in addition to c and 8d. In this case, it is easy to cope with the case where the number of channels is increased from 4 to 8 to increase the transmission capacity. In addition, the fiber gratings 8a, 8b, 8c, and 8d have 1.5485 to
When it corresponds to the signal light of four channels up to 1.5535 μm, in addition to these, 1.5533 μm to
If another fiber grating 8 corresponding to the signal light of four channels up to 1.5582 μm is connected to the optical switching means 11, it is possible to easily cope with a change in the combination of the channel wavelengths.

[0026]

Third Embodiment FIG. 3 shows a third embodiment of the optical amplifier according to the present invention, in which a fiber is provided by interposing an optical connector 12 in the second port 6 of the optical circulator 4 of the optical amplifier shown in FIG. Grating 8 (8a, 8b, 8c, 8
d) is connected. In this example, the second
One end (male connector or female connector) 12b of the optical connector 12 is connected to the port 6, and the fiber grating 8
By connecting the other (female connector or male connector) 12a of the optical connector 12 to a, 8b, 8c and 8d,
Various fiber gratings 8a, 8b, 8c, 8d having different characteristics can be easily attached to and detached from the second port 6 of the optical circulator 4. The characteristics of the fiber gratings 8a, 8b, 8c, 8d to be connected are determined, for example, by the input signal characteristics. For example, the selection may be made according to the strength of each channel of the input signal, or may be selected according to a change in the combination of the channel wavelengths of the wavelength multiplexed signal. According to this configuration example, the characteristics of the amplifier can be easily changed only by replacing the fiber gratings 8a, 8b, 8c, and 8d.

[0027]

[Fourth Embodiment] FIG. 4 shows a fourth embodiment of the optical amplifier according to the present invention. In the optical amplifier shown in FIG. A switching means 19 is provided between the signal light monitor 18 and the optical switching means 11.
The signal light monitor 18 branches a part of the signal light input to the signal light input port 1, monitors the branched light with a light receiving element or the like, and measures the intensity of the wavelength-multiplexed signal light for each channel, The sum, the intensity, the wavelength arrangement, the number of channels, and the like are detected, and the detection result is output to the switching means 19 as an information signal. The switching means 19 includes:
By comparing the information of the information signal input from the signal light monitor 18 with a database or the like indicating the characteristics of the fiber gratings 8a, 8b, 8c and 8d attached to the optical switching means 11, the four fiber gratings are obtained. 8a, 8b, 8c and 8d, a fiber grating 8 suitable for the input signal light at that time.
One of a, 8b, 8c, and 8d is specified, and based on the result, the optical switching means 11 is controlled to switch so that appropriate fiber gratings 8a, 8b, 8c, and 8d are selected. The signal light monitor 18 may be provided at any position between the signal light input port 1 and the signal light output port 3.

[0028]

Fifth Embodiment FIG. 5 shows a fifth embodiment of the optical amplifier according to the present invention.
a, insert a 4-port optical circulator 4 between 2b
The first port 5 propagates through the erbium-doped optical fiber 2a.
The light input to the second port 6 is output from the second port 6, the light input to the second port 6 is output from the third port 7, and propagates to the erbium-doped optical fiber 2b, and further propagates through the erbium-doped optical fiber 2b. Then, the light input to the third port is output from the fourth port 16 and the fourth port 1
The light input to 6 can be output from the first port 5 and propagated to the erbium-doped optical fiber 2a. In this case, the fiber grating 8 for selectively reflecting each wavelength light of the wavelength multiplexed signal light is connected to the second port 6 as in the other embodiments, but the erbium-doped optical fiber 2b is connected to the fourth port 16. A fiber grating 17 for selectively reflecting the pumping light from the pumping light source 15b that is propagated through the fiber grating 17 is connected. In this embodiment, the excitation light from the excitation light source 15b is also propagated to the erbium-doped optical fiber 2a via the fiber grating 17 connected to the optical circulator 4 to excite the fiber 2a.

[0029]

Sixth Embodiment FIG. 6 shows a sixth embodiment of the optical amplifier according to the present invention, in which the pump light of the pump light source 15 is inputted from the signal light incident end side of the erbium-doped optical fiber 2 and the optical fiber is input. 2 is an example in which an optical circulator 4 is provided at the end of the erbium-doped optical fiber 2 with forward excitation for exciting 2. That is, the end of the erbium-doped optical fiber 2 is connected to the first port 5 of the optical circulator 4, the signal light output port 3 is connected to the third port 7 of the optical circulator 4, The wavelength multiplexed signal light output to the two ports 6 is reflected back by the reflection means 8 and output from the third port 7 to the signal light output port 3.

The optical amplifier of the present invention may have the following configuration in addition to the above description. 1. In FIG. 2 using the optical switching means 11, the optical switching means 11 may be configured to be detachable from the second port 6 of the optical circulator 4 using the optical connector 12. In this example, the fiber grating 8 can be replaced together with the optical switching means 11. 2. The fiber grating 8 connected to the second port 6 of the optical circulator 4 can have various desired characteristics. The desired reflection wavelength, reflection, and the like depend on the wavelength of the signal light, the number of multiplexed signal lights, the characteristics of the amplifier, and the like. You can create something with a rate.

[0031]

According to the optical amplifier according to the first and second aspects of the present invention, it is possible to amplify a wavelength-division multiplexed signal without wavelength deviation by correcting the wavelength dependency.

According to the optical amplifier of the third aspect of the present invention, since the attaching and detaching of the reflecting means 8 is easy, for example, even in a system in which the intensity deviation between the signals varies, the reflecting means 8 is used each time. In other words, stable communication without intensity deviation can be performed.

According to the optical amplifier according to the fourth aspect of the present invention, it is possible to mount a plurality of reflecting means 8 having necessary characteristics in advance, and to switch between them by the switching means 1.
For example, even in a system in which the intensity deviation between signals fluctuates, the reflection unit 8 is switched each time, and stable communication without an intensity deviation can be performed.

According to the optical amplifier according to the fifth aspect of the present invention, since an appropriate reflecting means 8 is automatically selected according to the characteristics of the input signal light, the characteristics of the input signal light change. Automatic operation of the system is also possible with the system.

According to the optical amplifier of the present invention, the switching means 11 can be easily attached and detached. For example, the reflection means 8 is switched every time even in a system in which the intensity deviation between signals varies. In addition, the communication can be performed stably without any intensity deviation by changing or changing the communication.

According to the optical amplifier of the present invention, at least one of the reflecting means 8 connected to the port 10 of the switching means 11 has a combination of selective reflection wavelengths of other reflecting means. Since this is different from the combination of the selected wavelengths, it is possible to cope with a change in the communication channel.

According to the optical amplifier of the present invention, since a fiber grating is adopted for the reflection means 8, the degree of freedom in designing the reflection wavelength and the reflectance of the reflection means 8 is high, so that it can be applied to various systems. Suitable products can be easily manufactured.

[Brief description of the drawings]

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

FIG. 2 is a schematic diagram showing a second embodiment of the optical amplifier of the present invention.

FIG. 3 is a schematic diagram showing a third embodiment of the optical amplifier of the present invention.

FIG. 4 is a schematic diagram showing a fourth embodiment of the optical amplifier of the present invention.

FIG. 5 is a schematic diagram showing a fifth embodiment of the optical amplifier of the present invention.

FIG. 6 is a schematic diagram showing a sixth embodiment of the optical amplifier of the present invention.

FIG. 7 is an explanatory diagram showing an example of the characteristics of a fiber grating.

FIG. 8 is a schematic diagram of a wavelength selection filter using a conventional optical circulator.

FIG. 9 is a schematic diagram of an optical amplifier used for conventional wavelength division multiplexing communication.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 signal light input port 2 optical amplification fiber 3 signal light output port 4 optical circulator 5 first port 6 second port 7 third port 8 reflecting means 9 input port 10 output port 11 switching means 12 optical connector 18 signal light monitor 19 switching means

Claims (8)

[Claims] A signal light input to a signal light input port (1) is input to an optical amplification fiber (2), and is excited by pumping light and has an optical amplification effect by stimulated emission. An optical amplifier which is optically amplified inside and is output from a signal light output port (3), has at least three ports between the signal light input port (1) and the signal light output port (3). Optical circulator (4)
Is inserted such that the light input to the first port (5) is output from the second port (6) and the light input to the second port (6) is output from the third port (7). A reflection unit (8) for reflecting light emitted from the port (6) back to the second port (6) of the optical circulator (4);
And the reflection means (8) selectively reflects each of two or more signal lights having different wavelengths input from the signal light input port (1), and from the signal light output port (3). An optical amplifier, which has a reflection characteristic to output and reflect so as to reduce a light intensity deviation between two or more output signal lights. 2. An optical amplifier according to claim 1, wherein the optical circulator (4) connected to the reflection means (8) is inserted before, after, or in the middle of the optical amplification fiber (2). 3. An optical circulator (4) and a reflecting means (8).
3. The optical amplifier according to claim 1, wherein said optical amplifier is detachably connected by an optical connector. 4. An optical circulator (4) having at least one input port (9) at a second port (6) and at least two output ports (10), and light incident on the input port (9). Is connected to a switching means (11) capable of switching to and outputting a desired one of two or more output ports (10), and to each output port (1) of the switching means (11).
0) is connected to reflection means (8) having different characteristics for reflecting the signal light input to the signal light input port (1), and each reflection means (8) reflects a predetermined signal light, 3. An optical amplifier according to claim 1, wherein said optical amplifier has a reflection characteristic such that a light intensity deviation between two or more signal lights outputted from said signal light output port and outputted is reduced. 5. A signal light input to a signal light input port (1) or a signal light propagated between a signal light input port (1) and a signal light output port (3) to monitor the signal light. A signal light monitor (18) for detecting the wavelength arrangement, light intensity for each wavelength, and the like; and an output port (10) of the switching means (11) based on information on the signal light detected by the signal light monitor (18). The optical amplifier according to claim 4, further comprising a switching unit (19) for switching and controlling the switching. 6. The optical amplifier according to claim 4, wherein the optical circulator (4) and the switching means (11) are connected by an optical connector (12) and are detachable. 7. At least one of the reflection means (8) connected to each output port (10) of the switching means (11) has a combination of the selective reflection wavelength and the combination of the selection wavelengths of the other reflection means. 7. The optical amplifier according to claim 4, wherein said optical amplifier is different. 8. The optical amplifier according to claim 1, wherein the reflection means includes a fiber grating.