JPH0884122A - Optical communication system and its method - Google Patents

Abstract

PURPOSE: To transmit sub-signal light from a repeater in an optical transmission system without exerting influence upon a light amplifying function for a main signal light. CONSTITUTION: This optical communication system is provided with light amplifying fibers 5a, 5b constituting part of a transmission line for transmitting at least main signal light a 1st signal light), consisting of optical fibers for amplifying the main signal light and including an additional substance to be activated by exciting light, an exciting light source 13 for outputting exciting light to be made incident upon the fibers 5a, 5b from the main signal light output terminal sides of the fibers 5a, 5b by intensity corresponding to an inputted driving current signal and a driving means A consisting of a means for supplying a driving current signal with required intensity to the light source 13 and capable of supplying a driving current signal including prescribed information to the light source 13 and generating sub-signal light a 2nd signal light) without modulating the intensity of the exciting light outputted from the light source 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber amplifier mainly used as a repeater in optical communication and forming a part of a transmission line of an optical communication system, and further to an optical fiber amplifier using the optical fiber amplifier. The present invention relates to an optical communication method of a communication system.

[0002]

2. Description of the Related Art Conventionally, in an optical communication system using signal light (main signal light), as a method of monitoring the operating state of an optical amplifying device used as a relay optical amplifier, information indicating the operating state of the device is used. This is done by intensively transferring the signal light (surveillance signal) responsible for the above to the surveillance station. As a method of transferring the supervisory signal, for example, wavelength division multiplexing (WD) using signal light having a wavelength different from that of the main signal light is used.
M: Wavelength-Division-Multiplexing) communication technology is used, or a method of transferring by low frequency signal light using a frequency band lower than the frequency band of the main signal light is proposed (Japanese Patent Laid-Open No. 5-244098). JP-A-6-1048
No. 40).

[0003]

As described above, in the conventional optical communication system, if the supervisory signal light is transferred by using the wavelength division multiplexing communication technique in order to monitor the respective operating states of the repeater amplifier, it is very difficult. The number of optical components increases, and the signal detection circuit becomes complicated when low-frequency signal light is used. Specifically, it is necessary to newly provide an optical transmitter and an optical receiver for transferring the monitoring signal light, and a multiplexer for adding the monitoring signal light to the optical transmitter. The optical receiving section requires a wavelength separation filter or the like for extracting the signal light, which causes a problem that the relay optical amplifier itself becomes large-scaled and complicated.

The present invention has been made in order to solve the above problems, and does not require a new light source, and does not affect the optical amplification function of the main signal light in the repeater amplifier. An optical fiber amplifier as a relay amplifier, a relay optical fiber amplifier including the optical fiber amplifier, and a relay optical fiber amplifier that enable transfer of a sub-signal light that carries a monitoring signal different from light. Another object of the present invention is to provide a conventional optical communication system and an optical communication method thereof.

[0005]

An optical communication system according to the present invention comprises at least two communication stations (first and second communication stations) and an information transmission path installed between these communication stations, A plurality of optical fibers forming one or more signal light transmission lines and the optical fibers are installed between the optical fibers, and the optical fibers are optically connected to form a part of the transmission line. It is characterized by having a main path composed of a plurality of relay optical fiber amplifiers. Further, this optical communication system constitutes a bidirectional communication system by installing the main paths in parallel between the communication stations. Further, the optical communication method according to the present invention assumes the optical communication system having one or more main routes between the communication stations as described above.

In particular, the relay optical fiber amplifier is installed in the main path at predetermined intervals in order to enable long-distance communication in the optical communication system (light intensity amplifying means of signal light propagating in the main path). Optical fiber amplifier.
The optical fiber amplifier is an optical fiber that constitutes at least a part of a transmission line for propagating the main signal light (first signal light) and optically amplifies the main signal light. The optical amplification fiber to which a substance to be converted (for example, a rare earth element such as erbium) is added, and one end face of this optical amplification fiber (the side from which the main signal light is emitted) is incident on the optical amplification fiber. A pumping light source for outputting the pumping light to be output at an intensity corresponding to the input driving current signal, and a means for supplying a driving current signal of desired intensity to the pumping light source, the pumping light source including predetermined information. At least, a driving unit that supplies a drive current signal to the pumping light source and modulates the intensity of the pumping light output from the pumping light source to generate sub-signal light (second signal light). There is.

One end of the optical amplification fiber is optically connected to the output end of the adjacent optical fiber (input side optical fiber) in the preceding stage where the main signal light is propagated, and the other end is intensity-amplified. A part of the transmission path is formed by optically connecting with the input end of an adjacent optical fiber (output side optical fiber) in the subsequent stage for outputting the main signal light. Further, the pumping light generated as the sub-signal light is transmitted at least in a direction opposite to the propagation direction of the main signal light. Therefore, it further comprises a wavelength selective coupler for separating the sub-signal light incident from the output optical fiber and the reflected light of the main signal light.

The driving means is connected to the excitation light source,
Also, a first drive circuit that supplies a first drive current signal having a constant intensity to the pumping light source to realize a light amplification function, and a first driving circuit that is connected in parallel with the first driving circuit to the pumping light source, A second modulated signal corresponding to encoded data for transmitting signal light, which is superimposed on the first drive current signal;
Second driving circuit for supplying the driving current signal to the pumping light source, and a modulation signal obtained by coding the NRZ code corresponding to predetermined information into a ternary CMI code to the second driving circuit. Or a ternary CM for decoding a ternary CMI code corresponding to predetermined information received from the outside into an NRZ code
At least an I code / decoder is provided.

Further, this optical fiber amplifier can also adopt a structure capable of multistage amplification, and specifically, it is provided with a branching coupler for branching the pumping light containing predetermined information in at least two directions. , A first optical amplification fiber that realizes an optical amplification function by at least the first pumping light branched by the branching coupler, and a second pumping light branched by the branching coupler. You may comprise by connecting in series with the 2nd optical amplification fiber which implement | achieves an optical amplification function via a multiplexer / demultiplexer. Note that the multistage amplification configuration and the transmission of the above-described sub-signal light (pumping light) in the opposite direction to the main signal light are independent technical ideas. Therefore, the transmission direction of the sub-signal light in the case of the multistage amplification configuration may be either forward or reverse to the main signal light,
Further, when the sub-signal light is transmitted in the opposite direction to the main signal light, the amplification configuration may be only one stage or multi-stage amplification configuration.

The pulse width of the ternary CMI code is
It is set to be shorter than the photon lifetime of the excitation light.

On the other hand, as described above, the optical communication method according to the present invention is installed between a plurality of optical fibers which are transmission lines for transmitting signal light, and constitutes a part of the transmission lines. In an optical communication system including at least an optical fiber amplifier for relay having a pumping light source for outputting pumping light for optical amplification, modulating a driving current signal supplied to the pumping light source according to predetermined information. Is characterized in that the intensity of the pumping light is modulated and the pumping light is used as the sub-signal light. Then, the propagation direction of the sub-signal light is made opposite to the propagation direction of the main signal light, and this sub-signal light is used as signal light for propagating the supervisory signal in the optical communication system.

At this time, the driving current signal supplied to the pumping light source is a first driving current signal having a constant intensity for outputting the pumping light, and a second modulation signal carrying predetermined information.
The second driving current signal is a ternary CMI code in which the occurrence probabilities of the positive pulse and the negative pulse are equal to each other. It is characterized in that it is a modulated signal coded in.

[0013]

The optical communication system according to the present invention, in particular, the optical fiber amplifier as the repeater amplifying means outputs the exciting light so that the exciting light for optical amplification can be used as the information transmitting means independent of the main signal light. The drive means of the excitation light source is the transmission control means of the optical signal. As a result, it is not necessary to provide a control unit separate from the relay amplification unit, and an independent optical transmission unit can be easily realized in the main path of the optical communication system.

In particular, according to the present invention, the pumping light (the sub-signal light such as the monitor signal) is transmitted in the direction opposite to the main signal light,
It is possible to reduce the influence on the transmission of the main signal light and increase the output of the main signal light (backward pumping).

The drive current signal from the drive means to the excitation light source is a current signal in which a modulation signal carrying predetermined information is superimposed on a normal drive current signal. This modulation signal is a ternary CMI (C
Since the ode mark inversion code is used, there is no effect on the decrease in the light intensity of the excitation light (the average light intensity of the excitation light does not change). In particular, since the pulse width of the modulated signal is sufficiently shorter than the photon lifetime of the pumping light (about 10 msec), it does not affect the optical amplification characteristic of the optical fiber amplifier. In the case of multi-stage amplification, separate pumping lights branched in the front stage (main signal light incident side) and the rear stage (main signal light emitting side) are used, so the front stage pumping light is used as the sub-signal light. Even when used (usually, the latter stage has higher optical amplification characteristics than the former stage), the fluctuation of the former optical amplification characteristics does not affect the latter optical amplification characteristics, and the overall optical amplification characteristics are stable. Is obtained.

Further, in the optical communication system and the optical communication method according to the present invention, the pumping light usable as the sub-signal light is branched into two or more, so that not only the optical amplification and the sub-signal light but also the pumping light is obtained. Can also be applied to other uses.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. In the figure, the same parts are designated by the same reference numerals and the description thereof will be omitted.

FIG. 1 is a diagram showing a first basic configuration according to an embodiment of an optical communication system according to the present invention. The optical communication system includes at least a first communication station 1 and a second communication station 2. And a main path connecting these first and second communication stations 1 and 2. In particular, this main path is installed between a plurality of optical fibers 30b forming one or more signal light transmission paths and each optical fiber 30b,
In addition, a plurality of relay optical fiber amplifiers 30 that form a part of the transmission path by optically connecting the optical fibers 30b.
and a.

In this embodiment, the first communication station 1 is a transmission station having an optical transmitter 101 (indicated by OS in the figure), and the second communication station 2 is an optical receiver 201 (shown in the figure). , OR). The plurality of relay optical fiber amplifiers 30a are installed, for example, at intervals of 80 km, and constitute the inline amplifier group 3 in the main path.
Between the second communication station 1 and the in-line amplifier group 3, and a second amplifier between the second communication station 2 and the in-line amplifier 3 is provided between the second communication station 2 and the in-line amplifier 3. A preamplifier 4b (optical fiber amplifier) for improving the reception sensitivity at the communication station is installed.

Further, the sub-signal light which carries the supervisory signal or the like is transmitted in the opposite direction in order to reduce the influence on the transmission state of the main signal light. When the wavelength of the pumping light of each relay optical fiber amplifier 30a (including the other amplifiers 4a and 4b) is, for example, 1.55 μm as the wavelength of the main signal light, it practically affects the transmission of the main signal light. The wavelength may be set to, for example, 1.48 μm. This is because the optical fiber transmission line 3 used for transmission of the main signal light is used by utilizing the signal light having a wavelength relatively close to the wavelength of the main signal light.
Even if the pumping light is transmitted through 0b (optical fiber suitable for long-distance transmission of main signal light), there is not much difference in transmission loss.
This is because it is practically possible to use the optical fiber transmission line 30b for long-distance transmission of the main signal light. The transmission speed of this excitation light (sub-signal light as monitoring signal light, etc.) is
It is set to a low speed of 1 Mbps or less (for example, 9600 bps). This is a high-speed transmission (62
This is because the minimum reception level can be improved compared to 2 Mbps, 2.5 Gbps, 10 Gbps, etc.).

Further, in the optical communication method, the supervisory signal received from the next stage side (the side on which the main signal light is transmitted when viewed from a certain relay optical fiber amplifier 30a) is provided with information indicating the operating state of the device itself. (Reconstructing the monitoring information to be transmitted), and sequentially transmitting to the previous stage (the side where the main signal light is transmitted when viewed from a certain relay optical fiber amplifier 30a), and finally to the monitoring station (for example, transmission). It may be provided in the station), and the operation information of each device is concentrated. As a result, it becomes possible for each transmitting station to manage the network centered on itself. The optical communication system may have a configuration in which a monitoring station is provided separately from each of the communication stations and the network is centrally managed. The supervisory signal includes information about the pumping light source, signal light level, etc. at each relay station.

Next, a relay optical fiber amplifier 30a (another optical fiber amplifier 4) constituting the in-line amplifier group 3 is formed.
The same applies to the configurations of a and 4b).

FIG. 2 shows the relay optical fiber amplifier 30.
It is a figure which shows the 1st Example of a. In this figure, the relay optical fiber amplifier 30a is an optical fiber that constitutes at least a part of a transmission path for propagating the main signal light and optically amplifies the main signal light. Substances (eg, rare earth elements such as erbium)
For optical amplification (in this embodiment, the first and second erbium-doped fibers 5a, 5b are optically connected in series to enable multi-stage amplification. And the excitation light to be incident into the optical amplification fiber from one end surface (the side from which the main signal light is emitted) of the optical amplification fiber, the drive current signal I ₀ is input. A pumping light source 13 for outputting a driving current signal I ₀ having a desired intensity to the pumping light source 13 for outputting the driving current signal I ₀ containing predetermined information. At least a drive unit A that supplies the light source 13 and modulates the intensity of the excitation light output from the excitation light source 13 to generate the sub-signal light is provided.

As described above, this optical amplification fiber is composed of the first and second optical amplification fibers 5a and 5b, and the backward pumping (pumping light from the direction opposite to the main signal light is provided at each output end). A multiplexer / demultiplexer (wavelength selective couplers 6a, 6b) for performing incident light amplification is connected and configured in series. In addition, the second optical amplification fiber 5
In the path of b, an isolator 8a is provided on the incident end side in order to prevent passage of the excitation light incident from the wavelength selective coupler 6b. Further, the output end of the adjacent input side optical fiber 500 (corresponding to the optical fiber 30b in FIG. 1) at the preceding stage where the main signal light propagates is incident on the incident end of the first optical amplification fiber 5a. A branching coupler 7 for branching a part of the incident light in order to monitor the light
It is connected via a. On the other hand, the wavelength selective coupler 6
The output end side of the second optical amplification fiber 5b to which b is connected is an isolator 8b for blocking passage of a sub signal light such as a monitor signal light from the latter stage and the output for monitoring the output light and the like. The input end and the optical end of an adjacent output-side optical fiber 501 (corresponding to the optical fiber 30b in FIG. 1) at the subsequent stage for outputting the intensity-amplified main signal light via a branching coupler 7b that branches a part of the light. Connected to each other.
With the above configuration, the optical fiber is the main path (optical transmission path)
Form part of the.

A part of the incident light branched by the branch coupler 7a is a light receiving element 9a such as a photodiode.
After being received by (indicated by PD in the figure), it is converted into an electric signal corresponding to the light intensity of the incident light by the opto-electric conversion circuit 10a, and the micro controller 19 monitors the incident light based on this electric signal. I am doing it. Also,
In this microcontroller 19, the branch coupler 7
Similarly, with respect to a part of the emitted light branched via b, the emitted light received by the light receiving element 9c (indicated by PD in the figure) such as a photodiode is converted into the photoelectric conversion circuit 10c.
Then, the electric signal converted corresponding to the light intensity of the incident light is taken in and the emitted light is monitored.

Further, this microcontroller 19
Is an electric signal (three-valued CMI to be described later) converted by the photo-electric conversion circuit 10b after receiving the sub-signal light, which is incident from the latter stage through the output optical fiber 501 by the branch coupler 7b, by the light receiving element 9b. Code) and three-valued CMI
The NRZ-converted signal (NRZ code) is taken in by the encoder / decoder 18, and information indicating the operation status of the device is added to generate new information. The excitation light source 13 such as a laser diode having a built-in cooling cooler for outputting the excitation light is controlled by a drive current I ₀ from a drive unit A described later, but the excitation light source 13 is cooled. The cooler 14 as a means is feedback-controlled by the driving current output from the LD cooler driving circuit 15 according to the instruction of the microcontroller 19.

The pumping light output from the pumping light source 13 is branched into two directions by the branching coupler 11, and a part of the first pumping light is passed through the wavelength selective coupler 6a to the first optical amplification fiber. 5a is the sub-signal light that is emitted from the rear and is transmitted to the front stage, and the second pump light is also the wavelength-selective coupler 6b.
The light is emitted from the rear to the second optical amplification fiber 5b via. Since the second pumping light is blocked by the isolator 8a after activating erbium (Er), it is not redundantly transmitted with the first pumping light.
In the figure, reference numeral 12 is an optical terminal for preventing light reflection.

Next, the driving means A in the relay optical fiber amplifier is connected to the pumping light source 13 and has the first constant intensity so as to realize the light amplifying function in the pumping light source 13.
The first drive circuit 16 for supplying the drive current signal I ₁ (FIG. 4) and the excitation light source 13 are connected in parallel with the first drive circuit 16 and transmit the sub-signal light (excitation light). A second drive current signal I ₂ which is a modulation signal corresponding to encoded data for superimposing on the _first drive current signal I ₁
A second drive circuit 17 for supplying (see FIG. 5) to the excitation light source 13 is provided. Therefore, the drive current signal I ₀ supplied from the drive means A to the excitation light source 13 becomes a signal as shown in FIG. Further, the drive means A is the second
The NRZ code corresponding to the predetermined information generated by the microcontroller 19 is output to the drive circuit 17 of FIG. 3 as a modulation signal which is encoded into a ternary CMI code, or as described above, the optical fiber amplifier for relay in the subsequent stage is output. The ternary CMI code corresponding to the predetermined information received from the ternary CMI code is decoded into an NRZ code and output to the microcontroller 19.
It is composed of an MI encoder / decoder 18.

Particularly, the encoding / decoding technique for this ternary CMI code is described in, for example, US Pat. No. 4,44,44.
No. 2,528. The ternary CMI code has a characteristic that the occurrence probabilities of the positive pulse and the negative pulse are equal to each other, so that the average light intensity of the excitation light does not change, and there is no influence on the reduction of the light intensity of the excitation light. In addition, the pulse width of the modulated signal has a photon lifetime (10 nm) of the excitation light in consideration of the influence on the optical amplification characteristic of the relay optical fiber amplifier.
(msec).

As described above, in the first embodiment (FIG. 2),
The configuration in the case of simply receiving the sub-signal light (pumping light in the relay optical fiber amplifier of the latter stage) from the latter stage (on the side of the relay optical fiber amplifier where the main signal light is transmitted) has been described. May be configured to improve the light receiving level of.

FIG. 3 is a diagram showing a configuration of the relay optical fiber amplifier according to a second embodiment, which is a branch coupler 7b.
A wavelength-selective coupler 20 is provided for separating the sub-signal light from the subsequent stage and the reflected light of the main signal light emitted to the output optical fiber 501, among the light branched by the. Therefore, the sub-signal light separated by the wavelength-selective coupler 20 is received by the light receiving element 9b as described above, and then is converted into an electric signal (three-value CM by the opto-electric conversion circuit 10b).
I code), and the ternary code / decoder 18 outputs N
It is decoded into RZ code and taken into the microcontroller 19. On the other hand, the reflected light of the main signal light separated by the wavelength selective coupler 20 is similarly received by the light receiving element 9d, then converted into an electric signal by the opto-electric conversion circuit 10d, and taken into the microcontroller 19. Be done.

In the optical communication system, the main signal light and the sub signal light (monitor signal etc.) are transmitted in the opposite directions. However, in an actual optical communication line, an upstream line and a down line are used. Since the two-way communication is performed, the optical communication system is configured by the two main paths having the above-described configuration that transmit the main signal in the opposite direction between the first and second communication stations 1 and 2 described above. May be.

FIG. 7 is a diagram showing the configuration of the second embodiment of the optical communication system, in which the communication stations 100 and 200 are transmitters 100a and 200b and receivers 100b, respectively.
It is equipped with 200a and functions as a transmitting / receiving station. Further, in this embodiment, each of the communication stations 100 and 200 has a monitoring station for monitoring the operating state of each relay optical fiber amplifier 30a which constitutes each main path. The optical communication method according to the present invention also envisions the above-described bidirectional optical communication system.

[0034]

As described above, according to the present invention, in the optical fiber amplifier as the relay amplifying means, the pumping light for optical amplification is used so as to be used as the information transmitting means independent of the main signal light. The driving means of the pumping light source for outputting is the transmission control means of the optical signal. Accordingly, it is not necessary to provide a control unit (hardware for separately transmitting and receiving signal light for carrying a supervisory signal etc.) separate from the relay amplification unit, and an independent optical transmission unit can be easily provided in the main path of the optical communication system. There is an effect that can be realized.

In particular, according to the present invention, the pumping light (the sub-signal light such as the monitor signal) is transmitted in the direction opposite to the main signal light.
It is possible to reduce the influence on the transmission of the main signal light and to increase the output of the main signal light.

The drive current signal from the drive means to the excitation light source is a current signal in which a modulation signal carrying predetermined information is superimposed on a normal drive current signal, and in particular, this modulation signal is a positive pulse and a negative pulse. By using a ternary CMI code having the same occurrence probability of, it is possible to eliminate the influence on the decrease in the light intensity of the excitation light. The pulse width of the modulated signal is
Since it is sufficiently shorter than the photon lifetime of the excitation light (about 10 msec), it does not affect the optical amplification characteristic of the optical fiber amplifier.

Further, in the optical communication system and the optical communication method according to the present invention, the pumping light usable as the sub-signal light is branched into two or more, so that not only the optical amplification and the sub-signal light but also the pumping light can be performed. This has the effect of enabling application to other uses.

[Brief description of drawings]

FIG. 1 is a diagram showing a first basic configuration example according to an embodiment of an optical communication system according to the present invention.

FIG. 2 is a diagram showing a first configuration example according to an embodiment of a relay optical fiber amplifier in the optical communication system of the present invention.

FIG. 3 is a diagram showing a second configuration example according to an embodiment of a relay optical fiber amplifier in the optical communication system of the present invention.

FIG. 4 is a diagram showing a first drive current signal in the present invention.

FIG. 5 is a diagram showing a second drive current signal (modulation signal by a ternary CMI code) in the present invention.

FIG. 6 is a diagram showing a drive current signal output from the drive means to the excitation light source according to the present invention.

FIG. 7 is a diagram showing a second basic configuration example according to an embodiment of the optical communication system according to the present invention.

[Explanation of symbols]

1 (100) ... 1st communication station, 2 (200) ... 2nd communication station, 3 ... In-line amplifier group, 5a, 5b ... Optical amplification fiber (EDF), 11 ... Multiplex / demultiplexer (branch coupler) ,
13 ... Excitation light source (LD), 16 ... First drive circuit, 1
7 ... Second drive circuit, 18 ... Ternary CMI encoder / decoder,
20 ... Wavelength selective coupler, A ... Driving means.

Claims (13)

[Claims] 1. An optical fiber, which constitutes at least a part of a transmission path for propagating the first signal light and optically amplifies the first signal light, the substance being activated by the excitation light. The optical amplification fiber added, and the excitation light to be incident into the optical amplification fiber from the emission end side of the first signal light in the optical amplification fiber, to the input drive current signal A pumping light source for outputting with a corresponding intensity, a means for supplying a driving current signal of desired intensity to the pumping light source, supplying the driving current signal containing predetermined information to the pumping light source, An optical fiber amplifier comprising at least a driving unit that modulates the intensity of pumping light output from a light source to generate the pumping light as second signal light. 2. The optical fiber amplifier according to claim 1, further comprising a branching coupler for branching the pumping light including the predetermined information in at least two directions. 3. The optical amplification fiber is at least,
A first optical amplification fiber that realizes an optical amplification function by the first pumping light branched by the branching coupler, and a second fiber that realizes an optical amplification function by the second pumping light branched by the branching coupler. The optical fiber amplifier according to claim 1 or 2, wherein the optical fiber and the optical amplification fiber are connected in series via a multiplexer / demultiplexer. 4. The first driving circuit is connected to the pumping light source, and supplies a first driving current signal having a constant intensity to the pumping light source so as to realize an optical amplification function. A modulation signal which is connected to the pumping light source in parallel with the first drive circuit and carries predetermined information for transmission as the second signal light, and which is superposed on the first drive current signal. A second drive circuit that supplies a second drive current signal to the excitation light source, and a modulation signal that carries the predetermined information is output to the second drive circuit or predetermined information received from the outside. The optical fiber amplifier according to any one of claims 1 to 3, further comprising: a code / decoder that decodes the modulated signal. 5. The modulation signal is a drive current signal in which the predetermined information is encoded into a ternary CMI code in which the occurrence probabilities of a positive pulse and a negative pulse are equal, and in particular, the pulse width of the ternary CMI code is The optical fiber amplifier according to claim 4, wherein the photon lifetime of the pumping light is shorter than the photon lifetime. 6. An input-side optical fiber and an output-side optical fiber which form at least a part of a transmission path for propagating the first and second signal lights, and one end of which is an optical output end of the input-side optical fiber and an optical part. The optical fiber for optically amplifying the first signal light by optically connecting the other end to the input end of the output side optical fiber to form a part of the transmission line, An optical amplification fiber added with a substance that is activated by excitation light, and the excitation light to be incident into the optical amplification fiber from the emission end side of the first signal light in the optical amplification fiber, A pumping light source that outputs an intensity according to an input driving current signal, and a means that supplies a driving current signal of a desired intensity to the pumping light source, the driving current signal including predetermined information. The excitation light source is supplied to the excitation light source. An optical fiber amplifier for relay, comprising at least a driving unit that modulates the intensity of the pumping light output from the pumping light to generate the pumping light as the second signal light. 7. A wavelength-selective coupler for separating the second signal light incident from the output optical fiber and the reflected light of the first signal light is further provided. The optical fiber amplifier for relay according to claim 6. 8. Between the first communication station and the second communication station,
A plurality of optical fibers that are transmission lines for transmitting the main signal light from the first communication station to the second communication station, and are installed between the respective optical fibers, and form a part of the transmission lines. In the optical communication system including at least a first main path configured by optically connecting a plurality of relay optical fiber amplifiers to each other in series, the relay optical fiber amplifier has the both ends adjacent to each other. An optical fiber for optically amplifying the main signal light that constitutes a part of the transmission line by optically connecting to one end of each optical fiber, and is a light to which a substance that is activated by excitation light is added. An amplification fiber and the pumping light to be incident into the optical amplification fiber from the emission end side of the main signal light in the optical amplification fiber are output with an intensity according to an input drive current signal. Excitation light And a means for supplying a driving current signal of desired intensity to the excitation light source, the driving current modulated corresponding to predetermined information is supplied to the excitation light source, and is output from the excitation light source. An optical communication system comprising at least a driving unit that modulates the intensity of pumping light to generate the pumping light as sub-signal light. 9. A plurality of optical lines, which are transmission lines for transmitting the main signal light from the second communication station to the first communication station, between the first communication station and the second communication station. 7. A fiber and a plurality of relay optical fiber amplifiers, each of which is provided between the optical fibers and constitutes a part of the transmission path, are optically connected in series. 9. The optical communication system according to claim 8, further comprising a second main path. 10. A pumping light source for outputting a pumping light for optical amplification, the pumping light source being installed between a plurality of optical fibers that are transmission lines for transmitting main signal light, constituting a part of the transmission line. In an optical communication system including at least an optical fiber amplifier for relaying, by modulating a driving current signal supplied to the pumping light source according to predetermined information, the intensity of the pumping light is modulated to perform the pumping. An optical communication method, wherein light is used as sub-signal light, and the sub-signal light is transmitted in a direction opposite to the transmission direction of the main signal light. 11. A drive current signal supplied to the excitation light source is a first drive current signal having a constant intensity for outputting the excitation light and a modulation signal carrying predetermined information.
11. The optical communication method according to claim 10, wherein the optical signal is a current signal obtained by superimposing the current signal for driving on. 12. The second drive current signal is a modulation signal obtained by encoding the predetermined information into a ternary CMI code in which the occurrence probabilities of a positive pulse and a negative pulse are equal to each other. The optical communication method described. 13. The optical communication method according to claim 10, wherein the sub-signal light is signal light for propagating a supervisory signal in the optical communication system.