JP2009267950A - Optical communication system and optical communication apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical communication system capable of suppressing deterioration of communication quality by accurately correcting variation in transmission line loss, and to provide an optical communication apparatus. <P>SOLUTION: A transmitting-side apparatus A includes: an optical amplifying section 5a for amplifying power of an optical signal to be transmitted to a receiving-side apparatus B; and a variable optical attenuator (VOA) 7, connected to an output of the optical amplifying section 5a, for adjusting power of the optical signal output from the optical amplifying section 5a to a fixed level in accordance with a power level of a control optical signal received from the receiving-side apparatus B via a transmission line fiber 4. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical communication system and an optical communication apparatus that compensate for signal degradation due to transmission loss fluctuations in a transmission line.

  An optical communication system that is currently in wide use is an optical node connected to each other via a transmission line fiber, a transmission side device that modulates signal light power or optical frequency according to information to be transmitted, and this transmission side A receiving-side device that receives an optical signal transmitted from the device. Further, in a conventional optical communication system, an optical variable attenuator (hereinafter referred to as a VOA (Variable Optical Attenuator)) is provided on the input side of an optical amplifier serving as a receiving side device, and the amount of attenuation of the VOA is controlled. Thus, the transmission line loss variation of the transmission line fiber was compensated (see, for example, Patent Documents 1 to 3).

JP 2003-174421 A JP 2006-166478 A Japanese Patent Laid-Open No. 2004-11212

  In the conventional optical communication system, a VOA is provided on the input side of the optical amplifier serving as the receiving side device and the transmission line loss fluctuation is absorbed only on the receiving side. There was a need to do.

  Transmission path loss of the transmission path fiber occurs due to external factors such as outside air temperature and humidity, and human factors. For example, the transmission line loss of a transmission line fiber arranged outdoors may vary depending on the weather. Further, as a human factor, there is a case where the transmission line loss fluctuates due to stress applied to the transmission line fiber, for example, when an operator steps on the transmission line fiber.

  As described above, since the transmission line loss fluctuates due to various factors, when the fluctuation amount of the transmission line loss generated in the transmission line fiber is larger than the value set in the VOA, the power level of the signal light decreases. Signal-to-noise ratio (SNR) deteriorates, causing a communication error and cannot perform stable long-distance transmission.

  Further, when the distance of the transmission path to the transmission side apparatus is short and the transmission path loss is small, the signal light power received by the reception side apparatus is relatively high. In this case, the optical amplifier of the reception side apparatus is required to amplify the received signal light with higher power, and there is a problem that a high-performance optical amplifier is required.

  The present invention has been made to solve the above-described problems, and provides an optical communication system and an optical communication apparatus capable of appropriately correcting fluctuations in transmission line loss and suppressing deterioration in communication quality. For the purpose.

  An optical communication system according to the present invention is an optical communication system comprising: a transmission side device that transmits an optical signal; and a reception side device that receives an optical signal transmitted from the transmission side device via a transmission line fiber. The transmission side device includes an optical variable attenuating unit that adjusts the power of the optical signal transmitted to the reception side device to a constant level according to the power level of the control optical signal, and the reception side device includes the control optical signal. And a control light generation unit that outputs the control light signal to the transmission side device via the transmission line fiber.

  According to this invention, the transmission side device includes the optical variable attenuation unit that adjusts the power of the optical signal to a constant level according to the power level of the control optical signal received from the reception side device via the transmission line fiber. In addition, it is possible to absorb (correct) the fluctuation of the transmission line loss in the transmission line fiber, and to easily change the transmission power of the signal light according to the type of the transmission line fiber. Also, since the fluctuation of the transmission line loss is absorbed according to the power level of the control optical signal from the receiving side device, the attenuation amount of the optical variable current element can be set appropriately, the signal light is not attenuated excessively, and the SNR There is an effect that deterioration can be prevented.

Embodiment 1 FIG.
FIG. 1 is a diagram showing a system configuration to which an optical communication system according to the present invention is applied, and shows a WDM (Wavelength Division Multiplexing) communication system 1A in which nodes are connected in a ring shape. FIG. 2 is a diagram showing another system configuration to which the optical communication system according to the present invention is applied, and shows a WDM communication system 1B in which a plurality of nodes are connected in series.

  1 and 2, nodes 2-1 to 2-6 constituting the WDM communication systems 1A and 1B are WDM optical communication apparatuses to which the optical communication apparatus according to the present invention is applied. In addition, although the case where the number of nodes was six was shown, it differs for every system, and six is not necessarily the maximum number. Each node (optical communication apparatus) 2-1 to 2-6 is connected by an optical fiber called a transmission line.

  There are usually two transmission and transmission lines, and they are called E system (East system) / W system (West system) and 0 system / 1 system. Here, it is described as E system / W system. WDM communication systems have been introduced into long-distance trunk lines and metro ring networks with the spread of communication networks such as the Internet. A transmission line of a WDM communication system applied to such a wide communication network is usually arranged outdoors, and the transmission line loss may fluctuate due to external factors such as weather and human factors.

  The fluctuation of the transmission path loss affects stable communication (communication quality) between the terminal station apparatuses 3-1 to 3-6 installed in the nodes 2-1 to 2-6. For example, when the transmission path loss suddenly increases, the optical power of the optical signal reaching the terminal station devices 3-1 to 3-6 decreases, and a communication error occurs and the SNR deteriorates.

Accordingly, the present invention provides an optical communication system and an optical communication apparatus that can appropriately correct the above-described fluctuations in the transmission path loss and suppress deterioration in communication quality.
FIG. 3 is a block diagram schematically showing the configuration of the optical communication apparatus according to Embodiment 1 of the present invention. In FIG. 3, a transmission side device A that transmits signal light includes an optical amplification unit 5a, an optical filter 6a, and an optical variable attenuator (hereinafter referred to as VOA) (optical variable attenuation unit) 7. The receiving-side apparatus B that receives the signal light via the transmission line fiber 4 includes an optical amplifier 5b, an optical filter 6b, and a control light generator 8.

  The transmission line fiber 4 is a transmission medium for transmitting the signal light transmitted from the transmission side device A, and is configured by an optical fiber cable. The optical amplifiers 5a and 5b are components that amplify the input signal light, and are configured by a pump laser or the like. The optical filter 6a is a filter for demultiplexing the signal light and the control light signal, and the optical filter 6b is a filter for multiplexing the signal light and the control light signal.

  The VOA 7 adjusts the power of signal light related to information to be transmitted to the receiving-side apparatus B. The control light generation unit 8 is a component that transmits a control light signal for controlling the operation of the VOA 7 to the transmission side device A, and includes a laser diode or the like.

  As shown in FIG. 3, in the optical communication system according to the present invention, unlike the conventional optical communication system described above, the power of the signal light is varied to the transmitting side device A that transmits the signal light (the optical signal of the transmission information). VOA 7 is provided. That is, the transmission side apparatus A adjusts the attenuation amount of the VOA 7 according to the power level of the control light signal transmitted from the control light generation unit 8 of the reception side apparatus B, and controls the signal light power.

Next, the operation will be described.
The control light signal generated by the control light generator 8 is combined with the signal light by the optical filter 6 b and transmitted to the transmission side device A via the transmission line fiber 4. At this time, the control light signal is transmitted through the transmission line fiber 4 in the opposite direction to the signal light. That is, the signal light is transmitted from the transmission side apparatus A toward the reception side apparatus B, while the control light signal is transmitted from the reception side apparatus B toward the transmission side apparatus A.

  In the transmission side apparatus A, the control optical signal is demultiplexed from the signal light by the optical filter 6a. The demultiplexed control light signal is converted into an electric signal by a photodiode (not shown) or the like, and the converted voltage value or the modulation frequency or the like modulated in advance by the transmission side apparatus A is detected. Subsequently, a difference between the voltage value of the electrical signal for the control light signal and a predetermined threshold value set in advance is detected by a comparator (not shown), and the VOA 7 of the transmitting apparatus A is controlled according to this difference.

  For example, when the transmission line loss increases in the transmission line fiber 4 and the power of the control optical signal input to the transmission side apparatus A decreases, the loss in the VOA 7 is reduced by adjusting the attenuation amount accordingly. Thereby, the signal light power level transmitted to the transmission line fiber 4 is increased. Conversely, when the transmission path loss decreases and the power of the control optical signal input to the transmission side apparatus A increases, control is performed so that the loss at the VOA 7 increases. In this way, the signal light power level received by the receiving-side apparatus B can always be kept constant.

  As described above, according to the first embodiment, in the optical communication systems 1A and 1B, the transmission side apparatus A responds to the power level of the control optical signal received from the reception side apparatus B via the transmission line fiber 4. And a VOA 7 for adjusting the power of the optical signal to a constant level. In particular, the transmission side device A is connected to the output of the optical amplification unit 5a that amplifies the power of the optical signal to be transmitted to the reception side device B, and the output of the optical amplification unit 5a. VOA 7 that adjusts the power of the optical signal output from the optical amplifying unit 5a to a constant level according to the power level of the received control optical signal. By configuring in this way, it is possible to absorb (correct) the fluctuation of the transmission line loss in the transmission line fiber 4 and to easily change the transmission power of the signal light according to the type of the transmission line fiber 4. In addition, since the depth (attenuation amount) of the VOA 7 is adjusted according to the power level of the control optical signal from the receiving-side apparatus B, the signal light is appropriately attenuated and deterioration of SNR can be prevented.

Embodiment 2. FIG.
4 is a block diagram schematically showing a configuration of an optical communication apparatus according to Embodiment 2 of the present invention. In FIG. 4, the transmitting apparatus A includes an optical coupler 9 and a monitor unit 10 in addition to the configuration shown in FIG. 3 of the first embodiment. In FIG. 4, the same components as those in FIG.

  The optical coupler (branch unit) 9 branches a part of the power of the control optical signal input to the VOA 7 to the monitor unit 10. The monitor unit 10 is a component that monitors the power of the control light signal input to the VOA 7, and includes a photodiode that performs photoelectric conversion of the control light signal, and a voltage level of the electrically converted control light signal as a predetermined threshold value. It consists of a comparator to compare.

Next, the operation will be described.
The control light signal generated by the control light generator 8 is combined with the signal light by the optical filter 6 b and transmitted to the transmission side device A via the transmission line fiber 4. At this time, the control light signal is transmitted through the transmission line fiber 4 in the opposite direction to the signal light. That is, the signal light is transmitted from the transmission side apparatus A toward the reception side apparatus B, while the control light signal is transmitted from the reception side apparatus B toward the transmission side apparatus A. Here, it is assumed that the control light signal is always transmitted to the transmitting apparatus A.

  In the transmission side device A, a part of the power of the control optical signal transmitted from the reception side device B is branched to the monitor unit 10 by the optical coupler 9. In the monitor unit 10, when the power of the control optical signal branched by the optical coupler 9 is input, this is photoelectrically converted, and the voltage level of the electrically converted control optical signal is compared with a predetermined threshold value. The presence or absence of a control light signal from the receiving-side apparatus B is determined according to the comparison result. Based on the determination result by the monitor unit 10, the operation of the VOA 7 is controlled.

  For example, if the monitor unit 10 determines that there is no control optical signal from the receiving-side apparatus B, it is determined that the transmission line fiber 4 has been disconnected, and the attenuation amount is increased by the VOA 7, thereby Stop signal light output. Alternatively, the operation of the VOA 7 is held in front. In addition, if the monitor unit 10 determines that there is a control light signal from this state, it can be determined that the transmission line fiber 4 is connected, and can be used as a trigger for starting the operation of the VOA 7.

  Note that the operation control of the VOA 7 according to the power level of the control light signal is the same as in the first embodiment.

  As described above, according to the second embodiment, the transmission side apparatus A splits a part of the control optical signal input to the VOA 7 and the control optical signal branched by the optical coupler 9. And the monitor unit 10 for monitoring the power, so that the transmission side device A can detect the presence / absence of the control light signal based on the monitoring result of the power of the control light signal. Thus, the breakage of the transmission line fiber 4 can be detected.

Embodiment 3 FIG.
FIG. 5 is a block diagram schematically showing a configuration of an optical communication apparatus according to Embodiment 3 of the present invention. In FIG. 5, the receiving side device B includes a VOA 11 in addition to the configuration shown in FIG. 3 of the first embodiment. In FIG. 5, the same components as those in FIG.

  A VOA (optical variable attenuator) 11 is used when compensating for transmission line loss fluctuations. The receiving apparatus B includes, for example, means for detecting the number of wavelengths of the signal light as means for controlling the VOA 11, and controls the operation of the VOA 11 according to the number of wavelengths to control the power level of the signal light at a constant level. In addition, the same control as in the first embodiment may be performed by transferring the power of the signal light from the transmission side apparatus A to the reception apparatus B.

  For example, when the transmission line loss increases in the transmission line fiber 4 and the signal light power input from the transmission side device A decreases, the loss in the VOA 11 is reduced by adjusting the attenuation amount accordingly. On the contrary, when the transmission line loss decreases and the signal light power input from the transmission side device A increases, control is performed so that the loss in the VOA 11 increases.

  In this way, large fluctuations in transmission path loss as shown in FIG. 5 are absorbed by both the VOA 7 installed in the transmission side apparatus A and the VOA 11 installed in the reception side apparatus B.

  As described above, according to the third embodiment, the power of the optical signal transmitted to the reception side apparatus B by the transmission side apparatus A according to the power level of the control optical signal from the reception side apparatus B is constant. And the receiving side apparatus B includes the VOA 11 that adjusts the power of the optical signal to a constant level. Therefore, both the VOA 7 of the transmitting side apparatus A and the VOA 11 of the receiving side apparatus B have transmission path loss. Since the fluctuation is compensated, a larger fluctuation can be absorbed.

Embodiment 4 FIG.
FIG. 6 is a block diagram schematically showing a configuration of an optical communication apparatus according to Embodiment 4 of the present invention. In FIG. 6, the transmitting apparatus A includes an optical filter 12 a and a control light generation unit 13 in addition to the configuration shown in FIG. 3 of the first embodiment. In addition to the configuration shown in FIG. 5 of the third embodiment, the reception-side device B includes an optical filter 12b. In FIG. 6, the same components as those in FIGS. 3 and 5 are denoted by the same reference numerals, and description thereof is omitted.

  The optical filter 12a is a filter for combining the control light signal generated by the control light generation unit 13 with the signal light, and the optical filter 12b is a control light signal from the control light generation unit 13 of the transmission side device A. Is a filter for demultiplexing from the signal light.

  The control light generation unit 13 is a component that transmits a control light signal for controlling the operation of the VOA 11 of the reception-side device B to the reception-side device B, and includes a laser diode or the like. The control light signal generated by the control light generation unit 13 is a signal for realizing the same function as the control light signal generated by the control light generation unit 8 installed in the reception-side apparatus B. However, these control light signals have different wavelengths.

Next, the operation will be described.
The control light signal generated by the control light generator 8 is combined with the signal light by the optical filter 6 b and transmitted to the transmission side device A via the transmission line fiber 4. At this time, the control light signal is transmitted through the transmission line fiber 4 in the opposite direction to the signal light. That is, the signal light is transmitted from the transmission side apparatus A toward the reception side apparatus B, while the control light signal is transmitted from the reception side apparatus B toward the transmission side apparatus A.

  In the transmission side apparatus A, the control optical signal is demultiplexed from the signal light by the optical filter 6a. The demultiplexed control light signal is converted into an electric signal by a photodiode (not shown) or the like, and the converted voltage value or the modulation frequency or the like modulated in advance by the transmission side apparatus A is detected. Subsequently, a difference between the voltage value of the electrical signal for the control light signal and a predetermined threshold value set in advance is detected by a comparator (not shown), and the VOA 7 of the transmitting apparatus A is controlled according to this difference.

  On the other hand, the control light signal generated by the control light generation unit 13 is combined with the signal light by the optical filter 12 a and transmitted to the receiving-side apparatus B through the transmission line fiber 4. At this time, the control light signal is transmitted through the transmission line fiber 4 in the same direction as the signal light.

  In the receiving apparatus B, the control light signal is demultiplexed from the signal light by the optical filter 12b. The demultiplexed control light signal is converted into an electric signal by a photodiode (not shown) or the like, and the converted voltage value or the modulation frequency or the like modulated in advance by the receiving apparatus B is detected. Subsequently, a difference between the voltage value of the electrical signal for the control light signal and a predetermined threshold value set in advance is detected by a comparator (not shown), and the VOA 11 of the receiving apparatus B is controlled according to this difference.

  For example, when the transmission line loss increases in the transmission line fiber 4 and the power of the control optical signal input to the receiving side apparatus B decreases, the loss in the VOA 11 is reduced by adjusting the attenuation amount accordingly. . Thereby, the signal light power level is increased. Conversely, when the transmission path loss decreases and the power of the control optical signal input to the receiving apparatus B increases, control is performed so that the loss at the VOA 11 increases. In this way, the signal light power level can always be kept constant.

  As described above, according to the fourth embodiment, the transmission side apparatus A generates the control optical signal to the reception side apparatus B, and outputs the control optical signal to the reception side apparatus B through the transmission line fiber 4. The VOA 11 of the receiving side device B adjusts the power of the optical signal to a certain level according to the power level of the control light signal from the transmitting side device A. In particular, the receiving side device B is connected to the input of the optical amplifying unit 5b for amplifying the power of the optical signal received from the transmitting side device A, and from the transmitting side device A via the transmission line fiber 4. The VOA 11 adjusts the power of the optical signal input to the optical amplifier 5b to a constant level according to the power level of the received control optical signal. By configuring in this way, as in the third embodiment, both the VOA 7 of the transmission side apparatus A and the VOA 11 of the reception side apparatus B compensate for the fluctuation of the transmission path loss, so that a larger fluctuation can be absorbed. Can do. Further, since the control light generators 8 and 13 can be configured by substantially the same circuit, the configuration of the optical communication apparatus can be simplified.

Embodiment 5 FIG.
FIG. 7 is a block diagram schematically showing a configuration of an optical communication apparatus according to Embodiment 5 of the present invention. The receiving-side apparatus B includes an optical coupler 14 and a monitor unit 15 in addition to the configuration shown in FIG. In FIG. 7, the same components as those in FIGS.

  The optical coupler (branching unit) 14 branches a part of the power of the control optical signal input to the VOA 11 to the monitor unit 15. The monitor unit 15 is a component that monitors the power of the control light signal input to the VOA 11, and similarly to the monitor unit 10, the photodiode that photoelectrically converts the control light signal, and the voltage of the control light signal that has been electrically converted. The comparator is configured to compare the level with a predetermined threshold.

Next, the operation will be described.
The control light signal generated by the control light generation unit 13 is combined with the signal light by the optical filter 12 a and transmitted to the reception side device B through the transmission line fiber 4. In the receiving side apparatus B, the power of a part of the control optical signal from the transmitting side apparatus A is branched to the monitor unit 15 by the optical coupler 14.

  When the power of the control optical signal branched by the optical coupler 14 is input to the monitor unit 15, the power is photoelectrically converted, and the voltage level of the electrically converted control optical signal is compared with a predetermined threshold value. The presence / absence of a control optical signal from the transmission side apparatus A is determined according to the comparison result. Based on the determination result by the monitor unit 15, the operation of the VOA 11 is controlled.

  The purpose of the optical coupler 14 and the monitor unit 15 installed in the reception side apparatus B is to realize the same functions as the optical coupler 9 and the monitor unit 10 of the transmission side apparatus A shown in the second embodiment. For example, if both the monitoring units 10 and 15 determine that there is no control light signal, it is determined that the transmission line fiber 4 is disconnected, and if it is determined that there is a control light signal, the transmission line fiber 4 is connected. Judgment can be made.

  Therefore, for example, when it is detected that the transmission line fiber 4 is cut, a so-called eye-save process may be performed in which the VOA 7 of the transmission side apparatus A is controlled to reduce the power of the signal light. Eye safe means that when the transmission line fiber 4 is cut for some reason, the signal light power from the transmission side device A is not dangerous to the eyes of the worker who performs the repair work to reconnect the transmission line fiber 4. The process to lower.

  FIG. 8 is a diagram for explaining an eye-safe operation by the optical communication apparatus in FIG. In the example of FIG. 8, when the monitoring unit 10 of the transmission side apparatus A cannot detect the control optical signal from the reception side apparatus B and determines that the transmission line fiber 4 has been cut, the repair work of the transmission line fiber 4 is performed. It shows a case where the power of the output light is reduced to a power that is not dangerous to the eyes of the worker or the like.

For example, as shown in FIG. 8, there are the following two methods for controlling the power of output light.
(1) When the disconnection of the transmission line fiber 4 is determined by the monitor unit 10, the attenuation amount of the VOA 7 is controlled according to this and the output optical power is reduced to a predetermined low output value.
(2) When the disconnection of the transmission line fiber 4 is determined by the monitor unit 10, the output power of the pump laser of the optical amplifying unit 5a is controlled accordingly to reduce the output light power to a predetermined low output value.

  The eye-safe operation in the conventional optical communication system is realized by transferring an alarm from the receiving side device B to the transmitting side device A in the reverse direction of the transmission line fiber 4 (W system to E system). . That is, if the receiving side device B detects the disconnection of the transmission line fiber 4 in the forward direction and the transmission line fiber 4 itself in the reverse direction is not connected, it is impossible to shift to the eye-safe operation.

  In contrast, in the present invention, since both the transmission side device A and the reception side device B can separately detect the disconnection of the transmission line fiber 4, both systems (E system and W system) of the transmission line fiber 4 can be detected. ) Can be shifted to the eye-safe operation even when both are disconnected.

  As described above, according to the fifth embodiment, the transmission-side apparatus A splits a part of the control optical signal input to the VOA 7 and the control optical signal branched by the optical coupler 9. And a monitoring unit 10 for monitoring power, and the receiving side device B splits a part of the control optical signal input to the VOA 11 and the power of the control optical signal branched by the optical coupler 14. And a monitor unit 15 for monitoring. By configuring in this way, as in the third embodiment, both the VOA 7 of the transmission side apparatus A and the VOA 11 of the reception side apparatus B are compensated for fluctuations in the transmission path loss, and the larger fluctuations can be absorbed. it can. In addition, since both the transmission side device A and the reception side device B separately detect the disconnection of the transmission line fiber 4, even if both the upstream and downstream systems of the transmission line fiber 4 are disconnected, It is possible to execute other output optical power control processing required when the transmission line is disconnected.

It is a figure which shows the system form with which the optical communication system by this invention is applied. It is a figure which shows the other system form to which the optical communication system by this invention is applied. 1 is a block diagram schematically showing a configuration of an optical communication apparatus according to Embodiment 1 of the present invention. It is a block diagram which shows roughly the structure of the optical communication apparatus by Embodiment 2 of this invention. It is a block diagram which shows roughly the structure of the optical communication apparatus by Embodiment 3 of this invention. It is a block diagram which shows roughly the structure of the optical communication apparatus by Embodiment 4 of this invention. It is a block diagram which shows roughly the structure of the optical communication apparatus by Embodiment 5 of this invention. It is a figure for demonstrating the eye safe operation | movement by the optical communication apparatus in FIG.

Explanation of symbols

  1A, 1B WDM communication system, 2-1 to 2-6 nodes (optical communication device), 3-1 to 3-6, terminal station device, 4 transmission line fiber, 5a, 5b optical amplification unit, 6a, 6b, 12a, 12b Optical filter, 7, 11 Optical variable attenuator (VOA) (optical variable attenuator), 8, 13 Control light generator, 9, 14 Optical coupler (branch unit), 10, 15 Monitor unit.

Claims (9)

In an optical communication system comprising: a transmission side device that transmits an optical signal; and a reception side device that receives an optical signal transmitted from the transmission side device via a transmission line fiber;
The transmitting device is:
In accordance with the power level of the control optical signal, the optical variable attenuation unit for adjusting the power of the optical signal transmitted to the receiving side device to a constant level,
The receiving side device
An optical communication system comprising: a control light generation unit that generates the control light signal and outputs the control light signal to the transmission side device via the transmission line fiber. The sending device is
A branching unit that branches a part of the control optical signal input to the optical variable attenuation unit;
The optical communication system according to claim 1, further comprising: a monitor unit that monitors power of the control optical signal branched by the branch unit. The receiving device
3. The optical communication system according to claim 1, further comprising an optical variable attenuating unit that adjusts the power of the optical signal to a constant level. The sending device is
A control light generation unit that generates a control light signal and outputs the control light signal to a reception-side device via a transmission line fiber;
The optical variable attenuator of the receiving device is
4. The optical communication system according to claim 3, wherein the power of the optical signal is adjusted to a constant level in accordance with the power level of the control optical signal received from the transmission side device. The receiving device
A branching unit that branches a part of the control optical signal input to the optical variable attenuation unit;
The optical communication system according to claim 3, further comprising a monitor unit that monitors power of the control optical signal branched by the branch unit. In an optical communication device that transmits an optical signal to an optical communication device on the receiving side that is connected via a transmission line fiber,
An optical amplifying unit for amplifying the power of the optical signal transmitted to the optical communication device on the receiving side;
The power of the optical signal output from the optical amplifying unit is connected to the output of the optical amplifying unit according to the power level of the control optical signal received from the receiving side optical communication device via the transmission line fiber. An optical communication apparatus comprising: an optical variable attenuator that adjusts to a constant level.   The optical communication device according to claim 6, further comprising a control light generation unit that generates a control light signal and outputs the control light signal to a receiving-side optical communication device via a transmission line fiber. In the optical communication apparatus which receives an optical signal from the optical communication apparatus of Claim 7 connected via a transmission line fiber,
An optical amplifying unit for amplifying the power of the optical signal received from the optical communication device;
The power of the optical signal input to the optical amplifying unit is fixed according to the power level of the control optical signal connected to the input of the optical amplifying unit and received from the transmission side optical communication device via the transmission line fiber. An optical communication apparatus comprising: an optical variable attenuator that adjusts to a level. A branching unit that branches a part of the control optical signal input to the optical variable attenuation unit;
The optical communication apparatus according to claim 6, further comprising a monitor unit that monitors power of the control optical signal branched by the branch unit.

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