JP2000307519A - Two-way optical communication system and method for setting its optical transmission reception level - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep transmission quality constant by easily and surely adjusting a level of an optical signal and correcting fluctuation in the level of the optical signal in real time. SOLUTION: A monitor controller 22 in a center station 1 monitors a transmission reception state of an outgoing optical transmitter 3 and an incoming optical receiver 6, sets an attenuation of an optical variable attenuator 19 to a specified value and a status monitor circuit 23 in a node optical transmitter 2 monitors an outgoing optical receiver 4 and an incoming optical transmitter 5 and sets an attenuation of an optical variable attenuator 10 to a specified value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bidirectional optical communication system suitable for setting a transmission / reception level of an optical signal and a method for setting the transmission / reception level of the optical signal.

[0002]

2. Description of the Related Art In general, an optical communication system is capable of two-way communication, and an optical transmission level and an optical reception level are set to predetermined specified values.

FIG. 3 shows a conventional bidirectional C using optical communication.
It is a block diagram showing an example of an ATV system. First,
The flow of a downstream signal from the center station 1 to the coaxial repeater 15 will be described.

[0006] From the input point 26 of the center station 1, the downstream optical transmitter 3 receives an electrical signal of a video signal and a data signal, which are downstream signals. Inside the downstream optical transmitter 3, the electric signal amplified by the amplifier 7 is converted into an optical signal by the E / O converter 8.

The converted optical signal is transmitted to a remote node optical transmission device 2 via an optical fiber 24. In the optical node transmission device 2, the optical signal that has passed through the optical fixed attenuator 28 is converted by the O / E converter 11 of the downstream optical receiver 4 into an electric signal of a video signal and a data signal.

[0006] The converted electric signal is amplified by the amplifying unit 12 and then transmitted from the coupling / distributing unit 14 to the coaxial repeater 15 via the coaxial line 30.

At this time, the level of the electric signal converted by the O / E converter 11 and further amplified by the amplifier 12 is determined by the status monitor circuit 2 having the CPU 13.
3 is being monitored.

Next, the flow of an upstream signal from the coaxial repeater 15 to the center station 1 will be described. The electric signals of the video signal and the data signal from the coaxial repeater 15 are
, And then input to the upstream optical transmitter 5. The electrical signal input to the upstream optical transmitter 5 is amplified by the amplification unit 16 and then the E / O conversion unit 1
7 to be converted into an optical signal.

At this time, the level of the optical signal converted by the E / O converter 17 is monitored by the status monitor circuit 23. The converted optical signal is input from the fixed optical attenuator 29 of the center station 1 to the upstream optical receiver 6 via the optical fiber 25.

The optical signal input to the upstream optical receiver 6 is O
The signal is converted into an electric signal of a video signal and a data signal by the / E conversion unit 20, further amplified by the amplification unit 21, and output to the output point 27. At this time, the level of the electric signal amplified by the amplifier 21
2 is being monitored.

The two-way communication is performed by the flow of the down signal and the up signal as described above.

Here, in long-distance transmission in optical communication, transmission loss occurs in the optical fibers 24 and 25, which are optical transmission paths. In addition, it is necessary to prevent breakage of the downstream optical receiver 4 and the upstream optical receiver 6 at the time of excessive input, and the input levels of the downstream optical receiver 4 and the upstream optical receiver 6 are set to a certain prescribed value. .

In general, the specified value is determined by the loss amount of the maximum optical transmission line length that satisfies the system performance. However, in particular, the optical transmission path length varies depending on the installation location of the downstream optical receiver 4, and when the optical transmission path length is short, the optical reception level becomes higher than a specified value, so that desired performance cannot be obtained.

For this reason, an optical fixed attenuator 28 corresponding to the optical transmission path length is manually attached to the input side of the downstream optical receiver 4 installed at a remote place from the center station 1. At this time, the worker at the installation location of the downstream optical receiver 4 and the worker at the center station 1 are in contact with each other, and the light reception level is set to a constant value. Similarly, a fixed optical attenuator 29 is attached to the input side of the upstream optical receiver 6 to set the optical reception level to a constant value.

[0015]

However, in the conventional method for setting the optical reception level described above, it is not only necessary to select the optical fixed attenuators 28 and 29 having an appropriate attenuation amount corresponding to the optical transmission line length. Since fine adjustment is required while maintaining communication between the downstream optical receiver 4 and the upstream optical receiver 6,
In particular, there is a problem in that setting and adjusting the light reception level at a remote location is complicated.

In particular, a remote node optical transmission device 2
On the side, when the installation location of the downstream optical receiver 4 is at a high place such as on a pole, the workability of mounting the optical fixed attenuator 28 is poor, and the optical fiber 24 is damaged or disconnected. May also occur.

Further, even when the optical receiving attenuators 28 and 29 are attached and the optical receiving level is set to a constant value,
When the input / output levels of the downstream optical receiver 4 and the upstream optical receiver 6 fluctuate due to environmental changes and changes over time,
There is also a problem that it is not possible to respond instantly.

The present invention has been made in view of such a situation, and can easily and surely adjust the level of an optical signal, and can correct the level fluctuation of the optical signal in real time to achieve transmission. An object of the present invention is to provide a bidirectional optical communication system capable of maintaining a constant quality and a method for setting an optical transmission / reception level thereof.

[0019]

According to the first aspect of the present invention, there is provided a bidirectional optical communication system for performing bidirectional communication between a center station and a remote node optical transmission device via an optical transmission line. In a communication system, a downstream optical transmitter for transmitting a downstream signal, an upstream optical receiver for receiving an upstream signal, and a variable attenuation amount for preventing excessive input to the upstream optical receiver are provided in a center station. A first optical variable attenuator, and a monitoring control device that monitors the transmission / reception state of the downstream optical transmitter and the upstream optical receiver and sets the attenuation of the first optical variable attenuator to a specified value. In the node optical transmission device, a downstream optical receiver for receiving a downstream signal, an upstream optical transmitter for transmitting an upstream signal, and a variable attenuation amount to prevent excessive input to the downstream optical receiver. A second optical variable attenuator, a downstream optical receiver and an upstream Monitors the reception state of the transmitter, the status monitor circuit for setting the attenuation amount of the second optical variable attenuator specified value, characterized in that it is provided. In addition, on the output side of the downstream optical transmitter and the upstream optical transmitter, a third and a fourth optical variable attenuator whose attenuation is variable to set the transmission level of the downstream signal and the upstream signal to a specified value. May be provided. The monitoring control device calculates an attenuation amount of a difference between an optical conversion level and a specified value in the upstream optical transmitter, controls the attenuation amount of the first optical variable attenuator based on the difference, and outputs a status monitor circuit. Can control the amount of attenuation of the second variable optical attenuator to a specified value based on information indicating a difference between a specified value of an optical conversion level in the downstream optical transmitter from the monitoring control device. Further, the monitoring control device calculates an attenuation amount of a difference between an optical conversion level in the upstream optical transmitter and an attenuation level of the fourth optical variable attenuator and a specified value, and based on the difference, a third optical variable attenuation. The status monitor circuit controls the attenuation amount of the third optical variable attenuator based on the information indicating the difference between the optical conversion level in the downstream optical transmitter and the attenuation value of the third optical variable attenuator. Can be controlled to a specified value.
The optical transmission / reception level setting method for a bidirectional optical communication system according to claim 5, wherein the optical transmission / reception of the optical signal in the bidirectional communication performed between the center station and the remote node optical transmission device via the optical transmission line. An optical transmission / reception level setting method for a bidirectional optical communication system for setting a level, comprising: a first step of transmitting a downlink signal; a second step of receiving an uplink signal; A third step of varying the amount of attenuation in order to prevent it, a fourth step of monitoring the transmission / reception state of the downlink and uplink signals, and setting the attenuation in the reception of the uplink signal to a specified value; A fifth step of receiving, a sixth step of transmitting an uplink signal, a seventh step of varying the amount of attenuation in order to prevent excessive input during reception of the downlink signal, and a transmission / reception state of the downlink and uplink signals Monitor Together, characterized in that it comprises an eighth step of setting the attenuation amount in the reception of the downlink signal to the specified value. Further, the first and sixth steps may include a ninth step in which the amount of attenuation is made variable in order to set the transmission levels of the downstream signal and the upstream signal to specified values. The fourth step is a step of calculating the amount of attenuation of the difference between the optical conversion level and the specified value in the upstream optical transmitter, and setting the amount of attenuation in receiving the upstream signal to the specified value based on the difference. The eighth step may include a step of setting the amount of attenuation in receiving a downlink signal to a specified value based on information indicating a difference between the specified values. The ninth step is a step of calculating an attenuation amount of a difference between an optical conversion level and an attenuation level in an upstream signal and a specified value, and controlling the attenuation amount in transmission of a downstream signal to a specified value based on the difference. And a step of controlling the amount of attenuation in the transmission of the upstream signal to a specified value based on information indicating the difference between the specified value of the optical conversion level and the specified value of the attenuation level in the transmission of the downstream signal. . In the bidirectional optical communication system and the optical transmission / reception level setting method according to the present invention, the monitoring / control device in the center station monitors the transmission / reception state of the downstream optical transmitter and the upstream optical receiver and performs the first optical variable attenuation. The attenuation amount of the second optical variable attenuator is set by monitoring the transmission / reception state of the downstream optical receiver and the upstream optical transmitter by the status monitor circuit in the node optical transmission device. Set to the specified value.

[0020]

Embodiments of the present invention will be described below. In the drawings described below, portions common to FIG. 3 are denoted by the same reference numerals.

(First Embodiment) FIG. 1 is a block diagram showing a first embodiment of a bidirectional optical communication system according to the present invention.

The bidirectional optical communication system includes a center station 1 and a node optical transmission device 2. The center station 1 and the node optical transmission device 2 are connected by optical fibers 24 and 25.

The center station 1 includes a downstream optical transmitter 3, an upstream optical receiver 6, and a supervisory control device 22. The downstream optical transmitter 3 transmits an optical signal to the node optical transmission device 2, and includes an amplifier 7 and an E / O converter 8.

The amplifying unit 7 amplifies a downstream video signal and a data signal which are electric signals input from the input point 26 of the center station 1. The E / O converter 8 converts a video signal and a data signal into an optical signal.

The upstream optical receiver 6 receives an optical signal from the node optical transmission device 2 and outputs it to an output point 27. The optical variable attenuator 19, the O / E converter 20, and the amplifier 2
1 is provided.

An optical variable attenuator 19 as a first optical variable attenuator varies the level of an optical signal from the node optical transmission device 2 side. The O / E converter 20 converts an optical signal from the node optical transmission device 2 into an electric signal of a video signal and a data signal. The amplifier 21 amplifies the electric signals of the video signal and the data signal.

The monitoring control device 22 outputs a monitoring control signal to the amplifier 7 and controls the level of the optical signal converted by the E / O converter 8 to be constant. At this time, the monitoring control device 22 monitors the level of the optical signal converted by the E / O converter 8.

The monitoring control device 22 sets the attenuation of the variable optical attenuator 19 to a predetermined constant attenuation value (initial value) so that the optical output level of the variable optical attenuator 19 does not become excessive. ).

Further, the monitoring control device 22 monitors the level converted by the O / E converter 20 and
The monitoring control response signal from the status monitor circuit 23 on the node optical transmission device 2 side is taken in via the amplifier 21.

The node optical transmission device 2 includes a downstream optical receiver 4,
An upstream optical transmitter 5, a coupling distributor 14, and a status monitor circuit 23 are provided.

The downstream optical receiver 4 receives an optical signal from the center station 1, and has an optical variable attenuator 10, an O / O
An E-converter 11 and an amplifier 12 are provided.

The variable optical attenuator 10 as a second variable optical attenuator varies the amount of attenuation of the level of the optical signal from the center station 1 side. The O / E converter 11 converts an optical signal from the center station 1 into an electric signal of a video signal and a data signal. The amplifier 12 amplifies the electric signals of the video signal and the data signal.

The upstream optical transmitter 5 transmits the optical signal to the center station 1
And an amplification unit 16 and an E / O conversion unit 17.

The amplifier 16 amplifies the electric signals of the video signal and the data signal. The E / O converter 17 converts an electric signal of a video signal and a data signal into an optical signal.

The coupling distributor 14 is connected to the coaxial repeater 15 via the coaxial line 30. The status monitor circuit 23 includes the CPU 13. The CPU 13 sets the attenuation of the variable optical attenuator 10 to a predetermined constant attenuation value (initial value) so that the optical output level of the variable optical attenuator 10 does not become excessive output.

Next, an optical transmission / reception level setting method of the bidirectional optical communication system having such a configuration will be described.

First, when an optical signal is transmitted by the downstream optical transmitter 3 on the center station 1 side, a monitoring control signal is output from the monitoring control device 22 to the amplifier 7. In the E / O converter 8, the electric signals of the video signal and the data signal are converted into optical signals. At this time, the level of the optical signal is controlled to be constant by the monitoring control device 22. The optical signal converted by the E / O converter 8 includes a monitoring control signal.

The optical signal converted at a certain level in the E / O converter 8 is transmitted to the optical variable attenuator 10 of the node optical transmission device 2 via the optical fiber 24. At this time, the variable optical attenuator 10 is connected to the status monitor circuit 2
The third CPU 13 sets a predetermined constant attenuation value (initial value) so that the output level of the optical signal does not become excessive output.

The optical signal output from the variable optical attenuator 10 is converted into an electric signal of a video signal and a data signal by the O / E converter 11 and then amplified by the amplifier 12. At this time, the monitoring control signal of the monitoring control device 22 is taken into the status monitor circuit 23. Then, the electric signal amplified by the amplifier 12 is output to the coaxial repeater 15 via the coupling distributor 14 and the coaxial line 30.

Next, a signal (uplink signal) from the node optical transmission device 2 to the center station 1 will be described. First, an electric signal output from the coaxial repeater 15 via the coupling distributor 14 and the coaxial line 30 is taken into the upstream optical transmitter 5.

When the upstream optical transmitter 5 transmits an optical signal to the center station 1, a monitoring control response signal from the status monitor circuit 23 is given to the amplifier 16. At this time, the electric signal amplified by the amplifier 16 is converted into an optical signal by the E / O converter 17.
The converted optical signal also includes a supervisory control response signal.

The converted optical signal reaches the optical variable attenuator 19 of the center station 1 via the optical fiber 25.
At this time, the variable optical attenuator 19 is set to a predetermined constant attenuation value (initial value) by the monitoring control device 22 so that the output level of the optical signal does not become excessive output.

The optical signal that has passed through the optical variable attenuator 19 is O
After being converted into an electric signal of a video signal and a data signal by the / E converter 20, the signal is amplified by the amplifier 21 and output from the output point 27. At this time, the monitoring control device 22
The monitoring control response signal of the status monitor circuit 23 is taken in from the amplifier 21.

In this state, the monitoring control device 22 and the status monitor circuit 23 can communicate with each other.

Next, the downstream optical receiver 4 and the upstream optical receiver 6
The method of adjusting the level of the optical signal in the above will be described.

In order to set the reception level of the optical signal of the O / E conversion unit 11 of the downstream optical receiver 4 to a specified value, first, the monitoring control unit 22 controls the E / O conversion unit 8 of the downstream optical transmitter 3. The signal of the conversion level state is captured.

The signal in the conversion level state is E /
This is an analog voltage when the electric signal of the video signal and the data signal is converted into an optical signal in the O conversion unit 8. This analog voltage is supplied to A
It is converted into a digital signal by a / D converter.

Then, the supervisory control signal is output from the supervisory control device 22 to the E / O converter 8 via the amplifying unit 7, so that the supervisory control signal is converted into an optical signal converted by the E / O converter 8. included.

On the node optical transmission device 2 side, when the optical signal is converted into an electric signal of a video signal and a data signal by the O / E converter 11 of the downstream optical receiver 4, the monitoring control device 2
2 from the status monitor circuit 23
Read by PU13.

The CPU 13 sends the monitoring control signal to the A / D
The signal is converted into a digital signal by a converter, is included in the optical signal converted by the E / O converter 17 of the upstream optical transmitter 5 as a monitoring control response signal, and is transmitted to the center station 1 side.

The supervisory control device 22 of the center station 1 fetches the supervisory control response signal from the electric signal of the video signal and the data signal converted by the O / E converter 20 of the upstream optical receiver 6, and obtains the difference between the specified value. Is calculated.

Then, information indicating the difference between the specified values is
It is sent to the CPU 13 inside the status monitor circuit 23. Thus, on the node optical transmission device 2 side, the CPU 13 of the status monitor circuit 23 sets the attenuation of the variable optical attenuator 10 to a specified value. By setting the attenuation of the variable optical attenuator 10 to a specified value, the conversion level of the O / E converter 11 is set to the specified value.

Similarly, in order to set the reception level of the O / E conversion unit 20 of the upstream optical receiver 6 by the monitoring control unit 22, the conversion level state of the E / O conversion unit 17 of the upstream optical transmitter 5 is set. The signal is captured as a supervisory control response signal.

The signal in the conversion level state is E /
This is an analog voltage when the electric signal of the video signal and the data signal is converted into an optical signal in the O conversion unit 17.

This analog voltage is converted by an A / D converter (not shown) of the monitoring control device 22. Then, the monitoring control device 22 calculates the amount of attenuation of the difference between the monitoring control response signal and the specified value, and controls the amount of attenuation of the variable optical attenuator 19 based on the difference. As a result, the optical reception level of the O / E converter 20 of the upstream optical receiver 6 is set to a specified value.

In this order, the variable optical attenuators 10, 1
By controlling the amount of attenuation of No. 9, the optical reception levels in the downstream optical receiver 4 and the upstream optical receiver 6 are set to specified values.

The monitoring controller 22 constantly monitors the level states of the E / O converter 8 of the downstream optical transmitter 3, the O / E converter 20 of the upstream optical receiver 6, and the optical variable attenuator 19. I have. When a level change occurs in each location, the level change amount is calculated, the difference is corrected, and the level is automatically controlled to a specified value. It is also possible to control manually.

As described above, in the first embodiment, the supervisory control device 22 in the center station 1 causes the downstream optical transmitter 3
And monitoring the transmission / reception state of the upstream optical receiver 6,
The attenuation amount of the optical variable attenuator 19 is set to a specified value, and the status monitor circuit 23 in the node optical transmission device 2 monitors the transmission / reception state of the downstream optical receiver 4 and the upstream optical transmitter 5 and also performs optical variable attenuation. Since the attenuation of the optical device 10 is set to the specified value, the level adjustment of the optical signal can be performed easily and reliably.

In the first embodiment, since existing components can be used as they are, it is possible to reconstruct a bidirectional optical communication system at low cost.

In particular, the variable optical attenuator 1 in a remote place
Since the amount of attenuation due to 0 is automatically adjusted by the status monitor circuit 23 in the node optical transmission device 2, the operation cost is greatly reduced.

The monitoring control device 22 in the center station 1
And the status monitor circuit 23 in the optical node transmission device 2 constantly communicates, and the level fluctuation of the optical signal is corrected in real time, so that the transmission quality can be kept constant.

The monitoring control device 22 in the center station 1
Thus, the transmission / reception state of the downstream optical transmitter 3 and the upstream optical receiver 6 and the attenuation state of the optical variable attenuator 19 are monitored, and the downstream optical receiver 4 and the upstream light are monitored by the status monitor circuit 23 in the node optical transmission device 2. Since the transmission / reception state of the transmitter 5 and the attenuation state of the optical variable attenuator 10 are monitored, it is possible to easily specify a portion where the level variation of the optical signal has occurred.

(Second Embodiment) FIG. 2 is a block diagram showing a second embodiment of the optical transmission / reception level setting device of the bidirectional optical communication system according to the present invention.

In the second embodiment, variable optical attenuators 9 and 18 are added to the downstream optical transmitter 3 on the center station 1 side and the upstream optical transmitter 5 on the node optical transmission apparatus 2 side, respectively.

In such a configuration, a control signal is supplied from the monitoring control device 22 to the optical variable attenuator 9. This control signal is set to a predetermined constant attenuation value (initial value) so that the optical output of the optical variable attenuator 9 as the third optical variable attenuator does not become excessive.
Thus, the optical signal output via the variable optical attenuator 9 is output at a constant level.

The output optical signal reaches the optical variable attenuator 10 on the node optical transmission device 2 side via the optical fiber 24. At this time, the status monitor circuit 23 prevents the optical output level of the optical variable attenuator 10 from becoming excessive.
Is set to a predetermined constant attenuation value (initial value).

The optical signal output from the variable optical attenuator 10 is converted into an electric signal by the O / E converter 11 and then output via the amplifier 12.

Here, a signal (uplink signal) from the node optical transmission device 2 to the center station 1 will be described.

The status monitor circuit 23 supplies a control signal to the variable optical attenuator 18 as a fourth variable optical attenuator. This control signal is set to a predetermined constant attenuation value (initial value) so that the optical output of the optical variable attenuator 18 does not become excessive.

At this time, the optical signal converted by the E / O converter 17 is also controlled to a constant level. The optical signal output from the upstream optical transmitter 5 passes through the optical fiber 25 and reaches the optical variable attenuator 19 of the center station 1. At this time, the attenuation of the variable optical attenuator 19 is set to a constant attenuation value (initial value) so that the optical output level of the variable optical attenuator 19 does not become excessive output.

The optical signal output from the variable optical attenuator 19 is converted into an electric signal by the O / E converter 20, amplified by the amplifier 21, and output. At this time, the supervisory control response signal from the status monitor circuit 23 is taken into the supervisory control device 22.

Next, the downstream optical receiver 4 and the upstream optical receiver 6
Will be described.

First, in order to set the optical reception level of the O / E converter 11 of the downstream optical receiver 4 of the node optical transmission device 2 to a specified value, the supervisory control device 22 sets the E level of the downstream optical transmitter 3. /
The signals of the level state of the O conversion unit 8 and the attenuation state of the optical variable attenuator 9 are captured.

The monitoring and control device 22 operates the O
An instruction (signal) is issued to the status monitor circuit 23 to measure the optical reception level of the / E conversion unit 11. The status monitor circuit 23 is controlled by the CPU 13 to execute the O / E conversion unit 1.
A level value of 1 is read, and information is sent to the supervisory control device 22 using an up signal.

The monitoring and control device 22 determines, based on the information,
The amount of attenuation of the difference between the specified values is calculated, and the result is sent to the status monitor circuit 23 using a downstream signal. The CPU 13 of the status monitor circuit 23 controls the optical variable attenuator 10 based on the information, and
The light reception level of the E conversion unit 11 is set to a specified value.

Similarly, to set the reception level of the O / E conversion unit 20 of the upstream optical receiver 6 by the monitoring control unit 22, the E / O conversion unit 17 of the upstream optical transmitter 5 and the optical variable attenuator The signal of 18 level states is captured.

Next, the supervisory control device 22 reads the level value of the O / E converter 20 of the upstream optical receiver 6, calculates the amount of attenuation of the difference between the specified values, and based on the calculation result, determines the optical variable attenuation. The control unit 19 is controlled. As a result, the optical reception level of the O / E converter 20 of the upstream optical receiver 6 is set to a specified value.

In this order, the variable optical attenuators 10, 19
, The light reception level is set. In addition, the monitoring control device 22 transmits the E /
The level status of the O conversion unit 8 and the variable optical attenuator 9 and the level status of the O / E conversion unit 20 and the variable optical attenuator 19 of the upstream optical receiver 6 are constantly monitored.

When a level change occurs at each point, the level change amount is calculated, the difference is corrected, and the level is automatically controlled to a specified value. It is also possible to control manually.

As described above, in the second embodiment, the optical variable attenuators 9 and 18 are connected to the downstream optical transmitter 3 and the upstream optical transmitter 5.
Is provided on the transmission side of the optical signal, the degree of freedom in setting the level of the optical signal can be given, and flexible optical signal transmission can be constructed.

In the downstream optical receiver 4 and the upstream optical receiver 6 in the first and second embodiments, the initial values of the variable optical attenuators 10 and 19 are set before the optical signal is input. It is desirable to keep. This initial value is determined by the CPU 1 in the status monitor circuit 23 of the node optical transmission device 2.
3 and the monitoring control device 22 in the center station 1.

This initial value is set to an amount of attenuation equal to or greater than the difference between the prescribed values of the optical transmission / reception level, and after the communication between the monitoring control device 22 and the status monitor circuit 23 has been established,
Change the initial settings. As a result, destruction when the reception levels of the downstream optical receiver 4 and the upstream optical receiver 6 are equal to or higher than a specified value is prevented.

[0083]

As described above, according to the bidirectional optical communication system and the optical transmission / reception level setting method according to the present invention, the transmission / reception state of the downstream optical transmitter and the upstream optical receiver is monitored by the monitoring control device in the center station. At the same time, the attenuation of the first optical variable attenuator is set to a specified value, and the status monitor circuit in the node optical transmission device monitors the transmission / reception state of the downstream optical receiver and the upstream optical transmitter, and The attenuation of the variable optical attenuator is set to a specified value, so that the level adjustment of the optical signal can be performed easily and reliably, and the transmission quality is corrected by correcting the level fluctuation of the optical signal in real time. Can be kept constant.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of an optical transmission / reception level setting device for a bidirectional optical communication system according to the present invention.

FIG. 2 is a block diagram showing a second embodiment of the optical transmission / reception level setting device of the bidirectional optical communication system of the present invention.

FIG. 3 is a block diagram showing an example of a conventional optical transmission / reception level setting device of a bidirectional optical communication system.

[Explanation of symbols]

 Reference Signs List 1 center station 2 node optical transmission device 3 downstream optical transmitter 4 downstream optical receiver 5 upstream optical transmitter 6 upstream optical receiver 7, 12, 16, 21 amplifying unit 8, 17 E / O conversion unit 9, 10, 18 , 19 Optical variable attenuator 11, 20 O / E converter 13 CPU 14 Coupling distributor 15 Coaxial repeater 22 Monitoring and control device 23 Status monitor circuit 24, 25 Optical fiber 26 Input point 27 Output point 28, 29 Fixed optical attenuator 30 Coaxial cable

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yukio Yanagishita 2-25-25 Shiba 2-chome, Minato-ku, Tokyo Inside NEC Cable Media Co., Ltd. Miyagi NEC Co., Ltd. (72) Inventor Hiroshi Takahashi 2 Miyagi, Kurokawa-gun, Yamato-cho

Claims (8)

[Claims] 1. A bidirectional optical communication system for performing bidirectional communication between a center station and a remote node optical transmission device via an optical transmission line, wherein a down signal is transmitted in the center station. A downstream optical transmitter; an upstream optical receiver for receiving an upstream signal; a first optical variable attenuator having a variable attenuation to prevent an excessive input to the upstream optical receiver; A monitoring control device that monitors the transmission / reception state of the transmitter and the upstream optical receiver, and sets an attenuation amount of the first optical variable attenuator to a specified value; A downstream optical receiver for receiving a signal; an upstream optical transmitter for transmitting the upstream signal; and a second optical variable attenuator having a variable amount of attenuation to prevent excessive input to the downstream optical receiver. Transmission and reception of the downstream optical receiver and the upstream optical transmitter Monitors the status, bidirectional optical communication system characterized by the status monitor circuit for setting the attenuation amount of the second optical variable attenuator prescribed value is provided. 2. An output side of each of the downstream optical transmitter and the upstream optical transmitter has a third and a fourth variable attenuation amount for setting the transmission level of the downstream signal and the upstream signal to a specified value. The two-way optical communication system according to claim 1, wherein the variable optical attenuator is provided. 3. The monitoring control device calculates an attenuation amount of a difference between an optical conversion level and a specified value in the upstream optical transmitter, and calculates an attenuation amount of the first variable optical attenuator based on the difference. The status monitor circuit controls the attenuation amount of the second optical variable attenuator to a specified value based on information indicating a difference between a specified value of an optical conversion level in the downstream optical transmitter from the monitoring control device. The bidirectional optical communication system according to claim 1, wherein the bidirectional optical communication system is controlled. 4. The monitoring control device calculates an optical conversion level in the upstream optical transmitter and an attenuation amount of a difference between the attenuation level of the fourth optical variable attenuator and a specified value, and based on the difference, The status monitor circuit controls an attenuation amount of the third optical variable attenuator, and defines a light conversion level in the downstream optical transmitter from the monitoring control device and an attenuation level of the third optical variable attenuator. 3. The bidirectional optical communication system according to claim 2, wherein the amount of attenuation of the fourth variable optical attenuator is controlled to a specified value based on information indicating a difference between the values. 5. An optical transmission / reception level of a bidirectional optical communication system for setting an optical transmission / reception level of an optical signal in a bidirectional communication performed between a center station and a remote node optical transmission device via an optical transmission line. A setting method, comprising: a first step of transmitting a downlink signal; a second step of receiving an uplink signal; and a third step of varying an amount of attenuation to prevent excessive input in receiving the uplink signal. A fourth step of monitoring the transmission / reception state of the downlink and uplink signals and setting an amount of attenuation in receiving the uplink signal to a specified value; a fifth step of receiving the downlink signal; A sixth step of transmitting a signal, a seventh step of varying the amount of attenuation in order to prevent excessive input in the reception of the downlink signal, and monitoring the transmission / reception state of the downlink and uplink signals. Eighth step and the light receiving level setting method of two-way optical communication system characterized in that it comprises setting the attenuation amount in the reception signal to a specified value. 6. The method according to claim 1, wherein the first and sixth steps include a ninth step of varying an amount of attenuation to set a transmission level of the downlink signal and the uplink signal to a specified value. An optical transmission / reception level setting method for a bidirectional optical communication system according to claim 5. 7. The fourth step includes: calculating an attenuation amount of a difference between an optical conversion level and a specified value in the upstream optical transmitter; and an attenuation amount in receiving the upstream signal based on the difference. And setting the amount of attenuation in receiving the downlink signal to a specified value based on information indicating a difference between the specified values. The optical transmission / reception level setting method for a two-way optical communication system according to claim 5, wherein: 8. The ninth step is a step of calculating an attenuation amount of a difference between an optical conversion level and an attenuation level in the upstream signal and a specified value, and an attenuation in transmission of the downstream signal based on the difference. Controlling the amount to a specified value, and controlling the amount of attenuation in the transmission of the uplink signal to a specified value based on information indicating a difference between the specified value of the optical conversion level and the specified attenuation level in the transmission of the downstream signal. 7. The method for setting an optical transmission / reception level of a bidirectional optical communication system according to claim 6, wherein the method is included.