JPH02198232A - Optical reception level monitor circuit - Google Patents

Abstract

PURPOSE:To expand a relay interval of an optical communication line by providing a discrimination means outputting an alarm signal when an optical reception level is a fault discrimination level or below and a level fluctuation detection means outputting an alarm signal when the optical reception level is changed suddenly. CONSTITUTION:An optical signal inputted from a reception terminal A and converted into an electric signal by an optical reception circuit 10 is inputted to a detection circuit 16 via an AGC circuit 12, detected by the circuit 16 and inputted to a reception level discrimination circuit 18. Then the circuit 18 compares the level of the output signal of the circuit 16 with a preset fault discrimination level and when the level o the output signal of the circuit 16 is the fault discrimination level or below, an alarm signal is outputted from an alarm output terminal B. Moreover, a level fluctuation detection circuit 20 uses a differentiating circuit being the component of the circuit 20 so as to detect whether or not the level of the output signal of the circuit 16 is changed suddenly and in the case of level changed suddenly, an alarm signal is outputted from the terminal B. Thus, since the fault discrimination level is set lower than the reception level of the reflected light caused at a broken optical fiber, the relay interval of the optical communication line is expanded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical reception level monitoring circuit for an optical communication device using an optical fiber, and in particular, a directional coupler is used to monitor the optical reception level in both directions using a single optical fiber. The present invention relates to an optical reception level monitoring circuit for monitoring an abnormality in the optical reception level of an optical communication device that performs transmission.

[Conventional technology]

FIG. 2 shows the configuration of a conventional optical reception level monitoring circuit. In the figure, the optical reception level monitoring circuit includes an optical reception circuit IO, an AGC circuit 12, an AGC control circuit 14 that controls the gain of the AGC circuit 12, and a detection circuit 1B that detects the output signal of the AGC circuit 12. Reception level determination that compares the level of the output signal of this detection circuit 16 with a preset abnormality determination level and determines whether or not the reception level of the optical signal received by the optical reception circuit 1510 has decreased abnormally. It is composed of a circuit 18. In the above-described configuration, when an optical signal is input to the receiving terminal, the optical signal is converted into an electrical signal by the optical receiving circuit 10 and amplified to a predetermined level by the AGC circuit 12. This AGC circuit 12
The gain of is controlled by the AGC control circuit 14.

The output signal of the AGC circuit 12 is detected by a detection circuit 16, and the detected signal is input to a reception level determination circuit 18. The reception level determination circuit 18 compares the level of the output signal of the detection circuit 16 with a preset abnormality determination level, and issues an alarm signal if the level of the output signal of the detection circuit 16 is below the abnormality determination level. is output from alarm output terminal B.

In this way, conventional optical reception level monitoring circuits are configured to compare the optical reception level with a preset abnormality determination level, and output an alarm signal when the optical signal reception level falls below this abnormality determination level. was.

[Problem to be solved by the invention]

When performing bidirectional transmission with a single optical fiber using a directional coupler, if the optical fiber breaks, the optical signal sent from the device to the outside will be reflected at the point where the optical fiber broke, causing the light from the device to be transmitted. Human power is applied to the receiving circuit. Hereinafter, the lowest value of the reception level of this reflected light will be referred to as Lr.

In the conventional optical reception level monitoring circuit described above, when an optical fiber is broken, the abnormality determination level of the received optical signal is set to level Lr in order to determine that the reflected light from the broken point is abnormal. Must be set to a higher level.

Generally, the level Lr is considerably higher than the receiving sensitivity Ls of the optical receiving circuit. Therefore, even if an optical receiving circuit has good reception sensitivity, when receiving reflected light caused by a break in an optical fiber, the abnormality determination level of the optical signal is set to determine that the reception level of the received optical signal is abnormal. needs to be set to a higher level than Lr, and therefore there is a problem in that the relay interval of the optical communication path cannot be increased.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical reception level monitoring circuit that can extend the relay interval of an optical communication path.

[Means to solve the problem]

In order to achieve the above-mentioned object, the present invention provides an optical reception level monitoring circuit for monitoring abnormalities in the optical reception level of an optical communication device that performs bidirectional transmission over a single optical fiber using a directional coupler. A determination means that outputs an alarm signal when the reception level is below the abnormality determination level, and a determination means that detects a sudden change in the optical reception level and detects a sudden change in the optical reception level even if the optical reception level is equal to or higher than the abnormality determination level. The device is characterized in that it has level fluctuation detection means for outputting an alarm signal.

According to the present invention, even if the optical reception level is equal to or higher than the abnormality determination level, an alarm signal is output when the optical reception level suddenly changes.
When the optical fiber is broken, it can be set lower than the reception level of reflected light generated from the breakage point, and therefore it is possible to expand the relay interval of the optical communication path.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of an embodiment of an optical reception level monitoring circuit according to the present invention.

In the figure, the optical reception level monitoring circuit is an optical reception circuit 10.
, the AGC circuit 12 , the AGC control circuit 14 that controls the gain of the AGC circuit 12 , the detection circuit 16 that detects the output signal of the AGC circuit 12 , and the level of the output signal of the detection circuit 16 and is set in advance. A reception level determination circuit 18 that determines whether the reception level of the optical signal received by the optical reception circuit 10 has abnormally decreased by comparing it with an abnormality determination level, and a sudden change in the level of the output signal of the detection circuit 16. and a level fluctuation detection circuit 20 that outputs an alarm signal when the level of the detected output suddenly changes. In such a configuration, when an optical signal is input from the receiving terminal A, the optical signal is converted into an electrical signal by the optical receiving circuit 10 and amplified to a predetermined level by the AGC circuit 12. The gain of this AGC circuit 12 is controlled by an AGC control circuit 14.

The output signal of the AGC circuit 12 is detected by a detection circuit 16, and the detected signal is input to a reception level determination circuit 18. The reception level judgment circuit 18 compares the level of the output signal of the detection circuit 16 with a preset abnormality judgment level, and issues an alarm signal if the level of the output signal of the detection circuit 16 is below the abnormality judgment level. Output from alarm output terminal B.

On the other hand, the level fluctuation detection circuit 20 detects whether or not the level of the output signal of the detection circuit 16 has changed suddenly using a differentiating circuit that constitutes the level fluctuation detection circuit 20, and issues an alarm signal if the level has changed suddenly. Output from alarm output terminal B.

〔Effect of the invention〕

As explained above, in the present invention, even if the optical reception level is equal to or higher than the abnormality determination level, an alarm signal is output when the optical reception level suddenly changes. The level can be set lower than the reception level of the reflected light generated from the fractured part of the optical fiber, and therefore the relay interval of the optical communication path can be expanded.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an optical reception level monitoring circuit according to the present invention, and FIG. 2 is a block diagram showing the configuration of a conventional optical reception level monitoring circuit. 10... Optical receiving circuit, 12... AGC
Circuit, 14...AGC control circuit, 16...
...Detection circuit, 18... Reception level judgment circuit,
20...Level fluctuation detection circuit.

Claims (1)

[Claims] In an optical reception level monitoring circuit for monitoring an abnormality in the optical reception level of an optical communication device that performs bidirectional transmission over a single optical fiber using a directional coupler, the optical reception level is at an abnormality determination level. determining means for outputting an alarm signal when the optical reception level is below; 1. An optical reception level monitoring circuit comprising: level fluctuation detection means for outputting an output.