JPH114193A - Abnormal light output preventing circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid collision with other data and to prevent the stop of a network by providing a comparison part outputting an abnormal light signal and a gate part inhibiting the input of a burst signal to an electric/optic conversion part with, the abnormal light signal outputted from the comparison part. SOLUTION: A burst time measuring part 1 measures the burst time of the burst signal 101, shows time by pulse width and outputs it as a burst time pulse 102. A burst constant time output part 2 shows burst constant time which is previously decided by pulse width when the burst signal 101 is inputted and outputs it as a burst constant time pulse 103. The comparison part 3 compares the pulse width of the burst time pulse 102 with that of the burst constant time pulse 103 and considers that the light output signal of an LD part 5 becomes abnormal when the pulse width of the bust time pulse 102 is long. Then, it outputs the abnormal light signal 104 stopping the light output signal to the gate part 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for preventing abnormal optical output in optical burst transmission, which detects abnormal optical output due to device failure and stops optical output.

[0002]

2. Description of the Related Art Among conventional optical two-way communications, TCM (Time Compressed Bi-Directional Multiplexing) technology uses a single optical fiber to transmit data in a downstream direction and transmit data in an upstream direction. It is transmitted separately. FIG. 6 shows a frame configuration example of the TCM technology. In the TCM, in the first half of one frame, each of the slave devices 21 to 2
3 is sent to the slave devices 21 to 23 in the latter half.
Sends an upstream signal to the main unit 20 from the server. Each slave 21
23 transmit the uplink signal in synchronization with the transmission timing of the main device 20 and in accordance with the instruction of the main device 20. In this way, by controlling the transmission timing so that the signals from the main device 20 or the slave devices 21 to 23 do not collide, bidirectional communication can be performed with one core and one wavelength, and the accommodation efficiency can be greatly improved. Becomes

FIG. 7 is a block diagram showing a conventional optical abnormal output prevention circuit described in Japanese Patent Application Laid-Open No. 7-193602. In the figure, a laser diode (hereinafter referred to as LD) drive section 31 responds to a burst signal S1 to
A drive signal S2 is generated. LD 32 receives the LD drive signal S2
To generate an optical signal output S3. A photodiode (hereinafter referred to as PD) 33 monitors the optical signal output S3 and generates a monitor signal S4. The optical output disconnection detector 34 outputs an optical output disconnection signal S5 based on the monitor signal S4.

When the burst signal detector 35 confirms the burst signal S1, it generates a burst signal detection pulse S6. The comparing section 36 generates an optical output alarm pulse S7 in the alarm state “no burst signal exists but optical output exists” based on the burst signal detection pulse S6 and the optical output cutoff signal S5. Once detecting the alarm state, the latch unit 37 generates an optical output control signal S8 capable of holding the optical output stop state, and stops the optical output.

As described above, the abnormal optical output prevention circuit in FIG. 7 compares the presence or absence of a burst signal with the presence or absence of an optical output. It prevents collision with data from the terminal.

[0006]

Since the conventional optical abnormal output prevention circuit is constructed as described above, an optical signal is output when both the burst signal and the optical output signal are present. However, even if the burst signal is output, if the optical transmission timing is incorrect due to a device failure or the like, that is, if the burst signal time is longer than a predetermined time or the transmission speed of the burst signal is determined. If the transmission speed is different from the specified transmission speed, it collides with data transmitted at another specified timing, and other master devices or slave devices on the network cannot perform normal transmission / reception, and the network is stopped, There has been a problem that the influence of one device failure on another will be significant.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and has a case where the burst signal time is longer than a predetermined time or the transmission rate of the burst signal is different from the predetermined transmission rate. Even in such a case, an object of the present invention is to provide a circuit for preventing an abnormal optical output, which detects an abnormal optical output and prevents a collision with data transmitted at another designated timing.

[0008]

According to a first aspect of the present invention, there is provided an optical abnormal output preventing circuit which receives a burst signal and converts an electric signal into an optical signal, and an electric / optical converter for inputting the burst signal. A burst time measuring unit that measures and outputs a burst time of an input burst signal, a burst constant time output unit that inputs the burst signal and outputs a preset burst constant time, and a burst time measuring unit that outputs the burst signal. Comparing the burst time with the burst constant time output by the burst constant time output unit, and when the burst time is longer than the burst constant time, a comparing unit that outputs an optical abnormality signal; and the comparing unit. And a gate unit for preventing the burst signal from being input to the electrical / optical conversion unit in response to the output optical abnormality signal.

According to a second aspect of the present invention, there is provided an optical abnormal output preventing circuit which receives a burst signal, converts an electrical signal to an optical signal, and outputs an optical output signal, and an input of the optical output signal. An optical / electrical converter for converting the electric signal into an electric signal, and determining whether there is an optical output state based on a predetermined threshold level by inputting the electric signal converted by the optical / electrical converter, and A light output detection unit that outputs a signal, the monitor signal is input, a burst time measurement unit that measures and outputs a burst time of the light output signal, and a monitor signal is input, and a preset burst constant time is input. A burst constant time output section for outputting, a burst time outputted by the burst time measuring section and a burst constant time outputted by the burst constant time output section, and the burst time A comparing unit that outputs an optical abnormal signal when the burst time is longer than the fixed time, and a gate unit that blocks input of the burst signal to the electrical / optical converting unit by the optical abnormal signal output from the comparing unit It is provided with.

According to a third aspect of the present invention, there is provided an optical / optical converter for receiving a burst signal, converting the electrical signal into an optical signal, and outputting an optical output signal, and the electrical / optical converter. A bias monitor for monitoring a bias signal for driving the electric / optical conversion element, and a signal output from the bias monitor for inputting a signal to determine the presence or absence of an optical output state based on a predetermined threshold level. A light output detection unit for outputting a monitor signal, a burst time measurement unit for receiving the monitor signal, measuring and outputting a burst time of the light output signal, and a burst time input for receiving the monitor signal, A burst constant time output unit for outputting a time, a burst time output by the burst time measuring unit, and a burst constant output by the burst constant time output unit. A comparison unit that outputs an optical abnormality signal when the burst time is longer than the burst fixed time, and an optical abnormality signal that is output from the comparison unit. A gate section for blocking the input of the burst signal.

According to a fourth aspect of the present invention, there is provided an optical abnormal output prevention circuit which receives a burst signal, converts an electric signal into an optical signal, and outputs an optical output signal, and an optical / optical converter for inputting the optical output signal. An optical / electrical conversion unit for converting the electric signal into an electric signal; and inputting the electric signal converted by the optical / electrical conversion unit and determining whether there is an optical output state based on a predetermined threshold level. A first optical output detector for outputting a first monitor signal, a filter for receiving an electric signal converted by the optical / electrical converter and extracting a predetermined frequency component, and a predetermined frequency from the filter. A second light output detection unit that inputs a component, determines whether or not there is a light output state based on a predetermined threshold level, and outputs a second monitor signal; the first light signal and the second light signal; 2
When the first monitor signal is present and the second monitor signal is not present, a determination unit for outputting an optical abnormality signal, and a light abnormality signal output from the determination unit And a gate section for preventing the input of the burst signal to the electric / optical conversion section.

According to a fifth aspect of the present invention, there is provided a circuit for preventing abnormal optical output, comprising: an electrical / optical converter for receiving a burst signal, converting an electrical signal to an optical signal, and outputting an optical output signal; A bias monitor for monitoring a bias signal for driving the electric / optical conversion element, and a signal output from the bias monitor for inputting a signal to determine the presence or absence of an optical output state based on a predetermined threshold level. A first optical output detection unit that outputs a first monitor signal, a filter unit that receives a signal output from the bias monitor unit and extracts a predetermined frequency component, and a predetermined frequency component from the filter unit And a second optical output detection unit for determining the presence or absence of an optical output state based on a predetermined threshold level and outputting a second monitor signal, and the first monitor signal A determination unit that receives the second monitor signal and outputs an optical abnormality signal when the first monitor signal is present and the second monitor signal is not present; and a light output from the determination unit. By abnormal signal,
A gate section for blocking the input of the burst signal to the electric / optical conversion section.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below. Embodiment 1 FIG. FIG. 1 is a block diagram showing an optical abnormal output prevention circuit according to Embodiment 1 of the present invention. In the figure, reference numeral 1 denotes a burst time measuring unit which inputs a burst signal 101, measures the time thereof, and outputs a burst time pulse (burst time) 102, and 2 denotes a predetermined burst constant time as a burst constant time pulse (burst time). 3) a burst constant-time output unit, which is output as 103; 3 is a comparison unit that compares the pulse width of the burst time pulse 102 and the burst constant-time pulse 103, and outputs an optical abnormal signal 104; A gate unit which takes a logical product with the output unit 104 and outputs an input signal 105 to the LD unit 5;
Denotes an LD unit (electric / optical conversion unit) that generates an optical output signal according to the input signal 105.

Next, the operation will be described. Upon receiving the burst signal 101, the burst time measuring unit 1 measures the burst time of the burst signal 101, expresses the time as a pulse width, and outputs it as a burst time pulse 102.
Upon receiving the burst signal 101, the burst constant time output unit 2 represents a predetermined burst constant time with a pulse width and outputs it as a burst constant time pulse 103. TC
In the burst transmission using the M technology, since the burst time transmitted by one device is determined, the comparison unit 3 compares the pulse width of the burst time pulse 102 with the pulse width of the burst fixed time pulse 103, and determines the pulse width of the burst time pulse 102. When the width is long, the optical output signal of the LD unit 5 is regarded as abnormal, and the optical abnormal signal 104 for stopping the optical output signal is output.

The gate unit 4 calculates the logical product of the burst signal 101 and the optical abnormal signal 104, that is, the optical abnormal signal 1
04 is not output, the input signal 1 to the LD unit 5
05 is output. Then, the LD unit 5 converts the input signal 105 into an optical signal and generates an optical output signal. Gate part 4
Does not output the input signal 105 to the LD unit 5 when the optical abnormality signal 104 is output, and stops the generation of the optical output signal from the LD unit 5.

As described above, according to the first embodiment, the time of the input burst signal is measured, and if the time is longer than a predetermined time, the optical output is stopped. Thus, collisions with other data can be avoided, and network outages can be prevented.

Embodiment 2 FIG. FIG. 2 is a block diagram showing a circuit for preventing abnormal optical output according to a second embodiment of the present invention. In the figure, components having the same reference numerals as those in FIG. 1 have functions equivalent to those in the first embodiment. 6 is the LD unit 5
Is a PD unit (optical / electrical conversion unit) that receives the optical output signal 106 and converts the optical signal into an electric signal, and is disposed adjacent to the LD unit 5. Reference numeral 7 denotes an optical output detection unit that receives the electric signal converted by the PD unit 6 and outputs a monitor signal 107.

Next, the operation will be described. The PD unit 6
The optical output signal 106 of the LD unit 5 is input, and the optical signal is converted into an electric signal. Then, the light output detection unit 7 receives the electric signal converted by the LD unit 5 and determines the presence or absence of a light output state based on a predetermined threshold level, and determines whether the light output signal 106 of the LD unit 5 exists. Monitor signal 107 shown
Is output. The burst time measuring unit 1 receives the monitor signal 10
When an insignificance of 7 is input (light transmission state), a burst time is measured by measuring the insignificant time, the time is represented by a pulse width, and is output as a burst time pulse 102. The burst constant time output unit 2 outputs the monitor signal 10
When the intent of 7 is input, a predetermined burst constant time is represented by a pulse width and output as a burst constant time pulse 103.

In the burst transmission using the TCM technique, since the burst time transmitted by one device is determined, the comparison unit 3 compares the pulse width of the burst time pulse 102 with the pulse width of the burst constant time pulse 103, and
Is long, the optical output signal 106 generated from the LD unit 5 is regarded as abnormal, and the optical output signal 106
The optical abnormal signal 104 for stopping the operation is output. Gate part 4
Takes the logical product of the burst signal 101 and the optical abnormality signal 104, that is, outputs the input signal 105 to the LD unit 5 when the optical abnormality signal 104 is not output. The LD unit 5 converts the input signal 105 into an optical signal and generates an optical output signal 106. Further, the gate unit 4 is provided with the optical abnormal signal 10
4 is output, the input signal 105 to the LD unit 5 is output.
Is not output, and the generation of the optical output signal 106 from the LD unit 5 is stopped.

As described above, according to the second embodiment, the burst time of the light output signal of the LD unit 5 is measured, and if the time is longer than a predetermined time, the light output is stopped. As a result, collision with other data can be avoided, and network outage can be prevented. Further, since the output of the LD unit 5 is monitored, an abnormality up to the LD unit 5 of the device can be detected.

Embodiment 3 FIG. 3 is a block diagram showing an optical abnormal output prevention circuit according to Embodiment 3 of the present invention. In this embodiment, instead of monitoring a burst signal, an LD in the LD unit 5 corresponding to the burst signal is used.
The bias signal for driving the element is monitored.
In FIG. 3, components having the same reference numerals as those in FIG.
It has the same function as. Reference numeral 8 denotes a bias monitor that monitors a bias signal 108 that drives an LD element inside the LD unit 5.

Next, the operation will be described. The bias monitor 8 monitors a bias signal 108 that drives an LD element inside the LD unit 5. The optical output detector 7 receives the signal from the bias monitor 8 and determines the presence or absence of an optical output state based on a predetermined threshold level, and a monitor signal indicating the state of the bias signal 108 of the LD unit 5. 107 is output. The following operation operates in the same manner as in the second embodiment.

As described above, according to the third embodiment, the burst time of the optical output signal 106 is measured by the bias signal 108 of the LD element in the LD section 5, and the time is longer than a predetermined time. In this case, since the optical output is stopped, it is possible to avoid collision with other data and prevent the network from being stopped. Also in this embodiment, since the output of the LD unit 5 is monitored, an abnormality up to the LD unit 5 of the device can be detected.

Embodiment 4 FIG. 4 is a block diagram showing an optical abnormal output prevention circuit according to Embodiment 4 of the present invention. This embodiment detects an abnormality in the transfer speed indicated by the number of bits per unit time of a burst signal.

In FIG. 4, reference numeral 4 denotes a gate unit which takes a logical product of the burst signal 101 and the optical abnormality signal 104 and outputs an input signal 105 to the LD unit 5, and 5 generates an optical output signal 106 based on the input signal 105. The LD unit 6 is disposed adjacent to the LD unit 5 and monitors the optical output signal 106 of the LD unit 5 and converts the optical signal into an electric signal. The PD unit 7 converts the signal converted by the PD unit into an electric signal. First optical output detection for determining whether or not there is an optical output state based on a predetermined threshold level as input and outputting a first monitor signal 107 indicating the state of the optical output signal 106 of the LD unit 5 The filter unit 9 receives the signal converted by the PD unit 6 into an electric signal and extracts a predetermined frequency component. The filter unit 10 receives the signal from the filter unit 9 and outputs the optical output signal 106 of the LD unit 5. Of which The second optical output detector 11 outputs a second monitor signal 109 indicating the optical output state at the obtained frequency component. The second optical output detector 11 receives the first monitor signal 107 and the second monitor signal 109, This is a determination unit that determines the content and outputs the optical abnormality signal 104.

Next, the operation will be described. The PD unit 6
The optical output signal 106 of the LD unit 5 is input and converted into an electric signal. The first optical output detection unit 7 receives the electric signal converted by the PD unit 6, determines whether there is an optical output state based on a predetermined threshold level, and determines the presence or absence of an optical output state of the LD unit 5. Is output as the first monitor signal 107 indicating the state. The filter unit 9 receives the electric signal converted by the PD unit 6 and extracts a predetermined frequency component. Then, the second optical output detection unit 10 receives the signal from the filter unit 9 and determines whether or not there is an optical output state based on a predetermined threshold level. And outputs a second monitor signal 109 indicating the light output state at the determined frequency component.

Since the transmission speed is fixed, the judgment unit 11
Inputs the first monitor signal 107 and the second monitor signal 109, and when the first monitor signal 107 exists and the second monitor signal 109 does not exist, that is, "the light of a predetermined transmission rate" If there is no output, but there is some optical output, "the optical output signal of the LD unit 5 is regarded as abnormal, and an optical abnormality signal 104 for stopping the optical output is output. The gate unit 4 calculates the logical product of the burst signal 101 and the optical abnormality signal 104, that is, outputs the input signal 105 to the LD unit 5 when the optical abnormality signal 104 is not output.
The LD unit 5 converts the input signal 105 into an optical signal and outputs an optical output signal 106. Further, the gate unit 4 is provided with the optical abnormal signal 10
4 is output, the input signal 10 to the LD unit 5 is output.
5, the output of the optical output signal 106 from the LD unit 5 is stopped.

As described above, according to the fourth embodiment, the transmission speed of the optical output signal of the LD unit 5 is measured based on the frequency, and if the transmission speed is different from the predetermined transmission speed, the optical output is reduced. Since the operation is stopped, it is possible to avoid collision with other data and prevent the network from being stopped.

Embodiment 5 FIG. 5 is a block diagram showing a circuit for preventing abnormal optical output according to a fifth embodiment of the present invention. This embodiment detects an abnormality in the transfer speed of a burst signal. In the figure, components having the same reference numerals as those in FIG. 4 have functions equivalent to those in the fourth embodiment. Reference numeral 8 denotes a bias monitor that monitors a bias signal 108 that drives an LD element inside the LD unit 5.

Next, the operation will be described. The bias monitor 8 monitors a bias signal 108 for driving an internal LD element in the LD unit 5. The first optical output detection unit 7 receives a signal from the bias monitoring unit 8 and determines the presence or absence of an optical output state based on a predetermined threshold level, and monitors the state of the bias signal of the LD unit 5. The signal 107 is output. The filter unit 9 receives a signal from the bias monitor unit 8 and extracts a predetermined frequency component. The second optical output detection unit 10 receives the signal from the filter unit 9 and determines the presence or absence of an optical output state based on a predetermined threshold level, and determines a bias signal of the LD unit 5 from among the bias signals. The second monitor signal 109 indicating the light output state at the obtained frequency component is output. The following operation operates in the same manner as in the fourth embodiment.

As described above, according to the fifth embodiment, the transmission speed of the optical output signal of the LD unit 5 is measured by the frequency of the bias signal of the LD element in the LD unit 5, and the transmission speed is determined in advance. When the transmission speed is different from the transmission speed, the optical output is stopped, so that collision with other data can be avoided and a network stop can be prevented.

[0032]

As described above, according to the first aspect of the present invention, the burst time of the input burst signal is measured, and if the time is longer than a predetermined time, the optical output is stopped. With this configuration, it is possible to avoid collision with other data and to prevent the network from being stopped.

According to the second aspect of the invention, the burst time of the optical output signal of the electrical / optical converter is measured, and if the time is longer than a predetermined time, the optical output is stopped. Therefore, it is possible to avoid collision with other data and to prevent the network from being stopped.

According to the third aspect of the present invention, the burst time of the optical output signal is measured by the bias signal of the electrical / optical conversion element in the electrical / optical conversion unit, and when the time is longer than a predetermined time. Since the optical output is stopped, it is possible to avoid collision with other data and to prevent the network from being stopped.

According to the fourth aspect of the invention, the transmission speed of the optical output signal of the electric / optical conversion unit is measured by the frequency, and when the transmission speed is different from the predetermined transmission speed, the optical output is stopped. With this configuration, it is possible to avoid collision with other data and to prevent the network from being stopped.

According to the fifth aspect of the invention, the transmission speed of the optical output signal of the electrical / optical converter is measured by the frequency of the bias signal of the electrical / optical converter in the electrical / optical converter, and the transmission speed is measured. When the transmission speed is different from the predetermined transmission speed, the optical output is stopped, so that collision with other data can be avoided, and there is an effect that the stop of the network can be prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an optical abnormal output prevention circuit according to Embodiment 1 of the present invention.

FIG. 2 is a block diagram showing a circuit for preventing abnormal optical output according to a second embodiment of the present invention;

FIG. 3 is a block diagram showing an optical abnormal output prevention circuit according to Embodiment 3 of the present invention.

FIG. 4 is a block diagram showing a circuit for preventing abnormal optical output according to a fourth embodiment of the present invention.

FIG. 5 is a block diagram showing a circuit for preventing abnormal optical output according to a fifth embodiment of the present invention.

FIG. 6 is a frame configuration example of the TCM technology.

FIG. 7 is a block diagram showing a conventional optical abnormal output prevention circuit.

[Explanation of symbols]

1 Burst time measurement section, 2 burst constant time output section,
Reference Signs List 3 comparison section, 4 gate section, 5 LD section (electrical / optical conversion section), 6 PD section (optical / electrical conversion section), 7 optical output detection section, 1st optical output detection section, 8 bias monitor section, 9
Filter section, 10 second optical output detection section, 11 determination section, 101 burst signal, 102 burst time pulse (burst time), 103 burst constant time pulse (burst constant time), 104 optical abnormal signal, 106 optical output signal, 107 monitor signal, first monitor signal, 1
08 bias signal, 109 second monitor signal.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H04B 10/06 H04L 25/02 303

Claims (5)

[Claims] 1. An electrical / optical converter for receiving a burst signal and converting an electrical signal to an optical signal, a burst time measuring unit for receiving the burst signal, measuring and outputting a burst time of the input burst signal, A burst constant time output unit that receives the burst signal and outputs a preset burst constant time, a burst time output by the burst time measurement unit, and a burst constant time output by the burst constant time output unit. A comparison unit that outputs an optical abnormality signal when the burst time is longer than the burst constant time, and the burst to the electric / optical conversion unit based on the optical abnormality signal output from the comparison unit. A circuit for preventing abnormal light output, comprising: a gate section for preventing signal input. 2. An electrical / optical converter for receiving a burst signal, converting the electrical signal into an optical signal, and outputting an optical output signal, and an optical / electrical converter for receiving the optical output signal and converting the optical output signal into an electrical signal. An optical output detection unit that receives the electrical signal converted by the optical / electrical conversion unit, determines whether or not there is an optical output state based on a predetermined threshold level, and outputs a monitor signal; , A burst time measuring unit for measuring and outputting the burst time of the optical output signal, a burst constant time output unit for receiving the monitor signal and outputting a preset burst constant time, and the burst time measurement The burst time output by the burst unit and the burst constant time output by the burst constant time output unit are compared, and if the burst time is longer than the burst constant time, the optical difference A comparator for outputting a signal; and a gate for preventing the burst signal from being input to the electrical / optical converter in accordance with the optical abnormality signal output from the comparator. Prevention circuit. 3. An electrical / optical converter for inputting a burst signal, converting the electrical signal into an optical signal, and outputting an optical output signal, and monitoring a bias signal for driving an electrical / optical converter in the electrical / optical converter. A bias monitor unit that performs a signal output from the bias monitor unit, determines whether or not there is an optical output state based on a predetermined threshold level, and outputs a monitor signal; A burst time measuring unit that inputs a monitor signal, measures and outputs a burst time of the optical output signal, a burst constant time output unit that receives the monitor signal and outputs a preset burst constant time, and the burst The burst time output from the time measuring unit is compared with the burst constant time output from the burst constant time output unit, and the burst time is A comparison unit that outputs an optical abnormality signal when the time is longer than a predetermined time; a gate unit that blocks input of the burst signal to the electrical / optical conversion unit by the optical abnormality signal output from the comparison unit. A circuit for preventing abnormal light output, comprising: 4. An electric / optical converter for inputting a burst signal and converting an electric signal to an optical signal and outputting an optical output signal, and an optical / electric converter for inputting the optical output signal and converting the same to an electric signal. A first optical output detector for receiving the electrical signal converted by the optical / electrical converter, determining whether there is an optical output state based on a predetermined threshold level, and outputting a first monitor signal; A filter unit for inputting an electric signal converted by the optical / electrical conversion unit and extracting a predetermined frequency component; and a predetermined threshold component for inputting a predetermined frequency component from the filter unit and using a predetermined threshold level as a reference. A second optical output detection unit that determines whether or not there is a detected optical output state and outputs a second monitor signal; and inputs the first monitor signal and the second monitor signal, and outputs the first monitor signal. Signal is present and above A determination unit that outputs an optical abnormality signal when the second monitor signal does not exist; and a gate unit that blocks input of the burst signal to the electric / optical conversion unit by the optical abnormality signal output from the determination unit. A circuit for preventing abnormal light output, comprising: 5. An electrical / optical converter for receiving a burst signal, converting the electrical signal to an optical signal, and outputting an optical output signal, and monitoring a bias signal for driving an electrical / optical converter in the electrical / optical converter. A first monitor for receiving a signal output from the bias monitor, determining whether there is an optical output state based on a predetermined threshold level, and outputting a first monitor signal; An output detection unit, a filter unit that receives a signal output from the bias monitor unit and extracts a predetermined frequency component, and receives a predetermined frequency component from the filter unit and uses a predetermined threshold level as a reference. A second optical output detection unit for determining the presence or absence of an optical output state and outputting a second monitor signal; inputting the first monitor signal and the second monitor signal; A determination unit that outputs an optical abnormality signal when the monitor signal is present and the second monitor signal is not present; and the burst to the electric / optical conversion unit based on the optical abnormality signal output from the determination unit. A circuit for preventing abnormal light output, comprising: a gate section for preventing signal input.