JPH02108335A - Optical transmission circuit - Google Patents

Abstract

PURPOSE:To prevent an erroneous alarm from occurring due to the deterioration of a mark ratio by branching the input of a light emitting element to a driving circuit, detecting synchronizing step-out, and resetting an alarm generating circuit. CONSTITUTION:A light emitting element 1 emits light corresponding to electric input data following to a driving circuit 3, and an optical transmission is executed. The transmitted light is received and monitored by a light receiving element 2, the circuit 3 is feedback-controlled, and the light emitting output of the element 1 is held to a constant value. Simultaneously, when the light receiving output of the element becomes less than a threshold, the alarm is generated from an alarm generating circuit 4. The circuit 4 is reset by the output of a synchronizing step-out detecting circuit 5 to detect the synchronizing step-out of the branched electric input data. As a result, the erroneous alarm can be prevented from occurring due to the deterioration of the mark ratio.

Description

[Detailed Description of the Invention] [Regarding an optical transmission circuit used in a machine-side optical repeater, the optical output of a light emitting element is monitored and driven by a light receiving element (the output of the light emitting element is kept constant by an illumination path, and the output of the light emitting element is kept constant and the output of the light emitting element is In order to prevent false alarms from occurring due to a decrease in mark rate in an optical transmitter circuit that uses an alarm generation circuit to issue an alarm for a decrease in the level of optical output that has been detected, the electrical input signal of the drive circuit is branched to generate Equipped with an out-of-sync detection circuit that detects out-of-sync and resets the alarm generation circuit.

[Industrial application field]

This paper relates to optical transmission circuits, and particularly to optical transmission circuits used in optical repeaters.

The optical repeater has a configuration schematically shown in FIG. 3, and includes an optical receiving circuit 10 that receives an optical input signal, equalizes and amplifies it, shapes the waveform, and outputs an electrical signal (data + clock). , a drop/add circuit 20 that drops/adds the output signal of this optical receiver circuit 1O, and an optical transmitter circuit 30 that sends out the electrical output signal of this drop/add circuit 20 as an optical output signal of a required level. However, in the optical transmission circuit 30, it is necessary to monitor the deterioration of the light emitting element used in the output stage.

[Conventional technology]

Conventionally, a circuit as shown in Fig. 4 has been used as an optical transmitter circuit to monitor the deterioration of a light emitting element.
A laser diode (LD) 1 as a light emitting element is optically driven by a drive circuit 3 by inputting an electrical data signal and a clock from a branch/add circuit as shown in the figure, and the optical output of the laser diode 1 is received. It is monitored by a photodiode (PD) 2 as an element, and the monitor output is fed back to the drive circuit 3 to perform APC (automatic output control) to give a signal at a constant level to the laser diode 1, and the monitor output is is sent to the alarm light emitting circuit 4.

The alarm generation circuit 4 generates an average voltage of the monitor output from the photodiode 2 and compares it with a predetermined threshold Th.
When this threshold value Th is not exceeded, an alarm is generated because the performance of the laser diode 1 has deteriorated.

[Problem to be solved by the invention] In such an optical transmitter circuit, the laser diode 1
The original alarm function is to generate an alarm when the performance of the laser diode l has deteriorated, but even if the performance of the laser diode l has not deteriorated, the mark rate of the input data has decreased due to a line failure, etc. Since the monitor output from the photodiode 2 decreases, an alarm may occur.

For example, when optically regenerating the output data of the optical receiving circuit IO in the optical repeater shown in FIG.
As shown in the figure, the optical input level of the optical receiving circuit 10 varies from the full detection level (when below this level, an alarm is generated from the optical receiving circuit IO) to the minimum allowable reception corresponding to the allowable value of the bit error rate. If a code error occurs in the direction in which the mark rate of input data decreases up to the level (particularly in the shaded area), an alarm will be generated in exactly the same way even though the performance of laser diode l has not deteriorated. There was a problem with this.

Therefore, the present invention provides an optical system that monitors the light output of a light emitting element with a light receiving element, uses a drive circuit to keep the output of the light emitting element constant, and alarms a drop in the level of the monitored light output using an alarm generating circuit. The purpose is to prevent false alarms from occurring due to a decrease in mark rate in a transmitting circuit.

Means for Solving Problem C] FIG. 1 is a diagram showing the principle of an optical transmission circuit according to the present invention for achieving the above object.
an out-of-synchronization detection circuit 5 that branches the electrical input signal of the data to detect out-of-synchronization of the data and resets the alarm generation circuit 4;
It has been established.

[For production]

By providing the out-of-synchronization detection circuit 5 in this way, it is possible to detect out-of-synchronization of the electrical signals input to the drive circuit 3. If the alarm generation circuit 4 is reset by the detection signal, the light as shown in FIG. 4 can be detected. It is possible to prevent false alarms from occurring due to a decrease in the mark rate of data due to a decrease in the input level.

〔Example〕

FIG. 2 is a circuit diagram showing an embodiment of the out-of-sync detection circuit 5 used in the optical transmission circuit of the present invention shown in FIG. 1. In this embodiment, electrical input data signals and clock signals are Branch circuits 5152 that branch respectively, and overhead pits 0HB (frame bits) in the data by inputting data and clocks from these branch circuits 5152.
The OHB extraction circuit 53 extracts the frame bits, and the synchronization verification circuit 54 performs synchronization verification from the frame bits.

In operation, when the OHB extraction channel 53 extracts frame bits located in the overhead of input data based on the clock and sends them to the synchronization verification circuit 54, the synchronization verification circuit 54 allocates the frame bits in advance and determines the channel timestamp. identify whether it is located in the loft,
When it is not located, an asynchronous alarm indicating loss of synchronization is generated and the alarm generation circuit 5 is reset to prevent generation of an alarm.

In this way, an alarm is not generated for uncertain areas of data input to the optical transmission circuit.

Note that an asynchronous alarm indicating loss of synchronization can be separately displayed to notify the operator.

〔Effect of the invention〕

As described above, according to the optical transmitting circuit of the present invention, the out-of-sync detection circuit that branches the electrical input signal of the drive circuit, detects out-of-sync of the data, and resets the alarm generation is provided, so that the performance of the light-emitting element can be improved. Deterioration can be detected accurately, and asynchronous states of input data can also be detected.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the principle of an optical transmission circuit according to the present invention, Fig. 2 is a block diagram showing an embodiment of an optical transmission circuit according to the invention, and Fig. 3 is a conventional general optical relay. FIG. 4 is a block diagram showing a conventional optical transmission circuit, and FIG. 5 is a characteristic diagram showing the relationship between optical input level and code error rate of the optical repeater. In FIG. 1, 1... Light emitting element (LD), 2... Light receiving element (PD), 3... Drive circuit, 4... Alarm generation circuit, 5... Out-of-synchronization detection circuit. In the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] The light output of the light emitting element (1) is monitored by the light receiving element (2), and the drive circuit (3) keeps the output of the light emitting element (1) constant and the level of the monitored light output. In an optical transmitter circuit that uses an alarm generation circuit (4) to alarm for a drop in data, the electrical input signal of the drive circuit (3) is branched to detect an out-of-synchronization of the data and reset the alarm generation circuit (4). An optical transmission circuit characterized by being provided with a detection circuit (5).