JPH0348536A - Automatic output control circuit - Google Patents

Abstract

PURPOSE:To prevent the bias emission of a laser diode issued by delaying the cutoff of averaging output later than that of comparison output when it is not in operation. CONSTITUTION:A threshold value V1 is selected when an operation is performed, and input data is set as a DC component with an LPF consisting of a capacitor C1 and a resistor R1 via a distributor 11, and a voltage corresponding to a comparison result is applied on an amplifier 31 as a reference voltage. Meanwhile, the monitor output of the laser diode LD is applied on the amplifier 31 via a photodiode PD and an averaging circuit 33. Then, a bias supply circuit 32 is controlled so as to conform the averaging output to the reference voltage, and the output of the LD can be kept constant. Next, when an operation stopping instruction is inputted, the amplifiers 31 and 11 are turned off, and also, the value V2 is switched to the value less than a value V1, which prevents the bias current of the LD becoming higher abnormally.

Description

[Detailed Description of the Invention] [Summary] The purpose of this invention is to prevent bias light emission from occurring when an operation stop command is input to the optical communication transmission circuit in an automatic output control circuit used in the optical communication transmission circuit. , When driving a laser diode using a bias current and a pulse current corresponding to input data to extract an optical signal output corresponding to the input data, an averaging means for calculating the average value of the input data and an optical monitor output are used. an automatic output control circuit having comparison means for determining an average value and comparing it with the output of the averaging means and controlling the bias current so that the two average values match, and turning off the optical signal output. When an operation stop command is input, an output cutoff delay means is provided for delaying the cutoff of the output of the averaging means than the cutoff of the output of the comparing means.

[Industrial application field]

The present invention relates to an automatic output control circuit used in a transmission circuit for optical communication.

Generally, a digital optical relay transmission system is an optical terminal repeater installed at both ends of an optical cable. It consists of an optical repeater and optical fiber as the transmission medium.

now. If a failure occurs in one of the multiple optical relay devices, the optical signal from the failed optical relay device will be cut off, and the lower optical relay device will be able to transmit the optical signal from the optical transmission circuit. I have to turn off the output. At this time. It is necessary to prevent bias light emission from occurring.

[Conventional technology]

FIG. 4 is a block diagram of a conventional example, and FIG. 5 is an explanatory diagram of the operation of FIG. 4. below. The operation shown in FIG. 4 will be explained with reference to FIG.

First of all. As shown in Figure 5, a laser diode (hereinafter referred to as L)
(abbreviated as D) is because a large LD optical signal output can only be obtained by flowing a current exceeding the threshold current I. The bias supply circuit 14 always maintains this threshold current 1.
A current slightly smaller than th, that is, a bias current■. Let it flow.

Then, using the distributor 11 and the drive circuit 12, a pulse current IP corresponding to the input data is superimposed on the bias current 8. As a result, an optical signal output corresponding to the input data can be obtained.

However, since the value of the optical signal output of an LD changes depending on the ambient temperature, for example, the rear output light of the LD is transferred to a photodiode PD.
After converting the signal into an electrical signal, an averaging circuit 15 comprising a low-pass filter averages it, that is, extracts the DC component and adds it to the amplifier 13.

Since the DC component, that is, the reference voltage, extracted from the data distributed by the distributor 11 by the averaging circuit l2 having the same configuration as above is added here, the outputs of the two averaging circuits match. The bias supply circuit 14 is controlled in this manner.

This keeps the optical signal output of the LD constant.

Note that the above reference voltage has a pulse width of A when the mark rate of data is approximately 50χ.

[Problem to be solved by the invention]

here. If a failure occurs in the optical repeater of the previous station installed before the local station, the optical signal, that is, data, from the previous station will not be input to the local station, so the gain of the optical communication receiving circuit will increase. The noise component is sent to the optical communication transmitting circuit.
There is T-ability.

Therefore. In order to prevent this, the optical communication receiving circuit is turned off, and the distributor 11 and amplifier 13 of the optical communication transmitting circuit are turned off in response to an input operation stop command.

For this reason, the pulse current ■ and the output of the averaging circuit 12 are cut off, but the time constant of the divider l1 is smaller than the time constant of the amplifier l3. Output of averaging circuit 12. In other words, the disconnection of the reference voltage occurs earlier than the disconnection of the amplifier 13.
In the short time until 3 is cut off, the bias current becomes abnormally larger than the threshold current I, causing the LD to emit light (
This is sometimes called bias light emission.

In other words, when an operation stop command is input to the optical communication transmitter circuit,
There is a problem that bias light emission may occur. As a result, the LD is destroyed.

[Means to solve problems]

FIG. 1 shows a block diagram of the principle of the present invention.

In the figure, 2 is an averaging means for calculating the average value of input data.
Reference numeral 3 denotes a comparing means that calculates the average value of the output of the optical monitor and compares it with the output of the averaging means, and controls the bias current so that the two average values match. Also. Reference numeral 4 denotes an output cutoff delay means for delaying the cutoff of the output of the averaging means than the cutoff of the output of the comparison means.

[Effect]

In the present invention, an output cutoff delay means 4 is provided, so that when an operation stop command is input, the output cutoff of the 1,000 stages of averaging 2 is delayed compared to the output cutoff of the comparison means.

This eliminates the possibility that the LD will cause bias light emission when an operation stop command is input to the optical communication transmitting circuit.

? Embodiment] FIG. 2 is a block diagram of an embodiment of the present invention, and FIG. 3 is a block diagram of another embodiment of the present invention.

Here, capacitor C. Resistor Rl + amplifier 21 or capacitor C4 + resistor R2. The amplifier 2l is a component of the averaging means 2, and the switch S or the delay circuit 41 is a component of the output cutoff delay means 4. Note that the same reference numerals indicate the same objects throughout the figures. The operations shown in FIGS. 2 and 3 will be explained below.

First of all. In Fig. 2. During operation, switch SW
, selects the threshold value v1. Therefore, the input data is divided by the divider 11 and then divided into 1 capacitor C and resistor R.
An averaged DC component is obtained by a low-pass filter filtered by , and is compared with a threshold value v1 by an amplifier 2l, and a voltage corresponding to the comparison result is applied to an amplifier 31 as a reference voltage.

on the other hand. The rear output of the LD (monitor output corresponding to the optical signal output) is converted into an electrical signal by the PD and is also applied to the amplifier 3l via the averaging circuit 33.
Bias supply circuit 3 so that the output of 3 matches the reference voltage
2 to keep the optical signal output of the LD constant.

Here, when an operation stop command is input, the distribution amplifier 11
is turned off, but this command turns off the switch SW. is driven to switch to a threshold value V2 lower than the threshold value v1. Note that the threshold value v2 is a value that allows the amplifier 31 to send out the reference voltage from the time the operation stop command is input until the amplifier 31 is turned off.

As a result, the reference voltage corresponding to the comparison result is output from the amplifier 21 to the amplifier 31, but during this time the amplifier 31 is turned off by the operation stop command, so the bias current of the LD does not become abnormally large.

Next, FIG. 3 shows a delay circuit 41 that delays the output of the distributor.
However, the amount of delay time is the time it takes for the amplifier 3l to turn off after the operation stop command is input. This is the value that the reference voltage is sending out.

As a result, when an operation stop command is input to the optical communication transmitting circuit, there is no possibility that the LD will cause bias light emission.

〔Effect of the invention〕

As explained in detail above, according to the present invention, when an operation stop command is input to the optical communication transmitting circuit. This has the effect that bias light emission does not occur.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the principle of the present invention, FIG. 2 is a block diagram of an embodiment of the present invention, FIG. 3 is a block diagram of another embodiment of the present invention, FIG. 4 is a block diagram of a conventional example, FIG. 5 shows an explanatory diagram of the operation of FIG. 4. In the figure, 2 is an averaging means, 3 is a comparison means, and 4 is an output cutoff delay means. Ki Hatsurou's 7 Suga Ribu o-. Ku2 q 1 Pro of 4 loquats f1 of the 7th and 7th month of B, 2 Mouth V Ding Pro of the 311 Tora Ve example of the present invention, ・7 Ku Man 3 Figure $ 4 Figure

Claims (1)

[Claims] Averaging means for determining the average value of input data when driving a laser diode using a bias current and a pulse current corresponding to input data to extract an optical signal output corresponding to the input data. (2) and comparison means (3) for determining the average value of the optical monitor output, comparing it with the output of the averaging means, and controlling the bias current so that the two average values match. The circuit is characterized by being provided with output cutoff delay means (4) that delays the cutoff of the output of the averaging means than the cutoff of the output of the comparison means when an operation stop command to cut off the optical signal output is input. automatic output control circuit.