JPH05129691A - Light output controller - Google Patents

Abstract

PURPOSE:To rapidly perform laser diode rising by providing a transistor which outputs the control signal for LD drive circuit to drive the laser diode and grounding the emitter side of the transistor via a peak-value detecting circuit. CONSTITUTION:The titled controller is provided with a transistor 8 that outputs the control signal for an LD drive circuit 3 to drive a laser diode 1 and the emitter side of the transistor 8 is grounded via a peak-value detecting circuit 20. Since the voltage for controlling the circuit 3 has been impressed in the circuit 20, a time constant necessary for the conventinal mean value detecting circuit is unnecessary to be taken into account. Therefore the duration in which an optical amplitude will reach a constant level can be shortened. While, the emitter output voltage of the circuit 8 controls the circuit 3 according to the held values at every burst signal SB rise, and the output voltage of the circuit 3 controls the operation of the LD1. Thus an optical burst output signal with constant amplitude can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical output control device, and more particularly to an optical output control device (hereinafter referred to as APC) in an optical transmission circuit used in an optical communication system for transmitting burst signals.
Device).

[0002]

2. Description of the Related Art Conventionally, an optical transmitter having an APC device has a laser diode (hereinafter abbreviated as LD) 51 for converting an electric signal into an optical signal and two inputs, as shown in FIG. L that inputs an electric signal and drives LD51
D drive circuit 53, LD 51, photodiode 52 that receives background light and converts it into an electrical signal, and photodiode 52
A photodiode amplifier circuit 56 for amplifying the output of
A reference voltage generation circuit 54 that receives an input electric signal and outputs a reference voltage; and an APC comparison circuit 55 that compares the respective voltages with the output signal of the reference voltage generation circuit 54 and the output signal of the photodiode amplification circuit 56 as inputs. , An integrating circuit including a resistor 57 and a capacitor 62 for receiving the output of the APC comparing circuit 55, and an NPN transistor (hereinafter abbreviated as transistor) 58 for inputting the output of the integrating circuit to the base.
And the emitter output of the transistor 58 to the LD drive circuit 5
It is configured to feed back to the other input terminal of 3.
In this APC circuit, the emitter output of the transistor 58 obtained from the output of the APC comparison circuit 55 through the integration circuit controls the LD drive circuit 53, and the LD drive circuit 53 output voltage controls the drive current of the LD 51 to output light. A method of making the amplitude constant has been adopted.

[0003]

Consider a case where a burst signal is transmitted as an input signal in the optical transmission circuit having the above-mentioned conventional APC circuit. When there is no burst signal, the output voltage of the reference voltage generation circuit approaches 0, but the output voltage of the integration circuit also approaches 0 because of the rapid discharge. Therefore, a transient state occurs in which the output voltage of the integrator circuit rises from 0 to the output voltage of the integrator circuit at the time of inputting the burst signal at each rise of each burst signal, resulting in a problem that an optical burst output with a constant amplitude cannot be obtained. On the other hand, if the time constant of the integrating circuit is increased to shorten the time of this transient state and stabilize the light amplitude, a constant output burst output can be obtained, but a constant light amplitude can be obtained even after the power is turned on. However, there is a problem in that the time up to becomes longer with the time constant of the integration circuit.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a light output control device which can improve the disadvantages of the conventional example and can particularly quickly rise the laser diode.

[0005]

According to the present invention, an LD drive circuit having two input terminals and driving a laser diode by externally inputting a burst signal to one of the two input terminals, and a reference voltage based on the burst signal are provided. A reference voltage generation circuit that outputs a photo diode, a photodiode that inputs the backward light of the laser diode and converts it into an electrical signal, and an optical output that compares the output of this photodiode and the output of the reference voltage generation circuit and outputs a predetermined control signal. A configuration is provided in which a comparison circuit and a transistor that operates according to the output of the optical output comparison circuit and outputs a control signal for the LD drive circuit are provided, and the emitter side of this transistor is grounded via the peak value detection circuit. I am collecting. This aims to achieve the above-mentioned object.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. The embodiment shown in FIG. 1 has two input terminals, and an LD drive circuit 3 for driving a laser diode 1 by externally inputting a burst signal into one of the two input terminals, and outputting a reference voltage based on the burst signal. The reference voltage generating circuit 4 for controlling the output of the laser diode 1 and the photodiode 2 for converting the light into an electric signal are compared with the output of the photodiode 2 and the output of the reference voltage generating circuit 4 to output a predetermined control signal. The optical output comparison circuit 5 and the transistor 8 that operates according to the output of the optical output comparison circuit 5 and outputs a control signal for the LD drive circuit 3 are provided.
The emitter side of the transistor 8 is grounded via the peak value detection circuit 20.

The peak value detecting circuit 20 is composed of a parallel circuit of a resistance element 11 and a capacitor 10 in this embodiment.

This will be described in more detail. In the embodiment shown in FIG. 1, a laser diode 1 for converting an electric signal into an optical signal and a laser diode 1 having two inputs and inputting a burst signal S _B to one of them are provided. A laser diode drive circuit 3 for driving the laser diode 1, a photodiode 2 for receiving the rear light of the laser diode 1 and converting it into an electric signal, and a photodiode amplifier circuit 6 for amplifying the output of the photodiode 2.
A reference voltage generation circuit 4 that receives the burst signal 9 and outputs a reference voltage; and an APC comparison circuit 5 that receives the output signal of the reference voltage generation circuit 4 and the output signal of the photodiode amplification circuit 6 and compares the respective voltages. A resistance element 7 for receiving the output of the APC comparison circuit 5, a transistor 8 for inputting the output of the resistance element 7 to the base, and a resistance element 1.
Transistor 8 consisting of a parallel circuit of 1 and capacitor 10
The peak detection circuit 20 which receives the emitter output of the LD drive circuit and the APC circuit which returns the emitter output of the transistor 8 to the other input terminal of the LD drive circuit 3.

Next, the operation of this embodiment will be described. When the burst signal is input to the optical transmission circuit having the APC circuit shown in FIG. 1, when the burst signal disappears, the output voltage of the reference voltage generation circuit 4 approaches “0” and the base voltage of the transistor 8 also becomes “0”. When approaching, the transistor 8 is turned off (O
FF). However, due to the peak detection circuit 20 including the capacitor 10, the emitter output voltage of the transistor 8 holds the peak value. Therefore, the LD drive circuit 3 is controlled in accordance with the held value of the emitter output voltage of the transistor 8 at each rising edge of each burst signal, and the LD drive circuit 3 output voltage causes LD1
Drive current can be controlled. Therefore, as a result, an optical burst output signal having a constant amplitude is obtained.

On the other hand, the APC according to this embodiment when the power is turned on
Considering the transient response of the circuit, in this embodiment, since the voltage for controlling the LD drive circuit is given by the peak value detection circuit,
It is not necessary to consider the time constant in the case of the conventional average value detection circuit. Therefore, it is possible to shorten the time until a constant light amplitude is obtained.

[0011]

As described above in detail, according to the present invention, the peak value detection circuit is used to control the LD drive circuit for controlling the current flowing through the laser disk.
It is possible to provide an unprecedented excellent optical output control device in which a constant amplitude can be obtained at high speed when the power is turned on, and an optical burst output signal with a constant amplitude is continuously obtained when a burst signal is input. .

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram showing a conventional example.

[Explanation of symbols]

 1 Laser diode (LD) 2 Photodiode (PD) 3 LD drive circuit 4 Reference voltage generation circuit 5 Automatic optical output control (APC) comparison circuit 6 Photodiode output signal amplification circuit 20 Peak value detection circuit

Claims (2)

[Claims] 1. An LD drive circuit having two input terminals, one of which receives a burst signal from the outside to drive a laser diode, and a reference voltage generation circuit which outputs a reference voltage based on the burst signal. A photodiode for inputting the rear light of the laser diode and converting it into an electric signal, an optical output comparison circuit for comparing the output of the photodiode and the output of the reference voltage generation circuit and outputting a predetermined control signal, A light output control circuit, comprising: a transistor which operates in response to an output of a light output comparison circuit and outputs a control signal for the LD drive circuit, wherein an emitter side of the transistor is grounded through a peak value detection circuit. apparatus. 2. The light output control device according to claim 1, wherein the peak value detection circuit is configured by a parallel circuit of a resistance element and a capacitor.