JPH0548182A - Laser diode optical output control device - Google Patents

Abstract

PURPOSE:To provide a laser diode optical control device capable of obtaining fixed optical output. CONSTITUTION:A bias current which a bias control device 7 outputs is placed on a pulse current which a pulse drive section 6 outputs so as to drive a laser 1. A light receiving device 2 receives the rear light of the laser 1 and its output current is converted into voltage by a current/voltage converter 4 and A/D converted by an A/D converter 5. The converted value is compared with a predetermined reference value by a comparator 9. The output of the comparator 9 is D/A converted by the D/A converter 8, the bias current is supplied to the laser 1 by way of the bias control section 7 and a switch 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser diode light output control device in an optical communication device for transmitting burst data by using a laser light output.

[0002]

2. Description of the Related Art FIG. 2 shows the configuration of a conventional laser diode light output control device. In the figure, 1 is a laser diode (hereinafter referred to as a laser) that emits light by a bias current and a pulse current. The forward light of the laser 1 is coupled to an optical fiber or the like and transmitted to the outside. The back light of the laser 1 is monitored by the light receiving element 2. A current / voltage converter 4 converts the photocurrent of the light receiving element 2 into a voltage.
Reference numeral 11 is a peak hold circuit, which holds an input peak value. Further, the peak hold circuit 11 resets the output value with a reset pulse from the outside. Reference numeral 12 denotes a comparator, which compares the output of the peak hold circuit 11 with a predetermined reference value, and outputs increase / decrease information for the reference value to the bias controller 7.
Communicate to. The bias controller 7 controls the bias current applied to the laser 1 based on the output of the comparator 12. 6
Is a pulse drive unit for applying a pulse current to the laser 1 based on input data.

Next, the operation of the above conventional example will be described.
First, the relationship between the laser output optical signal and the bias current and pulse current will be described. The input current vs. optical output characteristics of the laser are shown in FIG. As shown in FIG. 3, an output optical signal is obtained by making the oscillation threshold current of the laser substantially equal to the bias current and superimposing the pulse current on the bias current. At this time, the threshold current of the laser changes depending on the ambient temperature and deterioration over time, so that it is necessary to control the bias current in order to obtain a constant output optical signal level. However, as shown in FIG. 4A, since the input data is burst data in which the mark ratio changes, it is necessary to detect the peak value of the output optical signal and control the bias current with the peak value. The conventional example of FIG. 2 realizes this control. After monitoring the backward light of the output optical signal of the laser 1, the peak hold circuit 11 detects the peak value, and the comparator 12 compares the level with the reference value. The bias control unit 7 controls the bias current to the laser 1 so that the laser light output peak becomes constant. The peak hold circuit 11 operates only in the burst period by the reset pulse as shown in FIG.

As described above, in the above-mentioned conventional laser diode light output control circuit, the peak hold circuit 11 can detect the peak value in the burst and control the laser output light constant within the burst.

[0005]

However, in the conventional laser diode light output control device described above, the output of the current / voltage converter 4 does not correspond to the long burst data (FIG. 5A) as shown in FIG. A pattern effect occurs due to the frequency characteristic of the circuit and the like, and level fluctuations as shown in FIG. 5B occur within the burst. Along with this, the peak hold circuit 1
The output of 1 (open loop) may fluctuate as shown in FIG. 5C, and the hold value may increase, but it does not decrease. Therefore, the optical output of the laser is shown in FIG.
As described above, there is a problem in that the light output apparently decreases, as it is not constant.

The present invention solves such a conventional problem, and an object of the present invention is to provide a laser diode light output control device capable of obtaining a constant light output within a burst.

[0007]

In order to achieve the above object, the present invention comprises an A / D converter and a D / A converter in a control circuit to detect and control laser output light constantly during a burst period. Have.

[0008]

Therefore, according to the present invention, even if a pattern effect occurs due to long burst data, the optical output is constantly monitored and controlled within the burst, so that there is no problem that the optical output apparently drops.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the configuration of an embodiment of the present invention. In FIG. 1, reference numerals 1, 2, 4, 6, and 7 are the same as those in the conventional example, which are a laser, a light receiving element, a current / voltage converter, a pulse driving section, and a bias control, respectively. 5 is A /
It is a D converter and outputs the output of the current / voltage converter 4 to A /
D-convert. Reference numeral 9 is a comparator, which compares the parallel data of the A / D converter 5 with a predetermined reference value and outputs the increase / decrease information to the D / A converter 8. D / A converter 8
Transmits the output of the comparator 9 to the bias controller 7. The output of the bias controller 7 is supplied to the laser 1 via the switch 10 to apply a bias current to the laser 1. The switch 10 is turned on by the high level of the burst gate pulse as shown in FIG. 5B, and the bias current is applied to the laser 1 only during the burst period.

Even if the output of the current / voltage converter 4 fluctuates due to the pattern effect during the burst period, the A / D converter 5 detects the optical output in response to the increase / decrease. The bias controller 7 controls the light output of the laser 1 to be constant by the output of the A / D converter 5.

As described above, according to this embodiment, when the A / D converter 5 detects the optical output of the laser 1 within the burst period, the bias current of the laser 1 is controlled based on the detected value. It does not cause the problem of apparent light output reduction as in the example.

[0012]

As is apparent from the above-described embodiment, according to the present invention, the output light of the laser is monitored by the A / D converter, and the A / D converter is used for the entire period within the burst data. Since the laser light is detected and controlled over time, it is possible to provide a laser diode light output control device that prevents an apparent decrease in light output when a peak hold circuit is used.

[Brief description of drawings]

FIG. 1 is a block diagram of a laser diode light output control device according to an embodiment of the present invention.

FIG. 2 is a block diagram of a conventional laser diode light output control device.

FIG. 3 Current-optical output characteristic diagram of laser

FIG. 4 is a waveform diagram of input data and control signals.

FIG. 5 is a waveform diagram of input data, in-circuit signal, and optical output in the conventional example.

[Explanation of symbols]

 1 laser diode 2 light receiving element 4 current / voltage converter 5 A / D converter 6 pulse drive unit 7 bias control unit 8 D / A converter 9 comparator 10 switch

Claims (1)

[Claims] 1. A laser diode that emits light by a pulse current with a bias current, a light receiving element that monitors the output light of the laser diode, a current / voltage converter that converts the output current of the light receiving element into a voltage, and the current. / A / D converter for A / D converting the output of the voltage converter, a comparator for comparing the output of the A / D converter with a predetermined reference value, and a D for D / A converting the output of the comparator / A converter, a bias control that controls the bias current applied to the radar diode by the output of the D / A converter, a switch that connects the output of the bias controller to the laser diode only during a burst period, and input data A laser diode light output control device comprising a pulse drive unit for applying a pulse current to the laser diode.