JPH02140986A - Optical output controller for semiconductor laser - Google Patents

Abstract

PURPOSE:To suppress current consumption in a driving circuit by generating a first pulse for applying a bias current and a second pulse for monitoring the optical output of a semiconductor laser, and superposing a driving current pulse on the first pulse to driving the laser. CONSTITUTION:When a semiconductor laser 1 is driven, its optical output is detected by a photodetector 2, and a level detector 9 detects the level of the photodetection signal at a position of generating timing of a second pulse P2. A comparison controller 11 increases or decreases the amplitudes of first and second pulses P1, P2 on the basis of difference between the detected value and a reference value to control to negatively feed back so that the optical output of the laser 1 becomes constant. In this case, a bias current is applied by the pulse P1 to the pulse-modulated driving current pulse. Thus, current consumption of the driving circuit can be suppressed to a small value.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a semiconductor laser light output control device used to control the light output of a semiconductor laser.

<Prior Art> Conventionally, as shown in FIG. 4, a pulse-modulated drive current pulse P0 and a bias current Ib are input to a semiconductor laser drive circuit, and the semiconductor laser is driven by a signal obtained by superimposing these inputs. and optical output pulse P. Output ut.

The DC bias current 1b is set to a value greater than or equal to the oscillation starting current t of the semiconductor laser.
th changes due to temperature changes, and its characteristics also change as shown by chain lines a and b in the figure, and the optical output pulse also changes as P O
IJ? ' + P 0117'.

Therefore, the optical output of the semiconductor laser is received by a monitoring photodiode, and after detecting the peak value and average value of the received light pulse, the DC bias current 1b is increased or decreased according to the difference between the detected value and the reference value. This performs negative feedback control to maintain a constant optical output.

<Problems to be Solved by the Invention> However, in such a system, since it is necessary to constantly flow the DC bias current I to the drive circuit, there is a problem that the current consumption of the drive circuit becomes large.

This invention was made with attention to the above problem, and provides a novel semiconductor laser optical output control device that suppresses current consumption by applying a bias current to the drive circuit section in pulses as needed. The purpose is to provide.

Means for Solving the Problems> The optical output control device of the present invention uses a semiconductor laser and a signal obtained by superimposing a pulse-modulated drive current pulse on a first pulse for providing a DC bias current to control the semiconductor laser. a drive circuit section for driving the semiconductor laser; a photodetection section for detecting the optical output of the semiconductor laser; It consists of a pulse generation circuit section for generating pulses.

The pulse generation circuit section includes a level detection circuit section for detecting the level of the light reception signal obtained by the photodetector at the position of the second pulse generation timing, and a detection value and a reference value by the level detection circuit section. 1st according to the difference between The comparison control circuit section controls the amplitude of each second pulse.

<Operation> When the semiconductor laser is driven, its optical output is received by the photodetector, and the level detection circuit detects the level of the received light signal at the position of the second pulse generation timing. The comparison control circuit section increases or decreases the amplitude of each of the first and second pulses based on the difference between the detected value and the reference value, thereby performing negative feedback control so that the optical output of the semiconductor laser becomes constant.

In this case, the bias current is applied by the first pulse to the pulse-modulated drive current pulse, so the current consumption of the drive circuit section can be kept low compared to the conventional method in which a direct current bias current is constantly flowing. .

Embodiment FIG. 1 shows the overall configuration of a semiconductor laser optical output control device according to an embodiment of the present invention. diode 2 and a first pulse P providing a bias current.

a laser drive circuit 3 that drives the semiconductor laser 1 with a signal obtained by superimposing a drive current pulse Pfl on the drive current pulse Pfl; a drive current control unit 4 that generates the drive current pulse Po and outputs it to the laser drive circuit 3; The bias current controller 5 generates a pulse P1 and a second pulse P at an intermediate timing of the generation timing of the first pulse P1, and outputs these pulses P1 and P2 to the laser drive circuit 3. has been done.

FIG. 2 shows the output characteristics of the semiconductor laser 1, in which the semiconductor laser 1 is driven by a first pulse P+, a driving current pulse P,
It is driven by a signal obtained by superimposing the two pulses and a second pulse Pt. 1st. The amplitude of each of the second pulses P+ and Pg is set to be greater than the oscillation starting current I of the semiconductor laser, and when the semiconductor laser 1 is driven by the superimposed signal and the second pulse P2, as shown in the figure. Optical output pulse Pou〒-1,
POLI? -2 occurs.

The drive current control section 4 includes a switch 7 to which a modulation voltage is applied, and a control pulse C having a timing shown in FIG. 3(1).
1 and a pulse generating circuit 6 which generates the pulse C1 and applies it to the switch 7, and the switch 7 generates the pulse C1 by a modulated voltage.
1 to generate a drive current pulse P0, which is output to the laser drive circuit 3.

In addition to the pulse generation circuit 6, the bias current control section 5 includes an amplifier circuit 8. Switch 9. Holby circuit 10. Comparison control circuit 11. The configuration includes a pulse generation circuit 12.

The amplifier circuit 8 amplifies the light-receiving current obtained by the photodiode 2 and converts it into voltage. The switch 9 detects the level of the pulse output of the amplifier circuit 8 at the timing position of the optical output pulse Pout-2, and the hold circuit 10 holds the detected value, and the control pulse C2 ( The above-mentioned level detection and detection value holding are performed in accordance with the timing shown in FIG. 3 (2). The output of the hold circuit 10 is given to a comparison control circuit 11, and the comparison control circuit 11 increases or decreases the value of the bias current given to the laser drive circuit 3 according to the difference between this input value and a predetermined reference value.

The next pulse generating circuit 12 is supplied with a control pulse C3 having the timing shown in FIG. 3 (3) from the pulse generating circuit 6. The first one with the corresponding amplitude. Second pulses PI and Pz are generated and output to the laser drive circuit 3.

In the above configuration, when the laser drive circuit 3 drives the semiconductor laser 1 with a signal obtained by superimposing the drive current pulse P on the first and second pulses P, , P, the semiconductor laser l outputs an optical output pulse P out - 1, P out-2 is generated, the light is irradiated onto the object to be measured, and is also received by the photodiode 2 for monitoring. The photodiode 2 outputs a light-receiving current through photoelectric conversion, and the amplifier circuit 8 provides a pulse output to the switch 9. The switch 9 receives a second pulse P! from the pulse generating circuit 6! A control pulse C2 having a timing corresponding to the control pulse C2 is applied, and the level of the received light pulse is detected at the timing of this control pulse C2, and the detected value is held in the hold circuit 10. This hold value is given to the comparison control circuit 11, and this comparison control circuit 11
increases or decreases the bias current applied to the laser drive circuit 3 based on the difference from a predetermined reference value, thereby maintaining the optical output of the semiconductor laser 1 constant. The reference value given to this comparison control circuit 11 is such that the bias current is the oscillation starting current
The bias current is set to be slightly larger than the bias current, so that the amount of light emitted by the semiconductor laser 1 due to the bias current is kept to a minimum.

The output of this comparison control circuit 11 is given to a pulse generation circuit 12, which is connected to the pulse generation circuit 6.
In response to the control pulse C3, the first . second pulse P,
Pt is generated and outputted to the laser drive circuit 3. Therefore, a bias current is not constantly applied to the laser drive circuit 3 (each of the first and second pulses P, P
Since the bias current is applied only for a period corresponding to the pulse width of R, the current consumption in the laser drive circuit 3 can be kept small.

<Effects of the Invention> As described above, the present invention generates a first pulse for applying a bias current and a second pulse for monitoring the optical output of a semiconductor laser, and adds a drive current pulse to the first pulse. Since we drove the semiconductor laser by superimposing
Compared to the conventional method of constantly applying a direct current bias current, the current consumption in the drive circuit section can be suppressed to a small level, and the present invention has a remarkable effect of achieving the purpose of the invention.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the overall configuration of a semiconductor laser optical output control device according to an embodiment of the present invention, FIG. 2 is an explanatory diagram showing the characteristics of the semiconductor laser and the principle of the present invention,
FIG. 3 is a time chart of the circuit of FIG. 1, and FIG. 4 is an explanatory diagram showing the characteristics of the semiconductor laser. 1... Semiconductor laser 2... Photodiode 3... Laser drive circuit 4... Drive current control section 5... Bias current control section 7.9... Switch 11. ... Comparison control circuit 12 ... Pulse generation circuit diagram Semiconductor trainer's cow sea lion master Explanation

Claims (1)

[Scope of Claims] A semiconductor laser; a drive circuit section for driving the semiconductor laser with a signal obtained by superimposing a pulse-modulated drive current pulse on a first pulse for applying a bias current; and light of the semiconductor laser. It consists of a photodetection section for detecting the output, and a pulse generation circuit section that generates the first pulse at the same timing as the drive current pulse and generates the second pulse at an intermediate timing, The generation circuit section includes a level detection circuit section for detecting the level of the light reception signal obtained by the photodetector at the position of the generation timing of the second pulse, and a difference between the detected value by the level detection circuit section and a reference value. 1. An optical output control device for a semiconductor laser, comprising: a comparison control circuit section that controls the amplitude of each of the first and second pulses according to the amplitude of the first and second pulses.