JPS62169486A - Semiconductor laser driving device - Google Patents

Abstract

PURPOSE:To always control the power level of an output pulse to be constant against fluctuations of a threshold value due to temperature change and fluctuations of an external differential quantum efficiency by subjecting the peak value of a laser luminescence to sample hold and feedback control. CONSTITUTION:A pulselike input current is inputted in a pulse driving part 2 through an input part 1 and a semiconductor laser 3 held in the vicinity of an oscillation (light) threshold value by a bias current 1b is pulsewise emitted by a pulse current 1p. The luminescence of the laser 3 is received and monitored by means of a photodiode 4, the output is amplified in a current amplifying part 5, a sampling hold part 8 performs sampling hold of the minimum value of the pulse of luminescence and the output keeps the bias current 1b at a constant value by feedback control via a D/C driving part 7. A sampling hold part 9 monitors the maximum value of the of luminescence, it is compared with a reference voltage Vref 12 in a pulse current control part 10, and by the output the pulse current of the pulse current driving part w is subjected to feedback control through a control terminal (c).

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a semiconductor laser drive device suitable for devices using semiconductor lasers such as optical communications, compact discs, and optical desks.

2. Description of the Related Art As shown in FIG. 3, a semiconductor laser is pulse-driven by applying a direct current bias to the semiconductor laser with an appropriate bias current IB and applying a pulse current 1p to the semiconductor laser. That is, a pulse signal is inputted from the input section 1 to the pulse current drive section 2, and the output drive pulse current 1p is applied to the semiconductor laser 3 in a superimposed manner with the bias current IB from the DC current drive section 7. The light emission of the laser 3 is monitored by a photodiode 4 as a detection means, and the output is amplified by a current amplification section 5 and a DC amplification section 6, and compared with a reference voltage V ref by a DC current drive section 7 to determine a DC bias is. . Also photodiode 4
, a negative feedback loop is formed by the current amplifying section 5, the DC amplifying section 6, the current driving section 7, and the semiconductor laser 3, and as the output power increases, the output of the semiconductor laser 3 increases, so the DC IB decreases and the output The laser oscillation threshold is compensated for by decreasing the laser oscillation threshold due to changes in the temperature of the laser.

Note that the peak value of the output pulsed light of the laser has also been kept constant by detecting the peak value of the output pulsed current of the photodiode °4.

Problems to be Solved by the Invention However, in the conventional semiconductor laser driving device described above, the value of the driving pulse current 1p is constant, and the output power fluctuation is controlled and kept constant by changing the bias current IB value. It has been impossible to perform sufficiently stable control against output power fluctuations due to changes in external differential quantum efficiency. Furthermore, feedback control is performed by detecting the average value of the output pulse or the peak value using a general peak detection method, so stable output power control is achieved with a sufficiently fast response speed for discontinuous pulse signals from optical discs, etc. was difficult.

The present invention solves these conventional problems, and has the advantage of being able to perform stable control with a sufficiently fast response speed even when the external differential quantum efficiency of the laser changes or when discontinuous pulse signals are received. It is an object of the present invention to provide a semiconductor laser driving device with improved performance.

Means for Solving the Problems In order to achieve the above object, the present invention monitors the laser emission with a fort diode etc. for both the bias current and pulse current that drive the semiconductor laser, and samples the peak value. It is configured to hold and thereby perform feedback control.

Operation Since the present invention is constructed as described above, changes in the external differential quantum efficiency can be compensated by the pulse current 1p, and changes in the threshold can be compensated for by the bias current It). As a result, stable laser emission control can be performed at all times.

Embodiment The structure of an embodiment of the present invention is shown in Fig. 1 and Fig. 2.
This will be explained with figures. In figure B71, 8.9 is the first
, a second sampling hold section, 10 a pulse current control section, Vref 1 and Vref 2 the first,
The second reference voltage input terminal C is a control terminal of the pulse drive unit 2. Other symbols similar to those in FIG. 2 represent the same names.

Next, the operation of the above embodiment will be explained. When a pulsed input current is input from the input section 1 to the pulse drive section 2, the semiconductor laser 3, which is held near the threshold of oscillation (light) by the bias current 1b, emits light in a pulsed manner by the pulse current IP.

The light emitted from the semiconductor laser 3 is monitored by the photodiode 4, and the output thereof is amplified by the current amplification section 5, and then
The second sampling and holding section 8.9 is inputted onto a flat plate. The first sampling and holding unit 8 holds the O of the light emission pulse.
Sample and hold the level (minimum value) in synchronization with the input pulse. The output of the serving ring and hold section 8 is passed through the DC drive section 7 to feedback control the bias current IB to a constant value. - The sampling hold section 9 of the blade 2 monitors the level (maximum value) of the light emission pulse,
The pulse current controller 10 compares it with the second reference voltage Vref2, and the pulse current of the pulse current driver 2 is similarly feedback-controlled via the control terminal C based on its output.

The control situation will be explained with reference to Figure 2 (1), in which the horizontal axis represents snow and flow (1), and the vertical axis represents the output (
P, ), A is the emission characteristics of the semiconductor laser, and
: bias current ip, and c is bias current 1b. Even if the external differential quantum efficiency changes and the emission characteristics change as shown by the broken line E, the pulse current 1p can be increased as shown in 2 by detecting the level of the emission pulse [2], and the peak value of the emission pulse -. 7 shows that it is possible to keep constant.

Further, for temperature changes, correction is performed by detecting the 0 level of the light emission pulse and changing the bias current 1b.

In the above configuration, since the peak value of the output pulse is sampled and held, a faster response can be expected compared to the conventional method of detecting the average value of the laser output light or detecting the peak value.

Effects of the Invention As is clear from the above embodiments, the present invention is capable of detecting and feedback controlling the 0 level and 1 level of the output pulsed light of the laser, and is capable of controlling threshold fluctuations due to temperature changes and external This has the advantage that the power level of the laser output pulse can always be controlled to be constant despite variations in the differential quantum efficiency. Furthermore, there is an effect that follow-up control can be performed with a fast response speed even to discontinuity of input pulses.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a semiconductor laser driving device according to an embodiment of the present invention, FIG. 2 is a current-output characteristic diagram of the same, and FIG. 3 is a block diagram of a conventional driving device. 1... Input section, 2... Pulse current drive section, 3...
Semiconductor laser, 4... Photodiode, 7... DC current drive unit, 8.9... Sampling hold unit,
10... Pulse current control section. Name of agent: Patent attorney Toshio Nakao and 1 other person
1 Figure 2 Figure 3

Claims (1)

[Claims] a semiconductor laser driven by a combined current of both a pulse drive section synchronized with an input pulse signal and a DC drive section regulating bias current; a detection means for detecting a maximum value and a minimum value of a light emission pulse of the semiconductor laser; and a sampling hold circuit that holds the outputs of the detection means, respectively,
A semiconductor laser driving device, wherein the pulse driving section and the DC driving section are feedback-controlled by the output of the sampling and holding circuit.