JPH06318337A - Semiconductor laser driving device - Google Patents

Abstract

PURPOSE:To provide a semiconductor laser driving device solving a requirement to an information reproducing device by driving a semiconductor laser with three current sources of a bias current source, a low power current source and a high power current source. CONSTITUTION:The semiconductor laser is driven by three current sources of the bias current source 1, the low power current source 2 and the high power current source 3 at an information recording time. Further, the laser is driven by two current sources of the bias current source 1 and the low power current source 2 at a reproducing time. The occurrence of noise in the semiconductor laser due to a feedback beam at a low power time is suppressed by switching a current I1 from the low power current source 2 in a switching circuit 4 with a signal from a high freqency oscillator 6 at a high speed. The operation to the current source 2 is interrupted at a high power time, and the current I2 from the current source 3 is added to the current I1 from the current source 2. The output current value I1 of the current source 2 is controlled at an information reproducing time. The low power light intensity is held always to a fixed level by the control.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention irradiates a magneto-optical disk with light emitted from a semiconductor laser to record / reproduce information.
The present invention relates to a semiconductor laser driving device used in an optical memory system that executes erasing and the like.

[0002]

2. Description of the Related Art A known structure of a magneto-optical disk has a structure in which an amorphous thin film of a rare earth → iron alloy is formed on a substrate such as a glass substrate by sputtering and an easy axis of magnetization is perpendicular to the film surface. An optical memory system for recording / reproducing / erasing information is constructed by adding a head for irradiating a semiconductor laser beam to the magneto-optical disk. In this optical memory system, information is recorded by irradiating the magnetic film surface with a laser beam focused to about 1 μmφ to locally raise the temperature of the magnetic film and reduce the coercive force of the temperature rising portion. At the same time, the direction of magnetization is reversed by applying an auxiliary magnetic field from the outside (erasing can be performed in the same manner.) Also, the recorded information can be reproduced on the surface of the recorded magnetic film with a weaker light intensity than when recording. The linearly polarized light from the semiconductor laser is used to change the intensity of light using the inclination of the polarization plane due to the influence of the magnetic field of the reflected light, and the light is detected by a photodetector.

[0003]

From the above structure, the semiconductor laser requires a structure for emitting a high-output laser beam during recording and a low-output laser beam during reproduction, and the outputs of these two levels can be promptly achieved. Switching by means is required for the drive.

On the other hand, the magneto-optical effect (Kerr effect), which is the principle of information reproduction of a magneto-optical disk, utilizes the fact that the polarization characteristic of the reflected light from the disk is changed, so that it is essentially the feedback light to the semiconductor laser. Is difficult to prevent.
Therefore, it is necessary to use a semiconductor laser so that noise does not appear in the feedback light, but it is generally more advantageous to perform recording with high-power light with respect to the S / N ratio of the reproduction signal. Therefore, it is necessary to use a high power semiconductor laser. However, in general, a high-power semiconductor laser is weak against the incidence of feedback light because its output end face has a low reflectance, and noise due to the feedback light appears particularly at low power. Therefore, when using a high-power semiconductor laser, it is necessary to provide means for suppressing the generation of noise.

Further, the semiconductor laser has a temperature characteristic, and the output light intensity of the laser oscillation changes because the threshold current fluctuates depending on the ambient temperature. However, the output light intensity of the laser during the high output oscillation during recording changes. If the value fluctuates, insufficient or excessive writing of information occurs on the recording medium, and the error rate of information processing of the entire system deteriorates. This also applies to the low output oscillation of the laser during reproduction, and if the output light intensity fluctuates, it appears as deterioration of the S / N ratio of the reproduction signal.

For the above reasons, it is clear that stable oscillation of laser light is essential at both high and low output levels.

[0007]

The present invention has been made to solve the above problems, and is a semiconductor laser driving device incorporated in an optical memory system, which drives a semiconductor laser near its oscillation threshold. A first current source, a second current source which, when added to the first current source, oscillates a semiconductor laser to a level required to reproduce information from a recording medium, the first current source and the second current source. And a third current source that oscillates the semiconductor laser to a level required for recording by adding the current source to the semiconductor laser driving device.

Further, the present invention provides a semiconductor laser driving device provided with a control circuit for detecting the output light intensity of a semiconductor laser and controlling the output current value of the second current source according to the detection. Is.

[0009]

As a result, it is possible to provide a semiconductor laser driving device which solves the demand for an information reproducing device using a recording medium such as a magneto-optical disk as described above.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In order to achieve the above object, the present invention comprises three current sources for supplying a semiconductor laser driving current.

An embodiment according to the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing a semiconductor laser driving device according to an embodiment of the present invention, and FIG. 2 is a waveform diagram for explaining the operation of the device of FIG.

In FIG. 1, three current sources are a first current source (hereinafter referred to as a bias current source 1) for driving a semiconductor laser near the oscillation threshold, and a second current for oscillating a light intensity for information reproduction. And a third current source (hereinafter referred to as high output component current source 3) that enables high output oscillation during recording.

During information recording, the semiconductor laser is driven by three current sources, a bias current source 1, a low output current source 2 and a high output current source 3. Further, when reproducing information, it is driven by two current sources, that is, the bias current source 1 and the low output current source 2.

The generation of noise of the semiconductor laser due to the feedback light at the time of low output is caused by the signal from the high frequency oscillator 6 as shown in FIG.
The current I ₁ from is suppressed by switching at high speed. When the switching duty ratio is set to 50%, the average value of the light intensity during reproduction is 50% of the light intensity P ₁ due to the current I ₀ and the current I ₁ by the bias current source 1, that is, P _1/2 .

At the time of high output, the high frequency switching operation for the low output current source 2 is stopped and the switching circuits 4 and 5 are driven according to the recording information signal 7, so that the current I from the low output current source 2 is generated. _In addition to ₁ , the current I ₂ from the high output current source 3 is further added, so that the output light intensity becomes P ₂ as shown in FIG.

Here, at the time of reproducing information, that is, at the time of low output, the output light intensity is detected by the photodetector 9, and the value of this signal and the value from the reference voltage source 12 are passed through the preamplifier 10 to the comparator 12.
At the low-pass filter 1
3 and let the low frequency component power up 14
The output current value I ₁ of the low output current source 2 is controlled via. Low output light intensity P _1/2 This control will be maintained constant at all times irrespective of the temperature change. Generally, in semiconductor lasers, only the threshold current varies with temperature, so the inclination of the linear portion from the threshold does not change. Therefore, since the current value I ₂ of the high output current source 3 is constant,
If low output light intensity P _1/2 is constant high output power P ₂ is also a constant light output intensity.

As described above, by configuring the driving current source of the semiconductor laser by three independent current sources, the current value I ₁ can be controlled at the time of low output oscillation even in automatic output light intensity control (hereinafter referred to as APC). Control is realized during both high and low oscillations. Since it is not necessary to have a large dynamic range of the APC circuit, it is very advantageous in APC circuit design.

[0018]

As described above, according to the present invention, the bias current source for driving the semiconductor laser to near the oscillation threshold, the low output current source for reproducing information, and the high output current source for recording information are used. By driving with three current sources, it is possible to obtain a good semiconductor laser driving device in an information recording / reproducing device using a magneto-optical disk or the like as a recording medium. Further, the configuration of the three current sources makes it very easy to design the drive circuit and realizes cost reduction.

[Brief description of drawings]

FIG. 1 is a block diagram showing a semiconductor laser driving device according to an embodiment of the present invention.

FIG. 2 is a waveform diagram for explaining the operation of the apparatus of FIG.

[Explanation of symbols]

 1 Bias Current Source 2 Low Output Current Source 3 High Output Current Source 4,5 Switching Circuit 6 High Frequency Oscillator 7 Recorded Information 8 Semiconductor Laser 9 Photodetector 10 Preamplifier 11 Comparator 12 Reference Voltage Source 13 Low Pass Filter 14 Power Amplifier

Claims (2)

[Claims] 1. A semiconductor laser driving device incorporated in an optical memory system, comprising: a first current source for driving a semiconductor laser near its oscillation threshold; and information from a recording medium by addition to the first current source. A second current source that oscillates the semiconductor laser to a level required to reproduce the data, and a second current source that oscillates the semiconductor laser to a level required to record by the addition to the first current source and the second current source. 3. A semiconductor laser drive device, comprising: a current source of 3. 2. The semiconductor according to claim 1, further comprising a control circuit for detecting an output light intensity of the semiconductor laser and controlling an output current value of the second current source according to the detection. Laser drive device.