JPS6289248A - Light quantity controller for optical recording and reproducing device - Google Patents

Abstract

PURPOSE:To stabilize the intensity of the laser light at the time of recording mode by using the 1st and 2nd current sources that oscillate a semiconductor laser, the 1st and 2nd holding means that hold data when the information is recorded and erased to a recording medium, and the 1st and 2nd control means which control the current value. CONSTITUTION:In a reproduction mode an automatic optical output control APC for reproduction is actuated by the 1st current source 1, the 1st holding circuit 7 and the 1st control means 15. While an APC for erasion is actuated in an erasion mode by the 2nd current source 2, the 2nd holding circuit 6 and the 2nd control means 14 in addition to the current source 1. Then both APC for reproduction and erasion are frozed in a record mode. In such a way, the intensity of the laser light is stabilized at the time of recording.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to semiconductors used in optical memory systems that record, reproduce, and erase information by irradiating light emitted from a semiconductor laser onto a magneto-optical disk. The present invention relates to a laser light amount control device.

(Prior art) Magneto-optical diode is a rare earth material deposited on a substrate such as a glass substrate.
It is constructed by depositing an amorphous iron alloy film by sputtering and covering it with a magnetic film having an axis of easy magnetization perpendicular to the film surface. An optical memory system that records, reproduces, and erases information is constructed by adding a 1. code to the beam irradiation.In this memory system, information is recorded using a laser beam focused to a diameter of about 1 μm. is applied to the surface of the magnetic film to locally increase the temperature of the magnetic film to reduce the coercive force in the temperature-increased area, and at the same time, apply an auxiliary magnetic field from the outside to reverse the direction of magnetization. (Deleting is also possible in a similar manner).

In addition, to reproduce the recorded information, the surface of the recorded magnetic material film is irradiated with linearly polarized light from a semiconductor laser with a weaker light intensity than during recording, and the intensity of the light is changed using the tilt of the polarization plane due to the magnetic field of the reflected light. , and detect it with a photodetector.

Because of the above structure, semiconductor lasers require a configuration that emits high-power laser light during recording and low-power laser light during playback, and the driving device is required to quickly switch between these two levels of output by some means. be done.

Further, a semiconductor laser has temperature characteristics, and its threshold current varies depending on the ambient temperature, so the output light intensity of laser oscillation changes. However, if the output light intensity fluctuates during high output oscillation of the laser during recording, it is expected that insufficient or excessive information will be written to the recording medium, reducing the reliability of the information processing of the entire system.

This is also true when the laser oscillates at low output during reproduction (when reproducing information), and if the output light intensity fluctuates, this will appear as a deterioration in the S/N ratio of the reproduced signal.

In view of the above points, a light amount control device having a configuration as shown in FIG. 3 has already been proposed. Two currents ib and c are provided for supplying drive currents to the semiconductor laser a, and when reproducing information from a recording medium, a drive current I is provided by a low-output current source.

The semiconductor laser a is driven only by the semiconductor laser a.

When recording information on a recording medium, a high-output laser beam is obtained by further adding a driving current (2) from another high-output current source C, which is another current source.

Here, for the low output current ab, the intensity of the output light of the semiconductor laser a is detected by a photodetector d, and is inputted to a sample and hold circuit r through a preamplifier e. This sample and hold circuit f is controlled by a sample and hold signal SI, and holds data when the sample and hold signal SI is at rHJ level, and passes the data as is when it is at rLJ level. This data is compared with a reference voltage source g in a comparator, and the low frequency component after passing through a low-pass filter i is input to a power amplifier j, and the drive current 1. control. If the hold timing signal Sl is always at the rLJ level, this control will always keep the low output light intensity constant regardless of the temperature characteristics of the semiconductor laser a. Note that such automatic light output control for obtaining output light of a constant intensity is called APC.

Next, during high output oscillation (when recording information), the hold timing signal S becomes rHJ level to hold data and freeze the APC. On the other hand, the hold timing signal S1 is used in the A N D gate j to generate the recording data signal S only during recording.

Accordingly, the high output current (recording current) 2 is added to the low output current 11 via the switching circuit k, and recording on the medium is performed. The purpose of freezing the APC is to avoid lowering the output intensity in response to high output oscillation. By making the freezing time sufficiently shorter than the time for changes in the temperature characteristics of the semiconductor laser, APC operates in a pseudo manner during recording.

(Problems to be Solved by the Invention) The characteristics of the oscillation operation during information recording in this type of light amount control device are that only the oscillation threshold changes as a temperature characteristic of the semiconductor laser, and the drive current of the semiconductor laser - The precondition is that the slope of the linear portion above the threshold value in the optical output curve does not change, and based on this, it can be said that if the low output light intensity is constant, the high output light intensity is also constant.

However, in actual semiconductor lasers, the slope of the linear portion of the drive current-optical output curve above the threshold value changes due to aging and ambient temperature. Therefore, if only a constant current (2) is applied by a high-output current source, the high-output light intensity changes and good recording (erasing) characteristics cannot be obtained.

(Means for Solving the Problems) The present invention is a semiconductor laser light amount control device incorporated in an optical recording/reproducing device, which oscillates the semiconductor laser to a level necessary for reproducing information from a recording medium. a first current source for oscillating a semiconductor laser to a level necessary for erasing and recording information on a recording medium by adding it to the first current source;
a first holding circuit that detects the output light intensity of the semiconductor laser when reproducing information on a recording medium, and holds data based on the detection when erasing or recording information on the recording medium; a first control means for controlling the output current value of the first current source during erasing and recording of information on the recording medium; and a first control means for detecting the output light intensity of the semiconductor laser when erasing information on the recording medium; a second holding circuit that holds data during recording and reproduction of information on a recording medium; and an output current value of the second current source when recording information on the recording medium based on the output of the holding circuit; and second control means for controlling.

(Function) During reproduction, the first current source, the first holding circuit, and the first
A reproduction APC is operated by the control means, and when erasing, in addition to the first current source, the second current source and the second current source are activated.
The erasing APC operates by the holding circuit and the second control means. On the other hand, during recording, the reproducing APC and erasing APC are frozen, and the laser beam intensity during recording is stabilized.

(Example) Hereinafter, a case in which the light amount control device for a semiconductor laser according to the present invention is applied to a magneto-optical disk device will be described in detail.

FIG. 1 is a block diagram showing a light amount control device according to an embodiment of the present invention.

FIG. 2 shows the timing waveforms required for the apparatus of FIG.

In FIG. 1, a semiconductor laser 3 is driven by a low output current source 1 and a high output current #2.

In other words, when reproducing information from a recording medium, only the current 11 from the low output current tA1 is used, and when recording (erasing) information, the current I2 from the high output current source 2 is used by 11
In addition to this, the semiconductor laser 3 is driven.

A for low output current source 1 during low output oscillation (during playback)
The PC is realized as follows.

The intensity of the output light from the semiconductor laser 3 is detected by a photodetector 4 and introduced into a sample and hold circuit 7 through a preamplifier 5. Here, the sample and hold circuits 6 and 7 hold the data at the rising edge of the hold timing signal Sl+S2 when it is at rHJ level, and pass the data as is when it is at rLJ level. As shown in FIG. 2, during reproduction, S1 is at the rLJ level, so the sample and hold circuit 7 passes the data as it is, and its output is compared with the reference voltage source 11 in the comparator 9, and after passing through the low-pass filter 13. Direct power amplifier 15 for low frequency components
APC is realized by controlling the drive current of the semiconductor laser 3 using the output. By this control, the low output light intensity is always kept constant regardless of the temperature characteristics of the semiconductor laser 3.

On the other hand, the APC for the high output current source 2 during high output oscillation
is realized as follows.

First, as shown in Fig. 2, the hold timing signal S1 is set to the rHJ level immediately before extinguishing, and the AP during low output oscillation is
Freeze C. This is to avoid lowering the output intensity in response to high output oscillation.

Next, the erase signal SE goes to the rHJ level, which closes the switching circuit 16 via the OR gate 17, and the current 2 from the high output current source 2 changes to the current rl from the low output current source 1. The semiconductor laser 3 oscillates a high-degree output necessary for erasing and erases the data. Next, immediately after entering the erase operation, the hold timing signal S2 becomes rLJ level, and the sample hold circuit 6 passes the data as it is, and introduces the low frequency component after passing through the low pass filter 12 to the power amplifier 14. By controlling the high output current source 2, APC at the time of erasing is realized.

Next, just before starting the recording operation, hold timing signal S2
reaches the rHJ level and freezes the APC at the time of erasure. Then, when the erase signal SE becomes the rLJ level, a recording operation starts, and the information signal SD causes the OR gate 1
7, the switching circuit 16 is opened and closed and information is recorded. Since the APC at the time of erasing is frozen here, the APC at the time of recording is realized in a pseudo manner.

As described above, in the semiconductor laser light amount control device with this configuration, APC of the high-output current source is performed during erasing before recording, so stable control of the light output intensity can be performed even when recording information. be exposed.

(Effects of the Invention) As described above, according to the present invention, APC is performed during high-output oscillation during erasing performed before recording, and by freezing this, the laser light intensity during recording is stabilized. be able to. Therefore, it is possible to obtain a semiconductor laser light amount control device with good characteristics for an information recording/reproducing apparatus using a magneto-optical disk or the like as a recording medium.

[Brief explanation of drawings]

FIG. 1 is a process diagram showing an embodiment of the light amount control device according to the present invention, FIG. 2 is a timing waveform diagram necessary for the operation of the device shown in FIG. 1, and FIG. 3 is a conventional semiconductor laser light amount control diagram. FIG. 2 is a block diagram showing the device. 1...Low output current source (first current source) 2...High output current source (second current source) 3...Semiconductor laser
4...Photodetector 5...Preamplifier 8
．． 9...Comparator 6...Sample and hold circuit (second
holding circuit) 7...Sample hold circuit (first holding circuit) 10.11...Reference voltage source 12.13...Low pass filter 1.4.15...Power amplifier 16...Switching Circuit 17...OR gate row 2 diagram 3

Claims (1)

[Claims] 1) A light amount control device for a semiconductor laser incorporated in an optical recording/reproducing device, comprising: a first current for oscillating the semiconductor laser to a level necessary for reproducing information from a recording medium; a second current source for oscillating the semiconductor laser to a level necessary for erasing and recording information on the recording medium by adding it to the first current source; a first holding circuit that detects the output light intensity of the laser and holds data based on the detection when erasing and recording information on a recording medium; erasing information on the recording medium based on the output of the holding circuit;
A first controller that controls the output current value of the first current source during recording.
a second holding circuit that detects the output light intensity of the semiconductor laser when erasing information on the recording medium and holds data based on the detection when recording or reproducing information on the recording medium; and the holding circuit. a second control means for controlling an output current value of the second current source when recording information on a recording medium based on the output of the second current source.