JPS59184578A - Controlling device for stabilizing output of semiconductor laser oscillator - Google Patents

Abstract

PURPOSE:To prevent the breakdown of an oscillator by preventing the flow of over current exceeding the rating by outputting a constant reference voltage in a fixed time after outputting the voltage gradually becoming larger according to the change-over of a change-over switch by means of a control signal. CONSTITUTION:A reference voltage source 23 generating the reference voltage to set the oscillation output of a laser oscillator 14 is composed of an integrating circuit 33. A change-over switch 24 is turned on-off by changing over a change- over contact 24a according to the control signal (a'), thus outputting the signal from the reference voltage source 23. When the change-over contact 24a is opened by means of the control signal (a'), a capacitor 32 is charged with a power source voltage Vc, and the output signal (d) of said voltage source 23 gradually becomes larger and then reaches a constant value in a fixed time. Thereby, an error amplifier 25 amplifies the difference between the output signal (b') of an amplifier 22 and the reference voltage (d) and then supplies the signal according to the error to a driving circuit 27 via filter 26.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a semiconductor laser oscillator output stabilization control device for stabilizing the oscillation output of a semiconductor laser oscillator used as a light source of an optical disk device, for example.

[Technical background of the invention and its problems]

Optical disk devices optically record or reproduce information by irradiating a rotating optical disk with a laser beam, and have recently attracted a lot of attention as an unprecedentedly large-capacity information memory. Application to large-capacity image file devices is being considered.

Recently, in such optical disk devices, semiconductor laser oscillators have been used as light sources for the purpose of improving stability and increasing access speed by downsizing the optical head. However, semiconductor laser oscillators have a problem in terms of stability because their oscillation output fluctuates greatly due to changes in ambient temperature and the like. That is, in general, the oscillation threshold current Tth of a semiconductor laser oscillator depends on the junction temperature Tj, and has the following relationship: j Ith oc exp (-) (K: constant). Therefore, even if the drive current of the semiconductor laser oscillator is constant, the oscillation output will vary significantly if the ambient temperature (junction temperature) changes.

Therefore, control is normally performed to stabilize the oscillation output by detecting the oscillation monitor light from the semiconductor laser oscillator and feeding it back to the drive circuit of the semiconductor laser oscillator. That is, as shown in FIG. 1, the laser output to the semiconductor laser oscillator 2 in the optical head 1 for recording and reproducing the optical disk 8 is turned on and off via the switch 4 connected to the output section of the laser drive circuit 3. It is being done. This switch 4 is turned on and off by a control signal a. The laser oscillation response of the semiconductor laser oscillator 2 is very fast, and responds instantaneously within 1 ns (10-' seconds) to generate a laser beam. For this reason, switch 4
In the off state, laser oscillation is stopped and the monitor light output voltage of the amplifier 5 is zero. Then, this output voltage b (zero) and the reference voltage C for setting the laser output from the reference voltage source 6 are compared and amplified by the error amplifier 7, and the maximum drive voltage is supplied to the drive circuit 3. It looks like this.

In this state, when the switch 4 is turned on as shown in FIG. 2(b), laser oscillation as seen in the monitor light output shown in FIGS. Excessive oscillation occurs due to overdriving.At this time, amplifier 5.
Error amplifier7. The oscillation response of the semiconductor laser oscillator 2 is much faster than the response of the drive circuit 3. For this reason, the semiconductor laser oscillator 2 is overdriven beyond its rating, and
The problem was that it could be destroyed instantly. Furthermore, in addition to deterioration and damage caused by the temperature rise at the junction, the semiconductor laser oscillator 2 also suffers from excessive current exceeding its rating due to deterioration due to the optical output of the wall-to-wall surfaces forming the optical resonator.
There was also the problem that it was easy to invite destruction.

[Purpose of the invention]

The present invention has been made in view of the above circumstances, and an object thereof is to provide an output stabilization control device for a semiconductor laser oscillator that can prevent damage to the semiconductor laser oscillator.

[Summary of the invention]

This invention outputs a voltage that gradually increases in response to switching of a changeover switch by a control signal, and after a predetermined time elapses,
A reference voltage source that outputs a constant reference voltage is provided, and the semiconductor laser oscillator is driven in accordance with the difference between the output signal of this reference voltage source and the detection signal of the oscillation output of the semiconductor laser oscillator'.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 3 to 5.

FIG. 3 mainly shows the optical system of the optical disk device according to the present invention, and the optical disk 12 has recording tracks 11 formed in advance in a square shape by pre-groups on the front surface (lower surface). A motor rotates the optical disk 11, and 13 is an optical head for recording and reproducing. This optical head 13 is linearly moved in the radial direction of the optical disk 11 by a linear motor mechanism 5- (not shown), and is driven by a semiconductor laser oscillator 14- which outputs laser beam light in two directions, front and rear. Collimator lens 15. Polarizing beam splitter 16°λ/4 plate 17. Objective lens 18. Condensing lens 19° first photodetector 20. and a second photodetector 21. That is, the laser oscillator 14 is driven and controlled by a drive circuit 22, which will be described later, and its oscillation output level can be switched between two beam powers: a reproduction beam light and a recording beam light. The main beam output from the front of the laser oscillator 14 is collimated by the collimator lens 15, guided to the objective lens 18 via the beam splitter 16, where it is converged to approximately 1 μmφ, and the optical disk 11 Irradiates the top (bottom) side. Then, the reflected light from the optical disk 11 is transmitted through an objective lens 18. The light is then guided to a condensing lens 19 via a beam splitter 16, where it is condensed and imaged onto a first photodetector 20, where it is converted into an electrical signal. Note that the output signal of the first photodetector 2o is sent to a signal processing circuit (not shown) and used as a reproduction signal, a tracking control signal, a focus control signal, and the like. On the other hand, the monitor light output from the rear of the laser oscillator 14 enters the second photodetector 21, where it is converted into an electrical signal.

Further, 22 is an amplifier that amplifies the output signal of the second photodetector 21, and 23 is a reference voltage source that generates a reference voltage for setting the excavation output of the laser oscillator 14 to a predetermined value. As shown in the figure, the resistor 3o and the resistor 31. It is constituted by an integrating circuit 33 made up of a capacitor 32. 24! This switch is turned on and off by switching the switching contact 24& in accordance with the i control signal a', and when turned on and off, the signal from the reference voltage source 23 is output.

25 is an error amplifier that amplifies the difference between the output signal b' of the amplifier 22 and the reference voltage d supplied from the switch 24;
26 is a filter with a characteristic of -20 dB/decade. Furthermore, 27 is a drive circuit for driving and controlling the laser oscillator 14, which connects the error amplifier 25 to the filter 26.
and the beam modulation signal e. This drive circuit 27 includes an adder 28° that adds the signal from the filter 26 and the beam modulation signal, and a current that corresponds to the output of this adder 28 to the laser oscillator 1.
The current supply circuit 29 is composed of a constant current circuit that supplies a constant current to the current supply circuit 4.

Here, the amplifier 22. Reference voltage source 23° switch 2
4. Error amplifier 25. Filter 26 and drive circuit 27
constitutes an output stabilization control circuit that stabilizes the oscillation output of the laser oscillator 14.

Next, the operation in such a configuration will be explained. For example, a control signal as shown in FIG. 5 (IL) is now supplied to the changeover switch 24, turning on the changeover switch 24 and opening its changeover contact 24IL. Then, the power supply voltage Ve
The capacitor 32 is charged, and the reference voltage source 23
The output signal d gradually increases as shown in FIG. 5(b), and reaches a constant value after a predetermined period of time. This results in
The error amplifier 25 outputs the output signal b/(FIG. 5) of the amplifier 22.
C) and the reference voltage d is amplified, and a signal corresponding to the difference is supplied to the adder 28 via the filter 26. The adder 28 adds the output signal of the filter 26 and the beam modulation signal e (usually zero is the default), and sends the addition result (in this case, the output signal of the filter 26) to the current supply circuit 29.
supply to. The current supply circuit 29 is supplied with the adder 2
A drive current corresponding to the output signal of 8 is supplied to the laser oscillator 14. Through this operation, the laser oscillator 14 oscillates, and the output level of the reproduction beam increases as the reference voltage d increases, and is then controlled to a constant value according to the predetermined reference voltage. . That is, when the control signal a' is supplied, the reference voltage becomes O? The drive current of the laser oscillator 14 increases gradually from the default, and as the reference voltage increases, the drive current of the laser oscillator 14 also increases, and after the reference voltage reaches a predetermined value, the drive current 9- of the laser oscillator 14 remains constant. .

When recording information in such a state, the optical head 1
3 to a predetermined position on the optical disc 11, the laser oscillator 14 outputs a reproduction beam light, and the objective lens 18 focuses it on the recording track on the optical disc 11. At this time, the optical disc II is rotating at a predetermined speed, so the reproduction beam scans the recording track and starts tracking while detecting the pre-group. Note that this tracking control is not the gist of this invention, and has already been described. Various methods are well known and will not be described further.

Next, in order to record information, the beam modulation signal e()
When a recorded signal (4 pulses) whose phrase width is several hundred ns or less is supplied to the adder 28, the adder 28 adds the beam modulation signal e to the output signal of the filter 26 and supplies it to the current supply circuit 29. . As a result, the current supply circuit 29 supplies a current corresponding to the amplitude of the beam modulation signal e to the laser oscillator 14 for the period of the signal e, and switches the output level to a high level to produce a recording beam light. , optical disk 1
Data bits are formed within pregroups forming one recording track.

Information is recorded in this way.

As mentioned above, -20dB is included in the output stabilization control circuit.
Since a filter with /decade characteristics is provided, the control circuit is configured to return to a multi-stage amplifier, and the Luso r iso increases to stabilize the laser output, making it unstable and causing the closed loop to oscillate. This allows stable control to be achieved.

In addition, in the above embodiment, the case where the implementation is applied to a semiconductor laser oscillator used as a light source of an optical disk device has been described, but the implementation is not limited to this, and the implementation can be similarly applied to a semiconductor laser oscillator used as a light source of other optical devices. can.

〔Effect of the invention〕

As described in detail above, according to the present invention, it is possible to provide an output stabilization control device for a semiconductor laser oscillator that can prevent damage to the semiconductor laser oscillator.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing the optical system of a conventional optical disk device, FIG. 2 is a signal waveform diagram of the main part in FIG. 1, and FIGS. 3 to 5 show an embodiment of the present invention. Figure 3 is a configuration diagram showing the optical system of the optical disk device, Figure 4 is a configuration diagram of the reference voltage source and changeover switch, and Figure 5 is a signal waveform diagram of the main parts to explain the operation. . 11... Optical disk, 13... Optical head, 14.
...Semiconductor laser oscillator, 2...Photodetector, 22.
... Amplifier, 23... Reference voltage source, 24... Changeover switch, 25... Error amplifier, 26... Filter,
27... Drive circuit, 33... Integrating circuit.

Claims (1)

[Claims] an output detector that detects the oscillation output from the semiconductor laser oscillator; a changeover switch that switches the semiconductor laser oscillator between on and off according to a control signal that specifies on-off; and a reference voltage source that outputs a voltage that increases and then outputs a constant reference voltage after a predetermined period of time has elapsed; 1. An output stabilization control device for a semiconductor laser oscillator, comprising a drive circuit for driving an oscillator.