JPH06139580A - Optical disk device and method for suppressing change of semiconductor laser emission power - Google Patents

Abstract

PURPOSE:To suppress the fluctuation in reproducing power by detecting the fluctuational characteristic in the reproducing power at the time of switching on/off of superposition of high frequency current to the drive current of a semiconductor laser and correcting the drive current. CONSTITUTION:A high frequency current superposition module 22 is turned on by a control signal from a CPU 23, and the reproducing power from the semiconductor laser 11 is controlled by a reproducing power control part 21. In such a state, by a detection amplifier 20, the output current of a light emitting power detecting photodetcter 14 is detected, and is sampled by a peak detection part 27 and sent to the CPU 23. By a comparator 29, a comprison output between the output signal voltage of the amplifier 20 and a prescribed voltage of a reference voltage setting part 28 is sent to the CPU 23. By the CPU 23, a time from when a module 22 is turned on to when the output signal of the comparator 29 becomes '1' is measured, and a current value with a characteristic opposite to the fluctuation characteristic of the reproducing power is set to an addition current generation part 30, and is added to the drive current of the laser 11 by an adder part 31. Thus, the fluctuation in the reproducing power is suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk device and a semiconductor laser emission power change suppressing method.

[0002]

2. Description of the Related Art Optics Vol. 14, No. 5 (October 1985)
Mon.) pp. 377-384, "Reduction of laser noise in semiconductor laser-equipped video disc player by high-frequency current superposition method". In this case, in order to reduce the influence of light returning from the optical disk to the semiconductor laser, a method of superposing a high frequency current on the drive current of the semiconductor laser when reading data from the optical disk has been conventionally performed.

However, according to this method, when the emission power of the semiconductor laser is increased from the reproduction power to the recording power or the erasing power in a state where the high frequency current is superposed on the drive current of the semiconductor laser in the optical disk device, the emission of the semiconductor laser is emitted. The power may exceed the rating, the life of the semiconductor laser may be shortened, and in the worst case, the semiconductor laser may be destroyed. Therefore, in an optical disk device, a method of controlling on / off of superimposing a high frequency current on a driving current of a semiconductor laser by a high frequency current superimposing module at the time of reproduction and recording is used.

[0004]

In the above method, the superposition of the high frequency current with respect to the drive current of the semiconductor laser is controlled by the high frequency current superposition module during on / off control during reproduction and recording, so that the following problems occur. . The left part of FIG. 2 shows the IL characteristic (relationship between the drive current I and the emission power P) when the semiconductor laser is turned on / off with the high frequency current superimposed.

In FIG. 2, point A is the state where the emission power of the semiconductor laser is controlled to the reproduction power Pr by the reproduction power control system when the high frequency current superposition is turned on with respect to the semiconductor laser drive current. When the high frequency current superposition is turned off in this state, the state changes to point B. Point B to point C
The transition to is due to the reproduction power control being applied by the reproduction power control system in the high frequency current superposition off state. The transition from point C to point D is due to turning on the high frequency current superposition. The transition from point D to point A is due to the reproduction power control being applied by the reproduction power control system in the high frequency current superposition ON state.

Generally, the high frequency current superposition on / off time (transition from point A to point B, transition from point D to point A) takes several μs depending on the characteristics of the high frequency current superposition module. Originally, it is ideal that the reproduction power Pr fluctuation during this time is controlled by the reproduction power control system, but a control band for this is required to be several MHZ or more, which is weak against noise and easy to oscillate. The cost is high and the cost is high.

Therefore, it is conceivable to lower the band of the reproduction power control system, but if this is done, for example, when the reproduction mode is changed to the recording mode, the high frequency current superimposition is performed immediately before the write sector (target sector) on the optical disk. When is turned off, the SM (sector mark) on the optical disc cannot be read because the reproduction power Pr is reduced, and the reliability of the recorded data on the optical disc is reduced. On the other hand, when the high frequency current superposition module is turned on by the superposition control signal as shown in FIG. 3 when the recording mode is changed to the reproduction mode, the reproduction power Pr increases and in the worst case, the recorded data on the optical disk is destroyed. May occur.

The present invention solves the above-mentioned drawbacks, and can suppress the fluctuation of the reproducing power due to ON / OFF of the high frequency current superposition even when the band of the reproducing power control system is low, and the semiconductor laser emission power change. The purpose is to provide a suppression method.

[0009]

In order to achieve the above object, the invention according to claim 1 condenses light from a semiconductor laser on a recording medium by an objective lens to record and reproduce information, In an optical disk device for switching on / off of high frequency current superimposition on the drive current of the semiconductor laser during reproduction of information and during recording of information, the high frequency current superimposition is switched from an on state to an off state and / or from an off state to an on state. It is provided with a detecting means for detecting a reproducing power fluctuation characteristic at the time of switching to and a reproducing power fluctuation suppressing means for suppressing a reproducing power fluctuation by the reproducing power fluctuation characteristic detected by the detecting means.

According to a second aspect of the present invention, in the optical disc apparatus according to the first aspect, there is provided a detecting means for detecting a temperature change in the optical disc apparatus, and the reproducing power fluctuation of the reproducing power is detected according to an output signal of the detecting means. The suppression operation is performed.

According to a third aspect of the present invention, light from a semiconductor laser is focused on a recording medium by an objective lens to record and reproduce information, and the semiconductor laser is used at the time of reproducing information and at the time of recording information. ON / OFF of high frequency current superposition on the drive current of
A method for suppressing change in semiconductor laser emission power of an optical disk device for switching off, wherein the emission power of the semiconductor laser is detected to detect the characteristic of the change in emission power, and the change in emission power of the semiconductor laser is detected by this characteristic. A predetermined current is added to the drive current of the semiconductor laser so as to correct it.

[0012]

According to the present invention, the reproducing power fluctuation characteristic when the high frequency current superposition is switched from the on state to the off state and / or from the off state to the on state is detected by the detecting means, and is detected by the detecting means. The reproducing power fluctuation suppressing unit suppresses the fluctuation of the reproducing power due to the reproducing power fluctuation characteristic.

According to the second aspect of the invention, the temperature change in the optical disk device is detected by the detecting means, and the reproducing power fluctuation suppressing operation is performed according to the output signal of the detecting means.

[0014]

FIG. 1 shows an embodiment of the present invention. In the optical disk device of this embodiment, the semiconductor laser 11 is driven by the semiconductor laser driving section 12 to be DC-lighted during reproduction,
A part of the light emitted from the semiconductor laser 11 is input to the light-emission power detection light-receiving element 14 by the beam splitter 13 and converted into a current by the light-emission power detection light-receiving element 14, whereby the light-emission power of the semiconductor laser 11 is detected. To be done.

The remaining part of the light emitted from the semiconductor laser 11 is condensed on the recording medium 17 of the optical disk by the objective lens 16 via the prism 15, and this recording medium 1
7 is rotationally driven by a motor. The reflected light from the recording medium 17 is again passed through the objective lens 16 and the prism 15 by the beam splitter 13 to detect the reproduction signal.
The reproduction signal is detected by being guided to the laser beam 8 and converted into a current by the reproduction signal detecting light receiving element 18. The output current of the reproduction signal detecting light receiving element 18 is current-voltage converted by the detection amplifier 19 and sent to the signal processing system.

The output current of the light-receiving element 14 for detecting the emission power is converted into a current-voltage by the detection amplifier 20 and sent to the reproduction power controller 21. The reproduction power control unit 21 compares the output voltage of the detection amplifier 20 with the reference voltage and sends a reproduction power control signal to the semiconductor laser drive unit 12 so that the reproduction power of the semiconductor laser 11 becomes constant. The semiconductor laser drive unit 12 is controlled by the reproduction power control signal from the reproduction power control unit 21, and the reproduction power of the semiconductor laser 11 is controlled to a constant value. At this time, the high frequency current superposition module 22 is in the ON state by the control signal from the microcomputer (CPU) 23, and outputs the high frequency current via the capacitor 24 and superimposes it on the drive current of the semiconductor laser 11.

At the time of recording, a recording power control signal is output from the recording power control unit 25 so that the recording power becomes a constant value, and this recording power control signal is modulated by the data in the modulation unit 26 and is reproduced from the reproduction power control unit 21. Is sent to the semiconductor laser drive unit 12 in a form of being superimposed on the recording power control signal. The semiconductor laser drive unit 12 is controlled by the recording power control signal, and the recording power from the semiconductor laser 11 is controlled. At this time, the high frequency current superposition module 22 is turned off by the control signal from the CPU 23, and the high frequency current superposition is not performed on the drive current of the semiconductor laser 11. Further, the light from the semiconductor laser 11 is applied to the recording medium 17 via the beam splitter 13, the prism 15 and the objective lens 16, and the data is recorded on the recording medium 17.
Recorded in.

Next, in the present embodiment, the semiconductor laser 1
The point of suppressing the fluctuation of the reproduction power at the time of the transition of the high frequency current superposition for one drive current from the off state to the on state (point C → point D → point A in FIG. 2: characteristic of curve α) will be described. FIG. 4 shows an operation flow of this embodiment, and FIG. 5 shows a timing chart of this embodiment.

The high frequency current superposition module 22 is the CPU 2
The reproduction power control unit 21 is turned on by the control signal from
As a result, the reproduction power from the semiconductor laser 11 is controlled and the state of point A is reached. In this state, the output signal of the detection amplifier 20 is sampled by the peak detection unit 27, A / D converted, and sent to the CPU 23. At this time, the sample voltage (the detection amplifier 20 sampled by the peak detection unit 27
The output signal voltage) and V _1.

Next, the CPU 23 waits until the high frequency current superposition module 22 is turned off and the reproduction power control is applied (change from point A to point B to point C). After that, when the high frequency current superposition module 22 is turned on by the control signal from the CPU 23, the reproduction power changes from point C to point D to point A, and the output signal voltage of the detection amplifier 20 at the point D, that is, when the high frequency current superposition is turned on. Of the reproduction power fluctuation amount of the CPU is sampled by the peak detection unit 27 and A / D converted, and then the CPU
Sent to 23. At this time, the sample voltage is V ₂ .

The CPU 23 uses V ₁ and V ₂ to obtain (V ₂ −V ₁ ) /
A voltage V ₃ of e + V ₁ is calculated and this V ₃ is set in the reference voltage setting unit 28 as a reference voltage. Here, e is 2.7.
It is a constant of 18 ... The comparator 29 subtracts the reference voltage of the reference voltage setting unit 28 from the output signal voltage of the detection amplifier 20 to obtain the difference. After setting V _{3, the} CPU 23 turns off the high frequency current superposition module 22 and turns it on again.

The CPU 23 is the high frequency current superposition module 2
The time ton from when 2 is turned on to when the output signal of the comparator 29 becomes "1" is measured. This ton is a time constant of the reproducing power fluctuation (curve α in FIG. 2) from the time of turning off the high frequency current superposition to the time of turning it on. After that, the CPU 23 approximates the curve α with an exponential function by ton during the high frequency current superimposition from off to on, sets the current value having the inverse characteristic to the curve α in the addition current generation unit 30, and adds this. The current value of the current generator 30 is added to the drive current of the semiconductor laser 11 by the adder 31 to suppress the fluctuation of the reproduction power.

Here, when the high-frequency current superimposition is switched from OFF to ON, if the data reproduction position on the recording medium 17 is the data portion immediately before the target sector, the recording medium 17 is SM (sector mark). No more worries about not being able to read. Further, since the reproduction power does not change due to the turning on of the high frequency current superposition from the turning on to the turning on, there is no fear of destroying the data on the recording medium 17.

Further, the transition of the superposition of the high frequency current with respect to the driving current of the semiconductor laser 11 from the on state to the off state (see FIG. 2).
(Point A → point B → point C: characteristic of curve β), the fluctuation of the reproducing power is similarly suppressed. That is, the high frequency current superposition module 22 is turned on by the control signal from the CPU 23, and the reproduction power from the semiconductor laser 11 is controlled by the reproduction power control unit 21 to reach the state of point A. In this state, the output signal of the detection amplifier 20 is sampled by the peak detection unit 27, A / D converted, and sent to the CPU 23. At this time, the sample voltage (the output signal voltage of the detection amplifier 20 sampled by the peak detection unit 27) is set to V ₄ .

Next, when the high frequency current superposition module 22 is turned off by the CPU 23, the reproduction power is changed from point A to point B.
→ It changes from point C, and the output signal voltage of the detection amplifier 20 at point B, that is, the amount of reproduction power fluctuation when the high frequency current superposition is off is sampled by the peak detector 27 and A / D converted, and then sent to the CPU 23. . At this time, the sample voltage is V ₅ .

The CPU 23 uses V ₄ and V ₅ to obtain (V ₅ −V ₄ ) /
A voltage V ₆ of e + V ₄ is calculated and this V ₆ is set in the reference voltage setting unit 28 as a reference voltage. The comparator 29 calculates the reference voltage setting unit 28 based on the output signal voltage of the detection amplifier 20.
Subtract the reference voltage of to obtain the difference. CPU 23 is V ₆
After setting, the high frequency current superposition module 22 is turned on and turned off again.

The CPU 23 is the high frequency current superposition module 2
The time ton 'from the turning off of 2 to the time when the output signal of the comparator 29 becomes'1' is measured. This ton 'is a time constant of the reproduction power fluctuation (curve β in FIG. 2) from the on time to the off time of the high frequency current superposition. After that, the CPU 23
Is ton 'during high-frequency current superposition from on to off
Then, the curve β is approximated by an exponential function, and a current value exhibiting an inverse characteristic of the curve β is set in the addition current generator 32. The current value of the addition current generator 32 drives the semiconductor laser 11 by the addition unit 31. The fluctuation of the reproduction power is suppressed by being added to the current. As a result, even if the high frequency current superposition changes from on to off, there is no concern that the track will be off due to a reduction in reproduction power.

Further, in this embodiment, semiconductor parts are used for the circuit for turning on / off the high frequency current superposition,
Since the characteristics such as the curves α and β change due to the temperature change inside the optical disk device, the temperature inside the optical disk device is detected by the inside temperature detecting means 32, and the CPU 23 detects the inside of the device from the output signal of the inside temperature detecting means 32. Each time a temperature change (for example, a change of 10 ° C.) occurs, the characteristics of the curves α and β are detected again as described above. Therefore, the high frequency current superposition is turned on /
The fluctuation of the reproduction power due to the OFF state is further suppressed, and the reliability of data reproduction can be improved. Further, in the present embodiment, a CPU is used as a means for detecting the characteristic of the change in reproduction power.
23 is used, it is possible to realize with a simple configuration, and it is possible to easily and inexpensively detect the fluctuation of the reproducing power.

[0029]

As described above, according to the present invention, since the reproduction power fluctuation characteristic is detected to suppress the fluctuation of the reproduction power, the high frequency current superposition is turned on / off even when the band of the reproduction power control system is low. It is possible to suppress the fluctuation of the reproducing power due to, and it is possible to improve the reliability by eliminating the off-track and the reading error of the sector mark due to the decrease of the reproducing power when the high frequency current superposition is turned off. Further, the reproduction power can be kept constant even when the high frequency current superimposition is turned on and the data destruction due to the increase of the reproduction power is eliminated. Further, since the temperature change in the optical disk device is detected by the detecting means and the reproducing power fluctuation suppressing operation is performed in accordance with the output signal of the detecting means, the reproducing power fluctuation can be further suppressed, and the reliability of the data reproduction can be improved. You can improve your sex.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a diagram for explaining the same embodiment.

FIG. 3 is a diagram for explaining a conventional example.

FIG. 4 is a flowchart showing an operation flow of the embodiment.

FIG. 5 is a timing chart of the embodiment.

[Explanation of symbols]

 11 semiconductor laser 12 semiconductor laser drive unit 13 beam splitter 14 light receiving element for light emission power detection 16 objective lens 17 recording medium 20 detection amplifier 21 reproduction power control unit 22 high frequency current superposition module 23 CPU 27 peak detection unit 28 reference voltage setting unit 29 comparator 30, 32 Addition current generation unit 31 Addition unit

Claims (3)

[Claims] 1. The light from a semiconductor laser is focused on a recording medium by an objective lens to record and reproduce information, and a high frequency is applied to a drive current of the semiconductor laser during reproduction of information and during recording of information. In an optical disk device for switching on / off of current superposition, a detection means for detecting reproduction power fluctuation characteristics when the high frequency current superposition is switched from an on state to an off state and / or from an off state to an on state, and the detection means An optical disk device comprising: a reproduction power fluctuation suppressing unit that suppresses fluctuations in the reproduction power based on the detected reproduction power fluctuation characteristic. 2. The optical disk device according to claim 1, wherein
An optical disc device having a detecting means for detecting a temperature change in the optical disc device, and performing an operation of suppressing the reproduction power fluctuation according to an output signal of the detecting means. 3. The light from a semiconductor laser is focused on a recording medium by an objective lens to record and reproduce information, and a high frequency to a drive current of the semiconductor laser at the time of reproducing information and at the time of recording information. A method for suppressing change in semiconductor laser emission power of an optical disk device for switching on / off of current superposition, comprising detecting the emission power of the semiconductor laser and detecting a characteristic of the change in the emission power. A semiconductor laser emission power change suppression method, characterized in that a predetermined current is added to the drive current of the semiconductor laser so as to correct the change in emission power.