JPH05197994A - Noise reduction circuit for semiconductor laser and optical disk device - Google Patents

Abstract

PURPOSE:To obtain a stable light source even against the fluctuation in the quantity of return light by increasing the superposed quantity of high-frequency currents by a high-frequency superposing circuit at the time of focus control setting by a focus servo system. CONSTITUTION:A control signal is outputted from a CPU 22 to light a laser 1 while the laser 1 is not lighted. The high-frequency currents are so controlled that the amplitude thereof increases by applying data from the CPU 22 to a D/A converter 24. A focus control circuit 19 is controlled by the CPU 22 in the state, by which focus setting is executed and the focus control is turned on. The data is again transferred to the converter 24 and the amplitude of the high-frequency currents is decreased. The track control is thereafter turned on and is operated, by which the amplitude of the high-frequency currents is controlled. Namely, the superposing quantity of the high-frequency currents is increased only at the time of the focus setting and, therefore, the unnecessary heat generation of the high-frequency superposing circuit 23 is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser noise reduction circuit and an optical disk device in an electronic device having a semiconductor laser as a light source for an optical disk device, a laser printer, an optical card drive device, and the like, and more particularly to a focus pull-in operation. The present invention relates to a noise reduction circuit for a semiconductor laser and an optical disk device, which can obtain a sufficiently stable emission power of a semiconductor laser even when a large amount of return light changes due to crossing a track after being pulled in.

[0002]

2. Description of the Related Art In an electronic device having a semiconductor laser as a light source, the noise of the semiconductor laser may remarkably increase due to reflected light (return light) from an information recording medium. In the case of a semiconductor laser, the returned light does not always increase noise. For example, the noise increases under various conditions such as the reflectance of the disk, the ambient temperature, the emission power of the semiconductor laser, the variations in the characteristics of the semiconductor laser,
It doesn't do so, so it's not uniform.

When the noise of the semiconductor laser increases, it becomes impossible to correctly read the signal recorded on the information recording medium. Here, the emission power of the conventional semiconductor laser and the variation of the emission power with respect to the return light will be described.

When the semiconductor laser is driven by a constant current, if the temperature does not change, the semiconductor laser is turned on with a constant power.
It should be noted that in reality, deterioration due to life has an influence, but this is not taken into consideration here. FIG. 5 is a diagram showing an example of the relationship between the emission power of the semiconductor laser and the emission power for the return light. The horizontal axis of the figure shows the emission power, and the vertical axis shows the power increase rate.

In FIG. 5, as an example, the case where the amount of return light with respect to the amount of emitted light is 4% is shown, and the horizontal axis represents the semiconductor laser emission power when there is no returned light. Also,
The vertical axis represents the power increase rate when there is return light.

If the emission power fluctuates due to the return light of the semiconductor laser, for example, the focus pull-in operation becomes difficult. Here, detection of the focus signal by the astigmatism method will be described.

FIG. 6 is a diagram for explaining the focus signal detection system and the detection circuit by the astigmatism method, and the operation thereof.
If (1) is closer to the focus position, (2) is the focus position, (3) is farther than the focus position, and (4) is closer to the focus position on the light receiving element. The spot, (5) indicates the spot on the light receiving element at the focus position, and (6) indicates the spot on the light receiving element at a position farther from the focus position. In the figure,
Reference numeral 31 is a cylindrical lens, 32 is a detection lens, 33 is an objective lens, 34 is a disk, 35 is a light receiving element, A to D are each four-division light receiving elements, 36 and 37 are addition circuits, and 38 is a subtraction circuit, Further, S is the detection lens 32 and the cylindrical lens 3
1 is the combined focus, M is the focus of the detection lens 32, F is the position of the 4-division light receiving element, and S ', M', F'are S, M, F, S ", M" when they are closer than the in-focus position. , F ″ represent S, M and F when the focus position is farther.

The focus signal detection system by the astigmatism method has the structure shown in FIGS. 6 (1) to 6 (3), and its detection circuit has the structure shown in FIG. 6 (4). .. With the focus signal detection system and the detection circuit as shown in FIGS. 6 (1) to 6 (6), the focus signal Fe = (A + B)-(C +
In addition to D), the sum signal of the focus signals is detected.

FIG. 7 is a diagram showing the sum signal and the S-shaped curve of the focus signal in the focus signal detection system by the astigmatism method. In the figure, the horizontal axis represents defocus (μm) and the vertical axis represents the focus signal (V).

In the focus signal detection system based on the astigmatism method, as shown in FIG. 7, when the focus deviates from the in-focus position, the focus signal changes into an S shape. When actually performing the focus pull-in, in addition to such a focus signal Fe, a sum signal of the four-division light receiving element is detected, and the focus servo is pulled in when the sum signal exceeds a predetermined value. ing.

However, since this sum signal also occurs on the glass surface of the disk 34, as shown in FIG.
If the light emission power (emission power) of the semiconductor laser increases due to the return light, there is a fear that the surface of the disk 34 may be focused. In addition, even if the sum signal of the focus signals on the disc surface is sufficiently small, when focusing on the actual recording surface,
Since the emission power of the semiconductor laser increases, the slope of the S-shaped curve shown in FIG. 7 changes, and as a result, the gain of the focus servo system changes, which may make it difficult to pull in the focus.

In order to solve such a problem, as a conventional noise reduction method for a semiconductor laser, for example, a noise reduction method for a semiconductor laser-mounted video disk player by a high frequency current superposition method has been proposed (Journal of the Society). Optics "Vol. 14, No. 5, October 1985, 377-3
84).

However, in this high-frequency current superposition method, the frequency of the superposed current needs to be as high as several hundred MHz, so a circuit for superposing the high-frequency current is put in a shield case, or wiring to the semiconductor laser is performed. In order to minimize the distance between the two, the semiconductor laser must be placed in the immediate vicinity of the circuit. Therefore, the heat generated in the high-frequency superposition circuit is transmitted to the semiconductor laser and its temperature rises, which causes a disadvantage that the life of the semiconductor laser becomes shorter than the normal operating temperature.

For the above reasons, it is preferable that the current amplitude superimposed on the semiconductor laser as a high frequency current is as small as possible. However, due to the modulation degree dependency, in order to obtain a predetermined noise characteristic, a predetermined current amplitude is obtained. Are known to be necessary. However, the problems described above are all due to static noise evaluation.

As described above, in the conventional semiconductor laser noise reduction method, no consideration is given to the fluctuation of the emission power with respect to a large change in the amount of return light which occurs during the focus pull-in operation or when the track is crossed after the pull-in operation. However, there is an inconvenience that stable operation cannot be performed when the focus is actually drawn.

[0016]

SUMMARY OF THE INVENTION In the present invention, these disadvantages of the conventional semiconductor laser noise reduction method are solved, and a large fluctuation in the amount of return light that occurs during focus pull-in operation or when crossing over a track after pull-in is performed. In order to obtain a sufficiently stable semiconductor laser emission power, a high frequency current is superposed, and
It is an object of the present invention to provide a noise reduction circuit for a semiconductor laser and an optical disc device, which realizes a high frequency superposition circuit that generates less heat after the track servo operates.

[0017]

According to a first aspect of the present invention, in a noise reduction circuit of a semiconductor laser which is a light source of an optical disk device, a high frequency superimposing circuit for variably controlling a current for superimposing a high frequency current on the semiconductor laser, A focus servo system for condensing light emitted from the semiconductor laser on an optical disk, and configured to increase a superposition amount of a high frequency current by the high frequency superposition circuit when pulling in focus control by the focus servo system. ing.

Secondly, in a noise reduction circuit of a semiconductor laser which is a light source of an optical disk device, a high frequency current superimposing circuit for variably controlling a current for superimposing a high frequency current on the semiconductor laser, and a light emitted from the semiconductor laser. A track servo system that follows tracks on the optical disk is provided, and in a state other than the track control state by the track servo system, the superposition amount of the high frequency current by the high frequency superposition circuit is increased.

Thirdly, in the optical disk device, a high frequency current superimposing circuit for variably controlling a current for superimposing a high frequency current on a semiconductor laser as a light source, and a focus servo for condensing the light emitted from the semiconductor laser on the optical disk. And a system for increasing the superposition amount of the high frequency current by the high frequency superposition circuit when an error occurs when the focus control system pulls in the focus control system.

[0020]

In the present invention, attention is paid to the point that substantial noise can be reduced by controlling so that the fluctuation of the light emission power becomes small when the amplitude of the high frequency current is increased. Next, the principle will be described.

As shown in FIG. 5, the fluctuation state of the emission power with respect to the return light of the semiconductor laser decreases as the emission power increases. Here, the current-light emission characteristics (IL characteristics) of the semiconductor laser will be described.

FIG. 2 is a diagram showing an example of current-light emission characteristics of a semiconductor laser. In the figure, the horizontal axis represents current and the vertical axis represents emission power.

FIG. 2 shows the case of high-frequency currents I ₁ and I ₂ , and the relationship of I ₁ <I ₂ is assumed. Then, when the direct current I (dc1) is set so as to have the average power [P] of FIG. 2 at the high frequency current I ₁ , the peak power becomes P ₁ .

Next, when the direct current I (dc2) is set so that the average power [P] is the same even at the high frequency current I ₂ , the peak power P ₂ can be obtained. The current control in this case, that is, the change of the direct currents I (dc1) and I (dc2) is performed by the control of the semiconductor laser control circuit (6 in FIG. 1 described later).

As described above, when the amplitude of the high frequency current is increased, the peak value of the light emission power is increased and the time during which light is actually emitted can be reduced. That is, the actual light emission power is increased, the influence on the return light is reduced, and the light emission time is shortened.

Therefore, the fluctuation amount as the average power becomes small, and at the same time, the noise also becomes small on average. The semiconductor laser noise reduction circuit of the present invention pays attention to the above points.

[0027]

First Embodiment A semiconductor laser noise reduction circuit of the present invention will be described in detail with reference to the drawings. This embodiment corresponds to the inventions of claims 1 and 2.

FIG. 1 is a functional block diagram showing an embodiment of the main configuration of a noise reduction circuit for a semiconductor laser according to the present invention. In the figure, 1 is a semiconductor laser, 2
Is a coupling lens, 3 is a beam splitter, 4 is a first condenser lens, 5 is a light receiving element for power monitoring, 6 is a semiconductor laser control circuit, 7 is a semiconductor laser drive circuit, 8 is an objective lens, and 9 is magneto-optical. Disk 10, 10 is a second condenser lens, 11 is a 1 / 2λ plate, 12 is a polarization beam splitter, 13 is a light receiving element for a transistor, 14 is a track control circuit, 15 is a track drive circuit, 16 is a tracking actuator, 17 is a cylindrical lens, 1
8 is a light receiving element for focus, 19 is a focus control circuit, 20 is a drive circuit for focus, 21 is a focus
An actuator, 22 is a CPU, 23 is a high-frequency superimposing circuit, 23a is its high-frequency oscillation circuit, 23b is an amplifying circuit,
24 is a D / A converter, and 25 is a capacitor.

First, the operation common to the conventional one will be described. The light emitted from the semiconductor laser 1 is collimated by the coupling lens 2 and separated by the beam splitter 3. Then, one of the lights is condensed by the first condenser lens 4 on the power monitor light-receiving element 5.

The output of the light receiving element 5 for power monitor is given to the semiconductor laser control circuit 6, and the light quantity of the semiconductor laser 1 is controlled via the semiconductor laser drive circuit 7. Also,
The other light separated by the beam splitter 3 is condensed by the objective lens 8 and applied to the magneto-optical disk 9 which is an information recording medium.

The reflected light from the magneto-optical disk 9 again passes through the objective lens 8 and the beam splitter 3 and is then returned to the second
The light is condensed by the condenser lens 10 and is incident on the polarization beam splitter 12 through the 1 / 2λ plate 11. Then, the polarization beam splitter 12 separates the P-polarized component and the S-polarized component.

One of the lights separated by the polarization beam splitter 12 is incident on a light receiving element 13 for a transistor, and its detection output is given to a tracking actuator 16 via a track control circuit 14 and a track driving circuit 15. Be done. By such an operation, the tracking actuator 16 is driven and tracking control is performed.

The other light separated by the polarization beam splitter 12 is incident on the light receiving element 18 for focusing through the cylindrical lens 17. This detection output is given to the focus actuator 21 via the focus control circuit 19 and the focus drive circuit 20, and the focus actuator 21 is driven to perform focus control.

In this case, the track control circuit 14 and the focus control circuit 19 are controlled by the CPU 22 to perform operations such as turning on / off the track control, turning on / off the focus control, and pulling the focus. Further, in the semiconductor laser 1, reflected light from the magneto-optical disk 9 returns and noise is added to the light emission output. Therefore, in order to prevent this, at the time of reproducing power output, a high frequency current is superposed from the high frequency superposing circuit 23.

The high frequency superimposing circuit 23 is composed of a high frequency oscillating circuit 23a and an amplifying circuit 23b. The amplifying circuit 23b has its amplification degree controlled by the output of the D / A converter 24 and is superposed on the semiconductor laser 1. The amplitude of the high frequency current is controlled. This D / A converter 24 is C
It is connected to the PU 22, and the CPU 22 controls the amplitude of the high frequency current.

The capacitor 25 is a coupling capacitor for supplying the output of the semiconductor laser driving circuit 7 to the D / A converter 24. The above operation is basically the same as that of the conventional device.

The semiconductor laser noise reduction circuit of the present invention is characterized in that the CPU 22 controls the amplitude of the high frequency current. Next, the operation will be described with reference to a flowchart.

FIG. 3 is a flow chart showing the main processing flow of the amplitude control of the high frequency current in the semiconductor laser noise reduction circuit of the present invention. In the figure, # 1
# 5 indicates a step.

First, in step # 1, while the semiconductor laser 1 is not turned on, the CPU 22 outputs a control signal to turn on the semiconductor laser 1. In the next step # 2, data is given from the CPU 22 to the D / A converter 24 and controlled so that the amplitude of the high frequency current becomes large.

In this state, the process proceeds to step # 3 and the CPU
The focus control circuit 19 is controlled by 22 to perform focus pull-in, and the focus control is turned on. In the next step # 4, the data is transferred again to the D / A converter 24 to reduce the amplitude of the high frequency current.

After that, in step # 5, the track control is turned on and operated, and the process proceeds to the next step. The amplitude of the high frequency current is controlled by the processing of steps # 1 to # 5 described above. That is, since the superposition amount of the high-frequency current is increased only when the focus is pulled in, unnecessary heat generation of the high-frequency superposition circuit is prevented, and the light source that is stable against fluctuations in the amount of return light when the focus is pulled in is also provided. Is obtained.

In the flow of FIG. 3, the amplitude of the high frequency current is increased only when the focus is pulled in. However, the amplitude of the high frequency current may be increased until the track control is turned on. It is possible. In this case, step # 4 and step # 5 in FIG. 3 may be exchanged.

[0043]

[Embodiment 2] An embodiment of the optical disk device of the present invention will be described. This embodiment corresponds to the invention of claim 3. Also in this embodiment, the hardware configuration is basically the same as that in FIG.

FIG. 4 is a flow chart showing the main processing flow of the amplitude control of the high frequency current in the optical disk device of the present invention. In the figure, # 11 to # 20 indicate steps.

First, in step # 11, the error flag is reset. In the next step # 12, the semiconductor laser 1
Lights up. Go to step # 13
Data is supplied to the A / A converter 24 so that the amplitude of the high frequency current is controlled to be small.

In step # 14, focus pull-in is performed, and in the next step # 15, it is checked whether or not a focus pull-in error has occurred. When a focus pull-in error occurs, the process proceeds to step # 16 and the error flag is set.

In step # 17, the data is transferred again to the D / A converter 24 to increase the amplitude of the high frequency current.
After that, the process returns to the previous step # 14 to perform focus pull-in. Then, as a result of checking whether a focus pull-in error has occurred in step # 15, if no error occurs, the process proceeds to the next step # 18.

In step # 18, the track control is operated, and in the next step # 19, it is checked whether or not the error flag is set. If the error flag is set, in step # 20, the data is transferred again to the D / A converter 24 to reduce the amplitude of the high frequency current, and the process proceeds to the next step. The flow ends.

Also, when the error flag is not set, the process proceeds to the next step and the flow of FIG. 4 is ended. With the above processing of steps # 11 to # 20, it is possible to increase the amplitude of the high frequency current only when an error occurs during focus pull-in.
Unnecessary increase of high frequency current is prevented.

In the second embodiment, after the track control is operated, the amplitude of the high frequency current is reduced unless an error occurs (when the error flag is not set). Since it is possible to increase the amplitude of the high frequency current during the operation such as track jump, the optical disk device of the present invention includes these cases.

[0051]

According to the first aspect of the present invention, the amount of superposition of the high frequency current is increased only when the focus is pulled in. Therefore, unnecessary heat generation of the high frequency superposition circuit is prevented and the return light when the focus is pulled in is increased. A stable light source can be obtained even when the light amount changes.

According to the second aspect of the present invention, the amount of superposition of the high frequency current is increased in a state other than the track control state. Therefore, unnecessary heat generation of the high frequency superposition circuit is prevented and at the time of focus pull-in and track control. It is possible to obtain a stable light source even with respect to variations in the amount of return light from the previous track straddling or track jumping.

In the invention of claim 3, since the amount of superposition of the high frequency current is changed according to the error at the time of pulling in the focus, unnecessary heat generation of the high frequency superposition circuit is reduced as compared with the invention of the first aspect. Moreover, a stable light source can be obtained even when the focus is pulled in or when the amount of return light across the tracks before the track control is changed.

[Brief description of drawings]

FIG. 1 is a functional block diagram showing an embodiment of a main part configuration of a noise reduction circuit for a semiconductor laser according to the present invention.

FIG. 2 is a diagram showing an example of current-light emission characteristics of a semiconductor laser.

FIG. 3 is a flowchart showing a main processing flow of amplitude control of a high frequency current in the noise reduction circuit for a semiconductor laser according to the present invention.

FIG. 4 is a flowchart showing a main processing flow of amplitude control of a high frequency current in the optical disc device of the present invention.

FIG. 5 is a diagram showing an example of the relationship between the emission power of a semiconductor laser and the emission power of return light.

FIG. 6 is a diagram illustrating a focus signal detection system and a detection circuit by the astigmatism method, and the operation thereof.

FIG. 7 is a diagram showing a sum signal and an S-shaped curve of a focus signal in a focus signal detection system by the astigmatism method.

[Explanation of symbols]

 1 semiconductor laser 2 coupling lens 3 beam splitter 4 first condensing lens 5 light receiving element for power monitor 6 semiconductor laser control circuit 7 semiconductor laser drive circuit 8 objective lens 9 magneto-optical disk 10 second condensing lens 11 1 / 2λ plate 12 Polarization beam splitter 13 Transistor light receiving element 14 Track control circuit 15 Track driving circuit 16 Tracking actuator 17 Cylindrical lens 18 Focus light receiving element 19 Focus control circuit 20 Focus driving circuit 21 Focus actuator 22 CPU 23 High frequency superposition Circuit 23a High frequency oscillation circuit 23b Amplification circuit 24 D / A converter

Claims (3)

[Claims] 1. A noise reduction circuit for a semiconductor laser which is a light source of an optical disk device, wherein a high frequency superimposing circuit for variably controlling a current for superimposing a high frequency current on the semiconductor laser, and light emitted from the semiconductor laser on an optical disk. A noise reduction circuit comprising: a focus servo system for condensing; and a high frequency current superposition amount of the high frequency superposition circuit is increased when the focus control system is pulled in by the focus servo system. 2. A noise reduction circuit for a semiconductor laser which is a light source of an optical disk device, wherein a high frequency current superimposing circuit for variably controlling a current for superimposing a high frequency current on the semiconductor laser, and light emitted from the semiconductor laser on an optical disk. And a track servo system that follows the track, and in a state other than the track control state by the track servo system, the superposition amount of the high frequency current by the high frequency superposition circuit is increased. 3. In an optical disk device, a high-frequency current superimposing circuit for variably controlling a current for superimposing a high-frequency current on a semiconductor laser as a light source, a focus servo system for condensing light emitted from the semiconductor laser on an optical disk, And an optical disc device, wherein when an error occurs when pulling in the focus control by the focus servo system, the amount of superposition of the high frequency current by the high frequency superposition circuit is increased and the optical disc device is retried.