JP2003059083A - Optical head and optical disk playing-back device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the variance or change in a peak power level of laser ejection beams caused by the variance of laser performance or the change due to the temperature. SOLUTION: A photodetecting part 17 for power monitor is divided into a photodetector 17b for peak power monitor having a small photodetecting area of the center part and photodetectors 17a for average power monitor having a large photodetecting area of the circumference or both sides. A laser driving circuit 1 is controlled so that a level of DC component in a photodetecting output current Ia of the photodetector 17a coincides with a target value, to control a level of a DC current Id for driving the laser. Further, a high frequency superimposing circuit 3 is controlled so that the amplitude of high frequency component of the photodetecting output current Ib (or an added current of the photodetecting output Ia of the photodetector 17a and the photodetecting output current Ib of the photodetector 17b) of the photodetector 17b coincides with the target value, then the amplitude of an high frequency current Ih superimposed to the DC current Id is controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head for reproducing or recording / reproducing an optical disk, and an optical disk reproducing apparatus for reproducing or recording / reproducing an optical disk by the optical head.

[0002]

2. Description of the Related Art In an optical head for reproducing or recording / reproducing an optical disk, laser emission light is condensed by an objective lens and irradiated onto the optical disk, and return light from the optical disk is received by a light receiving element and reproduced. Signals, focus error signals, and tracking error signals are detected, but in order to suppress laser noise and obtain a reproduction signal with a high S / N (signal-to-noise ratio), the DC current for laser drive needs a few
A high frequency current of 00 MHz (at least about 100 MHz) is superimposed to cause the laser to emit light intermittently.

This is because the oscillation spectrum width of the laser is widened by modulating the laser drive current with a high frequency,
As a result, the coherence of the laser is reduced and so-called return light noise is reduced.

In this case, conventionally, in consideration of variations in laser characteristics and changes due to temperature, a high-frequency current of a sufficient level is generated and applied to the laser so that the laser noise falls within an allowable range. For example, Japanese Patent Laid-Open No. 6-2
No. 67102, a laser drive circuit receives a laser emission light by a light receiving element for power monitoring and, based on the received light output signal, a laser drive circuit so that the average power level of the laser emission light becomes a predetermined level. Control.

FIG. 5 shows an example of such a conventional optical head, which is an optical head for recording / reproducing a magneto-optical disk.

In this optical head, a direct current Id for driving a laser is generated in the laser drive circuit 1, and at the same time, in the high frequency superposition circuit 3 connected to the output side of the laser drive circuit 1 via the capacitor 2. 100 MH
A high frequency current Ih of z is generated, and a laser drive current in a state where the high frequency current Ih is superimposed on the direct current Id is applied to the semiconductor laser (laser diode) 4.

Laser light emitted from the semiconductor laser 4 enters a beam splitter 6 through a grating 5 that forms three beams for tracking error detection by the three-beam method, and passes through the beam splitter 6. It is split into light and light reflected by the beam splitter 6.

The light transmitted through the beam splitter 6 is incident on a collimator lens 7, is collimated by the collimator lens 7, is incident on an objective lens 8, and is collected on an optical disc (magneto-optical disc) 9 by the objective lens 8. Be illuminated. The light reflected by the beam splitter 6 is received by the power monitor light-receiving element 15.

The light that has entered the optical disk 9 is reflected by the recording layer (reproduction layer) of the optical disk 9, and enters the beam splitter 6 through the objective lens 8 and the collimator lens 7 as return light, and is reflected by the beam splitter 6. The reflected light is passed through the Wollaston prism 11 and the multi-lens 12 for the magneto-optical disk, and the light receiving element IC (integrated circuit) 13
And is received by the light receiving element of the light receiving element IC13.

The light-receiving element IC13 is a current-voltage conversion circuit for converting each light-receiving output current into a voltage for the light-receiving element divided for detecting the reproduction signal, the focus error signal and the tracking error signal, and its output voltage. It is an integrated circuit such as an amplifier circuit that amplifies the.

The light receiving output current of the power monitor light receiving element 15 is supplied to the control circuit 16, and in the control circuit 16, the DC level of the light receiving output current of the power monitor light receiving element 15 becomes a predetermined level, that is, the semiconductor. The laser drive circuit 1 is controlled so that the average power level of the emitted light of the laser 4 becomes a predetermined level, and the level of the direct current Id is controlled.

[0012]

However, in the above-mentioned conventional optical head, the level of the direct current Id for driving the laser is controlled so that the average power level of the emitted light of the semiconductor laser 4 becomes a predetermined level. However, since the high-frequency current Ih is superimposed on the DC current Id with a constant amplitude, the peak power level of the emitted light of the semiconductor laser 4 varies or changes due to variations in the characteristics of the semiconductor laser 4 or changes due to temperature.

Therefore, when reproducing a super-resolution magneto-optical disk whose reproduction characteristics depend on the temperature distribution due to the light spot on the disk, the emission light of the semiconductor laser 4 changes due to variations in characteristics of the semiconductor laser 4 and changes due to temperature. Variations and changes in the peak power level cause variations and changes in the temperature distribution due to the optical spot on the disc,
The size or the change of the size of the super-resolution part occurs, and the read signal amount also changes or changes.

When reproducing a phase change type optical disk for recording by the heat of the light spot, the peak power level of the emitted light of the semiconductor laser 4 is changed due to the variation in the characteristics of the semiconductor laser 4 and the change due to temperature. When the level exceeds the level, erroneous recording or erasing (change or destruction of recorded signal) occurs.

Therefore, the present invention is an optical head for reproducing or recording / reproducing an optical disk, which can suppress variations and changes in peak power level of laser emission light due to variations in laser characteristics and changes due to temperature. When reproducing a resolving magneto-optical disk, it is possible to suppress variations and changes in the reproduction signal level due to variations and changes in the peak power level of laser emission light, and at the time of reproduction of a phase change optical disc, the peak power level of laser emission light is reduced. It is possible to prevent erroneous recording and erasing due to an excessive level.

[0016]

The optical head of the present invention comprises a laser, an optical branching element for branching the light emitted from the laser into two light beams, and one light beam branched by the optical branching element. An optical system having an objective lens for condensing on an optical disk, a power monitor light receiving unit for receiving the other light beam split by the light splitting element, and a laser drive for applying a driving DC current to the laser A circuit, a high frequency superimposing circuit for superimposing a high frequency current on the direct current thereof, and the high frequency so that the peak power level of the emitted light of the laser becomes a predetermined level based on the light reception output signal of the power monitor light receiving section. And a drive control unit having a control circuit for controlling the amplitude of the current.

In the optical head of the present invention having such a structure, the DC current for driving the laser is set so that the peak power level of the laser emission light becomes a predetermined level based on the light reception output signal of the light receiving unit for power monitor. The amplitude of the high-frequency current superimposed on is controlled. Therefore, the peak power level of the laser emission light is constant regardless of variations in laser characteristics and changes due to temperature.

[0018]

DETAILED DESCRIPTION OF THE INVENTION [Embodiment of Optical Head ...
3] FIG. 1 shows an embodiment of an optical head according to the present invention, which is an optical head for recording / reproducing of a magneto-optical disk.

In this optical head, the laser drive circuit 1 generates a direct current Id for laser drive, and the high frequency superposition circuit 3 connected to the output side of the laser drive circuit 1 via the capacitor 2 outputs several hundred MHz.
The high frequency current Ih is generated and the laser drive current in the state where the high frequency current Ih is superimposed on the direct current Id is applied to the semiconductor laser (laser diode) 4.

The laser light emitted from the semiconductor laser 4 is made incident on the beam splitter 6 through the grating 5 which forms three beams for tracking error detection by the three-beam method, and is transmitted through the beam splitter 6. The light is split into the light and the light reflected by the beam splitter 6.

The light transmitted through the beam splitter 6 is made incident on a collimator lens 7, collimated by the collimator lens 7 and made incident on an objective lens 8, and is condensed on an optical disc (magneto-optical disc) 9 by the objective lens 8. . The light reflected by the beam splitter 6 is received by a power monitor light receiving unit 17 described later.

The light incident on the optical disc 9 is reflected by the recording layer (reproducing layer) of the optical disc 9. The returned light is incident on the beam splitter 6 via the objective lens 8 and the collimator lens 7, reflected by the beam splitter 6, and passed through the Wollaston prism 11 and the multi-lens 12 for the magneto-optical disk, and the light receiving element. The light is incident on the IC (integrated circuit) 13 and is received by the light receiving element of the light receiving element IC 13.

The light-receiving element IC13 is a current-voltage conversion circuit for converting the light-receiving output current of each of the light-receiving elements divided for detecting the reproduction signal, the focus error signal and the tracking error signal, and its output voltage. It is an integrated circuit such as an amplifier circuit that amplifies the.

As an example, as shown in FIG. 2A, the power monitor light receiving section 17 includes a circular peak power monitor light receiving element 17b in the center and an annular average power monitor surrounding the light receiving element 17b. The light receiving element 17a is divided into a light receiving element 17a and a circular light receiving surface, and the light receiving area of the light receiving element 17b is smaller than that of the light receiving element 17a.

Since the equivalent capacitor capacity of the light receiving element (photodiode) is proportional to the light receiving area, the frequency characteristic of the light receiving element 17b is high in the high frequency region by reducing the light receiving area of the light receiving element 17b in this way. Therefore, the light receiving element 17b can detect a high frequency component of several 100 MHz of the emitted light of the semiconductor laser 4 with high accuracy.

The light beam reflected by the beam splitter 6 and incident on the power monitor light-receiving portion 17 has a light intensity at the central portion in the X and Y directions of FIG. 2A in the plane perpendicular to the optical axis. Is the highest. In the example of FIG. 2 (A), the position of the power monitor light receiving unit 17 in the X direction and the Y direction is adjusted so that the light receiving element 17b receives the central portion where the light intensity of the incident light is highest.

As another example, as shown in FIG. 2B, the power monitor light-receiving section 17 includes a band-shaped peak power monitor light-receiving element 17b at the center and band-shaped average power monitors on both sides thereof. The light receiving area of the light receiving element 17b is smaller than the light receiving area of the light receiving element 17a. Also in this example, the light receiving element 17
Depending on b, the number of emitted light of the semiconductor laser 4 is 100 MHz
The high frequency component can be detected with high accuracy.

Further, in this example, the position of the power monitor light receiving portion 17 in the X direction is adjusted so that the light receiving element 17b receives the central portion where the light intensity of the incident light is the highest.
No exact alignment is required for orientation.

As shown in FIG. 1, the received light output current Ia of the light receiving element 17a for average power monitoring is converted into a voltage by the current-voltage conversion circuit 21, and the received light output voltage is supplied to the low pass filter 22. , The DC component of the received light output voltage is extracted from the low-pass filter 22, and the differential amplifier circuit 2
3, the DC component voltage is compared with the target value so that the difference between the two becomes zero, that is, the DC component voltage from the low-pass filter 22 matches the target value.
The laser drive circuit 1 is controlled to control the level of the direct current Id.

Further, the received light output current Ib of the light receiving element 17b for peak power monitoring is converted into a voltage by the current-voltage conversion circuit 31, and the received light output voltage is supplied to the high pass filter 32, and the high pass filter is supplied. A high-frequency component of the received light output voltage is extracted from 32, the amplitude of the high-frequency component is detected (detected) by the amplitude detection circuit 33, and the amplitude detection voltage is compared with a target value by the differential amplifier circuit 34. The high frequency superposition circuit 3 is controlled so that the difference becomes zero, that is, the high frequency component amplitude detection voltage from the amplitude detection circuit 33 matches the target value, and the direct current I
The amplitude of the high frequency current Ih superimposed on d is controlled.

The semiconductor laser (laser diode) 4 is
As indicated by the solid line 18 in FIG. 3, when the drive current I exceeds a certain threshold value, the emitted light power P rises, and
A direct current Id superposed with a high frequency current Ih of several 100 MHz is applied as the drive current I, so that light is emitted intermittently as indicated by the emitted light power P1.

Further, the characteristics of the emitted light power P with respect to the drive current I of the semiconductor laser 4 become the characteristics shown by the solid line 18 in one optical head, and the characteristics shown by the broken line 19 in another optical head. Of the optical head, the characteristics of the same optical head (semiconductor laser) are shown by the solid line 18 when the temperature is low, and the characteristics are shown by the broken line 19 when the temperature is high.

Therefore, when the level of the direct current Id is not controlled and the amplitude of the high frequency current Ih is not controlled as described above, variations in the characteristics of the semiconductor laser 4 and changes due to temperature change the semiconductor laser 4. The average power level of the emitted light fluctuates or changes as indicated by levels Pa1 and Pa2 in FIG. 3, and the peak power level of the emitted light of the semiconductor laser 4 also changes to the level P in FIG.
As indicated by b1 and Pb2, there are variations or changes.

On the other hand, as described above, the light receiving element 1
By controlling the level of the direct current Id so that the level of the direct current component of the received light output current Ia of 7a matches the target value, the semiconductor laser 4 can be controlled regardless of variations in characteristics of the semiconductor laser 4 and changes due to temperature. The average power level of the emitted light becomes constant.

However, even if the average power level of the emitted light of the semiconductor laser 4 is controlled to be constant in this way,
The variation or change in the peak power level of the emitted light of the semiconductor laser 4 cannot be eliminated.

On the other hand, as in this embodiment, the amplitude of the high frequency current Ih superimposed on the direct current Id is adjusted so that the amplitude of the high frequency component of the light receiving output current Ib of the light receiving element 17b matches the target value. By controlling, the peak power level of the emitted light of the semiconductor laser 4 also becomes constant regardless of variations in the characteristics of the semiconductor laser 4 and changes due to temperature.

Therefore, during reproduction of the super-resolution magneto-optical disk, the temperature distribution due to the light spot on the disk becomes constant, the size of the super-resolution portion becomes constant, and the reproduction signal level becomes constant. Further, also during recording, the peak power level of the laser light for recording from the semiconductor laser 4 can be controlled to be constant.

Further, the optical head of the embodiment of FIG. 1 can be used for recording / reproducing of a phase change type optical disk by removing the Wollaston prism 11 for the magneto-optical disk.

Therefore, during reproduction of the phase change type optical disc, erroneous recording and erasing due to the peak power level of the emitted light of the semiconductor laser 4 becoming an excessive level can be prevented. Further, also during recording, the peak power level of the laser light for recording from the semiconductor laser 4 can be controlled to be constant.

Regarding the level control of the DC current Id, the light receiving output current Ia of the light receiving element 17a and the light receiving element 17a
The light-receiving output current Ib of b is combined to generate the current-voltage conversion circuit 2
1 or the light receiving output current I of the light receiving element 17a
The light receiving output current Ib of the light receiving element 17b and the light receiving element 17b may be converted into voltages, combined, and supplied to the low pass filter 22.

Further, for the amplitude control of the high frequency current Ih, the amplitude detection circuit 33 is used to control the high pass filter 32.
Instead of detecting the amplitude of the high frequency component from, the peak detection circuit may detect (detect) the peak value of the high frequency component from the high pass filter 32.

[Embodiment of optical disc reproducing apparatus ... FIG. 4]
FIG. 4 shows an embodiment of an optical disk reproducing apparatus of the present invention, which is an apparatus for recording and reproducing a super-resolution magneto-optical disk.

The optical head 40 includes an optical system and a drive controller (drive circuit and control circuit) as shown in FIG. 1, and includes a biaxial actuator 41 that drives the objective lens 8 in the focus direction and the tracking direction. A magnetic head 50 for recording is provided separately from the optical head 40.

The super-resolution magneto-optical disk 9a is driven to rotate by a spindle motor 61, and the optical head 40 and the magnetic head 50 are driven in a radial direction of the super-resolution magneto-optical disk 9a by driving a feed mechanism 63 by a feed motor 62. Sent.

The light receiving element I of the optical head 40 shown in FIG.
The light reception output signal of C13 is sent from the optical head 40 to the RF amplifier 71, and the RF amplifier 71 outputs the DSP (Dig
ital signal processor) 72
Then, a reproduction signal RF, a focus error signal FE, a tracking error signal TE, etc. are transmitted. Also, DSP
A signal such as the above-described target value is sent from 72 to the optical head 40 through the RF amplifier 71.

The DSP 72 is controlled by the controller 73 to control the driver 64. The driver 64 sends drive signals to the spindle motor 61 and the feed motor 62, respectively, and the optical head 40.
The drive signal FS for focus control and the drive signal TS for tracking control are sent to the biaxial actuator 41. During recording, the magnetic head 50 is driven by the driver 65.

[0047]

As described above, according to the present invention, it is possible to suppress variations and changes in the peak power level of laser emission light due to variations in laser characteristics and changes due to temperature, and at the time of reproducing a super-resolution magneto-optical disk. It is possible to suppress variations and changes in the reproduction signal level due to variations and changes in the peak power level of the laser emission light, and to prevent the peak power level of the laser emission light from becoming excessive levels during reproduction of the phase change optical disk. It is possible to prevent erroneous recording and erasing.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a specific example of a power monitor light-receiving unit in FIG.

FIG. 3 is a diagram for explaining control of a peak power level in the present invention.

FIG. 4 is a diagram showing an embodiment of an optical disc reproducing apparatus of the present invention.

FIG. 5 is a diagram showing an example of a conventional optical head.

[Explanation of symbols]

Since the main parts are all described in the figure, they are omitted here.

Claims (5)

[Claims] 1. A laser, an optical branching element for branching light emitted from the laser into two light beams, an objective lens for focusing one of the light beams branched by the optical branching element on an optical disk, An optical system having a power monitor light-receiving unit that receives the other light beam split by the light splitting element, a laser drive circuit that applies a driving DC current to the laser, and a high-frequency current superimposed on the DC current. And a control circuit for controlling the amplitude of the high frequency current so that the peak power level of the emitted light of the laser becomes a predetermined level based on the light reception output signal of the power monitor light receiving unit. An optical head comprising: a drive controller. 2. The optical head according to claim 1, wherein the power monitor light receiving section is divided into an average power monitor light receiving element and a peak power monitor light receiving element, and the control circuit receives the average power monitor light receiving element. Based on the received light output signal of the element, the level of the DC current is controlled so that the average power level of the emitted light of the laser becomes a predetermined level, and based on the received light output signal of the peak power monitor light receiving element. An optical head that controls the amplitude of the high-frequency current so that the peak power level of the emitted light of the laser becomes a predetermined level. 3. The optical head according to claim 2, wherein the light receiving area of the peak power monitor light receiving element is smaller than the light receiving area of the average power monitor light receiving element. 4. An optical disk reproducing apparatus provided with the optical head according to claim 1. 5. The optical disk reproducing apparatus according to claim 4, wherein the optical disk reproducing apparatus reproduces or records / reproduces a super-resolution magneto-optical disk.