JP2880823B2 - Optical disk device - Google Patents

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 for recording and reproducing information on and from an optical disk, and more particularly to an optical disk device capable of applying a stable focus servo even when the wavelength suddenly changes. Things.

[0002]

2. Description of the Related Art A magneto-optical disk drive capable of recording and reproducing records a light beam from a laser light source as a spot on a magneto-optical disk as a recording medium to reproduce or record a signal. The output of the laser light source is small during reproduction and large during recording. In order to accurately record and reproduce a signal, it is necessary to narrow a laser beam on a disk to a spot diameter on the order of the diffraction limit, and to accurately trace on a recording track. For this reason, the optical disk device has a detecting means for detecting a focusing error and a track error, and drives the spot position of the laser beam in the direction of the optical axis of the optical system and in the radial direction of the disk so that the detected error signal becomes zero. And a driving device for performing the operation.

Since the oscillation wavelength of a semiconductor laser used as a light source of a magneto-optical disk drive shifts due to a change in output, the convergence point of the laser light is changed by the chromatic aberration of the objective lens when switching between reproduction and recording. Move in the axial direction.

[0004]

However, in the conventional optical disk apparatus, the focusing error signal is adjusted to be 0 when the convergence point coincides with the optical disk. Causes a large focusing error signal

Since the servo mechanism moves the objective lens so that the focusing error signal becomes 0, it takes a long time until the convergence point coincides with the disk. And accurate recording and reading cannot be performed.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and provides an optical disk apparatus capable of performing accurate recording and reading of information with little signal deterioration when switching the wavelength of a light source. The purpose is to do.

[0007]

According to the present invention, there is provided an optical disk apparatus for achieving the above object .
The invention relates to switching of laser light intensity during recording and reproduction.
Laser light source whose wavelength fluctuates due to
An objective lens that focuses these light beams on an optical disc,
Focusing on receiving the light beam reflected by the optical disk
Focusing error detecting means for generating a switching error signal
And a predetermined offset to the focusing error signal.
Offset adjusting means for adding a reset voltage;
Focusing with offset by adjusting means
Based on the error signal, the objective lens is set so that the signal becomes 0.
Driving means for driving the lens in the direction of its optical axis.
The offset adjusting means includes an oscillation wavelength of the laser light source.
Polarity of the offset voltage to be added in response to the
It is characterized by being inverted. The invention according to claim 2 is a recording method.
Wavelength changes with the switching of laser light intensity during
A moving laser light source and a light beam from the laser light source
An objective lens for forming an image on a disk, and the optical disk
Focusing error signal by receiving the light beam reflected by
Focusing error detecting means for generating
The gain of the focusing error signal at the short wavelength
Gain control means for adjusting the gain, and output from the gain control means.
Off to add offset voltage to output signal and output
Off by the set adjusting means and the offset adjusting means
Based on the set focusing error signal,
Move the objective lens in the optical axis direction so that the signal becomes 0.
Driving means for driving, the offset adjusting means
Is the convergence point of the luminous flux at the short wavelength,
デ ィ ス ク of the distance between the convergence point and the short wavelength
Output signal becomes 0 when it is located on the objective lens side.
The offset voltage is added, and the polarity is
Add an offset voltage with the same absolute value
And features. With this configuration , a predetermined offset voltage is added to the focusing error signal output from the light receiving element, and the polarity of the offset voltage is inverted in accordance with the switching of the wavelength. The objective lens is driven in the direction of the optical axis so that the signal becomes zero based on the focusing error signal offset by the offset adjusting means.

[0008]

An embodiment of the present invention will be described below with reference to the drawings. FIGS. 1 to 4 show an embodiment in which the present invention is applied to a magneto-optical disk information recording / reproducing apparatus.

First, an optical system of an optical disk device according to an embodiment will be described with reference to FIG. This optical system includes a light source unit 10, an objective optical system 20, a prism block 30, and a signal detection optical system 40. The light source unit 10 includes a semiconductor laser 11 that generates a divergent light beam, a collimator lens 12 that converts the divergent light beam into a parallel light beam, two anamorphic prisms 13 and 14 that shape the cross section of the light beam, and a mirror 15. Generates a parallel beam with a circular cross section.

The objective optical system 20 includes an objective lens 21 for focusing the beam on the signal recording surface of the magneto-optical disk MOD,
And a mirror 22. Objective lens 21 and mirror 2
2 is provided in a head (not shown) that slides in the radial direction X of the magneto-optical disk MOD. On the other hand, the light source unit 10, the prism block 30, and the signal detection optical system 40 are fixed with respect to the center of rotation of the disk. The objective lens 21 is provided on an actuator provided in the head, and is driven in the optical axis direction z.

The prism block 30 includes a first block 31 having two half mirror surfaces 31a and 31b,
The second block 33 is joined to the first block via the λ / 2 plate 32 and has a polarization splitting surface 33a and a total reflection surface 33b.

A part of the light beam from the light source unit 10 is reflected by the second half mirror surface 31b, and is converged by the converging lens 34 onto the light receiving element 35 for adjusting the automatic output of the semiconductor laser.

On the other hand, the light beam reflected from the disk is reflected by the second half mirror surface 31b, and
2, the polarization direction is rotated by 45 °, and the P-polarized light component passes through the polarization splitting surface 33a and is focused on the first light receiving element 42a for detecting the first magnetic recording signal via the focusing lens 41a. The S-polarized light component is reflected by the polarization splitting surface 33a and the total reflection surface 33b, and is focused on the second light receiving element 42b for detecting a magnetic recording signal via the focusing lens 41b.

The polarization direction of the laser beam incident on the magneto-optical disk MOD is rotated by 45 ° by the magnetic Kerr effect in accordance with the magnetization direction of the disk at the position where the spot is formed. The recording signal can be read out from the intensity difference by separating the light into the S component and detecting the light with the separate light receiving elements 42a and 42b.

The component transmitted through the twentieth half mirror surface 31b of the reflected light from the disk is reflected by the first half mirror surface 31a and given astigmatism by the cylindrical lens 44 via the focusing lens 43. Are focused on the error detecting light receiving element 45.

The light receiving area of the error detecting light receiving element 45 is:
They are arranged as shown in FIG. These light receiving regions include light receiving regions A, B, C, and D divided into four regions along respective axes of a direction X corresponding to the radial direction of the disk and a direction Y corresponding to the tangential direction. .

The focusing error detection circuit 50 includes two adders 51 and 52 for calculating the sum of outputs from the light receiving areas located at diagonal positions of the light receiving element 45, and a subtractor 53 for calculating the difference between the outputs of these adders. An automatic gain adjustment (AGC) device 54 for adjusting the level of the output of the subtractor 53;
And an offset adjusting circuit 55 for adding an offset to the output of the circuit.

The offset adjusting circuit 55 includes a variable resistor 55a for setting a reference voltage of an offset level by a divided voltage value of a resistor between + V and -V, a buffer amplifier 55b,
A computing unit 55d for inverting the polarity of the output voltage from the buffer amplifier 55b based on the state of the switch 55c. The resistor R1 is connected to the non-inverting input terminal of the arithmetic unit 55d, and the resistor R2 and the feedback resistor R3 are connected to the inverting input terminal. At least the resistors R2 and R3
Are the same.

The switch 55c is turned on during recording, that is, when the oscillation wavelength of the semiconductor laser 11 is long, and turned off during reproduction, that is, when the wavelength is short. Switch 5
When 5c is OFF, the output voltage E of the buffer amplifier 55b is output as it is as the offset voltage δ (= E). When the switch 55c is turned on, the non-inverting input of the arithmetic unit 55d is connected to GND, and the voltage of which polarity is inverted-
E is output. Note that the switch 55c is switched.
The combination is not necessarily limited to ON at the time of recording and OFF at the time of reproduction as described above. The combination may be reversed depending on the setting of the reference voltage or the direction of the cylindrical lens.

The focusing error signal FE output from the subtractor 53 is expressed as FE = (A + D)-(B + C) when the voltage corresponding to the light receiving area of the light receiving element is represented by the same symbol.

Here, the focusing error signal FE1 inputted to the phase compensation circuit 56 by adding the offset δ is represented by FE1 = FEO + δ = (A + D)-(B + C) + δ.

Next, the operation of the above-described optical disk device will be described with reference to FIG.
This will be described with reference to FIG. The convergence point of the light beam converged toward the optical disk MOD by the objective lens 21 is a point P1 during reproduction with a short wavelength used and a point P2 during recording with a long wavelength used due to chromatic aberration of the objective lens.

In the apparatus of this embodiment, the gain of the focusing error signal at the time of long wavelength and short wavelength is adjusted to the same level by the AGC circuit 54, and an offset voltage δ is added to this signal and input to the phase compensation circuit 56. Let it.

The offset adjustment circuit 55, re-illustrated in FIG. 3
The distance between the converging point P2 at the time of recording the convergence point P1 at the time of raw D, and the distance between the recording converging point of time P2 disk D2, as the distance between the reproduction time of the convergence point P1 and the disk D1, D
An offset voltage δ is added so that 1 = D2 = D / 2, that is, so that the focusing error signal FE1 becomes 0 when the convergence point P1 at the time of reproduction is located closer to the objective lens 21 than the disk by D / 2. I do.

With this setting, the focusing error signal FE1 input to the phase compensation circuit 56
Is 0 when the convergence point is located closer to the objective lens than the disc by D / 2 during reproduction, as shown in FIG. 4, and is 0 when the convergence point is away from the objective lens by D / 2 during recording. Becomes In this graph, the distance from the objective lens to the convergence point is represented by horizontal coordinates with the disc as the origin, and the level of the focusing error signal is represented by vertical coordinates with the direction in which the convergence point approaches the objective lens 21 side being plus.

By inverting the sign of the offset voltage δ and adding the offset voltage δ in accordance with the switching of recording / reproducing, the focusing error signal FE1 after adding the offset becomes 0 without moving the objective lens. Thus, the lens does not move at the time of switching, and stable recording and reproduction can be performed.

In this embodiment, an astigmatism method is used for detecting a focusing error signal. However, the present invention can be applied to an optical disk apparatus using another detection method.

Next, the processing in the case where the AGC circuit 54 is not provided in the detection circuit 50 or the case where the AGC circuit is provided in the subsequent stage of the offset adjustment circuit will be described.
This will be described using two examples. In this case, since the power of the laser beam differs between recording and reproduction, the relationship between the focus error signal FEO and the distance of the convergence point from the disc has a different slope as shown by the broken line in FIG. It can be represented as two straight lines.

In the example of FIG. 5, by adjusting the resistance values of the resistors R2 and R3, not only the polarities of the offset voltages δ1 and δ2 but also the absolute values of the signals are changed at the time of wavelength switching. By combining the resistance values, the distance D2 between the convergence point during recording and the disk and the distance D1 between the convergence point during reproduction and the disk can be adjusted. As shown in the example of FIG.
= D2 = D / 2.

In the example of FIG. 6, only the polarity of the offset voltage is switched as in the example of FIG. The distance between the disk and the convergence point at the time of recording and reproduction need not always be set to be equal. As shown in FIG. 6, the distance D2 between the convergence point at the time of recording and the disk is set smaller than the distance D1 at the time of reproduction. You may.

In the present invention, the convergence points P1,
It is necessary to keep the distance from P2 to the disk to such an extent that the drop in amplitude does not hinder signal detection, and the moving distance D of the convergence point determined by the difference in wavelengths to be switched and the chromatic aberration of the objective lens is too large. Not applicable in cases. In such a case, it can be applied by correcting the chromatic aberration of the objective lens to some extent and suppressing the moving distance D.

[0032]

As described above in detail, according to the present invention, a focusing error signal does not occur due to a focus shift due to wavelength switching, and an objective lens does not move, so that recording and reproduction can be stably performed immediately after switching. It can be carried out.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an optical system of an optical disk device according to an embodiment.

FIG. 2 is a circuit diagram showing a control system of the optical disk device shown in FIG.

FIG. 3 is an explanatory diagram showing an operation of the optical disk device shown in FIG.

FIG. 4 is a graph showing a focusing error signal of the optical disc device shown in FIG.

FIG. 5 is a graph showing an example of adding an offset when a gain adjustment circuit is not provided.

FIG. 6 is a graph showing another example of adding an offset when a gain adjustment circuit is not provided.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Semiconductor laser 21 ... Objective lens MOD ... Magneto-optical disk 45 ... Light detecting element for error detection 50 ... Focus error detection circuit 55 ... Offset adjustment circuit 57 ... Actuator

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-40631 (JP, A) JP-A-4-205928 (JP, A) JP-A-4-26414 (JP, U) (58) Survey Field (Int.Cl. ⁶ , DB name) G11B 7/09-7/095 G11B 7/085 G11B 7/135 G11B 11/10 556

Claims (2)

(57) [Claims] 1. Intensity switching of laser light during recording and reproduction
A laser light source whose wavelength fluctuates with the light source, an objective lens that forms a light beam from the laser light source on an optical disk, and a focusing error detection unit that receives the light beam reflected by the optical disk and generates a focusing error signal. An offset adjusting means for adding a predetermined offset voltage to the focusing error signal; and the objective lens is moved in the optical axis direction such that the signal becomes zero based on the focusing error signal offset by the offset adjusting means. and a driving means for driving the front Symbol offset adjusting means, the optical disk apparatus characterized by reversing the polarity of the offset voltage to be added in response to switching of the oscillation wavelength of the laser light source. 2. Switching of laser light intensity during recording and reproduction
A laser light source whose wavelength fluctuates with the light source, an objective lens that forms a light beam from the laser light source on an optical disk, and a focusing error detection unit that receives the light beam reflected by the optical disk and generates a focusing error signal. Gain control means for adjusting the gain of the focusing error signal at the long wavelength and short wavelength to the same level; offset adjustment means for adding an offset voltage to a signal output from the gain control means and outputting the signal; A driving means for driving the objective lens in the optical axis direction such that the signal becomes zero based on a focusing error signal offset by the means, wherein the offset adjusting means is configured to converge a light beam when the wavelength is short. The point is half the distance between the convergence point at the long wavelength and the convergence point at the short wavelength. Ri output signal when positioned on the objective lens side adds an offset voltage so as to be 0, the optical disk apparatus characterized by adding an equal offset voltage of an absolute value which polarity is inverted as it while longer wavelengths.