JP2001183121A - Tilt detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tilt detecting device which uses a short-wavelength light source and can detect the tilt of a recording medium with high precision even when the NA of an objective is large. SOLUTION: The light beam emitted by the light source 1 is collimated by a collimator 2 into a parallel beam, which is reflected by an optical branching filter 3 and converged by the objective 4. When light reflected by the recording surface of an optical disk 5 reaches the objective 4, the light is made by the objective 4 into a parallel beam, which is transmitted through the optical branching filter 3 and reaches the collimator 6. The parallel beam is converged by the collimator 6 and passes through an aberration generating lens 7 to have its spot diameter expanded radially from the center of the image, thereby irradiating respective photodetection parts 10-A to 10-D of an optical detector 10.

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 more particularly to a tilt detection device for detecting an angle at which an axis of a light beam applied to a recording medium is inclined.

[0002]

2. Description of the Related Art In an optical disk apparatus, in order to accurately record and reproduce information, a laser beam emitted from a light source needs to be irradiated perpendicularly to a recording surface of the optical disk. However, if the optical disc surface is warped or distorted,
The optical disk surface is tilted with respect to the axis of the light emitted from the light source. That is, the laser light emitted from the light source is emitted in a state inclined with respect to the optical disk surface. When the optical disk surface is inclined, the distance traveled by the laser light in the optical disk substrate changes depending on the location. For this reason, the shape of the beam spot is disturbed, and the reproduced signal cannot be read accurately, which has an adverse effect.

A conventional tilt detecting device for solving the above problem will be described with reference to FIG. In FIG. 2, the photodetector 10 includes light receiving units 10-A to 10-D that output detection results according to the amount of light to be received. When light is irradiated while the optical disk is tilted and the light is reflected from the recording surface of the optical disk, the shape of the light that reaches the light receiving surface of the photodetector 10 has coma and does not become a perfect circle, but It becomes a deformed elliptical shape as shown by reference numeral 11.

In this state, when the light detector 10 receives light, the sum of the outputs of the light receiving sections 10-A and 10-B is input to the low-pass filter 12-1. Similarly, in the light receiving sections 10-C and 10-D, the light receiving sections 10-C
The sum of C and the output of the light receiving unit 10-D is
-2. Next, the tilt component extracted by the low-pass filter 12-1 and the low-pass filter 1
The tilt of the optical disc in the radial direction (radial tilt) is detected by detecting the difference between the output signals of the tilt components extracted by 2-2 by the comparator 13-1.

At the same time as this detection operation, the light receiving unit 10
-A and the sum of the outputs of the light receiving units 10-D is the low-pass filter 1
2-3, and the light receiving unit 10-B and the light receiving unit 10
The sum of the outputs of −C is input to the low-pass filter 12-4. Then, the difference between the output signal of the tilt component extracted by the low-pass filter 12-3 and the output signal of the tilt component extracted by the low-pass filter 12-4 is calculated by the comparator 13-
2, the tilt (tangential tilt) in the circumferential direction of the optical disk is detected.

[0006]

In recent years, a light source having a short wavelength has been used, and a numerical aperture of an objective lens (hereinafter, referred to as a numerical aperture) has been proposed.
It is necessary to increase the data recording density of the optical disk device by setting a large “NA” and narrowing the spot diameter. However, when the light source has a short wavelength and the NA of the objective lens is large, the read error of the reproduced signal due to the tilt of the optical disk becomes larger than when the light source has a long wavelength and the NA of the objective lens is small. Also, when the NA of the objective lens is set large and the spot diameter is narrowed down, the area of the reflected light from the optical disk irradiated on the photodetector is reduced, thereby reducing the slight tilt of the optical disk. It could not be detected accurately. The present invention has been made in view of such a point, and a purpose thereof is to use a light source with a short wavelength and to detect a tilt of a recording medium with high accuracy even when an NA of an objective lens is large. It is to provide a device.

[0007]

According to a first aspect of the present invention, a recording medium is irradiated with laser light from a light source, and reflected light from the recording medium is transmitted through an optical system. A tilt detection device that guides the reflected light to an optical system for returning the reflected light to the recording medium based on a light receiving state of the photodetector; An optical member for enlarging an imaging spot is provided.

According to a second aspect of the present invention, a recording medium is irradiated with a laser beam from a light source, reflected light from the recording medium is guided to a photodetector through an optical system, and based on a light receiving state of the photodetector. In a tilt detection device for detecting a tilt of an optical axis of irradiation light applied to the recording medium, the tilt detection device includes a condensing unit that condenses the reflected light to the photodetector, and the condensing unit includes the reflected light Is characterized by being enlarged and condensed. According to a third aspect of the present invention, in the tilt detecting device according to the second aspect, the light collecting means has a numerical aperture set to a predetermined value or less.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic block diagram showing a configuration of a tilt detection device according to an embodiment of the present invention. In this figure, reference numeral 1 denotes a light source for emitting laser light. Reference numeral 2 denotes a collimator that converts a laser beam emitted from the light source 1 into a parallel beam.

The optical splitter 3 reflects the parallel beam that has passed through the collimator 2 to the objective lens 4,
Is guided to the collimator 6. Objective lens 4
Receives the parallel beam reflected by the optical splitter 3 and condenses it on a track of the recording surface of the disk 5 on which recording information is recorded. Further, the objective lens 4 irradiates the light reflected from the recording surface of the optical disk 5 to the optical splitter 3 as a parallel beam.

The collimator 6 is disposed at a position 1 where the distance from the photodetector 10 is the focal length, and focuses a parallel beam emitted from the objective lens 4 and transmitted through the optical splitter 3 onto the photodetector 10. I do. The aberration generating lens 7 is configured by, for example, a concave lens or the like, and is disposed between the collimator 6 and the photodetector 10. Then, the light emitted from the collimator 6 to the photodetector 10 generates an aberration radially in the radial direction of the light beam. That is, the spot diameter of the light applied to the photodetector 10 is increased.

As the photodetector 10, the conventional photodetector shown in FIG. 2 is applied. The photodetector 10 includes four light-receiving units 10-A to 10-A which output detection results according to the amount of light received.
10-D, the sum of the outputs of the light receiving units 10-A and 10-B is input to the low-pass filter 12-1, and the output of the light receiving units 10-C and 10-D is output. The sum is input to the low-pass filter 12-2. The sum of the outputs of the light receiving units 10-A to 10-D is:
It is taken out as a signal output of the recording information of the optical disc 5.

The low-pass filter 12-1 receives the sum of the output voltages of the light receiving sections 10-A and 10-B, and outputs a low-frequency component (RF) indicating a tilt component from the input signal.
The signal envelope is extracted and output to one input terminal of the comparator 13-1. Low-pass filter 12-2
Receives the sum of the output voltages of the light receiving units 10-C and 10-D, extracts a tilt component from the input signal, and outputs the tilt component to the other input terminal of the comparator 13-1. The comparator 13-1 calculates the difference between the output from the low-pass filter 12-1 and the output from the low-pass filter 12-2. This difference in output corresponds to the amount of tilt of the optical disk 5 in the radial direction, and is output as a radial tilt signal.

In the photodetector 10, the light receiving section 10
-A and the sum of the outputs of the light receiving units 10-D is the low-pass filter 1
2-3, and the sum of the outputs of the light receiving units 10-B and 10-C is input to the low-pass filter 12-4. The low-pass filter 12-3 includes the light receiving units 10-A, 10-A
The sum of the output voltages of −D is input, a tilt component is extracted from the input signal, and output to one input terminal of the comparator 13-2. The low-pass filter 12-4 receives the sum of the output voltages of the light receiving units 10-B and 10-C, extracts a tilt component from the input signal,
The signal is output to the other input terminal of the comparator 13-2. Comparator 1
3-2 takes the difference between the output from the low-pass filter 12-3 and the output from the low-pass filter 12-4. This difference in output corresponds to the amount of tilt in the circumferential direction of the optical disk 5, and is output as a tangential tilt signal.

Next, the operation of this device will be described.
The light beam emitted from the light source 1 is converted into a parallel beam by the collimator 2, reflected by the optical splitter 3, and reaches the objective lens 4. Then, the parallel beam is condensed by the objective lens 4, irradiated on the recording surface of the optical disk 5, and reflected by the recording surface. When the light reflected by the recording surface reaches the objective lens 4, the light is converted into a parallel beam by the objective lens 4, passes through the optical splitter 3, and reaches the collimator 6. And
The parallel beam is condensed by the collimator 6 and passes through the aberration generating lens 7 so that the spot diameter is widened, and the light receiving units 10-A to 10-D of the photodetector 10 are used.
Is irradiated.

Next, when the irradiated light is received by the photodetector 10, the sum of the outputs of the light receiving sections 10-A and 10-B is input to the low-pass filter 12-1. The low-pass filter 12-1 extracts the tilt component from the sum of the output voltages of the light receiving units 10-A and 10-B, and outputs the tilt component.
1 to one input terminal.

The sum of the outputs from the light receiving sections 10-C and 10-D is input to the low-pass filter 12-2. The low-pass filter 12-2 receives the input light receiving unit 10-
The tilt component is extracted from the sum of the output voltages of C and 10-D and output to the other input terminal of the comparator 13-1. Then, the comparator 13-1 takes the difference between the output from the low-pass filter 12-1 and the output from the low-pass filter 12-2, and outputs the result as a radial tilt signal.

Further, the light receiving sections 10-A and 10-D
Is input to the low-pass filter 12-3.
The low-pass filter 12-3 is connected to the light receiving unit 10-
A tilt component is extracted from the sum of the output voltages of A and 10-D and output to one input terminal of the comparator 13-2.

The sum of the outputs of the light receiving sections 10-B and 10-C is input to the low-pass filter 12-4. The low-pass filter 12-4 is connected to the light receiving unit 10-
The tilt component is extracted from the sum of the output voltages of B and 10-C and output to the other input terminal of the comparator 13-2. Then, the comparator 13-2 takes the difference between the output from the low-pass filter 12-3 and the output from the low-pass filter 12-4 and outputs the result as a tangential tilt signal. Then, the sum of the outputs of the light receiving units 10-A to 10-D is
It is taken out as a signal output of the recording information of the optical disc 5.

By using a tilt correction mechanism for correcting a tilt angle based on the above-mentioned radial tilt signal and tangential tilt signal, the tilt of the optical disk 5 with respect to the photodetector 10 in the radial direction and the circumference of the optical disk 5 are corrected. It is possible to correct the inclination with respect to the direction.

In the above-described embodiment, the aberration generating lens 7 is disposed between the collimator 6 and the photodetector 10, but may be located at any position in the return optical system. Further, in the embodiment, the aberration generating lens 7 is configured by a concave lens, but can be replaced with an aberration generating diffraction grating or the like that generates aberration. Further, an aberration may be generated in the collimator 6. Further, in the above-described embodiment, the aberration generating lens 7 constituted by a concave lens is disposed between the collimator 6 and the photodetector 10. However, the aberration generating lens 7 may be replaced with an optical member having a substantially spherical shape. Alternatively, the aberration generating lens may be arranged on the light receiving surface of the photodetector 10. In the case where the optical member is provided on the light receiving surface, the optical member is not limited to the lens, and for example, an adhesive or the like is dropped on the light receiving surface of the photodetector 10 and the light collected by the collimator 6 And aberrations may be generated. Further, a plurality of the aberration generating lenses may be used, and a configuration in which a plurality of the above-described optical members are combined is also possible.

Further, the photodetector 10 is divided in a cross shape, but the present invention is not limited to this. Any photodetector may be used as long as a plurality of light receiving portions are arranged. The numerical aperture of the light condensing means (for example, the collimator 6) for condensing the light on the light detector depends on the size of the light receiving surface of the light detector 10, or the light condensing means and the light detector 10
Is set based on the distance of For example, it is preferable that the spot diameter is set to be about 程度 of the length of one side of the photodetector 10. The size of the area of the light collecting means is set according to the response speed required for the system.

[0023]

According to the present invention, the irradiation surface of the light reflected from the recording surface of the recording medium is expanded in the radial direction from the center of the image to irradiate the photodetector. Therefore, even when the NA of the objective lens is large, the inclination of the storage medium can be detected with high accuracy. Also,
According to the present invention, the irradiation surface of the light reflected from the recording surface of the recording medium is provided with an optical system that expands in the radial direction from the center of the image, so that the focal length between the collimator and the photodetector is not changed. The spot diameter can be increased. Further, since a conventional photodetector can be used, there is an effect that an increase in production cost can be suppressed. Also,
Since the relative value of the inclination of the storage medium with respect to the photodetector can always be detected, it can be used for feedback control.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a tilt detection device according to a first embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a conventional light detection unit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light source 2 Collimator 3 Optical splitter 4 Objective lens 5 Optical disk 6 Collimator 7 Aberration generating lens 10 Photodetector

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 2F065 AA31 BB18 CC03 EE00 FF44 GG04 GG12 HH04 JJ22 LL00 LL04 QQ25 QQ27 2H087 KA13 LA30 NA01 PA01 PA17 QA03 QA05 QA18 QA38 RA44 5D118 AA14 BA01 CC12 CD04 DA45

Claims (3)

[Claims] A recording medium is irradiated with laser light from a light source, reflected light from the recording medium is guided to a photodetector through an optical system, and the recording medium is irradiated based on a light receiving state of the photodetector. A tilt detection device for detecting a tilt of an optical axis of irradiation light, wherein an optical member for enlarging an imaging spot of the reflected light is provided in an optical system for returning the reflected light. 2. A laser beam from a light source is applied to a recording medium, and reflected light from the recording medium is guided to a photodetector through an optical system, and the recording medium is irradiated based on a light receiving state of the photodetector. A tilt detecting device for detecting a tilt of an optical axis of the irradiated light, the light detecting device having a light collecting means for collecting the reflected light onto the photodetector, wherein the light collecting means enlarges an imaging spot of the reflected light. A tilt detection device characterized in that light is collected by focusing. 3. The tilt detecting device according to claim 2, wherein the light condensing means has a numerical aperture set to a predetermined value or less.