JPH11120592A - Tilt detecting method of optical disk and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the lowering of detecting accuracy by an extraordinary light ray caused by birefringence in an optical disk in the technique projecting light on an optical disk and detecting the tilt of the front surface of the optical disk based on the angular change of the reflected light. SOLUTION: A polarizing beam transmitted from a laser beam source 11 is projected on the front surface of an optical disk D, an ordinary light ray and an extraordinary light ray whose polarizing directions are orthogonal to each other caused by birefringence at the time they are reflected by the optical disk D are separated by a polarizing beam splitter 12, only the ordinary light ray is selected and detected by a photodetector 13. In a calculating part 14 the reflecting angle of the ordinary light ray in the optical disk is calculated and the tilt angle on the front surface of the optical disk D is calculated. The influence of tilt detection of the optical disk by the extraordinary ray is eliminated and highly accurate tilt detection is enabled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tilt detecting method and a tilt detecting device for detecting a tilt of a surface of an optical disk such as a phase change optical disk or a magneto-optical disk with respect to a predetermined plane.

[0002]

2. Description of the Related Art Since an optical disc records and reproduces information by condensing light on the recording layer of the optical disc, if the plane of the optical disc has an inclination, the recording layer can be precisely formed. It is not possible to collect light, high-density recording,
Reproduction becomes difficult. For this reason, conventionally, the inclination of the optical disk has been detected. FIG. 6 is a schematic view conceptually showing a conventional inclination detecting device. A laser light source 101 is arranged to face an optical disc D to be detected, and a laser beam is emitted from the laser light source 101 and projected onto the optical disc D. Here, a HeNe laser is used as the laser light source 101, and a laser beam is projected from a direction slightly inclined from a direction perpendicular to the surface of the optical disc D. The light reflected by the laser beam from the optical disk D is detected by a photodetector 102 comprising an optical sensor having two light receiving surfaces 102a and 102b divided in a direction parallel to the radial direction of the optical disk. The photodetector 102 is arranged so that when the surface of the optical disc D is positioned at a predetermined plane angle position, the laser beam reflected by the optical disc D is positioned at the center of the two dividing lines of each light receiving surface. Is set.

In this tilt detecting apparatus, the optical disk D is rotated and driven, a laser beam from a laser light source 101 is projected onto the surface of the optical disk D, and the reflected light is detected by a photodetector 102 while the optical disk D is being detected. Is relatively moved in the radial direction, and the difference between the respective detection outputs of the two divided light receiving surfaces 102a and 102b of the photodetector 102 at that time is taken by the differential amplifier 103, so that the reflected laser beam is The angle Δθ deviated from the center position of the photodetector 102 is detected, and the tilt angle Δ
θ / 2 can be detected.

[0004]

In such a conventional tilt detecting device, the light from the laser light source 101 is linearly polarized. However, when this laser beam is reflected on an optical disc D made of a transparent resin. To be more precise, when the light is refracted and reflected in the transparent plate constituting the surface of the optical disc, it is divided into an ordinary ray and an extraordinary ray due to birefringence in the resin. Since the ordinary ray and the extraordinary ray have different refractive indices, they are reflected from the optical disc as different laser beams at different angles, and are detected by the photodetector 102. And
At the time of the above-described detection, the ordinary ray and the extraordinary ray are respectively detected as circular beam trajectories by the photodetector 102 due to the deviation of the reflection angle due to the rotation of the optical disk D. When performing, the extraordinary ray interferes with the ordinary ray and becomes noise. Therefore, as shown in FIG. 7, a detection error due to the influence of an extraordinary ray occurs, as shown by a broken line, with respect to the original tilt characteristic of the optical disk shown by a solid line, and it is difficult to perform accurate and highly accurate detection. There is.

An object of the present invention is to provide a method and an apparatus for detecting the tilt of an optical disk, which can accurately and accurately detect the tilt of the optical disk, and which can detect the tilt dynamically. .

[0006]

A method for detecting the tilt of an optical disk according to the present invention comprises projecting a polarized beam on the surface of an optical disk, detecting only ordinary rays of the polarized beam reflected by the optical disk, and detecting the ordinary beam. Calculating a reflection angle of the ordinary ray on the optical disk based on the calculated light and calculating a tilt angle of a surface of the optical disk. Here, it is preferable to detect the inclination of the optical disk while rotating the optical disk. Further, it is preferable that the tilt detection is performed while moving the projection position of the polarized beam in a radial direction of the optical disc.

[0007] The tilt detecting device for an optical disk of the present invention comprises means for projecting a polarized beam on the surface of the optical disk, and a polarized beam for separating an ordinary ray and an extraordinary ray from the polarized beam reflected by the optical disk. A splitter,
A photodetector that detects an ordinary ray separated by the polarizing beam splitter, and calculates a reflection angle of the ordinary ray reflected by the optical disk based on the ordinary ray detected by the photodetector, and calculates the reflection angle. A calculating unit for calculating a tilt angle of the surface of the optical disk based on Here, a quarter-wave plate is provided between the polarization beam splitter and the optical disk, wherein the polarization beam projected from the polarization beam projecting means onto the optical disk is circularly polarized light, and the circularly polarized light reflected on the optical disk is linearly polarized light. It may be arranged. Further, it is preferable that a spatial filter for limiting the beam diameter of the polarized beam projected from the polarized beam projecting means to the optical disc to be small is provided.

[0008]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing the configuration of the first embodiment of the present invention. Referring to FIG.
Are arranged so as to face the surface of the optical disc D to be detected. The tilt detecting device 1 has a HeNe laser light source 11, and forms a laser beam from a direction at an angle θ slightly tilted from a direction perpendicular to the surface of the optical disc D to form a laser beam. To project. Here, the laser light emitted from the laser light source 11 is linearly polarized as a P wave. Further, in the inclination detecting device 1, a polarization beam splitter 12 is disposed so as to straddle the optical path of the laser beam emitted from the laser light source 11 and the laser beam reflected by the optical disk. Then, a photodetector 13 is arranged on an optical path in which the reflected light from the optical disc D passes through the polarization beam splitter 12 and travels straight. The photodetector 13 has a light receiving surface 13 along a direction parallel to the radial direction of the optical disc D.
a and 13b are composed of two divided optical sensors,
The division line is set at the position where the center of the laser beam reflected when the surface inclination of the optical disk D is 0 degree is the same as the conventional configuration.

The photodetector 13 has an arithmetic unit 1
4 is connected to each light receiving surface 13 of the photodetector 13.
The outputs of a and 13b are amplified by taking the difference in the differential amplifier 15, the amplitude of the obtained difference signal is detected by the peak detector 16, and the center value of the amplitude is calculated by the calculator 17;
Based on the calculated value, the position detector 18 calculates the angle of the reflected laser light, and calculates the inclination of the optical disk from the calculated angle. Further, by detecting the center value temporally, the dynamic detector 19 calculates the rotation of the optical disc D and the tilt along the radial direction.

[0010] According to the tilt detecting device having this structure, the tilt detecting operation is performed while rotating the optical disc D and gradually moving the optical system portion of the tilt detecting device 1 particularly in the radial direction of the optical disc D. . That is, linearly polarized light of P wave is emitted from the laser light source 11 and is projected on the surface of the optical disk D through the polarization beam splitter 12. On the optical disc D, the projected laser beam is birefringent and is reflected as an ordinary ray and an extraordinary ray. At this time, an ordinary ray composed of the same P-wave linearly polarized light as the incident light, Is an extraordinary ray composed of linearly polarized S-waves whose polarization directions are orthogonal to each other. Therefore, when the laser beam reflected by the optical disk D passes through the polarizing beam splitter 12 in the reverse direction, the ordinary ray goes straight and reaches the photodetector 13 while the extraordinary ray is reflected. Thus, the light does not reach the photodetector 13. Therefore, the photodetector 13 can detect the reflected light only with the ordinary ray, and the deviation Δθ of the reflected light with respect to the original inclination θ of the optical axis.
Thus, the tilt angle Δθ / 2 of the optical disk can be detected. At this time, since the photodetector 13 is not affected by the extraordinary ray, the detection error due to the extraordinary ray is eliminated.

In the photodetector 13, the output of each of the two divided light receiving surfaces 13a and 13b becomes a beam displacement output by the differential amplifier 15, and the amplitude between peaks is determined by the peak detector 16.
And a dynamic displacement output in the radial direction of the optical disc is obtained. Further, by calculating the center of the amplitude between the peaks of the displacement output from the calculator 17, the inclination of the optical disc D during the rotational driving is calculated. Further, the dynamic tilt variation of the optical disk in the radial direction is calculated by using a ± value with respect to the output of the calculator 17 as a peak detection output.

FIG. 2 is a graph showing the dynamic tilt displacement in the radial direction of the optical disc and the tilt displacement with respect to the halfway length of the optical disc. The horizontal axis indicates the radius of the optical disk D, the vertical axis indicates the surface inclination of the optical disk D, the solid line indicates the average value of the surface inclination of the optical disk D during rotation, and the broken line indicates the maximum value of the dynamic inclination of the optical disk D. Indicates the minimum value.
This tilt is shown only for the tilt in the radial direction of the optical disk. In detecting this dynamic surface tilt,
Since detection errors due to extraordinary rays are eliminated, highly accurate detection is possible.

Here, in the configuration of FIG. 1, the photodetector 1
3 is composed of a two-divided optical sensor, the optical disk D
Is detected only in the radial direction of the optical disk. However, by using a four-division optical sensor divided in the radial direction and the tangential direction, it is possible to detect the angular change not only in the optical disk radial direction but also in the optical disk tangential direction. It is possible. Further, a one-dimensional position detection sensor (PSD) may be used instead of the two-divided optical sensor,
A two-dimensional position detection sensor may be used instead of the split optical sensor. When using this two-dimensional position detection sensor, as shown in FIG.
Signal from each end in the X and Y directions of
The detection signals in each direction are respectively supplied to differential amplifiers 15A and 15B.
By obtaining the differential signal, the optical axis position of the laser beam reflected by the optical disk can be detected, and the tilt of the optical disk in the radial and tangential directions can be detected.

FIG. 4 is a schematic view of a second embodiment of the present invention, in which parts equivalent to those of the first embodiment are denoted by the same reference numerals. In this embodiment, the HeNe laser light source 1
The linearly-polarized laser light emitted from No. 1 is converted into circularly-polarized light and projected onto an optical disk D. Based on the reflected laser light, a change in radial tilt and a dynamic tilt of the optical disk are performed in the same manner as in the first embodiment. Shows the tide of change. Here, in addition to the configuration of FIG. 1, a quarter-wave plate 20 is disposed on the optical disk side of the polarization beam splitter 12, and a photodetector 13 is disposed at a 90-degree reflection position of the polarization beam splitter 12. It is characterized by having.

According to this configuration, the laser light emitted from the laser light source 11 is linearly polarized light as a P wave, travels straight through the polarization beam splitter 12, becomes circularly polarized at the quarter wavelength slope 20, and becomes an optical disk D. Is projected to The reflected light becomes clockwise and counterclockwise circularly polarized light due to the effect of birefringence in the resin constituting the optical disc D. Each of the left-handed and right-handed circularly polarized light is returned to linearly polarized light when passing through the quarter-wave plate 20 in the opposite direction. At this time, in the case of an ordinary ray reflected on the optical disk D, the light is converted into S-polarized light when transmitted through the quarter-wave plate 20, and is reflected in the direction of 90 degrees by the polarization beam splitter 12 and detected by the photodetector 13. You. In the case of an extraordinary ray, the return light from the optical disc is converted into P-polarized light by the 板 wavelength plate 20.
The light goes straight through the polarizing beam splitter 12 and is excluded from the detection system.

Also in the second embodiment, the inclination of the optical disk D can be detected in the same manner as in the first embodiment. However, in this embodiment, since the laser light source 11 and the photodetector 13 can be disposed on the same optical axis equivalently, the laser light source 11 can be disposed on a line perpendicular to the surface of the optical disc D. It becomes possible to immediately detect θ / 2 as the inclination of the optical disc D from the reflection angle θ with respect to the angle 0 detected by the photodetector 13. Also in this embodiment, the photodetector 13 is a two-divided photosensor or a four-part photosensor.
It can be composed of a split optical sensor or a one-dimensional or two-dimensional position detecting sensor.

FIG. 5 is a plan view of a third embodiment in which the tilt detecting device of the present invention is made compact. Here, a small-sized semiconductor laser 11A is used as a laser light source, and a polarizing beam splitter 12 that transmits light emitted from the semiconductor laser 11A, and a light beam emitted from the polarizing beam splitter 12 is used as a parallel light beam. The collimator lens 21 and the collimator lens 21
Quarter-wave plate 2 for converting light emitted from the light into circularly polarized light
0, and a spatial filter 22 for limiting the beam diameter of the laser beam projected onto the optical disc D to a very small diameter. Further, a photodetector 13 composed of a two-divided photosensor is disposed opposite to the side surface of the polarization beam splitter 12, and the photodetector 13 includes a differential amplifier 1 of an arithmetic unit 14.
5 is connected.

Also in the third embodiment, the second
It is possible to detect the inclination of the optical disc D in the same manner as in the embodiment. In this embodiment, since the laser beam emitted from the semiconductor laser 11A is diffusive, it is converted into a parallel light beam by the collimator lens 21.
Further, in this embodiment, the light beam diameter of the laser beam projected on the optical disc D is limited by the spatial filter 22 because the inclination change between the inner peripheral limit position and the outer peripheral limit position of the optical disc D is measured. When the laser beam diameter is 5 mm, the inclination can be detected only in a range from a position 2.5 mm outward from the inner periphery of the optical disk to a position 2.5 mm inward from the outer periphery of the optical disk in principle. However, when the diameter of the collimated light is 1 mm, it is possible to detect the tilt of the optical disk from the inner and outer circumferences of the optical disk to a range of 0.5 mm from each.

[0019]

As described above, according to the present invention, a polarized beam is projected on an optical disk, and only the ordinary ray is selected from the light reflected by the optical disk and detected by a photodetector.
Since the tilt of the surface of the optical disk is calculated based on this detection result, the influence of the extraordinary ray on the reflected light from the optical disk can be eliminated, and the tilt of the optical disk can be accurately and accurately detected. Become. Also, it is possible to detect a static or dynamic tilt along the radial direction of the optical disk, and it is possible to detect the tilt of the actual optical disk in the driving state with high accuracy.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a first embodiment of the present invention.

FIG. 2 is a diagram showing a detection result of an inclination of an optical disc.

FIG. 3 is a circuit diagram when a position detection sensor is used as a photodetector.

FIG. 4 is a schematic configuration diagram of a second embodiment of the present invention.

FIG. 5 is a plan view of a third embodiment of the present invention.

FIG. 6 is a schematic configuration diagram of an example of a conventional detection device.

FIG. 7 is a diagram illustrating a conventional inclination detection result.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Tilt detector 11 HeNe laser light source 11A Semiconductor laser light source 12 Polarization beam splitter 13, 13A Photodetector 14 Operation part 15 Differential amplifier 16 Peak detector 17 Calculator 18 Tilt detector 19 Dynamic detector 20 1/4 wavelength plate 21 Collimator lens 22 Spatial filter

Claims (7)

[Claims] 1. A method of projecting a polarized light beam on a surface of an optical disc, detecting only ordinary rays of the polarized light beam reflected by the optical disc, and calculating a reflection angle of the detected ordinary rays on the optical disc; A method for detecting the inclination of the optical disk, wherein the inclination of the surface of the optical disk is calculated. 2. The method for detecting the tilt of an optical disk according to claim 1, wherein the tilt of the optical disk is detected while the optical disk is driven to rotate. 3. The method for detecting the tilt of an optical disk according to claim 1, wherein the tilt is detected while moving the projection position of the polarized beam in a radial direction of the optical disk. 4. A means for projecting a polarized beam onto the surface of an optical disk, a polarized beam splitter for separating an ordinary ray and an extraordinary ray from the polarized beam reflected by the optical disk, and a beam splitter separated by the polarized beam splitter. A photodetector for detecting the ordinary ray, and a reflection angle of the ordinary ray reflected on the optical disc based on the ordinary ray detected by the photodetector, and a surface of the optical disc based on the reflection angle. And an arithmetic unit for calculating an inclination angle of the optical disk. 5. The optical disc tilt detecting device according to claim 4, wherein the photodetector is constituted by an optical sensor having a light receiving surface divided into two or four, or a one-dimensional or two-dimensional position detecting sensor. 6. A quarter-wave plate for converting a polarized beam projected from the polarized beam projecting means to an optical disk into circularly polarized light and a circularly polarized light reflected from the optical disk into linearly polarized light, the light beam being transmitted between the polarizing beam splitter and the optical disk. 6. The optical disc tilt detecting device according to claim 4, wherein the tilt detecting device is arranged between the optical discs. 7. The optical disc tilt detecting device according to claim 4, further comprising a spatial filter that limits a beam diameter of a polarized beam projected from the polarized beam projecting means to the optical disc to a small diameter.