JP2001229571A - Diffraction grating, optical pickup, tilt detecting device and tilt detecting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tilt detecting method improving tilt detective precision of an optical disk. SOLUTION: This tilt detection method has a process S101 for diffracting a laser beam with a diffraction grating and for generating a 0-order diffracted beam and ±1st-order diffracted beams, a process S102 for emitting the 0-order diffracted beam and the ±1st-order diffracted beams to the track of the optical disk, processes S103, S104 for generating a regenerative signal according to the reflected light quantity of the ±1st-order diffracted beams reflected with the optical disk and a process S105 for detecting the tilt or the tilt angle of the optical disk based on a difference between the size of the fluctuation of the amplitude of the regenerative signal according to the reflected light quantity of the +1st-order diffracted beam and the size of the fluctuation of the amplitude of the regenerative signal according to the reflected light quantity of the -1st-order beam. Respective ±1st-order diffracted beams irradiating the optical disk are provided with a phase distribution equivalent to or virtually equivalent to the phase distribution by wave front aberration occurring on the optical disk in the case of that the tilt occurs on the optical disk.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diffraction grating, an optical pickup for irradiating an optical disk with laser light passing through the diffraction grating, a tilt detecting device for detecting the tilt of the optical disk, and a tilt detecting method.

[0002]

2. Description of the Related Art In an optical disk apparatus, if the optical disk has a tilt, the signal quality of a recording signal and / or a reproduction signal of the optical disk may be degraded. When correcting the tilt of the optical disk, it is necessary to detect the tilt of the optical disk and generate a signal corresponding to the tilt.

[0003] Japanese Patent Application Laid-Open No. 9-128785 discloses an invention of an optical pickup. This publication discloses that in an optical pickup having a laser light source, an objective lens, and a liquid crystal panel for correcting aberration, the refractive index of the liquid crystal panel is changed according to the thickness or tilt angle of the optical disk. . It is also disclosed that a tilt sensor detects a tilt angle, and a liquid crystal panel control circuit drives the liquid crystal panel to change the refractive index based on the tilt angle.

[0004]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Application Laid-Open No. 9-128 is disclosed.
In the optical pickup disclosed in Japanese Patent No. 785, there is a restriction on the position of the tilt sensor, and the laser light irradiation position on the optical disk is different from the detection position at which the tilt sensor detects the tilt, so that the tilt of the optical disk is accurately detected. It is difficult.

An object of the present invention is to provide a tilt detection device and a tilt detection method capable of improving the tilt detection accuracy of an optical disk, an optical pickup usable in the tilt detection device, a diffraction grating usable in the optical pickup, and Is to provide.

[0006]

According to the present invention, there is provided a diffraction grating for diffracting a laser beam to generate a zero-order diffracted light and a ± first-order diffracted light applied to an optical disk. Each of the second-order diffracted lights has a phase distribution equivalent or substantially equivalent to a phase distribution due to a wavefront aberration generated in the optical disc when the optical disc is tilted.

In the diffraction grating according to the present invention, preferably, the phase distribution of one of the ± 1st-order diffracted lights is a phase distribution generated when the tilt angle of the optical disk is a constant positive angle. The phase distribution of the other of the ± 1st-order diffracted lights is a phase distribution generated when the tilt angle of the optical disc is the negative constant angle.

In the diffraction grating according to the present invention, preferably, the wavefront aberration is a coma aberration generated on a transparent substrate of the optical disc, and the optical disc has a signal recorded by a change in reflectance or a pit.

An optical pickup according to the present invention comprises: a laser for outputting a laser beam; a diffraction grating for diffracting the laser beam from the laser to generate zero-order diffracted light and ± first-order diffracted light; An objective lens for converging the first-order diffracted light and irradiating the optical disc; and a photodetector for generating a signal corresponding to the ± first-order diffracted light reflected on the optical disc, wherein the ± 1 Each of the second-order diffracted lights has a phase distribution equivalent or substantially equivalent to a phase distribution due to a wavefront aberration generated in the optical disc when the optical disc is tilted.

In the optical pickup according to the present invention, preferably, the phase distribution of one of the ± 1st-order diffracted lights is:
A phase distribution that occurs when the tilt angle of the optical disc is a positive constant angle, and the phase distribution of the other of the ± 1st-order diffracted light is when the tilt angle of the optical disc is the negative constant angle. This is the phase distribution that occurs.

In the optical pickup according to the present invention, preferably, the wavefront aberration is a coma aberration generated on a transparent substrate of the optical disc, and the optical disc has a signal recorded by a change in reflectance or a pit.

A tilt detecting device according to the present invention comprises: a laser for outputting a laser beam; a diffraction grating for diffracting a laser beam from the laser to generate 0th-order diffracted light and ± 1st-order diffracted light; An objective lens for converging the ± 1st-order diffracted light to irradiate the track of the optical disc, a generating circuit for generating a reproduction signal corresponding to the reflected light amount of the ± 1st-order diffracted light reflected on the optical disc, and the + 1st-order diffracted light A detection circuit for detecting the inclination of the optical disk based on a difference between the magnitude of the variation of the amplitude of the reproduction signal according to the amount of reflected light of the optical disk and the magnitude of the variation of the amplitude of the reproduction signal according to the amount of reflection of the minus first-order diffracted light And each of the ± 1st-order diffracted lights applied to the optical disc has a position caused by a wavefront aberration generated in the optical disc when the optical disc is tilted. It has a distribution equivalent or substantially equivalent phase distribution.

In the tilt detecting device according to the present invention, preferably, the phase distribution of one of the ± 1st-order diffracted lights is:
A phase distribution that occurs when the tilt angle of the optical disc is a positive constant angle, and the phase distribution of the other of the ± 1st-order diffracted light is when the tilt angle of the optical disc is the negative constant angle. This is the phase distribution that occurs.

In the tilt detecting device according to the present invention, preferably, the wavefront aberration is a coma generated on a transparent substrate of the optical disk, and the optical disk has a signal recorded by a change in reflectance or a pit. .

In the tilt detecting device according to the present invention, preferably, the objective lens condenses the zero-order diffracted light and the ± first-order diffracted light and irradiates the same track.

In the tilt detecting method according to the present invention, a laser beam is diffracted to generate 0th-order diffracted light and ± 1st-order diffracted light,
Irradiating the generated 0th-order diffracted light and ± 1st-order diffracted light onto the track of the optical disc, generating a reproduction signal corresponding to the reflected light quantity of the ± 1st-order diffracted light reflected on the optical disc; Detecting the tilt of the optical disc based on the difference between the magnitude of the variation in the amplitude of the reproduction signal according to the reflected light amount of the folded light and the magnitude of the variation in the amplitude of the reproduction signal according to the reflected light amount of the -1st-order diffracted light. Wherein each of the ± 1st-order diffracted lights applied to the optical disc has a phase equivalent or substantially equivalent to a phase distribution due to wavefront aberration generated in the optical disc when the optical disc is tilted. Has a distribution.

In the tilt detecting method according to the present invention, preferably, the phase distribution of one of the ± 1st-order diffracted lights is:
A phase distribution that occurs when the tilt angle of the optical disc is a positive constant angle, and the phase distribution of the other of the ± 1st-order diffracted light is when the tilt angle of the optical disc is the negative constant angle. This is the phase distribution that occurs.

In the tilt detection method according to the present invention, preferably, the wavefront aberration is a coma aberration generated on a transparent substrate of the optical disc, and the optical disc has a signal recorded by a change in reflectance or a pit. .

The ± first-order diffracted light generated by the diffraction grating has a phase distribution equivalent to or substantially equivalent to the phase distribution due to the wavefront aberration generated in the optical disk when the optical disk is tilted. The magnitude of the fluctuation of the amplitude of the reproduction signal according to the amount of reflected light of one of the ± 1st-order diffracted lights becomes maximum when a predetermined tilt angle (θ) is generated, and becomes monotonous as the distance from the tilt angle (θ) increases Become smaller.
The magnitude of the fluctuation of the amplitude of the reproduction signal in accordance with the other reflected light amount of the ± 1st-order diffracted light becomes maximum when a predetermined tilt angle (−θ) is generated, and moves away from the tilt angle (−θ). Becomes monotonically smaller. The difference between the magnitudes of the amplitude fluctuations of these reproduction signals corresponds to the tilt angle of the optical disk. Even when the tilt angle of the optical disk is near 0 °, the tilt angle can be accurately detected, and the tilt angle of the optical disk can be detected. Detection accuracy can be improved.

[0020]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

The optical disk device generally has an optical pickup, and collects laser light output from a semiconductor laser in the optical pickup and irradiates the optical disk with a track. FIG. 1 is an explanatory diagram illustrating the relationship between the light intensity and the position of a light spot formed on an optical disk. FIG.
(A) is an explanatory view illustrating the relationship between the light intensity and the position when the optical disc has no tilt. FIG. 1 (B)
FIG. 4 is an explanatory diagram illustrating the relationship between the light intensity and the position when the optical disc has a tilt.

When the optical disc has a tilt,
The light intensity at the center of the light spot decreases, and side lobes are generated in an inclined direction. Also, due to the decrease in the center intensity of the light spot, the amplitude of the reproduced signal corresponding to the amount of reflected light is reduced, and the signal quality is reduced. This is because when laser light is incident on a transparent substrate (disk substrate) of a tilted optical disk, a spatial phase distribution, for example, a phase distribution due to wavefront aberration occurs in the laser light before passing through the transparent substrate and reaching the recording surface. This is because the light condensing performance of the light spot formed on the recording surface is reduced.

FIG. 2 is a characteristic diagram showing the variation of the amplitude of the reproduction signal (or the amplitude of the AC component of the reproduction signal) with respect to the tilt angle in the radial direction of the disk. The fluctuation of the amplitude of the reproduction signal becomes maximum when the optical disc has no tilt, that is, when the tilt angle is 0 degree, and monotonically decreases as the tilt angle (absolute value) of the optical disc increases.

From the characteristic diagram of FIG. 2, the tilt angle of the optical disk can be detected based on the fluctuation of the amplitude of the reproduction signal.
Since the linearity around 0 degree is not preferable and the sign of the amplitude is not inverted due to the positive / negative of the tilt angle of the optical disk, it cannot be said that it is sufficient for use as a signal corresponding to the tilt (tilt error signal).

Here, a phase distribution equivalent to or substantially equivalent to the phase distribution due to the wavefront aberration generated in the disk substrate is expressed by
By giving the laser light before entering the optical disc in advance, it is possible to laterally shift the magnitude of the fluctuation of the amplitude of the reproduction signal with respect to the tilt of the optical disc.

FIG. 3 shows the magnitude of the variation of the amplitude of the reproduction signal with respect to the tilt angle (or the AC component of the reproduction signal) when a phase distribution corresponding to the tilt angle of the optical disk of 1.0 degree is previously given to the laser beam. FIG. 6 is a characteristic diagram illustrating the magnitude of the amplitude of the above. Compared with the characteristic diagram of FIG. 2 corresponding to a case where no phase distribution is given (when a laser beam having a uniform phase distribution is used), the characteristic curve of FIG. When the tilt is -1.0 degrees and the tilt angle is -1.0 degrees, the fluctuation of the amplitude of the reproduced signal is maximum.

As described above, when the phase distribution corresponding to θ degrees is given to the laser beam in advance, a lateral shift corresponding to −θ degrees can be generated with respect to the fluctuation of the amplitude of the reproduction signal.
Therefore, for two laser beams having the same light intensity, one laser beam is given a phase distribution corresponding to θ degrees in advance, and the other laser beam is given a phase distribution corresponding to −θ degrees in advance.
The magnitude of the amplitude fluctuation of the reproduction signal obtained from each laser beam is as shown by the characteristic curves A1 and B1 in FIG.
Further, when the optical disc has no tilt, that is, when the tilt angle is 0 degree, the amplitude of the amplitude of each reproduction signal becomes equal.

Here, the difference between the magnitude of the amplitude fluctuation of the reproduction signal of the two laser beams (or the magnitude of the amplitude of the AC component of the reproduction signal) is obtained, and the error signal having good linearity is obtained. Can be obtained (see FIG. 4). In FIG. 4, the case where the value of the tilt error signal TS is 0 corresponds to the case where there is no tilt of the optical disk. Also, by increasing the value of θ, the range in which the tilt angle can be detected can be widened.

In order to detect the tilt of the optical disk as described above, a phase distribution equivalent to or substantially equivalent to the phase distribution generated by the tilt of the disk substrate in the disk radial direction is obtained by using a diffraction grating before entering the optical disk. To laser light.

In a conventional optical pickup, a laser beam is generated by passing a 0th-order diffracted beam generated by passing through a diffraction grating and ± 1 order.
The next-order diffracted light has a uniform or substantially uniform phase distribution in the traveling direction. The 0th-order diffracted light and ± 1st-order diffracted light simultaneously form one main light spot and two sub-light spots on the optical disk via the objective lens.

On the other hand, by forming the diffraction grating in a predetermined pattern, the 0th-order diffracted light has a uniform phase distribution, and the ± 1st-order diffracted light has a spatial phase distribution generated when passing through a positively or negatively inclined disk substrate. Can be given. As a result, through the objective lens, one main light spot when the optical disc has no tilt and two sub light spots equivalent or substantially equivalent to the case where the optical disc has a positive or negative tilt,
It is possible to form them simultaneously on an optical disc.

Here, by applying the computer generated hologram technology,
A laser beam having a uniform phase distribution perpendicularly incident on the screen, and a laser beam having a predetermined angle and azimuth with respect to the laser beam having the uniform phase distribution and having a positive or negative inclination. Laser light having a spatial phase distribution generated when passing through the substrate,
The interference fringes formed on the screen are obtained by an electronic computer. The angle and azimuth between the two laser beams are made to match the angle and azimuth between the 0th-order diffracted light and ± 1st-order diffracted light after passing through the diffraction grating when the optical pickup is used with a diffraction grating mounted thereon.

First, the phase distribution of the laser light passing through the tilted disk substrate is expressed by a mathematical formula. A description based on polynomial expansion of wavefront aberration is used in the mathematical expression. According to the polynomial expansion of the wavefront aberration, the wavefront aberration generated by the inclined transparent substrate is dominated by coma. This coma aberration Wc is represented by x
Is the position in the disk radial direction, and is expressed by the orthogonal coordinates (x, y) standardized by the pupil radius on the pupil plane of the objective lens.
It becomes like the following formula.

[0034]

Wc (x, y) = 2πW ₁₁ x + 2πW ₃₁ x (x ² + y ² ) + 2πW ₅₁ x (x ² + y ² ) ² .

In the above equation, W ₁₁ is a wavefront coefficient that determines the position of the light spot formed on the optical disk.
Since it does not affect the shape of the light spot, an arbitrary value can be selected. W ₃₁ and W ₅₁ are the coma aberration coefficients W ₃₁ (λ) and W normalized by the laser beam wavelength λ.
₅₁ (λ), and are represented by the following equations, respectively.

[0036]

W ₃₁ (λ) = {(n ² −1) n ² tNA ³ sin θcos θ} / {2λ (n ² −sin ² θ) ^5/2 }

[0037]

W ₅₁ (λ) = {(n ² −1) n ² tNA ⁵ (n ⁴ + 3n ² cos ² θ−5n ² sin ² θ +4 sin ² θ−sin ⁴ θ) sin θcos θ｝ / ｛8λ ^{(n 2 -sin 2 θ) 9/2} } ...

In the above equation, NA is the numerical aperture of the objective lens, λ is the laser wavelength from the laser light source, n is the refractive index of the disk substrate, t is the thickness of the disk substrate, θ Is a tilt angle indicating the inclination of the disk substrate. The material of the disk substrate is, for example, polycarbonate, and its refractive index is about 1.5.

The phase distribution Wd of the laser light incident on the laser light having a uniform phase while being inclined by the azimuth β and the angle α is:
When the position in the disk radial direction is x, and the coordinates are represented by orthogonal coordinates (x, y) normalized by the pupil radius r on the pupil plane of the objective lens, the following expression is obtained. The azimuth β is 0 degree in the radial direction (or x direction) and 90 degrees in the track direction.

[0040]

Wd (x, y) = {2πr (xcos β + ysin β) sin α} / λ

From the above, a laser beam having a phase distribution {Wc (x, y) + Wd (x, y)} when θ is a desired value and a laser beam having a uniform phase distribution perpendicularly incident on the screen And calculate the interference fringes generated by

FIG. 5 shows that θ = 1.0 degree, α = 0.2 degree, β
It is explanatory drawing which illustrates the interference fringe calculated at = 90 degrees.
NA = 0.6, λ = 650 nm, t = 0.6 m
m, n = 1.5, r = 2mm, W 11 = -2W 31/3-W
_51/2 . The ring in the figure corresponds to the pupil of the objective lens.

This interference fringe is represented by binary information of light and dark (light / dark ratio 1:
As 1), a desired diffraction grating can be obtained through a process of creating a photomask and forming a grating on a glass substrate using the created photomask. FIG. 6 is a configuration diagram illustrating a diffraction grating created based on the interference fringes of FIG. FIG. 6A is a top view of the diffraction grating 9,
FIG. 6B is a schematic cross-sectional view when the diffraction grating 9 is cut along the line C.

The diffraction grating 9 has undulating grooves 9B formed on a glass substrate 9A. The depth of the groove 9B is determined by the light amount ratio between the 0th-order diffracted light and the ± 1st-order diffracted light. The laser light that has passed through the diffraction grating 9 created as described above forms three light spots on the optical disk via the objective lens. The 0th-order diffracted light corresponds to the case where the optical disc has no tilt, and one of the ± 1st-order diffracted lights forms a light spot equivalent or substantially equivalent to the case where the disc has a positive tilt angle θ in the radial direction of the disc. The other of the first-order diffracted light forms a light spot equivalent or substantially equivalent to the case where there is a negative tilt angle (−θ) in the disk radial direction.

FIG. 7 is a schematic configuration diagram showing an optical pickup having the diffraction grating 9. This optical pickup 5
0 denotes a semiconductor laser 4, a collimator lens 5, a diffraction grating 9, a beam splitter 3, an objective lens 2, a condenser lens 6, a cylindrical lens 7, a photodetector 8, a lens holder 2H, Focusing actuator 2F
And a tracking actuator 2T.

The objective lens 2 is held by a lens holder 2H. The focusing actuator 2F is
Based on the drive signal Sfe, the lens holder 2H is moved in a focus direction perpendicular to the recording surface of the optical disc 80, and as a result, the objective lens 2 is moved in the focus direction.
The tracking actuator 2T moves the lens holder 2H in the radial direction of the optical disk 80 based on the drive signal Ste, and as a result, moves the objective lens 2 to the optical disk 80.
In the radial direction.

The semiconductor laser 4 outputs a linearly polarized laser beam based on the drive signal SL and supplies the laser beam to the collimator lens 5. The collimator lens 5 converts the laser light from the semiconductor laser 4 into parallel light and supplies the parallel light to the diffraction grating 9. The diffraction grating 9 separates the laser light from the collimator lens 5 into a main laser light composed of zero-order diffracted light and first and second sub-laser lights composed of ± first-order diffracted light. Laser light and first and second auxiliary laser light)
Is supplied to the beam splitter 3.

The beam splitter 3 passes the laser beam from the diffraction grating 9 and supplies it to the objective lens 2. The objective lens 2 condenses the laser light from the beam splitter 3 and supplies it to a track of an optical disk 80 having lands and / or grooves. The optical disk 80 is composed of, for example, a compact disk (CD), a digital video disk (DVD), a phase change optical disk (PD), and the like.

The objective lens 2 returns the laser beam reflected by the optical disk 80 to the beam splitter 3. The beam splitter 3 receives the laser beam from the objective lens 2, reflects and emits the entered laser beam, and supplies the laser beam to the condenser lens 6. The condenser lens 6 condenses the laser light from the beam splitter 3 and supplies it to a cylindrical lens (cylindrical lens) 7. The cylindrical lens 7 passes the laser light from the condenser lens 6 and supplies the laser light to the photodetector 8. The photodetector 8 receives laser light from the cylindrical lens 7 at a light receiving unit and generates output signals SA to SH.

FIG. 8 is a schematic configuration diagram showing a light receiving section of the photodetector 8 in FIG. The light detector 8 includes a main light receiving section 8S
0, and first and second sub-light receiving sections 8S1 and 8S2. The main light receiving section 8S0 includes two orthogonal dividing lines 8Sx.
It is equally divided into four by 0,8Sy0, and has four divided regions 8A to 8D. A main light spot MS is formed in the main light receiving portion 8S0 of FIG. 8 by (the reflected light of) the main laser light from the cylindrical lens 7.

The divided area 8A has an output signal SA corresponding to the light quantity (reflected light quantity) of the main laser beam supplied to the area 8A.
Generate The divided area 8B generates an output signal SB corresponding to the amount of main laser light supplied to the area 8B.
The divided area 8C generates an output signal SC corresponding to the amount of main laser light supplied to the area 8C. Division area 8D
Generates an output signal SD corresponding to the amount of main laser light supplied to the area 8D.

The direction of the generating line of the cylindrical lens 7 is
An angle of about 45 degrees or about 135 degrees with the direction of the dividing line 8Sx0 or 8Sy0 of S0. The main light receiving section 8 to which the main laser light reflected by the optical disk 80 is supplied
The dividing line 8Sy0 of S0 (or the dividing line 8Sx0) is parallel or substantially parallel to the track direction of the optical disk 80. The intersection of the dividing lines 8Sx0, 8Sy0 is located at the center or substantially the center of the main laser beam passing through the cylindrical lens 7.

Since the shape of the beam spot MS formed in the main light receiving portion 8S0 changes diagonally according to the distance between the optical disk 80 and the objective lens 2, the divided regions 8A to 8A
Based on the output signals SA to SD generated by D, it is possible to detect the defocus on the optical disk 80 by the astigmatism method.
The direction in which the light receiving units 8S0 to 8S2 are arranged and the dividing line 8Sx
The angle formed by 0 coincides or substantially coincides with the azimuth β.

The first sub-light receiving section 8S1 has a dividing line 8Sy1.
, And the two divided areas 8G, 8H
Having. In the first sub-light receiving portion 8S1 of FIG. 8, a sub-light spot SS1 is formed by (the reflected light of) the first sub-laser light from the cylindrical lens 7. The divided area 8G generates an output signal SG corresponding to the light amount (reflected light amount) of the sub laser light supplied to the area 8G. The divided area 8H generates an output signal SH corresponding to the amount of sub-laser light supplied to the area 8H. The central portion of the first sub-light receiving portion 8S1 is
The first sub-laser beam that has passed through the cylindrical lens 7 is located at or near the center.

The second sub light receiving portion 8S2 is provided with a dividing line 8Sy2.
, And the two divided areas 8E and 8F
Having. In the second sub-light receiving portion 8S2 of FIG. 8, a sub-light spot SS2 is formed by (the reflected light of) the second sub-laser light from the cylindrical lens 7. The divided region 8E generates an output signal SE corresponding to the light amount (reflected light amount) of the sub laser beam supplied to the region 8E. The divided area 8F generates an output signal SF according to the amount of laser light supplied to the area 8F. The center of the second sub-light receiving section 8S2 is located at or substantially at the center of the second sub-laser light that has passed through the cylindrical lens 7. The dividing lines 8Sy0 to 8Sy2 are parallel or substantially parallel to each other.

FIG. 9 is an explanatory diagram showing the arrangement of light spots on the recording surface of the optical disk. In the figure, vertically long pits P are arranged in a vertical direction in a track direction perpendicular to the disk radial direction (radial direction), and signals are recorded by the pits P. Note that the pits P may be embossed pits on an optical disc such as a CD, or may be pits corresponding to a change in reflectivity on a phase change optical disc.

On the recording surface of the optical disk 80, a main light spot MB formed by a main laser beam having a large light amount, and first and second sub light spots L1 and L2 formed by first and second sub laser beams having a small light amount are provided. Is formed. The first sub-light spot L1 is a spot L10 corresponding to the main lobe.
And a spot L11 corresponding to a side lobe. The second sub-light spot L2 has a spot L20 corresponding to a main lobe and a spot L21 corresponding to a side lobe.

The main laser light is reflected by the main light spot MB and supplied to the main light receiving section 8S0 of the photodetector 8. The first sub-laser light is reflected by the first sub-light spot L1 and supplied to the first sub-light receiving section 8S1 of the photodetector 8. Spot L
The central portion of the sub-laser light reflected by the first sub-light receiving portion 8
It is located at the center or substantially the center of S1. The second sub-laser light is reflected by the second sub-light spot L2 and supplied to the second sub-light receiving section 8S2 of the photodetector 8. The center of the sub laser beam reflected by the spot L2 is located at the center or substantially the center of the second sub light receiving section 8S2.

It is desirable that the first and second sub-light spots are accurately located on the same track or another track when the main light spot MB is on a desired track. The center of the first and second sub-light spots is located at the center of the same track or the center of another track when the center of the main light spot MB is at the center of a desired track. It is desirable. Note that the distance from the main light spot to the two sub light spots is equal, and this distance is determined by the angle α described above.

The diffraction grating 9 in the optical pickup 50
Is determined in advance so that the azimuth β of the sub-light spot with respect to the radial direction of the disk is such that two sub-light spots are located on the target track. To adjust the position of the two sub-light spots, the diffraction grating 9 is rotated to a predetermined rotation angle to arrange the spots on a desired track. At this time, it is desirable to finely adjust the rotation angle so that the fluctuation of the amplitude of each reproduction signal corresponding to the two sub-light spots is maximized.

In particular, the azimuth β is 90 degrees or substantially 90 degrees.
By arranging two sub-light spots on the same track as the main light spot, the influence of signal variations between tracks can be suppressed, and the amplitude of the reproduced signal can be reduced even when the tracks meander. Fluctuations can be detected stably. FIG. 10 illustrates an explanatory diagram showing the arrangement of light spots on the recording surface of the optical disk when the azimuth β = 90 degrees.

FIG. 11 is an explanatory diagram showing a waveform of a reproduced signal corresponding to two sub-laser lights, and an explanatory diagram showing a method of generating the tilt error signal TS. A signal Sa indicating the magnitude of the amplitude of the AC component of the reproduction signal obtained from the first sub-laser light, and a signal Sb indicating the amplitude of the AC component of the reproduction signal obtained from the second sub-laser light (or , A signal S obtained by subtracting the DC component of the reproduction signal from the reproduction signal.
a, Sb), the tilt error signal TS (1) is given by the following equation.

[0063]

## EQU5 ## TS (1) = Sa-Sb ...

Assuming that the DC component of the reproduction signal obtained from the first sub-laser beam is DCa and the DC component of the reproduction signal obtained from the second sub-laser beam is DCb, the normalized tilt error signal TS (2 ) Is represented by the following equation. By using the tilt error signal TS (2), a signal value obtained by correcting or correcting the difference in light intensity between the two sub laser beams can be obtained, and the reliability of tilt detection can be improved.

[0065]

TS (2) = Sa / DCa−Sb / DCb

FIG. 12 is an explanatory diagram exemplifying the relationship between the signals Sa and Sb indicating the magnitude of the amplitude of the AC component of the reproduced signal obtained from the first and second sub-laser beams, and the tilt error signal TS. FIG. 6 is a characteristic diagram when there is no tracking error (detrack). In FIG. 12, the values of the parameters are represented by θ = 0.7 degrees, α = 0.2 degrees, β = 90 degrees, N
A = 0.6, λ = 650 nm, t = 0.6 mm, n =
1.5, r = 2mm, and a _{W 11 = -2W 31/3-} W 51/2.

The signal Sa has the maximum value when the tilt angle in the radial direction of the disk is about -0.7 degrees, and monotonically decreases as the tilt angle increases. The signal Sb is
The maximum value is obtained when the tilt angle in the radial direction of the disk is about +0.7 degrees, and monotonically decreases as the tilt angle decreases. In FIG. 12, the tilt error signal TS = Sa
−Sb, and when the tilt angle is 0 degree, the signal value is 0, which has good linearity. Further, the sign is inverted according to the positive / negative of the tilt angle, and preferable characteristics are obtained.

FIG. 13 is an explanatory diagram illustrating the relationship between the signals Sa and Sb indicating the magnitude of the amplitude of the AC component of the reproduced signal obtained from the first and second sub-laser beams and the tilt error signal TS. FIG. 4 is a characteristic diagram when there is a detrack. The detrack amount is 0.05 μm.

As shown in FIG. 13, the tilt error signal TS
According to the above, good characteristics can be obtained even when detrack exists. As described above, according to the tilt detection method described in the present embodiment, a good tilt error signal corresponding to the tilt of the optical disk can be obtained regardless of the presence or absence of detrack, and the tilt angle around 0 degree can be obtained. Detection accuracy can be improved.

Incidentally, the light receiving sections 8S0 to 8S8 of the photodetector 8
S2 is a dividing line 8Sy0 to 8Sy parallel to the track direction.
It is divided by two. Therefore, the light receiving sections 8S0 to 8S0
A push-pull signal can be generated from the output signal of 8S2. Using the output signals SA to SD of the main light receiving section 8S0, the push-pull signal PP0 of the main laser light is
= SA + SB- (SC + SD), and this push-pull signal PP0 can be used as the tracking error signal TE.

The output signals SG, S of the first sub-light receiving section 8S1
H, the push-pull signal PP of the first sub laser beam
1 can be obtained, and the push-pull signal PP2 of the second sub laser beam can be obtained using the output signals SE and SF of the second sub light receiving section 8S2. The generation circuit 70 can detect the states of the optical pickup 50, the optical disk 80, and the like by performing various calculations based on the push-pull signals PP0 to PP2 and the like.

FIG. 14 shows the optical pickup 50 shown in FIG.
1 is a schematic block diagram showing an embodiment of an optical disk device having a suffix (a). The optical disk device 90 includes a motor 30, a motor drive circuit 35, a compensation circuit 40, an amplifier circuit 42, an optical pickup 50, an amplifier circuit (head amplifier) 52, a laser drive circuit 55, a generation circuit 6
0, an information detection circuit 65, a tilt detection circuit 66, and a control circuit 70. The optical disk device 90 reproduces the recorded information recorded on the optical disk 80.

The optical disk device 90 has a tilt detection device 95. The tilt detection device 95 includes a compensation circuit 40, an amplification circuit 42, an optical pickup 50, an amplification circuit 52, a laser drive circuit 55, and a generation circuit 60.
, An information detection circuit 65, a tilt detection circuit 66, and a control circuit 70.

The control circuit 70 is a controller that controls the entire optical disk device 90, and is composed of, for example, a microcomputer. The control circuit 70 controls the motor 30, the motor drive circuit 35, the laser drive circuit 55, the optical pickup 50, the compensation circuit 40, the generation circuit 60, the information detection circuit 65, the tilt detection circuit 66, and the like.

The optical pickup 50 irradiates a laser beam LB to a reproduction position of the optical disk 80 during reproduction. The laser drive circuit 55 generates a drive signal SL under the control of the control circuit 70, drives the semiconductor laser 4 in the optical pickup 50 with the drive signal SL, and causes the semiconductor laser 4 to output laser light LB.

The motor 30 is constituted by, for example, a spindle motor, and rotates the optical disk 80 at a predetermined rotation speed. The motor 30 rotates the optical disk 80 so that the linear velocity becomes constant, for example.

The motor drive circuit 35 supplies drive power to the motor 30 to drive the motor 30. The motor drive circuit 35 may perform rotation control of the motor 30 by PWM (Pulse Width Modulation) control, and may perform PLL (Ph
Rotation control may be performed by ase Locked Loop) control.

The amplification circuit 52 amplifies the output signals SA to SH of the respective light receiving units of the photodetector 8 included in the optical pickup 50 and supplies the amplified signals to the generation circuit 60.

The generation circuit 60 generates a reproduction signal RF corresponding to the light amount of the main laser light and a reproduction signal RF corresponding to the light amount of the first sub-laser light based on the amplified output signals SA to SH from the amplifier circuit 52. A signal RF1, a reproduction signal RF2 corresponding to the light amount of the second sub-laser light, a focus error signal FE,
The tracking error signal TE and the push-pull signal PP0
To PP2.

The generation circuit 60 includes, for example, the amplification circuit 5
2 (SA + SB + S)
C + SD) to generate a reproduction signal RF. Also,
The sum of the output signals SG and SH from the amplifier circuit 52 (SG
+ SH) to generate the reproduction signal RF1. Also,
The sum of the output signals SE and SF from the amplifier circuit 52 (SE
+ SF) to generate a reproduction signal RF2.

Further, the generation circuit 60 outputs, for example, a diagonal difference (SA + D) of the output signals SA to SD from the amplification circuit 52.
SC-SB-SD) to generate a focus error signal FE by an astigmatism method. Note that the generation circuit 60
Push-pull signal PP0 (= SA + SB-SC-SD)
And the push-pull signal PP0 is used as the tracking error signal TE, the push-pull signals PP1 and PP2 are generated, and these signals PP0 to PP2 are supplied to the control circuit 70.

The compensating circuit 40 calculates the focus error signal FE
A compensation signal is generated by compensating for the tracking error signal TE (phase compensation and / or frequency compensation), and supplies the compensation signal to the amplifier circuit.

The amplifying circuit 42 outputs the focus error signal FE
Is supplied to the focusing actuator 2F in the optical pickup 50. Further, the amplifier circuit 42 outputs the tracking error signal TE
Is supplied to the tracking actuator 2T in the optical pickup 50.

The tilt detection circuit 66 outputs the reproduced signals RF1,
Detecting the magnitudes Sa and Sb of the amplitude of the AC component of RF2,
The tilt or the tilt angle is detected based on the magnitudes Sa and Sb. Specifically, a tilt error signal TS corresponding to the tilt angle is generated based on the difference between the magnitudes Sa and Sb. This tilt error signal TS is a signal TS that is not normalized.
The normalized signal TS (2) is more preferable than (1). The tilt detection circuit 66 supplies the tilt error signal TS to the control circuit 70.

The information detection circuit 65 receives the reproduction signal RF from the generation circuit 60, demodulates the reproduction signal RF, reproduces the recorded information on the optical disk 80, and outputs the reproduced recorded information as an output signal So. The information detection circuit 6
5 detects the address of the optical disk 80 from the reproduction signal RF and reproduces the recorded information based on the address.

Incidentally, a tilt correction mechanism for correcting the tilt of the optical disk 80 may be provided in the optical disk device 90, and the control circuit 70 may control the tilt correction mechanism based on the tilt error signal TS.

For example, the control circuit 70 controls the tilt correction mechanism of the optical disc 80 in an open loop based on the tilt error signal TS. In addition, the tilt correction mechanism can be controlled in a closed loop so that the tilt error signal TS becomes zero. It is not necessary to obtain the reproduction signals RF1 and RF2 from the entire recording surface of the optical disk 80. The reproduction signals RF1 and RF2 are detected from the pits in the address area of the writable optical disk or the rewritable optical disk, and the reproduction signals RF1 and RF2 are detected. It is also possible to detect the tilt error signal TS based on this, and the tilt correction mechanism may be controlled by the tilt error signal TS.

FIG. 15 is a schematic flowchart showing a detection method for detecting the tilt of the optical disk 80 in the disk radial direction in the tilt detection device 95 in the optical disk device 90.

First, in step S101, the diffraction grating 9 in the optical pickup 50 diffracts the laser light from the semiconductor laser 4 and outputs the main laser light composed of the zero-order diffracted light to ±
The first and second sub-laser lights composed of the first-order diffracted light are generated. The first and second sub-laser beams are transmitted to the optical disk 8
0 when the optical disk 80 is tilted.
Has a phase distribution equivalent to or substantially equivalent to the phase distribution due to the wavefront aberration generated in. These laser beams (main laser beam and first and second sub-laser beams) are supplied to the objective lens 2 via the beam splitter 3.

In step S102, the objective lens 2
The laser beam (main laser beam and first and second sub-laser beams) from the diffraction grating 9 is condensed to irradiate the track of the optical disk 80. The laser light condensed by the objective lens 2 is reflected by the optical disc 80 and
Again, and is supplied to the photodetector 8 through the beam splitter 3, the condenser lens 6, and the cylindrical lens 7.

In step S103, the photodetector 8 receives the main laser beam and the first and second sub-laser beams reflected by the optical disk 80 by the light receiving sections 8S0 to 8S2 to generate output signals SA to SH. These output signals SA to
The SH is supplied to the generation circuit 60 via the amplification circuit (head amplifier) 52.

In step S104, the generation circuit 60
Based on the output signals SA to SH, reproduction signals RF, RF1, and RF2 corresponding to the amounts of reflected main laser light and first and second sub-laser lights are generated.

In step S105, the tilt detection circuit 6
6 is the magnitude of the amplitude fluctuation (or the reproduction signal R2) of the reproduction signals RF1 and RF2 corresponding to the first and second auxiliary laser beams.
The amplitudes Sa and Sb of the AC components of F1 and RF2 are detected, and the tilt or tilt angle of the optical disk 80 is detected based on the difference between the magnitudes Sa and Sb. Specifically, the difference (Sa−Sb or S−Sb) between the amplitudes Sa and Sb of the amplitude of the AC component between the two reproduction signals RF1 and RF2.
a / DCa-Sb / DCb), the optical disk 80
The tilt error signal TS corresponding to the tilt angle is generated.
The above embodiment is an exemplification of the present invention, and the present invention is not limited to the above embodiment.

[0094]

As described above, according to the present invention, according to the present invention, a tilt detecting device and a tilt detecting method capable of improving the accuracy of detecting a tilt of an optical disk, an optical pickup usable in the tilt detecting device, A diffraction grating usable in an optical pickup can be provided.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating a relationship between a light intensity and a position of a light spot formed on an optical disc.

FIG. 2 is a characteristic diagram showing a change in amplitude of a reproduction signal with respect to a tilt angle in a disk radial direction.

FIG. 3 is a characteristic diagram illustrating the magnitude of fluctuation of the amplitude of a reproduction signal with respect to a tilt angle when a phase distribution corresponding to a tilt angle of an optical disc of 1.0 degree is given to laser light in advance.

FIG. 4 shows magnitudes A1 and B1 of fluctuations in amplitude of a reproduction signal,
FIG. 4 is an explanatory diagram illustrating a relationship with a tilt error signal TS.

FIG. 5 is an explanatory diagram illustrating an interference fringe calculated using a computer generated hologram technique;

FIG. 6 is a configuration diagram illustrating a diffraction grating created based on the interference fringes of FIG. 5;

FIG. 7 is a schematic configuration diagram illustrating an optical pickup having the diffraction grating 9 of FIG. 6;

8 is a schematic configuration diagram illustrating a light receiving unit of the photodetector 8 in FIG.

FIG. 9 is a first explanatory diagram illustrating the arrangement of light spots on a recording surface of an optical disc.

FIG. 10 is a second explanatory diagram exemplifying an arrangement of light spots on a recording surface of an optical disc, and is a diagram illustrating a case where an azimuth β is 90 degrees.

FIG. 11 is an explanatory diagram showing waveforms of a reproduction signal corresponding to two sub laser beams.

FIG. 12 shows signals Sa and Sb indicating the magnitude of the fluctuation of the amplitude of the reproduction signal obtained from the first and second sub-laser lights,
FIG. 7 is a first explanatory diagram illustrating a relationship with a tilt error signal TS, and is an explanatory diagram when there is no detrack.

FIG. 13 shows signals Sa and Sb indicating the magnitude of the fluctuation of the amplitude of the reproduction signal obtained from the first and second sub laser beams,
FIG. 10 is a second explanatory diagram illustrating a relationship with the tilt error signal TS, and is an explanatory diagram when there is a detrack.

14 is a schematic block diagram showing an embodiment of an optical disk device having the optical pickup 50 shown in FIG. 7, and a schematic block diagram showing an embodiment of a tilt detection device.

15 is a schematic flowchart showing a tilt detection method for detecting a tilt of the optical disc 80 in the tilt detection device of FIG.

[Explanation of symbols]

2 ... Objective lens, 2F ... Focusing actuator, 2H ... Lens holder, 2T ... Tracking actuator, 3 ... Beam splitter, 4 ... Semiconductor laser (laser), 5 ... Collimator lens, 6 ... Condenser lens,
7 ... Cylindrical lens, 8 ... Photodetector, 8S0 ... Main light receiving section, 8
S1: first sub-light receiving portion, 8S2: second sub-light receiving portion, 8S
x0, 8Sy0 to 8Sy2: dividing line, 9: diffraction grating, 3
0 ... motor, 35 ... motor drive circuit, 40 ... compensation circuit,
42 ... amplifier circuit, 50 ... optical pickup, 52 ... amplifier circuit (head amplifier), 55 ... laser drive circuit, 60 ... generation circuit, 65 ... information detection circuit, 66 ... tilt detection circuit (detection circuit), 70 ... control circuit , 80 ... optical disk, 9
0: optical disk device, 95: tilt detection device, DCa,
DCb: DC component of reproduction signal, FE: Focus error signal, L1, L2, SS1, SS2: Sub-light spot, LB
… Laser light, MB, MS… Main light spot, P… Pit,
PP0 to PP2: push-pull signal, RF, RF1, R
F2: reproduction signal, TE: tracking error signal, TS:
Tilt error signal, β ... azimuth.

Claims (13)

[Claims] 1. A diffraction grating for generating zero-order diffracted light and ± 1st-order diffracted light irradiated on an optical disc by diffracting a laser beam, wherein each of the ± 1st-order diffracted lights causes a tilt on the optical disc. A diffraction grating having a phase distribution equivalent to or substantially equivalent to a phase distribution due to wavefront aberration generated in the optical disc in the above case. 2. The phase distribution included in one of the ± 1st-order diffracted lights is a phase distribution generated when the tilt angle of the optical disc is a constant positive angle, and the phase distribution included in the other of the ± 1st-order diffracted lights is included. 2. The diffraction grating according to claim 1, wherein the phase distribution is a phase distribution generated when a tilt angle of the optical disc is the negative constant angle. 3. The diffraction grating according to claim 1, wherein the wavefront aberration is a coma generated on a transparent substrate of the optical disk, and the optical disk has a signal recorded by a change in reflectance or a pit. 4. A laser for outputting a laser beam, a diffraction grating for diffracting a laser beam from the laser to generate a 0th-order diffracted light and a ± 1st-order diffracted light, and condensing the 0th-order diffracted light and the ± 1st-order diffracted light. An objective lens for irradiating the optical disc with the optical disc, and a photodetector for generating a signal corresponding to the ± 1st-order diffracted light reflected by the optical disc, wherein each of the ± 1st-order diffracted lights applied to the optical disc is An optical pickup having a phase distribution equivalent to or substantially equivalent to a phase distribution due to wavefront aberration generated in the optical disk when the optical disk is tilted. 5. The phase distribution of one of the ± 1st-order diffracted lights is a phase distribution generated when a tilt angle of the optical disc is a constant positive angle, and the other of the ± 1st-order diffracted lights has 5. The optical pickup according to claim 4, wherein the phase distribution is a phase distribution generated when the tilt angle of the optical disc is the negative constant angle. 6. The optical pickup according to claim 4, wherein the wavefront aberration is coma aberration generated on a transparent substrate of the optical disk, and the optical disk has a signal recorded by a change in reflectance or a pit. 7. A laser for outputting a laser beam, a diffraction grating for diffracting a laser beam from the laser to generate a 0th-order diffracted light and ± 1st-order diffracted light, and condensing the 0th-order diffracted light and ± 1st-order diffracted light. An objective lens for irradiating a track of an optical disc, and a generating circuit for generating a reproduction signal corresponding to the reflected light quantity of the ± first-order diffracted light reflected by the optical disc; A detection circuit for detecting an inclination of the optical disc based on a difference between a magnitude of a variation in the amplitude of the signal and a magnitude of a variation in the amplitude of the reproduction signal in accordance with the reflected light amount of the -1st-order diffracted light; Each of the ± 1st-order diffracted lights applied to the optical disk is equivalent to or substantially equal to a phase distribution due to wavefront aberration generated in the optical disk when the optical disk is tilted. A tilt detection device having a valuable phase distribution. 8. The phase distribution of one of the ± 1st-order diffracted lights is a phase distribution generated when a tilt angle of the optical disk is a constant positive angle, and the other of the ± 1st-order diffracted lights is The tilt detection device according to claim 7, wherein the phase distribution is a phase distribution generated when a tilt angle of the optical disc is the negative constant angle. 9. The tilt detection device according to claim 7, wherein the wavefront aberration is a coma aberration generated on a transparent substrate of the optical disk, and the optical disk has a signal recorded by a change in reflectance or a pit. 10. The tilt detecting apparatus according to claim 7, wherein the objective lens condenses the 0th-order diffracted light and ± 1st-order diffracted light and irradiates the same track. 11. A step of diffracting a laser beam to generate 0th-order diffracted light and ± 1st-order diffracted light, and irradiating the generated 0th-order diffracted light and ± 1st-order diffracted light to a track of an optical disc; Generating a reproduction signal corresponding to the reflected light amount of the ± 1st-order diffracted light, and varying the magnitude of the amplitude of the reproduction signal according to the reflected light amount of the + 1st-order diffracted light, and the reflected light amount of the −1st-order diffracted light. Detecting the tilt of the optical disc based on the difference between the amplitude of the amplitude of the reproduced signal and the magnitude of the fluctuation of the amplitude of the reproduced signal. Each of the ± 1st-order diffracted lights applied to the optical disc has a tilt on the optical disc. A tilt detection method having a phase distribution equivalent to or substantially equivalent to a phase distribution due to a wavefront aberration generated in the optical disc when the optical disc is present. 12. The phase distribution of one of the ± 1st-order diffracted lights is a phase distribution generated when the tilt angle of the optical disc is a constant positive angle, and the phase distribution of the other of the ± 1st-order diffracted lights is The tilt detection method according to claim 11, wherein the phase distribution is a phase distribution generated when the tilt angle of the optical disc is the negative constant angle. 13. The tilt detecting method according to claim 11, wherein the wavefront aberration is a coma aberration generated on a transparent substrate of the optical disk, and the optical disk has a signal recorded by a change in reflectance or a pit.