JP2001250250A - Optical pickup and tracking servo method - Google Patents

Abstract

(57) [Problem] In a tracking error signal detection method using a push-pull signal of a main beam and a sub beam, an offset generated by an objective lens shift or a disc tilt can be reduced without lowering the light use efficiency. Provide a way to cancel at cost. SOLUTION: A laser beam emitted from a semiconductor laser 1 is converted into a parallel beam by a collimator lens 2, and a main beam 30 and a sub beam (+ 1st-order beam) are output by a grating 3.
31 and a sub-beam (-1st order light) 32. After passing through the beam splitter 4, the light is focused on the track 61 of the optical disc 6 by the objective lens 5, the reflected light is reflected by the beam splitter 4 via the objective lens 5, and the light is detected by the light detector 8 ( 8A, 8B, 8C).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical pickup for optically recording and reproducing information on an information recording medium such as an optical disk or an optical card. The present invention also relates to a tracking servo method for easily and inexpensively correcting an offset generated in a tracking error signal.

[0002]

2. Description of the Related Art In recent years, optical discs are capable of recording a large amount of information signals at high density, and have been used in many fields such as audio, video, and computers. In particular, recently, the amount of data handled by computers and the like, such as video information, has increased dramatically.
Along with this, the capacity of optical disks has been increased by reducing recording pits and track pitches.

In the above-mentioned information recording medium, it is necessary to accurately track a light beam with respect to an information track in order to reproduce an information signal recorded in units of microns. Various methods are known as a method for detecting a tracking error signal (TES), and the push-pull method is known as the simplest method.

[0004] The detection principle and problems of the push-pull method will be described below. The focused beam from the objective lens
When the light is reflected at a track (or pit) forming portion on the optical disk, a diffraction pattern appears in the reflected light.

A method of calculating the tracking error signal by detecting the left-right symmetry of the intensity distribution of the far field pattern of the reflected light on the lens pupil plane is called a push-pull method.

[0006] For example, as shown in FIG.
Is converted into parallel light by the collimator lens 2, passes through the beam splitter 4, and is condensed on the track 61 of the recording medium 6 by the objective lens 5, and reflected light passes through the objective lens 5. The light is reflected by the beam splitter 4 and has a dividing line in the track direction by the condenser lens 2.
The signal is guided to the division detector 11, and the signal of each section is differentially detected to obtain a push-pull signal.

Here, as shown in FIG. 27, when the light beam is at the center of the track, the far field pattern has the same brightness on the left and right, and the differential signal of the two-segment photodetector becomes zero ( On-track state).

[0008] When the track is deviated from the center of the track, the left-right symmetry of the intensity distribution of the far field pattern is destroyed in accordance with the amount thereof, so that a push-pull signal (tracking error signal) as shown in FIG. 27 is obtained.

However, as shown in FIG. 28A, when tracking servo is performed with the objective lens 5 moved, the far field pattern of the beam on the two-divided photodetector 11 also moves, so that TES is turned on. A TES offset occurs regardless of the track state.

Also, as shown in FIG. 28B, when the recording medium 6 is tilted, the beam moves on the two-segment photodetector 11, so that a TES offset occurs.

(Conventional Example 1) As a method of canceling this offset, a method using a plurality of beams (Differential Push Pull (DPP)) is used.
Pull) method) is described in Japanese Patent Publication No. 4-34212.

This will be described with reference to FIG.
The light emitted from the light source 1 is divided into three beams by the grating 3, and as shown in FIG. 30A, the main beam 30, the + first order light 31 of the sub beam, and the -1 of the sub beam in the tangential direction of the track on the optical disk 6. The next light 32 is arranged.

At this time, the respective sub beams 31 and 32
Is 1 / to the track where the main beam 30 converges.
It is formed shifted in the radial direction by two track pitches.

Then, as shown in FIG. 30B, the far-field patterns of the reflected light of the main beam 30 and the sub-beams 31 and 32 are divided by two photodetectors 8A, 8B and 8C each having a dividing line in the track direction. Receive light.

Each of the two split photodetectors 8A, 8B, 8C
, Ie, push-pull signals PP30, PP
31 and PP32. As shown in FIG. 31, the push-pull signals PP31 and PP32 of the sub beam (+1 order light) 31 and the sub beam (−1 order light) 32 are the main beam 3
0, the push-pull signal P30 of the main beam 30
Is 180 ° out of phase (opposite phase).

On the other hand, the phase of the TES caused by the shift of the objective lens and the tilt of the disk shown in FIG. Therefore, by performing the calculation of PP = PP30−k (PP31 + PP32) (1), the push-pull signal canceling the offset can be detected.

Here, the coefficient k is 0th-order light 30 and + 1st-order light 3
This is for correcting the difference between the light intensities of the first and −1st order light 32, and the intensity ratio is 0th order light: + 1st order light: −1st order light = a:
b: If b, the coefficient k = a / (2b).

However, in this DPP method, since it is necessary to dispose the sub beam with respect to the main beam by exactly 1/2 track pitch in the radial direction of the disc, a plurality of types of optical discs having different track pitches are used. This is a problem when reproducing with two optical pickups.

Further, it is necessary to precisely rotate the grating or the like during assembly adjustment. Further, there is a structural restriction that the moving position of the objective lens must always be on the center line (radial direction) of the optical disk.
There is a disadvantage that it cannot be used for a swing arm type optical pickup.

(Conventional Example 2) As means for solving this,
Japanese Patent Application Laid-Open No. 9-81942 proposes a tracking error detection method in which the occurrence of offset is small and the dependency of detection sensitivity on the track interval is small.

This method will be described with reference to FIG. The point that the light emitted from the laser diode 1 is split into three beams by the grating 3 and condensed by the objective lens 5 is the same as that of the above-described conventional example 1, but the groove structure of the grating 3 is And different.

As shown in FIG. 33, the groove of the grating 3 has a phase difference of 180 ° in the periodic structure in two regions 3a and 3b in the radial direction divided by the dividing line in the track direction (y direction). I have.

As a result, in the sub beams 31 and 32 diffracted by the grooves, a phase difference of 180 ° occurs in the two semicircular regions divided by the dividing line in the track direction. The spot where this beam is focused on the optical disk 6 by the objective lens 5 has a shape composed of two elliptical sub-spots as shown in FIG.

As shown in FIG. 35, the push-pull signal PP310 of the sub-beams 31 and 32 has a phase difference of 180 ° compared to the push-pull signal P30 of the beam (corresponding to the main beam) when no phase difference is added. different.

Therefore, as shown in FIG. 34, even if the sub beams 31 and 32 are arranged on the same track as the main beam 30, the push-pull signal of each beam is similar to that of the prior art 1 described above with reference to FIG. The phase difference between the sub-beam push-pull signals PP31 and PP32 is shifted by 180 ° with respect to the main beam push-pull signal PP30.

Therefore, the DPP signal can be detected without disposing the sub-beams by a half pitch with respect to the main beam as in the first conventional example. Thus, a plurality of types of optical disks having different track pitches can be reproduced by one optical pickup.

However, in the second conventional example,
It is necessary to make fine adjustments so that the sub-beams are arranged on the same track, which is not suitable for simplifying the adjustment.

(Conventional Example 3) As another conventional example, Japanese Patent Application Laid-Open No. 10-162383 proposes a recording / reproducing method for an optical disk capable of canceling a push-pull offset at low cost.

This method will be described with reference to FIG. The point that the light emitted from the laser diode 1 is divided into three beams by the grating 3 and condensed by the objective lens 5 is the same as that of the prior art examples 1 and 2;
Is different from the above in that the groove is formed only at the center of the effective light beam.

Since the groove of the grating 3 is formed only at the center of the substrate as shown in FIG. 37, the beam diameter of the + 1st-order and -1st-order diffracted light by the groove is the effective light beam diameter (the aperture diameter of the objective lens). ).

That is, the numerical aperture of the objective lens for the diffracted light is substantially reduced. Since the zero-order light (main beam) of the grating 3 is set to be larger than the aperture of the objective lens, a diffraction-limited beam spot determined by the numerical aperture of the objective lens is formed on the disk 6.

When an optical system that forms a beam spot having an appropriate size with respect to the track pitch is used as the main beam 30, the sub beams 31 and 32 are large with respect to the track pitch as shown in FIG. A beam spot is formed.

By determining the radius of the groove of the grating 3 so that the optical cutoff frequency determined by the aperture ratio in the radial direction becomes higher than the spatial frequency of the track pitch, tracking from the + 1st order and -1st order light of the sub beam is performed. An error signal (push-pull signal) cannot be obtained.

However, since an offset signal due to an objective lens shift or the like can be obtained, the offset can be similarly canceled by the calculation of the above equation (1).

According to this, since no modulation signal is generated due to track traversal, it is not necessary to displace the sub beam with respect to the main beam by exactly 1/2 track pitch in the radial direction of the disk, and to move the objective lens. There is no need to always set the position on the center line (radial direction) of the optical disk.

[0036]

However, when the above-described grating is used, the light intensity of the main beam including the zero-order light is reduced by the diffraction efficiency with respect to the flat portion in the groove portion of the grating. The light intensity of the flat portion on the outer periphery of the grating becomes relatively strong.

Also, regarding the phase of the zero-order light, an optical phase difference is generated in the groove portion with respect to the flat portion. As a result, the shape of the condensed beam of the main beam on the disc changes, and the recording / reproducing characteristics deteriorate.

As a method of correcting this, a method has been proposed in which a diffraction grating having a diffraction direction different from that of the central portion is provided in the flat portion to make the intensity distribution and phase difference of the zero-order light uniform.
Since the diffracted light at that portion is not used (only the zero-order light is used), light is wasted.

The present invention has been made in view of the above problems, and provides a method of canceling a TES offset using a push-pull method at a low cost without lowering light use efficiency. . Moreover, the present invention provides an optical pickup that can greatly simplify the assembly adjustment and can be applied to disks having different track pitches.

[0040]

In order to achieve the above object, the present invention has the following arrangement.

According to a first aspect of the present invention, at least two or more light beams are focused on an optical disk by an objective lens.
The reflected light is substantially divided by a dividing line in the track direction and received by a two-divided detector, and an optical pickup that generates a tracking error signal from a difference signal of each two-divided detector, that is, a push-pull signal of each beam. A phase difference is given to a part of the light beam so that the amplitude of the push-pull signal becomes substantially zero in one light beam.

The second invention of the present application is characterized in that the offset of the push-pull signal of the other light beam is corrected using the push-pull signal of the light beam giving the phase difference.

According to a third aspect of the present invention, in the light beam giving the phase difference, when a region related to the push-pull signal in the light beam is A and a region giving the phase difference is B, the position of the region B The sum of the phase difference and the phase difference between the region B and the region C symmetrically positioned with respect to the origin of the beam center is 180 °.
, And the sum of the areas of the region B and the region C is substantially half of the area of the entire region A.

According to a fourth aspect of the present invention, in the light beam giving the phase difference, when the radial direction of the optical disk is the x direction and the track direction is the y direction with the center of the light beam as the origin, one of the four quadrants is obtained. Approximately 180 in one quadrant only
It is characterized by giving a phase difference of °.

According to a fifth aspect of the present invention, in the light beam giving the phase difference, when the radial direction of the optical disk is the x direction and the track direction is the y direction with the center of the light beam as the origin, the first of the four quadrants A phase difference of approximately 90 ° is provided only in the quadrant and the third quadrant, or only in the second quadrant and the fourth quadrant.

According to a sixth aspect of the present invention, in the light beam giving the phase difference, an area related to the push-pull signal in a semicircular area passing through the center and divided by a radial dividing line of the optical disk is defined as D, Assuming that the region providing the phase difference is E, the sum of the phase difference of the region E and the phase difference of the region E and the region F located symmetrically with respect to the center line in the track direction is an integral multiple of 180 °. In addition, the sum of the areas of the region E and the region F is substantially half of the entire region D, and the push-pull signal is detected using only this semicircular region.

The seventh invention of the present application is characterized in that a phase difference of 180 ° is given to a sector of approximately 20 ° in the circumferential direction in the semicircular region for detecting the push-pull signal.

According to an eighth aspect of the present invention, in the semicircular area for detecting the push-pull signal, one-fourth of the semicircular area includes:
It is characterized in that a phase difference of 180 ° is given to a substantially rectangular area whose width in the track direction is almost constant.

According to a ninth aspect of the present invention, a diffraction grating separates a light beam into at least two light beams of a 0th-order light, a + 1st-order light or a -1st-order light, and a part for giving a phase difference. The periodic structure of the diffraction grating is formed so as to be shifted from the other portions, and a phase difference is added only to the diffracted light other than the zero-order.

The tenth invention of the present application is characterized in that a phase difference of 180 ° is given to a substantially rectangular area in the diffraction grating where the radial width of the optical disk is almost constant.

According to an eleventh aspect of the present invention, a phase difference of 180 ° is provided between a region in the diffraction grating substantially affecting only the + 1st order light and a region substantially affecting only the −1st order light. It is characterized by giving.

The twelfth invention of the present application is characterized in that an integrated hologram laser unit is mounted.

According to a thirteenth aspect of the present invention, at least two or more light beams are converged on an information recording medium by an objective lens, and at least one of the reflected light beams is substantially divided in a track direction. An optical pickup that receives light with a two-split detector and detects a difference signal between the two-split detectors, ie, a push-pull signal, wherein the amplitude of the push-pull signal in the one light beam is substantially zero. Preferably, a phase difference is given to a part of the light beam, and the difference signal is used as a position detection signal of the objective lens.

According to a fourteenth aspect of the present invention, a phase difference is provided to a part of a sub-beam so that the amplitude of the push-pull signal of the sub-beam becomes almost zero for an optical disc of a different standard, ie, an optical disc in which a different push-pull pattern is generated. It is characterized by giving.

According to a fifteenth aspect of the present invention, a main beam for recording or reproduction and at least one or more sub-beams are condensed on an information recording medium by an objective lens, and the reflected light is substantially in the track direction. A tracking servo method for performing tracking using a difference signal of each two-divided detector, that is, a push-pull signal of each beam, wherein the light is received by a two-divided detector and the amplitude of the push-pull signal of the sub-beam , A phase difference is given to a part of the sub beam so that the offset of the tracking error signal of the main beam is corrected using the difference signal.

[0056]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The same parts as those in the above-described conventional example are denoted by the same reference numerals, and description thereof will be omitted.

(First Embodiment) A first embodiment of the present invention will be described in detail with reference to FIGS.

For example, as shown in FIG. 1, a laser beam emitted from a semiconductor laser 1 is converted into a parallel beam by a collimator lens 2, and a main beam 30, a sub beam (+1 order beam) 31, and a sub beam (−1 order beam) are converted by a grating 3. ) 3
Divide into two.

After passing through the beam splitter 4, the light is focused on the track 61 of the optical disk 6 by the objective lens 5, and the reflected light is passed through the objective lens 5.
And the photodetector 8 (8A, 8B,
8C).

The main beam 30, the sub beams 31, 32
The two-part photodetector 8 has a far-field pattern of the reflected light of FIG.
Light is received at A, 8B and 8C. Then, difference signals from the two split photodetectors 8A, 8B, 8C, that is, push-pull signals PP30, PP31, PP32 are obtained.

Here, the present embodiment is characterized by the structure of the groove of the grating 3. A direction corresponding to the radial direction of the optical disk 6 (hereinafter, referred to as a “radial direction”) is defined as an x direction, and a tangential direction orthogonal thereto, that is, a track length direction (hereinafter, referred to as a “track direction”) is defined as a y direction. , The groove of grating 3
As shown in FIG. 1B, for example, only in the first quadrant on the xy plane, the phase difference of the periodic structure is 180 ° compared to other regions.
Is different.

As a result, in the sub beams 31 and 32 diffracted by the grooves, only the portion in the first quadrant is 18
A phase difference of 0 ° occurs.

The spot where this beam is condensed on the optical disk 6 by the objective lens 5 has a shape as shown in FIG. FIG. 2A is a plan view of three beams on the optical disk, and FIG.
It is sectional drawing cut | disconnected by the x'-y 'axis | shaft of 5 degree direction.

At this time, as shown in FIG. 3, the amplitude of the push-pull signals PP31 and PP32 using the sub-beams 31 and 32 is substantially zero as compared with the push-pull signal PP30 of the main beam to which no phase difference is applied. .

Since the push-pull signal is not detected irrespective of the track position, as shown in FIG. 2A, even if the sub beams 31 and 32 are arranged on the same track as the main beam 30, Even if they are arranged on different tracks, the signals become almost the same.

On the other hand, with respect to the TES offset due to the objective lens shift and the disc tilt shown in FIGS. 28A and 28B, PP30 and PP31 are used as shown in FIG.
(PP32) is Δp and Δp 'according to the light amount, respectively.
The offset occurs only on the same side (in-phase).

Therefore, by performing the calculation of PP3 = PP30-k (PP31 + PP32), the push-pull signal PP3 canceling the offset can be detected.

Here, the coefficient k is 0th-order light 30 and + 1st-order light 3
This is for correcting the difference between the light intensities of the first and −1st order light 32, and the intensity ratio is 0th order light: + 1st order light: −1st order light = a:
b: If b, the coefficient k = a / (2b).

In the case of the present embodiment, since the amplitude of the push-pull signal of each sub-beam is almost 0, PP31 and PP
It is not necessary to calculate using two signals of 32, PP3
The push-pull signal PP3 canceling the offset can be detected by the calculation of PP3 = PP30-2k (PP31) or PP3 = PP30-2k (PP32) using only either 1 or PP32.

The push-pull signal P of each sub-beam
P31 or PP32 can also be used as a radial position detection signal of the objective lens.

Here, the principle that the push-pull signal of the sub-beam is not generated (amplitude 0) will be described.

As shown in FIG. 5, the light beam (sub-beam 31) condensed on the track 61 having the periodic structure by the objective lens is composed of the 0th-order diffracted light 310 and the ± 1st-order diffracted light 31.
1, 312, which is reflected and overlaps the overlapping area n
1 and n2 interfere with each other to generate a diffraction pattern (push-pull pattern) on the objective lens pupil.

FIG. 6 shows a beam incident on the objective lens. When the grating 3 shown in FIG. 1B is used, the phase difference (phase lead) of the incident light is 180 ° only in the first quadrant. ) Occurs.

FIG. 7 shows a beam pattern of reflected light (diffracted light) on the objective lens pupil projected onto the two-segment detector 8B. The diffracted light (reflected light) is a zero-order light in the third quadrant. 310 has a phase lead of 180 ° (mesh region), and the diffracted light 311 has a phase lead of 180 ° (hatched region) in the fourth quadrant.

Here, it is assumed that a radial dividing line n is virtually assumed in the two-divided detector 8B divided by the track dividing line m, and the detection areas in the first to fourth quadrants are respectively 8Ba-a. , 8B-b, 8B-c, and 8B-d, and the outputs of the respective regions are Ia, Ib, Ic, and Id.

In general, the reflected light (diffraction pattern) from the groove disk can be expressed as follows.

(Complex amplitude of zero-order light) A ₀ = E ₀ · exp (2πi) (2) (Complex amplitude of + first-order light) A ₁ = E ₁ · exp ｛(ψ ₁ + 2πv _t / v _p ) i ｝ (3) (complex amplitude of −1st order light) A ₋₁ = E ₁ · exp {(ψ ₁ -2πv _t / v _p ) i} (4) where E ₀ , E ₁ , E ₋₁ are each zero-order, first-order, the amplitude of -1-order light, [psi ₁ is the phase difference of the zero-order and ± 1-order light (those relating to groove depth), v _t is the amount of displacement of the track groove center, vp
v _p is the pitch of the track groove.

Normally, the push-pull signal is obtained by the detectors {(8B-a) + (8B-b)} and {(8B-c) +
(8B-d)} output (Ia + Ib) and (Ic + Id)
Calculated from the difference between

Each signal is expressed as follows: I _R = (Ia + Ib) = S ₀ | E ₀ · exp (2πi) | ² + S ₁ | E ₀ · exp (2πi) + E ₁ · exp ｛(ψ ₁ + 2πv _t / v _{p ^{) i} | 2 = E 0}} 2 (S 0 + S 1) + E 1 2 S 1 + 2E 0 E 1 S 1 · cos (ψ 1 + 2πv t / v p) (5) I L = (Ic + Id) = S 0 | _{E 0 · exp (2πi) |} 2 + S 1 | E 0 · exp (2πi) + E 1 · e xp {(ψ 1 -2πv t / v p) i} | 2 = E 0 2 (S 0 + S 1) + E ₁ ² S ₁ + 2E ₀ E ₁ S ₁ · cos (ψ ₁ -2πv _t / v _p ) (6)

Here, S ₀ is the area of a region where there is no ± first-order light and only zero-order light exists in the first and fourth quadrants (the same applies to the third and second quadrants), and S ₁
Is the area of the portion where the zero-order light and the ± first-order light overlap in the first quadrant and the fourth quadrant (the same applies to the third quadrant and the second quadrant).

[0081] than this, the push-pull signal PP31 is, PP31 = I _R -I _{L = 4S 1 E 0 E 1 ·} sinψ 1 · sin (2πv t / v p) and made (7).

Next, the push-pull signal when a phase difference is added to a part of the incident beam as in the present embodiment will be described.

The phase difference added to the zero-order light of the reflected beam (diffraction pattern) is represented by θ ₁ (fourth quadrant in FIG. 7), θ ₋₁ (third quadrant in FIG. 7), and 1 of the reflected beam (diffraction pattern). Δ ₁ (fourth quadrant in FIG. 7) is a phase difference applied to a portion of the secondary light that interferes with the zero-order light. The phase difference is δ ₋₁ (FIG. 7)
(The third quadrant), the complex amplitude of light in each quadrant is as follows from the above equations (2) to (4).

(Complex amplitude of zero-order light: first quadrant and fourth quadrant) A ₀ = E ₀ · exp {(2π + θ ₁ ) i} (8) (Complex amplitude of zero-order light: third quadrant and second quadrant) (Quadrant) A ₀ = E ₀ · exp {(2π + θ ₋₁ ) i} (9) (complex amplitude of + 1st-order light: first and fourth quadrants) A ₁ = E ₁ · expｅｘ (｛ ₁ + 2πv _t / v _p + δ ₁ ) i｝ (10) (complex amplitude of -1st order light: third quadrant and second quadrant) A ₋₁ = E ₁ · exp ｛(ψ ₁ −2πv _t / v _p + δ ₋₁ ) i (11) As shown in FIG. 7, the push-pull signal PPbc when the phase difference is applied only to the fourth and third quadrants is obtained.

Outputs Ib and Ib of detectors 8B-b and 8B-c
c is expressed by the following equations (8) to (11): Ib =＝ [S ₀ | E ₀ · exp {(2π + θ ₁ ) i} | ² + S ₁ | E ₀ · exp ｛(2π + θ ₁ ) _{i} + E 1 · exp {} (ψ 1 + 2πv t / v p + δ 1) i} | 2] = 1/2 [E 0 2 (S 0 + S 1) + E 1 2 S 1 + 2E 0 E 1 S 1 · cos _{(ψ 1 + 2π v t /} v p + δ 1 -θ 1)] (12) Ic = 1/2 [S 0 | E 0 · exp {(2π + θ -1) i} | 2 + S 1 | E 0 · ex p _{{(2π + θ -1) i} } + E 1 · exp {(ψ 1 -2πv t / v p + δ -1) i} | 2] = 1/2 [E 0 2 (S 0 + S 1) + E 1 2 S 1 _{+ 2E 0 E 1 S 1 ·} cos (ψ 1 -2π v t / v p + δ -1 -θ -1)] is expressed as (13).

Here, in FIG. 7, θ ₁ = 0, θ ₋₁
= Π (180 °), δ ₁ = π (180 °), δ ₋₁ = 0, so that Ib and Ic are respectively Ib = １ ／ [E ₀ ² (S ₀ + S ₁ ) + E ₁ ² S ₁ + 2E _{0 E 1 S 1 · cos (} ψ 1 +2 πv t / v p + π)] (14) Ic = 1/2 [E 0 2 (S 0 + S 1) + E 1 2 S 1 + 2E 0 E 1 S 1 · cos _{(ψ 1 -2 πv t / v} p -π)] (15) , and the push-pull signal PPbc is, PPbc = Ib-Ic _{= 2S 1 E 0 E 1 ·} sinψ 1 · sin {2π (v t / v p +1/2)} _{= -2S 1 E 0 E 1 ·} sinψ 1 · sin (2πv t / v p) and made (16).

[0087] PPab the phase difference is not relevant, the same as those obtained by multiplying 1/2 to the above equation (7) (the area is _{halved), PPad = 2S 1 E 0} E 1 · sinψ 1 · sin (2πv _t / v _p ) (17) As shown in FIG. 8, PPad and PPbc
Is a signal that is ピ ッ チ pitch or 180 ° out of phase (opposite phase) regardless of the groove depth (related to ψ1).

Therefore, the finally obtained push-pull signal from the detector 8B is PP31 = PPbc + PPad = 0, and the amplitude is always 0.

In the present embodiment, the case where the phase delay occurs only in the first quadrant has been described. However, the present invention is not limited to this, and the case where only one of the second to fourth quadrants has the phase delay may be used. Naturally, the same effect can be obtained. Further, the same result is obtained regardless of the phase difference to be applied, whether the phase is delayed or the phase is advanced.

Further, FIG. 1 shows the case where there is a phase difference in one quadrant as a whole. However, the regions related to the push-pull signal are the regions n1 and n2 where the diffracted light from the optical disk groove shown in FIG. 5 overlaps. Therefore, it is not necessary to add a phase difference to the entire quadrant. For example, if a phase difference is added only to the region n1 of the first quadrant, a sufficient effect can be obtained.

According to the present embodiment, the amplitude of the push-pull signal of the sub-beam becomes zero regardless of the groove depth. That is, since the amplitude is 0 at any position on the track, the position adjustment (rotation adjustment of the diffraction grating or the like) of the three beams is not necessary as in the above-described conventional examples 1 and 2, and thus the pickup is not required. Assembly adjustment can be greatly simplified.

Also, since the diffraction grating can be provided for the entire light beam, the light intensity distribution of the main beam does not change and the light use efficiency does not decrease as in the above-described conventional example 3. . Furthermore, the present invention can be applied to disks having different track pitches without any problem.

(Second Embodiment) A second embodiment of the present invention will be described in detail with reference to FIGS. The configuration of the optical pickup of this embodiment is the same as that shown in FIG. 1, but the structure of the groove of the grating 3 is different.

In the present embodiment, as shown in FIG. 9, the periodic structure of the first quadrant and the third quadrant is shifted by + ／ pitch as compared with the others. As a result, FIG.
As shown in FIG. 0, the phase difference between the first quadrant and the third quadrant in the sub-beams 31 and 32 of ± 1 order light is shifted by + 90 °.

Similar to FIG. 7, FIG. 11 shows a beam pattern on the detector 8B divided by the dividing line m in the track direction and the virtual dividing line n. In the first quadrant and the third quadrant, there is a phase difference of 90 ° on the side of the main beam 310 (mesh area), and in the fourth quadrant and the second quadrant, the sub beam 31
There is a phase difference of 90 ° on the 1,312 side (shaded area).

In this case, the push-pull signal PPad between the 1/4 circle beams in the first quadrant and the second quadrant is a signal whose phase is shifted by 90 ° as compared with the push-pull signal when no phase difference is given. On the contrary, the push-pull signal PPbc between the quarter-circle beams in the fourth and third quadrants is -90.
° The signal is out of phase.

Here, the principle that the push-pull signal of the sub-beam is not generated (amplitude 0) will be described in the same manner as in the first embodiment.

The phase difference applied to the zero-order light of the reflected beam (diffraction pattern) is represented by θ ₁ (first quadrant in FIG. 11) and θ ₁ ′ (FIG. 1).
1 in the fourth quadrant), θ ₋₁ (the second quadrant in FIG. 11), θ ₋₁ ′
(3rd quadrant in FIG. 11), the phase difference added to the part of the primary light of the reflected beam (diffraction pattern) that interferes with the zero-order light is δ
₁ (first quadrant in FIG. 11), δ ₁ ′ (fourth quadrant in FIG. 11),
The phase difference applied to the part of the reflected beam (diffraction pattern) that interferes with the 0th-order light among the -1st-order light is δ ₋₁ (second quadrant in FIG. 11), δ ₋₁ ′ (third quadrant in FIG. Then, the complex amplitude of light in each quadrant is calculated by referring to the above equations (8) to (11). (Complex amplitude of zero-order light: first quadrant) A ₀ = E ₀ · exp ｛(2π + θ ₁ ) i｝ (18) (complex amplitude of zero-order light: fourth quadrant) A ₀ = E ₀ · exp {(2π + θ ₁ ') i｝ (19) (complex amplitude of zero-order light: third quadrant) A ₀ = E ₀ · exp {(2π + θ _-1 ') i｝ (20) (Complex amplitude of zero-order light: second quadrant) A ₀ = E ₀ · exp {(2π + θ _-1 ) i｝ (21) (+ _1st- order light of the complex amplitude: the first _{quadrant) a 1 = E 1 · exp} {(ψ 1 + 2πv t / v p + δ 1) i} (22) (+1 order light of the complex amplitude: _1, the fourth quadrant) a ₁ = E exp ｛(ψ ₁ + 2πv _t / v _p + δ ₁ ′) i｝ (23) (complex amplitude of the −1st order light: third quadrant) A ₋₁ = E ₁ · exp ｛(ψ ₁ −2πv _t / v _p + δ ₋₁ ′) i ｝ (24) (complex amplitude of −1st order light: second quadrant) A ₋₁ = E ₁ · expｅｘ (ψ ₁ −2πv _t / v _p + δ ₋₁ ) i｝ (25)

In FIG. 11, θ ₁ = π / 2 (90
°), θ ₁ '= 0, θ _-1 ' = π / 2 (90 °), θ _-1 =
0, δ ₁ = 0, δ ₁ ′ = π / 2 (90 °), δ ₋₁ = 0, δ
_-1 ′ = π / 2 (90 °), so Ia, Ib, Ic, I
d is the formula (14), (15) a with reference, Ia = 1/2 [E 0 2 (S 0 + S 1) + E 1 2 S 1 + 2E 0 E 1 S 1 · cos (ψ 1 +2 πv _{t / v p -π / 2)} ] (26) Ib = 1/2 [E 0 2 (S 0 + S 1) + E 1 2 S 1 + 2E 0 E 1 S 1 · cos (ψ 1 +2 πv t / v p + π / 2)] (27 ) Ic = 1/2 [E 0 2 (S 0 + S 1) + E 1 2 S 1 + 2E 0 E 1 S 1 · cos (ψ 1 -2 πv t / v p -π / 2 )] (28) Id = 1 /2 [E 0 2 (S 0 + S 1) + E 1 2 S 1 + 2E 0 E 1 S 1 · cos (ψ 1 -2 πv t / v p + π / 2)] (29 ).

Then, the push-pull signals PPad, Pb
c is PPad = Ia−Id _{= 2S 1 E 0 E 1 ·} sinψ 1 · sin {2π (v t / v p +1/4)} (30) PPbc = Ib-Ic _{= 2S 1 E 0 E 1 ·} sinψ 1 · sin {2π (v t / v p -1/4)} and since (31), as shown in FIG. 12, PPad and PPbc
Is ± 1/4 pitch or ± 90 ° out of phase regardless of the groove depth (related to ψ1).

Since the signals are different in half pitch, that is, 180 degrees in phase, the finally obtained push-pull signal from the detector 8B is PP31 = PPbc + PPad = 0, and the amplitude is always 0. Become.

As described above, in the configuration in which the phase difference is given to the diagonal region divided into four parts, the displacement of the grating, the displacement of the laser emission light, and the shift of the objective lens due to tracking (beam) in both the x and y directions. Even when the center is shifted from the center of the grating, the area of the phase-shifting region does not change, which is advantageous.

In this embodiment, the case where the phase advance occurs in the first and third quadrants has been described. However, the present invention is not limited to this, and a phase difference of 90 ° (phase advance) occurs in the second and fourth quadrants.
And the same effect can be obtained even when a phase difference (phase lag) of −90 ° is given to each of them.

Although the case where there is a phase difference in one quadrant as a whole is shown, the regions involved in the push-pull signal are the regions n1 and n2 where the diffracted light from the optical disk groove shown in FIG. 5 overlaps. It is not necessary to add a phase difference to the whole, for example, the portion of the region n1 in the first quadrant and the third
A sufficient effect can be obtained by adding a phase difference to the portion of the quadrant region n2.

Further, the present invention is not limited to the combination of phase differences as shown in FIG. 11, but θ ₁ '+ θ _-1 = nπ (n: integer) and θ ₁ = θ _-1 '
= 0 (At this time, be sure to set δ ₁ + δ _-1 = nπ and δ ₁ '=
δ ₋₁ ′ = 0), for example, as shown in FIG. 13, even if the phase difference of the incident light is 45 ° in the first quadrant and the phase difference is 135 ° in the third quadrant, The amplitude of the push-pull signal becomes zero.

That is, in the conventional push-pull signal detection using the entire circular light beam, the region related to the push-pull signal in the entire light beam, that is, the zero-order light of the reflected light (diffracted light) from the groove and the Assuming that an area where the ± primary light overlaps (an area where they interfere with each other) is A and an area that gives a phase difference is B, the phase difference between the area B and the area C located symmetrically with respect to the origin of the center of the beam. If the sum is an integral multiple of 180 ° and the sum of the areas of the area B and the area C is set to approximately half the area of the area A, the push-pull signal amplitude of the entire light beam becomes almost zero.

For example, as shown in FIG. 13, when a phase is given to incident light so that a phase difference of 45 ° is added to a portion of the first quadrant of reflected light, a region symmetrically positioned with respect to the origin of the beam center. That is, if the phase difference is set to 135 ° in the third quadrant, 1/1 of the first quadrant and the second quadrant is set.
The push-pull signal PPad between the four circular beams is a signal whose phase is shifted by 45 ° as compared with the push-pull signal when no phase difference is given, and the push-pull signal between the quarter-beams in the fourth and third quadrants is used. The signal PPbc is -135.
° The signal is out of phase.

Therefore, the entire push-pull signal PP31
(= PPad + PPbc) has a phase difference of 180
Because of °, the amplitudes cancel each other and the amplitude becomes substantially zero.

In this embodiment, the beam is divided into four parts around the origin to give a phase difference to each region. However, the present invention is not limited to this. May be given.

Furthermore, in the above embodiment, the push-pull signal is detected by dividing the light beam into two on the detector. However, the light beam is separated by a multi-divided hologram, a wedge prism, etc. After the derivation, exactly the same effect can be obtained even when the push-pull signal is detected by calculating each signal.

(Third Embodiment) A third embodiment of the present invention will be described in detail with reference to FIGS. Here, an example will be described in which the pickup device is applied to a hologram laser unit in which a semiconductor laser as a light source, a three-beam grating, a hologram for generating a servo signal, and a photodetector are integrated.

As shown in FIG. 14, the light emitted from the semiconductor laser 1 is divided into three beams (a main beam and a sub-beam of ± first-order light) by a grating 3, and the zero-order diffracted light of the hologram element 9 is converted into a collimator lens. The light is condensed on an optical disk 6 via an objective lens 5 and 2. Then, the returned light is diffracted by the hologram element 9 and guided to the photodetector.

Here, as shown in FIG. 15, the hologram element 9 has a dividing line 9g extending in the y-direction corresponding to the radial direction of the optical disk 6, and a direction perpendicular to the radial direction of the optical disk 6 from the center of the dividing line 9g. A division line 9h extending in the x direction, that is, a direction corresponding to the track direction of the optical disk 6, is divided into three division regions 9a, 9b, and 9c, each corresponding to each of the division regions 9a, 9b, and 9c. Are formed.

The light receiving element 10 has two divided light receiving areas 10a and 10b for focusing and a light receiving area 10c for tracking.
10d, 10e, 10f, 10g, and 10h.

In the focused state, the main beam diffracted in the divided area 9a of the hologram element 9 forms a beam P1 on the division line 10y, and the main beams diffracted in the divided areas 9b and 9c are respectively received. Beams P2 and P3 are formed on regions 10c and 10d.

The ± first-order sub-beams diffracted by the divided area 9a are respectively divided into two divided light receiving areas 10a and 10b.
Beams P4 and P5 are formed outside the region 9b,
The ± 1st-order sub-beams diffracted by the light-receiving area 10e and 10f respectively emit beams P6 and P7 on the light-receiving area 10e and 10f.
Beams P8 and P9 are formed on 0g and 10h.

Light receiving areas 10a, 10b, 10c, 10
The output signals of d, 10e, 10f, 10g, and 10h are output as Ia, Ib, Ic, Id, Ie, If, Ig, and I, respectively.
Assuming that h, the focus error signal FES is obtained by the calculation of (Ia-Ib) by the single knife edge method.

The tracking error signal TES is given by TES = (Ic−Id) −k ((If−Ih) + (Ie)
-Ig)).

Here, (Ic-Id) of TES is a push-pull signal of the main beam, (If-Ih), (Ie-
Ig) is a push-pull signal of each of the sub beams ± 1st order light.

The difference from the first embodiment is that the push-pull signal uses half the light of the beam (light of only the divided areas 9b and 9c of the hologram element). In this case, the structure of the grating for reducing the amplitude of the push-pull signal of the sub-beam to zero is shown below.

In FIG. 15, for example, if the light incident on the divided areas 9b and 9c of the hologram element on the return path is the first quadrant and the second quadrant, the light is pushed only by subtracting the light output of the first quadrant and the second quadrant. It is necessary to cancel the pull signal amplitude to zero.

In this case, for example, as shown in FIG. 16, in the incident beam on the outward path, the periodic structure of the grating in the xy coordinate system from 180 ° to 200 ° in the circumferential direction is shifted by ピ ッ チ pitch, that is, As shown in FIG. 17, if the phase difference is shifted by π (180 °), the amplitudes of the push-pull signal, (If-Ih), and (Ie-Ig) become almost zero.

The principle of signal detection in this case will be described below. In the present embodiment, the light beam is divided by the hologram, and each light beam is guided to a different detector. However, this is the same as the case where the light beam is guided onto the detector without being divided and the detector is divided, so that the description will be made. For simplicity, the description will be made using a beam on a detector as shown in FIG. 18 as in the first and second embodiments.

In the detector shown in FIG.
Bd light is divided into hologram divided areas 9b and 9c, respectively.
Corresponds to the light diffracted by. In FIG. 19, it is assumed that the region to which the phase difference is added in FIG. 18 is temporarily divided as follows.

In the first quadrant, the region including the phase difference in the 0-order light of the reflected light is defined as SS2, the other region is defined as SS1, and the second region is defined as SS1.
In the quadrant, a region including a phase difference in the -1st order reflected light is defined as SS3, and the other region is defined as SS4.

Then, the regions SS1, SS2, SS3, S
In S4, the area of the region where there is no ± first-order light but only the zero-order light is S ₀₋₁ , S ₀₋₂ , S ₀₋₃ , S _0−4.
The area of the portion where the primary light overlaps is S _1-1 , S _1-2 , S
_1-3 and S _1-4 .

[0127] Here, the approximately equal, such as dividing the area S _1-1 and S _1-2 (in this embodiment, as shown in FIG. 18 is divided approximately 20 ° in the circumferential direction). That is, S
Divide so that _1-1 = S _1-2 and S _1-3 = S _1-4 .

Here, the regions SS1 to SS4 are defined by the first
By referring to the equations (12) to (17) in the case of considering the first quadrant and the second quadrant in FIG. 7 described as the embodiment, it can be easily understood that the amplitude of the push-pull signal becomes zero.

That is, the push-pull signals generated in the regions SS2 and SS3 and the push-pull signals generated in the regions SS1 and SS4 have the same amplitude but a phase difference of 1
80 ° off.

This is because the phase difference is 180 ° in a region related to the push-pull signal, that is, a region where the 0th-order light and ± 1st-order light of the reflected light (diffracted light) from the groove overlap (the region where they interfere with each other). Since the amplitude of the push-pull signal of the light in the given area and the push-pull signal of the light of the unrelated part are almost equal and the phases are shifted by 180 °, the amplitude of the push-pull signal becomes zero as a whole. Occurs.

Although S _0-2 and S _0-3 are different from S _0-1 and S _0-4 , (S _0-1 + S _0-2 ) and (S _0-3 + S _0-4 ) Therefore, if the DC component of the area of the region where only the zero-order light exists is subtracted, it becomes zero.

As described above, by using half the light of the beam,
The present invention can be applied to a hologram laser unit that detects a push-pull signal.

In the detection of a push-pull signal using a semi-circular beam, a region related to the push-pull signal in the semi-circular beam, that is, the 0th-order light and ± 1st-order light of the reflected light (diffracted light) from the groove is divided Overlapping areas (areas that interfere with each other)
Is defined as D, and the area providing the phase difference is defined as E. The area F is located symmetrically with respect to the area E with respect to the center line in the track direction.
Is an integral multiple of 180 ° and the region E
If the sum of the area of the area F and the area of the area F is set to approximately half the area of the area D, the amplitude of the push-pull signal of the entire light beam becomes almost zero.

The region where the phase difference is applied is not limited to the region shown in FIG. 17, but as shown in FIG. 20, the region where the phase difference is 180 ° is the same as the region where the width in the y direction is constant and which is within one quadrant. The same effect can be obtained even if the area is set to be about half the area.

As described above, if the width in the y direction is constant,
Even if the objective lens, that is, the light beam shifts in the radial direction due to tracking, the area that gives the phase difference in the interference region does not change, so that the influence of the position shift can be reduced.

(Fourth Embodiment) A fourth embodiment of the present invention will be described in detail with reference to FIGS.

The pickup device of this embodiment has a configuration using a hologram laser unit as in the third embodiment, and further improves the accuracy of the phase difference given to the sub-beam.

FIG. 21 schematically shows an optical system. The light emitted from the semiconductor laser 1 is split into three beams (a main beam 30 and sub-beams 31 and 32 of ± first-order light) by a grating 3, and the zero-order diffracted light of the hologram element 9 is transmitted through the collimator lens 2 and the objective lens 5. The light is condensed on the optical disk 6 via the optical disc 6.

Next, the displacement of the sub beam will be described. The sub beams 31 and 32 are split by the grating 3, which can be considered as light emitted from the virtual light sources 1-31, 1-32, as shown in FIG.

Therefore, as shown in FIG. 21 (b), the sub-beam light substantially incident on the objective lens 5 uses the light on the grating 3 and the hologram 9 which is shifted from the main beam 30. become.

The amount of this shift varies depending on the position of the grating or hologram in the optical axis direction, but it becomes a relatively large value in a small integrated hologram laser unit or the like.

Therefore, as in the third embodiment,
Grating 3 aligned with the center of the optical axis of the main beam
Even if a phase difference distribution is given to the sub-beams, the sub-beams of the ± 1st order light have phase difference distributions deviated from the respective centers.

In the case where the amount of deviation is so small as to be negligible with respect to the beam diameter, if a phase difference distribution is given at the center of the optical axis, ±
Although it can be considered that the same phase distribution is added to the primary light, when the shift amount is large, it is necessary to design in consideration of this.

The phase difference distribution in this case will be described below.
As shown in FIG. 21B, when the push-pull signal is detected using only the semicircular portion of the beam in the y-direction by the three-division hologram 9, the influence of the displacement of the sub-beam in the y-direction is affected. , ± 1st order beams. The present embodiment provides an effective phase difference distribution in such a case.

FIG. 22A shows y in grating 3.
A case where a phase difference is applied to the end portion of a semicircle in the x direction of the beam in a band shape with a substantially uniform width in the direction. FIG.
(B) shows a case where a phase difference is given near the center of a semicircle in the x direction of the beam in a band shape with a substantially uniform width in the y direction in the grating 3.

The width may be set so that the amplitude of the push-pull signal of the sub-beam shown in the third embodiment becomes almost zero. This configuration is in the y direction (track direction).
Since the phase difference distribution is uniform, the added phase difference distribution does not change even if the position of the sub beam is substantially shifted on the grating. Therefore, the accuracy of the phase difference distribution can be improved.

FIG. 22C shows a region 3 where a phase difference is added to only the + 1st-order sub-beam 31 by utilizing the fact that the position of the sub-beam is substantially shifted on the grating.
A and a region 3B in which a phase difference is added only to the -1 order sub-beam 32 to give a phase difference distribution.

As described above, since the phase difference distribution can be individually added to each sub beam, the push-pull signal of the ± primary beam can be generated by using the three-divided hologram as in the pickup device of the present embodiment. Even in the case of non-uniformity, a phase difference can be accurately added to each beam.

(Fifth Embodiment) A fifth embodiment of the present invention will be described in detail with reference to FIGS.

The pickup device of this embodiment uses a hologram laser unit similarly to the third and fourth embodiments, and provides a phase difference to be applied to the sub-beam even for disks having different pitches and groove depths. Is improved.

FIG. 23 schematically shows an optical system.
Since it is basically the same as FIG. 21, detailed description is omitted. However, the hologram element 9 is different from that of FIG.
As shown in (c), a case where a push-pull signal is detected using the entire light beam will be described, assuming four divisions or two divisions divided by a division line in the y direction.

As shown in FIG. 23B, the sub-beam 3
The points 1 and 32 use the light substantially deviated from the main beam 30 on the grating 3 in the same manner as described in the third embodiment.

Next, a push-pull diffraction pattern for optical disks having different specifications will be described. It is required to use the same optical pickup device to record / reproduce optical discs of different standards, but the push-pull pattern is greatly different especially when the pitch or depth of the groove structure changes.

For example, the push-pull pattern when the groove pitch is small is shown in FIG. 24A (regions n1 and n2 related to the push-pull signal).
(B) (regions n3 and n4 related to the push-pull signal)
Are shown below.

As described above, when the diffraction patterns are largely different from each other and the position of the sub beam is substantially shifted from the main beam on the grating 3, the optimum phase difference distribution pattern is also different. The present embodiment provides an effective phase difference distribution in such a case.

FIG. 25 shows the phase difference distribution of the present embodiment.
This means that in the grating 3, 180 ° is formed in three regions of 3C, 3D and 3E with respect to the semicircle in the x direction of the beam.
Gives a phase difference of

Among them, the area 3D adds a phase difference to both the sub beams 31 and 32, the area 3C gives a phase difference only to the sub beam 32, and the area 3E conversely applies a phase difference only to the sub beam 31. Give a phase difference.

The area 3D is shown in FIGS. 24 (a) and 24 (b).
Areas n2 and n where both diffraction patterns shown by
4 is included. On the other hand, the region 3C includes only the n4 region of the sub beam 32, and the region 3E includes only the n4 region of the sub beam 31.

Therefore, for example, as shown in FIG.
By optimizing the size and shape of D, the sub-beams 31, 32
, The amplitude of the push-pull signal is made substantially zero.

As shown in FIG. 24 (b), for the sub-beam 31 on a disk having a wide pitch, the size and shape of the phase difference addition regions 3E and 3D are optimized to make the push-pull signal amplitude almost zero. For the sub beam 32, the size and shape of the phase difference addition regions 3C and 3D are optimized to make the push-pull signal amplitude substantially zero.

Therefore, even when the positions of the two sub beams are substantially shifted from the main beam in different directions on the grating, the phase difference adding regions 3C and 3E which do not affect each other are provided as in the present embodiment. By doing
Since the phase difference distribution can be added to each sub beam individually, even for optical discs of different standards,
A phase difference can be accurately added to each beam.

In the above-described embodiment, a method of partially shifting the periodic structure of the grooves of the grating has been described as a method of giving a phase difference to ± first-order light of three beams, but the present invention is not limited to this. Instead, a transmission glass plate or a phase difference plate may be actually used.

[0163]

According to the present invention, in the TES detection using the push-pull method, the offset generated by the objective lens shift or the disc tilt can be canceled at low cost without lowering the light use efficiency. .

The amplitude of the push-pull signal of the sub-beam is 0 irrespective of the groove depth, and only the beam shift component on the detector due to the objective lens shift or disc tilt is detected.

That is, since the amplitude of the push-pull signal is 0 regardless of the position of the sub beam, not limited to 1/2 pitch, with respect to the main beam, the position adjustment of the sub beam (rotation adjustment of the diffraction grating or the like) can be performed. This is unnecessary, and the assembling adjustment of the pickup can be greatly simplified.

Also, since the diffraction grating can be provided for the entire light beam, the light intensity distribution of the main beam does not change and the light use efficiency does not decrease.

Further, the present invention can be applied to disks having different track pitches without any problem.

Further, since the present invention can be applied to push-pull signal detection using a half light beam, it can be used for an integrated hologram laser unit and the like.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an optical system of an optical pickup according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a beam spot shape on an optical disk when the optical pickup according to the first embodiment of the present invention is used.

FIG. 3 is an explanatory diagram illustrating a push-pull signal according to the first embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a push-pull signal when the objective lens shifts in the first embodiment of the present invention.

FIG. 5 is an explanatory diagram showing a diffraction pattern of a reflected beam from an optical disc.

FIG. 6 is an explanatory diagram illustrating a phase distribution of an objective lens incident beam according to the first embodiment of the present invention.

FIG. 7 is an explanatory diagram showing a diffraction pattern of a beam on a detector according to the first embodiment of the present invention.

FIG. 8 is a diagram for explaining a principle of detecting a push-pull signal according to the first embodiment of the present invention.

FIG. 9 is an explanatory diagram illustrating a structure of a diffraction grating of the optical pickup according to the second embodiment of the present invention.

FIG. 10 is an explanatory diagram showing a phase distribution of an objective lens incident beam according to the second embodiment of the present invention.

FIG. 11 is an explanatory diagram showing a diffraction pattern of a beam on a detector according to the second embodiment of the present invention.

FIG. 12 is a diagram for explaining a principle of detecting a push-pull signal according to the second embodiment of the present invention.

FIG. 13 is an explanatory diagram showing another pattern of the phase distribution of the objective lens incident beam in the second embodiment of the present invention.

FIG. 14 is a schematic configuration diagram illustrating an optical system of an optical pickup according to a third embodiment of the present invention.

FIG. 15 is an explanatory diagram showing the structure of a hologram and a photodetector in a hologram laser pickup according to a third embodiment of the present invention.

FIG. 16 is an explanatory diagram illustrating a structure of a diffraction grating according to a third embodiment of the present invention.

FIG. 17 is an explanatory diagram showing a phase distribution of an objective lens incident beam according to the third embodiment of the present invention.

FIG. 18 is an explanatory diagram illustrating a temporary beam pattern on a detector according to the third embodiment of the present invention.

FIG. 19 is an explanatory diagram showing temporary divided regions on a detector according to the third embodiment of the present invention.

FIG. 20 is an explanatory diagram showing another phase distribution according to the third embodiment of the present invention.

FIG. 21 is an explanatory diagram showing a pickup optical system and beam positions on a grating and a hologram according to a fourth embodiment of the present invention.

FIG. 22 is an explanatory diagram showing a phase difference addition pattern on a grating according to a fourth embodiment of the present invention.

FIG. 23 is an explanatory diagram showing a pickup optical system and beam positions on a grating and a hologram according to a fifth embodiment of the present invention.

FIG. 24 is an explanatory diagram showing push-pull patterns on disks of different standards.

FIG. 25 is an explanatory diagram showing a phase difference addition pattern on a grating according to a fifth embodiment of the present invention.

FIG. 26 is a schematic configuration diagram showing an optical system of a conventional optical pickup.

FIG. 27 is a diagram for describing a push-pull signal.

FIG. 28 is a diagram for explaining a cause of an offset occurrence of a push-pull signal.

FIG. 29 is a schematic configuration diagram showing an optical system of an optical pickup of Conventional Example 1.

FIG. 30 is an explanatory diagram showing a beam arrangement on an optical disc and a configuration of a detection system in Conventional Example 1.

FIG. 31 is a diagram for explaining the principle of detecting a push-pull signal in Conventional Example 1.

FIG. 32 is a schematic configuration diagram showing an optical system of an optical pickup of Conventional Example 2.

FIG. 33 is an explanatory view showing the structure of a diffraction grating of Conventional Example 2.

FIG. 34 is an explanatory diagram showing a beam arrangement on an optical disc in Conventional Example 2.

FIG. 35 is a diagram for explaining the principle of detecting a push-pull signal in Conventional Example 2.

FIG. 36 is a schematic configuration diagram showing an optical system of an optical pickup according to Conventional Example 3.

FIG. 37 is an explanatory diagram showing a structure of a diffraction grating and a focused beam on an optical disc in Conventional Example 3.

FIG. 38 is an explanatory diagram showing a beam arrangement on an optical disc in Conventional Example 3.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 Collimator lens 3 3 Beam diffraction grating 4 Beam splitter 5 Objective lens 6 Disk 7 Condensing lens 8 Photodetector 9 Hologram 10 Holographic laser detector 11 2-split detector 30 0th-order diffracted light 31 + 1st-order diffracted light 32 − 1st-order diffracted light 61 Track 310 0th-order reflected diffracted light of sub-beam 311 + 1st-order diffracted light of sub-beam 312 -1st-order diffracted light of sub-beam

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Miki Renzaburo 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Hiroshige Hirashima 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka F-term (for reference) 5D118 AA06 AA13 AA18 BA01 BA06 CA24 CD03 CF03 CG04 CG24 DA35 5D119 AA29 AA40 BA01 BA02 EA02 FA28 KA17

Claims (15)

[Claims] At least two or more light beams are condensed on an optical disk by an objective lens, and the reflected light is substantially divided by a dividing line in a track direction and received by a two-division detector. An optical pickup for generating a tracking error signal from a difference signal of a split detector, that is, a push-pull signal of each beam, wherein the optical pickup is positioned at a part of the light beam such that the amplitude of the push-pull signal becomes substantially zero in one of the light beams. An optical pickup characterized by providing a phase difference. 2. The optical pickup according to claim 1, wherein the offset of the push-pull signal of the other light beam is corrected using the push-pull signal of the light beam giving the phase difference. 3. In the light beam giving the phase difference,
When an area related to the push-pull signal in the light beam is A and an area that gives a phase difference is B, the phase difference between the area B and the area C that is symmetrical with respect to the area B and the center of the beam as the origin. The sum with the phase difference is an integral multiple of 180 °,
3. The optical pickup according to claim 1, wherein the sum of the area of the area B and the area C is substantially half of the area of the entire area A. 4. The light beam for providing a phase difference,
When the radial direction of the optical disk is the x direction and the track direction is the y direction with the center of the light beam as the origin, a phase difference of about 180 ° is given to only one of the four quadrants. Item 3. The optical pickup according to item 1 or 2. 5. In the light beam giving the phase difference,
When the radial direction of the optical disk is the x direction and the track direction is the y direction with the center of the light beam as the origin, approximately 90 ° is applied only to the first and third quadrants or the second and fourth quadrants of the four quadrants. The optical pickup according to claim 1, wherein the optical pickup has a phase difference of: 6. In the light beam giving the phase difference,
When a region related to the push-pull signal is defined as D and a region providing a phase difference is defined as E in a semicircular region divided by a radial dividing line of the optical disk passing through the center, the phase difference between the region E and the region E And the phase difference of the region F located symmetrically with respect to the center line in the track direction is an integral multiple of 180 °, and the sum of the areas of the region E and the region F is approximately half of the entire region D. 3. The method according to claim 1, wherein the push-pull signal is detected using only the semicircular region.
An optical pickup according to claim 1. 7. In the semicircular region for detecting the push-pull signal, a 180-degree region is formed in a sector region of approximately 20 degrees in the circumferential direction.
7. The optical pickup according to claim 6, wherein a phase difference of? 8. A phase difference of 180 ° is applied to a substantially rectangular area having a substantially constant width in the track direction in a quarter circle on one side of the semicircular area for detecting the push-pull signal. 7. The optical pickup according to claim 6, wherein the optical pickup is provided. 9. A diffraction grating converts a light beam into zero-order light and +
It is separated into at least two or more light beams of primary light or −1st order light, and the periodic structure of the diffraction grating at the portion providing the phase difference is formed shifted from the other portions to form a non-zero order light beam. 9. The optical pickup according to claim 1, wherein a phase difference is added only to the diffracted light. 10. A substantially rectangular area in which the radial width of an optical disc is substantially constant in the diffraction grating.
The optical pickup according to claim 9, wherein a phase difference of 180 ° is provided. 11. A phase difference of 180 ° is given to a region in the diffraction grating that substantially affects only the + 1st order light and a region that only affects the −1st order light. The optical pickup according to claim 9. 12. The optical pickup according to claim 1, further comprising an integrated hologram laser unit. 13. At least two or more light beams are converged on an information recording medium by an objective lens, and at least one of the reflected light beams is divided substantially by a dividing line in a track direction into two parts. What is claimed is: 1. An optical pickup for receiving a detector and detecting a difference signal between two split detectors, that is, a push-pull signal, wherein a part of the light beam is arranged such that the amplitude of the push-pull signal becomes substantially zero in the one light beam. And a phase difference, and using the difference signal as a position detection signal of an objective lens. 14. An optical disc of a different standard, that is, an optical disc in which a different push-pull pattern is generated, wherein a phase difference is given to a part of the sub-beam so that the amplitude of the push-pull signal of the sub-beam becomes almost zero. The optical pickup according to claim 13. 15. A main beam for recording or reproduction and at least one or more sub-beams are condensed on an information recording medium by an objective lens, and the reflected light is divided by a dividing line substantially in the track direction. A tracking servo method in which light is received by a two-split detector and tracking is performed using a difference signal of each two-split detector, that is, a push-pull signal of each beam, wherein the amplitude of the push-pull signal of the sub-beam is substantially zero. Wherein a phase difference is given to a part of the sub-beam and an offset of a tracking error signal of the main beam is corrected using the difference signal.