JP2003077151A - Optical pickup and optical disk device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the sufficient suppression of the offset of a tracking error signal due to the positional deviation of a diffraction grating as to an optical pickup and an optical disk device by applying to a mini-disk device, a recording/ reproducing device of DVD, etc. SOLUTION: The diffraction grating 14 is constituted by the repetition of at least three areas AR1, AR21 and AR22, AR3 having different optical distances, then the optical distances of widths W1, W21 and W22, W3 in three areas AR1, AR21 and AR22, AR3 are set so that the phase difference between a 0-order diffracted light and a ±1st order diffracted light becomes almost 0 deg. or 180 deg..

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup and an optical disk device, for example, a mini disk device, D
It can be applied to a VD recording / reproducing device and the like. The present invention configures a diffraction grating by repeating at least three regions having different optical distances so that the phase difference between the 0th-order diffracted light and the ± 1st-order diffracted light is approximately 0 degree or 180 degrees.
By setting the optical distance and width in these three regions, it is possible to sufficiently suppress the offset of the tracking error signal due to the displacement of the diffraction grating.

[0002]

2. Description of the Related Art Conventionally, there is an optical disc device which is designed to perform tracking control by a so-called three-spot method. In such an optical disc device, a diffraction grating is used to form 0th order and ± 1st order from a laser beam. The diffracted light is generated and the 0th order and the ± 1st order diffracted lights are applied to the optical disc.

That is, FIG. 9 is a side view showing an optical pickup applied to an optical disk device of this type. In the optical pickup 1, the semiconductor laser 2 emits a laser beam L1 having a predetermined wavelength, and the subsequent collimator lens 3 converts the laser beam L1 into parallel rays. The subsequent diffraction grating 4 converts the laser beam emitted from the collimator lens 3 into diffracted light of 0th order and ± 1st order, and the beam splitter 5 converts the laser beam L1 by the diffracted light of 0th order and ± 1st order. The light is transmitted and emitted to the objective lens 6.

The objective lens 6 focuses the laser beam L1 by the 0th and ± 1st order diffracted lights on the information recording surface of the optical disk 7, receives the return light obtained from the optical disk 7 as a result, and receives it from the beam splitter 5. Lead to. The beam splitter 5 reflects this return and outputs it to the collimator lens 8, and this collimator lens 8 focuses this return light on the light receiving surface of the light receiving element 9.

In the optical pickup 1, the laser beam L1 formed by the 0th order and ± 1st order diffracted lights applied to the optical disc 7 in this way is offset in the radial direction of the optical disc 7 by a predetermined distance to form a beam spot. In addition, the light-receiving surface of the light-receiving element 9 is formed so that the light amount of the return light due to the 0th and ± 1st-order diffracted light can be detected, and each light-receiving surface is divided and formed as necessary. With these, a track error signal can be generated by the so-called three-spot method.

In the diffraction grating 4 which generates the 0th order and ± 1st order diffracted light in this way, as shown in FIG. 10, on the glass substrate 4A which is a transparent substrate, repetitions corresponding to desired diffraction angles are repeated. It is formed by selectively stacking the dielectric layers 4B at the pitch P. In the conventional optical disk device, the width T of the dielectric layer 4B in the repeating direction is
The repetition pitch P is set to be approximately 1/2.

Further, as shown in FIG. 11, the light intensity of the ± 1st order diffracted light is 10 with respect to the light intensity of the 0th order diffracted light.
The thickness of the dielectric layer 4B is controlled so as to be about [%].

By the way, when these are applied to, for example, a mini disk, the diffraction grating 4 has a repeating pitch P.
Is 14 [μm], and the width T of the dielectric layer 4B is 7.0 [μm].
The dielectric layer 4B is made of a dielectric material having a refractive index of 1.5 and has a thickness of 250 [nm].
m] laser beam is used.

[0009]

By the way, in the conventional optical disk apparatus, there is a problem that when the diffraction grating 4 is displaced in the direction traversing the grating, an offset occurs in the tracking error signal. In the optical disk apparatus, this offset causes a problem. The accuracy of tracking control decreases.

If it is possible to sufficiently suppress the occurrence of the offset of the tracking error signal due to such a positional shift, the tolerance in the assembly work of the optical pickup can be expanded correspondingly, and the productivity of the optical pickup is improved. It is considered that it is possible to further simplify the design work. Further, it is considered that the allowable range of the variation of the light receiving elements is expanded and the productivity can be improved by this.

The present invention has been made in consideration of the above points, and an object of the present invention is to propose an optical pickup and an optical disk device capable of sufficiently suppressing the offset of the tracking error signal due to the displacement of the diffraction grating.

[0012]

In order to solve such a problem, in the invention of claim 1, the diffraction grating is applied to an optical pickup, and at least the first, second and third regions having different optical distances are provided. The first, second, and third regions are formed by being sequentially and cyclically repeated so that the phase difference between the 0th-order diffracted light and the ± 1st-order diffracted light is approximately 0 degrees or 180 degrees. The optical distance and the widths of the first, second and third regions in the repeating direction are set.

According to a sixth aspect of the present invention, applied to an optical disk device, the diffraction grating of the optical pickup has at least first, second and third regions having different optical distances sequentially and cyclically repeated. The optical distances of the first, second, and third regions and the first and second repeating directions are set so that the phase difference between the 0th-order diffracted light and the ± 1st-order diffracted light is approximately 0 degrees or 180 degrees. The widths of the second and third areas are set.

According to the structure of claim 1, when applied to an optical pickup, the diffraction grating is formed by cyclically repeating at least first, second and third regions having different optical distances, The optical distances of the first, second, and third regions and the first and second repeating directions are set so that the phase difference between the 0th-order diffracted light and the ± 1st-order diffracted light is approximately 0 degrees or 180 degrees. 2nd and 3rd
Since the width of the region is set, when the diffraction grating is displaced in the direction crossing the grating, the first-order diffracted light and -1
The 0th-order diffracted light similarly affects the condensing position of the 2nd-order diffracted light. That is, when the light intensity increases at the focus position of the first-order diffracted light, the light intensity can be increased at the focus position of the -1st-order diffracted light. It is possible to reduce the difference in the light intensity difference at the condensing position of the secondary diffracted light. On the other hand, in the conventional diffraction grating,
It was found that the 0th-order diffracted light had different effects on the 1st-order diffracted light and the -1st-order diffracted light when the diffraction grating was displaced in the direction crossing the grating. Thus, according to the configuration of claim 1, the light intensity at the condensing position of the first-order diffracted light and the light intensity at the condensing position of the -1st-order diffracted light do not differ depending on the displacement of the diffraction grating. Therefore, it is possible to sufficiently suppress the occurrence of the offset of the tracking error signal due to the difference in the light intensity.

Thus, according to the structure of claim 6, it is possible to provide an optical disk device capable of sufficiently suppressing the offset of the tracking error signal due to the displacement of the diffraction grating.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below in detail with reference to the drawings as appropriate.

(1) First Embodiment (1-1) Configuration of the First Embodiment FIG. 1 is a diffraction diagram of an optical pickup applied to an optical disk device according to the first embodiment of the present invention. It is sectional drawing which shows a grating. The optical pickup of the optical disk device according to this embodiment has the same configuration as the optical pickup of FIG. 9 except that the diffraction grating 14 is applied.

In this diffraction grating 14, a first area AR1, second areas AR21 and AR22, and a third area AR3 having different optical distances are sequentially and cyclically repeated.
By setting the optical distances of the third regions AR1 to AR3 and the widths W1, W21, W22, and W3 in the repeating direction, in the laser beam transmitted through the diffraction grating 14, the 0th-order diffracted light and the ± 1st-order The phase difference from the diffracted light is set to approximately 0 degree or 180 degrees.

Specifically, in this embodiment, the diffraction grating 14 is formed by repeating the selective stacking of the dielectric layer 14B on the glass substrate 14A which is a transparent plate material, so that these first to third regions are formed. AR1 to AR3 are formed. In the diffraction grating 14, the refractive index of the dielectric layer 14B is set to 1.5, and the repeating pitch P of these first to third regions AR1 to AR3 is set to 14.0 [μm]. In the diffraction grating 14, the first region AR1 has a thickness T1 = 0.52.
[Μm] and width W1 = 0.6 [μm], and the second regions AR21 and AR22 have a thickness T2 = 0.8.
[Μm] and widths W21 and W22 = 0.7 [μm]. In addition, the third area AR3 is the glass substrate 1
The width of the dielectric layer 14B should be 1
It is formed by 2.1 [μm].

The diffraction grating 14 is formed by first forming first and second regions with a film thickness of 0.52 [μm] on a glass substrate, and then further depositing a dielectric material on the upper layer, The second region is formed.

As a result, the diffraction grating 14 has the second area AR.
21 and AR22 have the same shape, the first area AR1
Are formed on both sides of the same, so that the same periodic structure is repeated symmetrically on the -1st order diffracted light side and the + 1st order diffracted light side with the 0th order diffracted light as the center.

The diffraction grating 14 has an optical distance of these first to third areas AR1 to AR3 and a width W1 in the repeating direction.
By setting W3 to W3, the light intensity of the 0th-order diffracted light is set to be 60% or more of all diffracted light, and the ± 1st-order diffraction is performed with respect to the light intensity of the 0th-order diffracted light. The light intensity of the light is set to 8 to 15%.

(1-2) Operation of the First Embodiment In the above configuration, in the optical pickup according to the present embodiment, the laser beam emitted from the semiconductor laser is 0th order, ± 1 by the diffraction grating 14. The laser beam is converted into the next diffracted light, and the laser beam by the 0th order and the ± 1st order diffracted light is applied to the optical disk, and the resulting 0 is obtained.
The returning light due to the diffracted light of the next ± 1st order is received by the light receiving element, and the tracking error signal is generated by the three-spot method.

In the diffraction grating 14 for generating the 0th and ± 1st order diffracted light in this way, the phase difference between the 0th order diffracted light and the ± 1st order diffracted light is approximately 0 degree or 180 degrees. By setting so that when the diffraction grating 14 is displaced in the direction crossing the grating, the 0th-order diffracted light with respect to the focus position of the 1st-order diffracted light and the focus position of the -1st-order diffracted light Will have the same effect. That is, when the light intensity increases at the focus position of the first-order diffracted light, the light intensity can be increased at the focus position of the -1st-order diffracted light.
As a result, the first-order diffracted light due to the displacement of the diffraction grating and −
The difference in light intensity at the condensing position of the first-order diffracted light can be significantly reduced as compared with the conventional case. As a result, in the optical disc device, the offset of the tracking error signal due to the displacement of the diffraction grating can be sufficiently suppressed.

That is, the laser beam incident on the diffraction grating has a uniform intensity distribution represented by a Gaussian distribution, and the same intensity is obtained for each n-th order diffracted light focused on the information recording surface of the optical disc. Depending on the distribution, it will be focused on the information recording surface. As a result, the light intensity at the condensing position of each diffracted light is affected by the diffracted light adjacent to or adjacent to each other.

In the diffraction grating 4 having the conventional configuration described above with reference to FIG. 10, as shown in FIG. 11, since the even-order diffracted light is sufficiently suppressed, the light amplitude at the converging position of the ± first-order diffracted light is obtained. Can be approximated by combining the amplitudes of the ± 1st-order diffracted light and the 0th-order diffracted light, respectively.

In the diffraction grating 4 having the conventional configuration, ±
The phase difference due to the complex amplitude of the 1st-order diffracted light and the 0th-order diffracted light is 90
When the diffraction grating 4 is displaced in the grating direction, the 0th-order diffracted light affects the + 1st-order diffracted light and the −1st-order diffracted light differently. As a result, it was found that the light intensity differs between the + 1st-order diffracted light focusing position and the -1st-order diffracted light focusing position, and an offset occurs in the tracking error signal.

Here, the absolute value of the difference value of the light intensities at the converging position of the + 1st order diffracted light and the −1st order diffracted light is divided by the added value of these light intensities, and the value obtained by this division is expressed as a percentage. Define strength balance. Figure 2
FIG. 4 is a characteristic curve diagram showing a result of calculating the intensity balance by sequentially changing the phase difference between the ± 1st-order diffracted light and the 0th-order diffracted light. In case of 90 degrees, the maximum is 0.59
It was found that a strength balance of [%] was produced. In this simulation, the absolute values of the amplitudes of the ± 1st-order diffracted light and the 0th-order diffracted light were set to be constant. As a result, the diffraction grating having the conventional configuration has a structure that is most easily affected by the positional shift in the direction crossing the grating, and the phase difference between the ± 1st-order diffracted light and the 0th-order diffracted light is almost 0 degree or 180 degrees. It can be seen that the strength balance becomes the smallest when set.

Therefore, from a practical viewpoint, the intensity balance is preferably set to 0.3 or less, more preferably 0.15 or less to sufficiently reduce the offset of the tracking error signal. In order to secure this intensity balance, the phase difference between the ± 1st-order diffracted light and the 0th-order diffracted light is set within the range of 0 ° ± 30 ° or 180 ° ± 30 °, and the tracking error due to the displacement of the diffraction grating is caused. The signal offset can be made sufficiently small.

FIG. 3 shows a diffraction grating 1 according to this embodiment.
FIG. 4 is a characteristic curve diagram showing a change in strength balance with respect to position deviation for No. 4; In the case of this diffraction grating 14, the complex amplitude phase difference between the ± 1st-order diffracted light and the 0th-order diffracted light is 169 degrees, and when the diffraction grating 14 is displaced in the direction traversing the grating, the intensity balance is at most 0. It can be suppressed to 14%, whereby the occurrence of tracking offset due to the displacement of the diffraction grating can be significantly reduced as compared with the conventional case.

Further, the ratio of the 0th-order diffracted light intensity to the total intensity is 62.0%, ± 1 with respect to the 0th-order diffracted light intensity.
The light intensity at the condensing position of the next-order diffracted light is 10.0 [%]
Therefore, it is possible to secure a practical light amount distribution that is almost the same as that of the diffraction grating of the conventional configuration. By replacing the diffraction grating of the conventional configuration with the diffraction grating of this embodiment, In addition, the accuracy of tracking control can be improved, and the productivity can be improved.

In the diffraction grating 14, the second regions AR21 and AR22 have the same shape, so that the first region A
Formed on both sides of R1, centering on the 0th-order diffracted light and -1
Since the same periodic structure is repeated symmetrically on the 2nd-order diffracted light side and the + 1st-order diffracted light side, the 0th-order and ± 1st-order diffracted lights are generated by the periodic structure of three types of regions having different optical distances. The difference in the characteristics of the ± 1st-order diffracted light can be reduced by making it.

(1-3) Effects of the First Embodiment According to the above configuration, three areas AR having different optical distances are provided.
The diffraction grating 14 is formed by repeating 1, AR21, AR22, AR3, and these three regions are arranged so that the phase difference between the 0th-order diffracted light and the ± 1st-order diffracted light is approximately 0 degrees or 180 degrees. By setting the optical distances and widths of AR1, AR21, AR22, and AR3, it is possible to sufficiently suppress the offset of the tracking error signal due to the displacement of the diffraction grating.

Further, with respect to the light intensity of the 0th-order diffracted light, ± 1
The light intensity of the next diffracted light is set to 8 to 15%, and the light intensity of the 0th diffracted light is 60% of all diffracted light.
By setting the ratio to be equal to or more than [%], it is possible to sufficiently suppress the offset of the tracking error signal due to the displacement of the diffraction grating while maintaining the compatibility with the diffraction grating having the conventional configuration.

(2) Second Embodiment FIG. 4 is a sectional view showing a diffraction grating applied to an optical disk device according to the second embodiment of the present invention. This diffraction grating 24 is applied in place of the diffraction grating 14 described above with reference to FIG. In the configuration shown in FIG. 4, the same components as those of the diffraction grating 14 are designated by the corresponding reference numerals, and duplicate description will be omitted.

Similar to the diffraction grating 14, the diffraction grating 24 has first to third areas AR1 and AR2 having different optical distances.
1 and AR22 and AR3 are sequentially and cyclically formed to form a phase difference between the 0th order diffracted light and the ± 1st order diffracted light of approximately 0 degree or 180 degrees. Optical distances of third regions AR1, AR21 and AR22, AR3, widths W1, W21 and W22, W3 in the repeating direction
Is set.

Further, these first to third areas AR1 to AR
By setting the optical distance of 3 and the widths W1 to W3 in the repeating direction, the light intensity of the 0th-order diffracted light is 60% of all diffracted light.
The light intensity of the ± 1st-order diffracted light is set to 8 to 15% with respect to the light intensity of the 0th-order diffracted light.

Specifically, the diffraction grating 24 is formed by repeating selective deposition of the dielectric layer on the glass substrate 14A, similarly to the diffraction grating 14 according to the first embodiment. In the above form, a dielectric layer having a refractive index of 1.5 is applied, and the repeating pitch P is set to 14.0 [μm]. The first region AR1 is formed with a film thickness T1 = 1.4 [μm] and a width W1 = 11.3 [μm], and the second regions AR21 and AR22 are
On both sides of the region AR1 of T2 = 0.68
[Μm] and width W21 = W22 = 0.85 [μm]. Also, the third area AR3
However, it is designed such that no dielectric layer is formed on the glass substrate 14A.

FIG. 5 is a characteristic curve diagram showing the characteristic of the diffraction grating 24. In the diffraction grating 24, the complex amplitude phase difference between the 0th order diffracted light and the ± 1st order diffracted light is 11 degrees,
The diffraction grating 24 was shifted so as to cross the grating, and the intensity balance changed to 0.066 [%] at the maximum. Further, the 0th-order diffracted light intensity can be set to 60.1 [%] with respect to the overall intensity, and the ± 1st-order diffracted light position intensity can be set to 9.0 [%] with respect to the 0th-order diffracted light intensity. did it.

With the configuration shown in FIG. 4, the same effect as that of the first embodiment can be obtained.

(3) Third Embodiment FIG. 6 is a sectional view showing a diffraction grating applied to an optical disk device according to a third embodiment of the present invention. This diffraction grating 34 is applied in place of the diffraction grating 14 described above with reference to FIG. In the configuration shown in FIG. 6, the same components as those of the diffraction grating 14 are designated by the corresponding reference numerals, and the duplicated description will be omitted.

Similar to the diffraction grating 14, the diffraction grating 34 has first to third areas AR1 and AR2 having different optical distances.
1 and AR22, AR31 and 32 are sequentially and cyclically formed, and the phase difference between the 0th-order diffracted light and the ± 1st-order diffracted light is approximately 0 degree or 180 degrees. 1st-3rd area | region AR1, AR21 and AR22, A
Optical distance of R31 and AR32, width W in repeating direction
1, W21 and W22, W31 and W32 are set.

The diffraction grating 34 has a refractive index of 1.5.
Of the dielectric layer, the first region AR1 has a film thickness T1 = 0.
8 [μm] and width W1 = 1.8 [μm],
The third regions AR31 and AR32 in which no dielectric layer is formed have the width W31 = on both sides of the first region AR1.
W32 = 5.2 [μm], and the second regions are formed outside the third regions AR31 and AR32, respectively.
Regions AR21 and AR22 have a film thickness T2 = 1.52.
[Μm] and width W21 = W22 = 0.9 [μm]. The repeating pitch P of these regions is 14 [μm].

With these, the diffraction grating 34 is set such that the light intensity of the 0th-order diffracted light is 60% or more of all the diffracted light, and the light intensity of the 0th-order diffracted light is
The light intensity of the ± 1st order diffracted light is set to 8 to 15%.

FIG. 7 is a characteristic curve diagram showing the characteristic of the diffraction grating 34. In this diffraction grating 34, the complex amplitude phase difference between the 0th order diffracted light and the ± 1st order diffracted light becomes 173 degrees, and the diffraction grating 34 becomes The intensity balance was changed to 0.033 [%] at the maximum by shifting across the lattice. Further, the 0th-order diffracted light intensity can be set to 60.0 [%] with respect to the overall intensity, and the ± 1st-order diffracted light position intensity can be set to 14.2 [%] with respect to the 0th-order diffracted light intensity. did it.

With the configuration shown in FIG. 6, the same effect as that of the first embodiment can be obtained.

(4) Other Embodiments In the above embodiment, the case where the first to third regions having different optical path distances are formed by controlling the film thickness of the dielectric layer has been described. The invention is not limited to this, and as shown in FIG. 8, dielectric films having different refractive indices n1 and n2 may be deposited to form regions having different optical path distances.

In the above embodiment, the case where the diffraction grating is formed by the first to third regions having different optical path distances has been described, but the present invention is not limited to this, and the diffraction grating is formed by four or more regions. A grid may be created.

Further, in the above-mentioned embodiments, the case where the dielectric is deposited on the glass substrate to form the diffraction grating has been described, but the present invention is not limited to this, and various transparent substrates are used instead of the glass substrate. Can be widely applied.

[0050]

As described above, according to the present invention, the diffraction grating is constructed by repeating at least three regions having different optical distances, and the phase difference between the 0th order diffracted light and the ± 1st order diffracted light is By setting the optical distances and widths in these three regions so as to be approximately 0 degrees or 180 degrees, it is possible to sufficiently suppress the offset of the tracking error signal due to the displacement of the diffraction grating.

[Brief description of drawings]

FIG. 1 is a sectional view showing a diffraction grating applied to an optical pickup of an optical disc device according to a first embodiment of the present invention.

FIG. 2 is a characteristic curve diagram for explaining the operation of the diffraction grating of FIG.

FIG. 3 is a characteristic curve diagram showing characteristics of the diffraction grating of FIG.

FIG. 4 is a sectional view showing a diffraction grating applied to an optical pickup of an optical disc device according to a second embodiment of the invention.

5 is a characteristic curve diagram showing characteristics of the diffraction grating of FIG.

FIG. 6 is a sectional view showing a diffraction grating applied to an optical pickup of an optical disc device according to a third embodiment of the invention.

7 is a characteristic curve diagram showing characteristics of the diffraction grating of FIG.

FIG. 8 is a cross-sectional view showing a diffraction grating applied to an optical pickup of an optical disc device according to another embodiment.

FIG. 9 is a side view showing an optical pickup.

FIG. 10 is a sectional view showing a diffraction grating applied to a conventional optical pickup.

FIG. 11 is a characteristic curve diagram showing characteristics of a conventional diffraction grating.

[Explanation of symbols]

1 ... Optical pickup, 4, 14, 24, 34 ... Diffraction grating, 4A, 14 ... Glass substrate, 4B, 14B ... Dielectric layer

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 5D118 AA07 AA18 BA01 CD03 CF16                       CG24 CG33 CG44                 5D119 AA29 AA39 BA01 EA02 EB14                       EC41 JA22                 5D789 AA29 AA39 BA01 EA02 EB14                       EC41 JA22

Claims (6)

[Claims] 1. A laser beam emitted from a laser light source is incident on a diffraction grating to generate at least 0th order and ± 1st order diffracted light, and the laser beam by the 0th order and ± 1st order diffracted light is recorded on an optical disk. In the optical pickup for irradiating the optical disc to access the optical disc, the diffraction grating is such that at least first, second, and third regions having different optical distances are sequentially and cyclically repeated, and the 0th-order diffracted light, The first, second, and so on, so that the phase difference with the ± 1st-order diffracted light is approximately 0 degrees or 180 degrees.
An optical pickup, wherein the optical distance of a third region and the widths of the first, second and third regions in the repeating direction are set. 2. The phase difference between the 0th-order diffracted light and the ± 1st-order diffracted light is in the range of 0 ° ± 30 ° or 180 ° ± 30 °. The optical pickup described. 3. The light according to claim 1, wherein the light intensity of the ± 1st order diffracted light is 8 to 15% with respect to the light intensity of the 0th order diffracted light. pick up. 4. The optical pickup according to claim 1, wherein the light intensity of the 0th-order diffracted light is 60% or more of the light intensity of all diffracted light. 5. The diffraction grating is formed by selectively laminating a dielectric on a transparent substrate, and the first region is a region where no dielectric is laminated on the transparent substrate. The optical pickup according to claim 1, wherein the second and third regions are regions in which the dielectric is laminated on the transparent substrate with different thicknesses. 6. An optical disk device for irradiating an optical disk with a laser beam emitted from an optical pickup to access the optical disk, wherein the optical pickup makes the laser beam emitted from a laser light source incident on a diffraction grating, and at least 0th order, ± 1st order diffracted light is generated, and the laser beam is emitted by the 0th order ± 1st order diffracted light, and the diffraction grating includes at least first, second, and third optical distances different from each other. Regions are sequentially and cyclically repeated so that the phase difference between the 0th-order diffracted light and the ± 1st-order diffracted light is approximately 0 degree or 180 degrees.
An optical disk device, wherein the optical distance of a third area and the widths of the first, second and third areas in the repeating direction are set.