JPH08329470A - Method and device for reproducing and optical disk - Google Patents

Abstract

PURPOSE: To obtain the condition becoming cross talk free by forming a phase difference ϕ when a land track is reproduced to be different from the phase difference ϕ when a groove track is reproduced. CONSTITUTION: The phase differences of respective pickups are controlled by a Bavinet-Soleil phase compensation plate 5. For instance, the control is performed so that the phase difference of a land track reproducing optical pickup is +5 deg., and the phase difference of a groove track reproducing optical pickup becomes -5 deg.. Then, a wavelength of alight source is 680nm, an NA of an objective lens is 0.55, an eclipse coefficient DEW is 0.8, a polarization state is linear polarization and its direction is parallel to a groove. In such a case, CTL=-56.2dB, CTG=-56.0dB. When the CTG is obtained by reproducing by the groove reproducing optical pickup as a usual example, CTG=-48.5 dB, and the CTG is increased remarkably. Thus, when reproduced using the optical pickup with the different phase difference, the cross talk is reduced by 7-8dB.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reproducing method, a reproducing apparatus and an optical disc, and more particularly to a reproducing method, a reproducing apparatus and an optical disc of a land / groove recording system for recording on both a land and a groove.

[0002]

2. Description of the Related Art An optical recording medium capable of storing information at high density is expected to expand its market as a large capacity external memory. For example, an optical disc has been attracting attention as an external memory of a computer because it can be reproduced at high speed, and various types of optical recording media having different information storage methods and different sizes have been proposed. For example, in the 5.25 inch diameter size, the write-once type that allows information to be written only once and the magneto-optical type that allows rewriting of information, and the 3.5 inch diameter in the ROM type that is read-only The magneto-optical type and the partial ROM type in which magneto-optical and ROM coexist are standardized by the ISO standard, and are expected to become more widely used in the future. In addition, recently, CD-ROM and
MD (Mini Disc) is rapidly spreading, and future trends are drawing attention.

Recording is performed on these optical disks by a laser beam from an optical pickup of a recording / reproducing apparatus.
The recorded portion is called a mark, and the area where the marks are continuously arranged is called a track. In order to increase the recording density, it is necessary to arrange these tracks in order, and for that purpose, it is necessary to guide the laser beam along the tracks. That is, we need a guide for tracking, which is generally in the form of a concave or convex groove,
The disk is formed in a spiral shape from the inner circumference to the outer circumference. This groove is called a guide groove.

Further, the guide groove will be described in detail. As defined in the ISO standard, a portion that is concave when viewed from the optical pickup, that is, a portion that is far away is called a land, and is viewed from the pickup. In this case, the part that becomes convex, that is, the part that becomes closer is called a groove. Information is recorded on either lands or grooves. Recording on a land is called a land recording method, and recording on a groove is called a groove recording method. A route for recording information is called a track. The track pitch from the track center to the adjacent track center is called the track pitch.

The width of the groove is defined as W = (Wtop + Wbottom) / 2, where Wtop is the width at the top of the groove and Wbottom is the width at the bottom of the groove. Also,
The height from the bottom of the groove to the top of the groove is called the groove depth. Among the optical discs currently on the market, the land recording type has a groove width of 0.3 to 0.6 μm, and the groove depth is the wavelength of the recording and reproducing laser λ and the refractive index of the optical recording medium substrate is n. Then, λ / (4 ・
n) to λ / (8 · n). Also, the track pitch is
1.6 μm. Recently, it has been reported that the track pitch is narrowed in order to record higher density information, and there are examples such as the track pitch of 1.4 μm, 1.2 μm and 1.0 μm.

The optical recording medium records information on either the land or the groove. The information recording area records a data area in which a user records information and address information such as a track number and a sector number which is not directly used by the user but is used by the recording / reproducing apparatus to manage information on an optical recording medium. Header area. These pieces of information are recorded as a mark string and a pit string.

The data area generally has different contents for each optical recording medium. On the other hand, the header area is generally the same in all optical recording media. Therefore, for mass production, the header region is generally provided in the form of a pit row at the stage of manufacturing the substrate of the optical recording medium. In this case, the header area may be called a preformatted area. The preformatted area is transferred from the stamper so as to form a pit row that is convex when viewed from the pickup.

By the way, to increase the recording density,
Various approaches have been taken for this purpose in order to further increase the advantages of the optical recording medium. For example, a method of narrowing the track pitch as described above has been proposed and studied. However, when a semiconductor laser beam with a wavelength of 780 to 830 nm is focused by an objective lens with a numerical aperture (NA) of 0.5 to 0.6, if the track pitch is made smaller than 1.4 μm, the information recorded on the adjacent track at the time of reproduction is recorded. There is a problem that the leakage (called crosstalk) is significantly increased, the tracking error signal necessary for the tracking operation is significantly decreased, and the tracking accuracy is deteriorated. Semiconductor lasers with wavelengths of 630 to 690 nm have been developed to avoid these problems.
The output is small and the price is high, so there was a problem in practicality.

Therefore, land / groove recording has been proposed as another approach for increasing the recording density. This is a method of increasing the recording capacity by recording the data, which has conventionally been recorded only on either the land or the groove, on both the land and the groove. In this method, the land width and the groove width are the same in order to read the data written in the land and the data written in the groove with the same C / N value. That is, when the track pitch is 1.4 μm, both the land width and the groove width are 0.7 μm. This method can make crosstalk between adjacent groove and land to zero or minimum value (crosstalk free) by selecting the groove depth appropriately, and it is very effective for high density. Is.

In the land / groove recording system, the first document relating to the groove depth at which crosstalk is free is JP-A-57-138065 (corresponding US Pat. No. 4,423,502). In this document, when the wavelength of the reproducing laser beam is λ and the refractive index of the optical disk substrate is n, the groove depth is λ /
It is described that if it is about (6n), the crosstalk becomes small. However, no optical analysis of the groove depth that makes crosstalk free is described, and a plurality of documents issued after that do not disclose.
Only the description similar to 38065 is seen.

By the way, the present inventor has previously analytically derived a conditional expression that makes crosstalk free in the data area. First, the derivation process will be briefly described below. Now, when data is recorded on an arbitrary land and there is no recording on the adjacent groove, the reproduction signal strength when reproducing the data recorded on the land is set to A. Next, when data is recorded in the adjacent groove and no data is recorded in the land, the reproduction signal strength (crosstalk signal strength from the adjacent groove) when reproducing the land is set to a. Assuming that the groove depth is d _G , the refractive index of the optical disk substrate is n, and the wavelength of the reproducing laser beam is λ, the reproduction signal strength when data is recorded on an arbitrary land and the groove adjacent thereto and the land is reproduced. I _L can be expressed by the following equation.

I _L = | A + a · exp (i4πnd _G / λ) | ² = A ² + a ² + 2Aa · cos (4πnd _G / λ) where I _L = A ² is a crosstalk-free condition, a ² + 2Aa · cos (4πnd _G / λ) = 0 (a) holds.

Contrary to the above case, let us consider the reproduction signal strength I _G when data is recorded on an arbitrary land and a groove adjacent thereto and the groove is reproduced. In this case, since the groove depth is −d _G , I _G = | A + a · exp (−i4πnd _G / λ) | ² = A ² + a ² + 2Aa · cos (−4πnd _G / λ) where I _G = A ² is a crosstalk-free condition, and therefore a ² + 2Aa · cos (4πnd _G / λ) = 0 holds. This is exactly the same as the expression (a). That is,
The crosstalk-free condition is the same regardless of whether data is recorded on an arbitrary land and a groove adjacent to the land, or whether the land is reproduced or the groove is reproduced.

However, this is true only when the recording mark is purely an intensity modulation mark. actually,
Not only magneto-optical discs, but also read-only optical discs such as CDs and phase-change optical discs, recording marks are mixed modulation marks of intensity and phase (for example, in magneto-optical discs, intensity modulation is phase modulation by Kerr rotation angle θ _K. Car ellipticity χ
According to _K), and the signal needs to be treated as a complex number. Therefore, the above relationship does not hold.

This will be described in more detail. When the data is recorded on the arbitrary land by the magneto-optical mark and there is no recording on the adjacent groove, the reproduction signal strength when reproducing the land is A + iB. A is the car rotation angle θ _K
And B is a modulation component due to the Kerr ellipticity angle χ _K. Next, when the data is recorded in the adjacent groove and the land is not recorded, the reproduction signal strength (crosstalk signal from the adjacent groove) when reproducing the land is a.
+ Ib. a is a modulation component due to the Kerr rotation angle θ _K , and b is a modulation component due to the Kerr ellipticity angle χ _K. Assuming that the groove depth is d _G , the refractive index of the optical disk substrate is n, and the wavelength of the reproduction laser beam is λ, the reproduction signal strength I when data is recorded on an arbitrary land and a groove adjacent thereto and the land is reproduced. _L can be expressed by the following formula.

I _L = | A + iB + (a + ib) · exp (i4πnd _G / λ) | ² = A ² + B ² +2 (aA + bB) ・ cos (4πnd _G / λ) +2 (aB-Ab) ・ sin (4πnd _G / lambda) where, I _L = from a ² + B ² is a condition for crosstalk-free, 2 (aA + bB) · cos (4πnd G / λ) +2 (aB-Ab) · sin (4πnd G / λ) = 0 (B) holds.

Contrary to the above case, let us consider the reproduction signal strength I _G when data is recorded on an arbitrary land and a groove adjacent thereto and the groove is reproduced. In this case, since the groove depth is −d _G , I _G = | A + iB + (a + ib) · exp (−i4πnd _G / λ) | ² = A ² + B ² +2 (aA + bB) · cos (4πnd _G / λ) −2 (aB−Ab) · sin (4πnd _G / λ) Here, since I _G = A ² + B ² is a crosstalk-free condition, 2 (aA + bB) · cos (4πnd _G / λ) −2 ( aB−Ab) · sin (4πnd _G / λ) = 0 (c) holds. As is clear here, since the equation (b) is not equal to the equation (c), the condition equation for crosstalk free is different between when the land track is reproduced and when the groove track is reproduced, and the optimum groove depth is obtained. I'm sorry.

[0018]

As described above,
When the recording mark is a mixed modulation mark of intensity and phase, the groove depth at which crosstalk is free is not determined regardless of whether the land track or the groove track is reproduced. However, there was a problem that high density could not be achieved.

The present invention solves such problems and, for example,
An object of the present invention is to provide a reproducing method and a reproducing apparatus for a land / groove recording type optical disk which can obtain a condition that crosstalk is free even in magneto-optical recording.

[0020]

In order to solve the above problems, the inventor of the present invention has found that the phase difference φ of the optical system when reproducing the land.
By setting the phase difference φ ′ of the optical system for reproducing the groove to a different value, the crosstalk-free condition can be satisfied in both cases, and especially when φ = −φ ′, The inventors have found that excellent results can be obtained and have completed the present invention.

Therefore, the first aspect of the present invention is, "In the reproducing method of the optical disc for recording information on both the land and the groove, the phase difference φ when reproducing the land track and the phase difference φ when reproducing the groove track. 'Providing a method of reproducing an optical disk characterized by different ", and secondly, in a method of reproducing an optical disk in which information is recorded on both a land and a groove, a phase difference φ of an optical system when reproducing a land track. And a method for reproducing an optical disk characterized in that the phase difference φ ′ of the optical system when reproducing the groove track is different. Thirdly, “the optical system for reproducing the land track and the groove track are provided. 3. The optical disc reproducing method according to claim 2, wherein the optical system for reproducing is provided separately. Fourthly, “substantially φ =
The optical disk reproducing method according to claim 1 or 2, characterized in that −φ ′ is satisfied. Fifth, in an optical disk reproducing apparatus for recording information on both lands and grooves, Phase difference φ when reproducing,
The present invention provides an "optical disc reproducing apparatus characterized in that a phase difference φ'when reproducing a groove track is set to different values", and sixthly, in an "optical disc reproducing apparatus for recording information on both a land and a groove". An optical system for reproducing the land track and an optical system for reproducing the groove track, and a phase difference φ of the optical system for reproducing the land track, and an optical system for reproducing the groove track. An optical disc reproducing apparatus characterized in that the phase difference φ ′ of the system is different.
= −φ ′, the optical disc reproducing apparatus according to claim 5 or 6 is provided, and eighthly, “the optical disc for recording information on both the land and the groove,
An optical disc characterized in that the in-plane birefringence direction of the substrate at the land and the in-plane birefringence direction of the substrate at the groove are different from each other. Ninth, "In an optical disc for recording information on both the land and the groove, An optical disc characterized in that the phase difference φ in the land and the phase difference φ ′ in the groove are different from each other, and tenthly, “The phase difference φ of the substrate in the land and the phase difference φ ′ of the substrate in the groove are different. 11. An optical disc according to claim 9, wherein the phase difference φ of the recording film at the land and the phase difference φ ′ of the recording film at the groove are different from each other. Optical disc described "
The twelfth aspect of the present invention provides a twelfth aspect of the present invention, "The optical disk reproducing apparatus according to claim 9, wherein: substantially φ = -φ '."

[0022]

In the past, the phase difference of the optical system for reproducing the magneto-optical disk was generally set to zero, but in the case where the reproduction optical system is provided with the phase difference φ (≠ 0). Think
First, when data is recorded on an arbitrary land and there is no recording on the adjacent groove, the reproduction signal intensity when reproducing the land is reproduced with respect to the phase modulation component B by the Kerr ellipticity angle χ _K described above. Since the phase modulation component C due to the phase difference φ of the optical system is multiplied, it becomes A + iBC. Next, when data is recorded in the adjacent groove and there is no recording in the land, the reproduction signal strength (crosstalk signal strength from the adjacent groove) when reproducing the land also depends on the Kerr ellipticity angle χ _K. Since the phase modulation component b is multiplied by the phase modulation component c due to the phase difference φ of the reproduction optical system, a + ibc
Becomes Assuming that the groove depth is d _G , the refractive index of the optical disk substrate is n, and the wavelength of the reproduction laser beam is λ, the reproduction signal strength I when data is recorded on an arbitrary land and a groove adjacent thereto and the land is reproduced. _L can be expressed by the following formula.

I _L = | A + iBC + (a + ibc) * exp (i4πnd _G / λ) | ² = A ² + (BC) ² + 2 (aA + bcBC) * cos (4πnd _G / λ) +2 (aBC-Abc) * sin ( 4πnd _G / λ) where, because ^{_{I L = a 2 + (BC}} ) 2 is a condition for crosstalk-free, 2 (aA + bcBC) · cos (4πnd G / λ) +2 (aBC-abc) · sin (4πnd _G / λ) = 0 (d) holds.

Next, consider the case where the groove is reproduced by the reproducing optical system to which the phase difference φ '(≠ 0) is given. When the data is recorded in an arbitrary groove and there is no recording in the adjacent land, the reproduction signal intensity when reproducing the groove is also the phase difference of the reproduction optical system with respect to the phase modulation component B due to the Kerr ellipticity angle χ _K. Since the phase modulation component C ′ due to φ ′ is multiplied, A +
iBC '. Next, when data is recorded in the adjacent groove and there is no recording in the groove, the reproduction signal strength (crosstalk signal strength from the adjacent land) when reproducing the groove also depends on the Kerr ellipticity angle χ _K. Since the phase modulation component b is multiplied by the phase modulation component c ′ due to the phase difference φ ′ of the reproducing optical system, a + ibc ′ is obtained. Assuming that the groove depth is d _G , the refractive index of the optical disk substrate is n, and the wavelength of the reproduction laser beam is λ, the reproduction signal strength I when data is recorded on an arbitrary land and a groove adjacent thereto and the groove is reproduced. _G can be expressed by the following formula.

I _G = | A + iBC ′ + (a + ibc ′) · exp (−i4πnd _G / λ) | ² = A ² + (BC ′) ² + 2 (aA + bc′BC ′) · cos (4πnd _G / λ) − 2 (aBC′−Abc ′) · sin (4πnd _G / λ) Here, since I _G = A ² + (BC ′) ² is a crosstalk-free condition, 2 (aA + bc′BC ′) · cos ( _{4πnd G / λ) -2 (aBC'} -Abc ') · sin (4πnd G / λ) = 0 (e) is satisfied.

If the relationship between the phase difference φ of the optical system when reproducing the land track and the phase difference φ ′ of the optical system when reproducing the groove track is φ = −φ ′,
Since C = −C ′ and c = −c ′, when these are substituted into the equation (e), the second term on the left side of the equation (e) is −2 (aBC′−Abc ′) · sin (4πnd _G / λ) = -2 (-aBC + Abc) -sin (4πnd _G / λ) = + 2 (aBC-Abc) -sin (4πnd _G / λ) This is the same as the second term on the left side of the equation (d), and (d ) Equation = (e) Equation This means that there is an optimum groove depth that is crosstalk-free during both land track reproduction and groove track reproduction, and this has solved the problem.

Actually, instead of strictly setting φ = −φ ′,
Even if φ + ε = − (φ ′ + ε ′), the substantial crosstalk can be sufficiently reduced during the land track reproduction and the groove track reproduction. Note that the phase adjustment may use another phase compensating means instead of using the Babinet Soleil phase compensating plate. For example, a crystalline element, a plastic element,
Any birefringent medium such as an element having strain due to stress can be used. Further, an element such as a KDP crystal or a Pockels cell that causes a phase difference due to an electro-optical effect such as a Pockels effect may be used. Furthermore, a phase difference may be added to the optical element itself by a collimator lens, a beam splitter, a polarized beam splitter, a half-wave plate, a hologram element, a grating, or the like.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

[0029]

Example 1 First, a method for measuring crosstalk will be described. When data is recorded in an arbitrary land and no data is recorded in the adjacent groove, the signal component strength of the reproduction signal when reproducing the data recorded in the land, that is, the carrier level is C _LM (dBm). Next, if the signal component strength of the reproduced signal when reproducing the adjacent groove having no recording, that is, the carrier level leaking from the recording of the land track to the groove is C _GO (dBm), from the land track to the groove track. The crosstalk CT _{L of} is expressed as

CT _L = C _GO −C _LM (dBm) Similarly, when data is recorded in an arbitrary groove and there is no recording in the adjacent land, the reproduction signal of the reproduction signal when reproducing the data recorded in the groove The signal component strength, that is, the carrier level is C _GM (dBm). Next, the signal component strength of the reproduction signal when reproducing the adjacent land having no recording, that is,
If the carrier level leaking from the recording of the groove track to the land is C _LO (dBm), the crosstalk CT _G from the land track to the groove track is expressed as follows.

CT _G = C _LO −C _GM (dBm) Then, the crosstalk is actually measured. First, a magneto-optical recording / reproducing apparatus equipped with two pickups, a land track reproducing optical pickup and a groove track reproducing optical pickup, is prepared. A magneto-optical disk was set in this device, and recording was performed on the land track and groove track of this disk with a magneto-optical mark, and crosstalk was measured. A conceptual diagram of the optical system of this magneto-optical recording / reproducing apparatus is shown in FIG.

The phase difference of each pickup can be controlled by a Babinet Soleil phase compensator incorporated in each optical system. Incidentally, the phase difference of the land track reproducing optical pickup was + 5 °, and the phase difference of the groove track reproducing optical pickup was controlled to be −5 °. In both optical pickups, the wavelength of the light source is 680 nm, the NA of the objective lens is 0.55, the vignetting coefficient is D / W 0.8, the polarization state is linearly polarized light, and its direction is parallel to the groove.
The magneto-optical disk has a track pitch = land width = groove width = 0.8 μm and a groove depth of 67.2 nm.

Select one land, mark length 2μm
After recording with a mark pitch of 4 μm, the land track was reproduced with an optical pickup for groove reproduction and the C _LM was measured with a spectrum analyzer. Next, the adjacent groove track was reproduced by the groove reproducing optical pickup, C _GO was measured, and CT _L was obtained from these values.
Then, after erasing the mark described above, select a single groove, marks length 2 [mu] m, after the recording mark pitch 4 [mu] m, C _GM with a spectrum analyzer to play the groove track in a land reproducing optical pickup Was measured. Next, the adjacent land track is reproduced by the land reproduction optical pickup to measure C _LO , and from these values, C
I asked for T _G. The results are CT _L = -56.2 dB, CT _G =
It was -56.0 dB.

[0034]

[Comparative Example 1] As a conventional example, reproduction was performed with an optical pickup for groove reproduction to obtain CT _G. The result is CT _G =
It was −48.5 dB, which was a significant increase. From this result and the result of Example 1, crosstalk is reduced by 7 to 8 dB by reproducing using an optical pickup having a different phase difference between the land reproduction and the groove reproduction, and both the land and the groove have a low crosstalk level. You can see that the data can be reproduced.

[0035]

Second Embodiment A magneto-optical recording apparatus equipped with an optical pickup having a Pockels cell as a part of an optical system and having a controllable phase difference is prepared. A magneto-optical disk is set in this apparatus, and recording is performed on a land track and a groove track of this disk with a magneto-optical mark, and crosstalk is measured. A conceptual diagram of the optical system of this magneto-optical recording / reproducing apparatus is shown in FIG. The Pockels cell is an element that produces a phase difference proportional to the applied voltage in the axial direction orthogonal to the incident light when a voltage is applied. When reproducing the land track, the phase difference is + 5 °, and the groove track is When reproducing, the phase difference is controlled to be -5 °. The wavelength of the light source is 680 nm, the NA of the objective lens is 0.5.
5, vignetting coefficient D / W 0.8, polarization state is linearly polarized light, and its direction is parallel to the groove. The magneto-optical disk has a track pitch = land width = groove width = 0.8μ.
m, the groove depth is 67.2 nm.

When CT _L and CT _G were obtained in exactly the same manner as in Example 1, the results were CT _L = -56.1 dB and CT _G = -56.2.
It was dB.

[0037]

Comparative Example 2 As a conventional example, the same measurement was carried out with the phase difference due to the Pockels cell fixed at + 5 °. The result is CT
_L = -56.1 dB, CT _G = -48.5 dB, and CT _G increased significantly. From this result and the result of Example 2, by controlling the optical system so that the phase difference between the land reproduction and the groove reproduction is different, the crosstalk can be reduced by 7 to 8 dB and the data can be obtained at a low crosstalk level for both the land and the groove. You can see that it can be played.

[0038]

Third Embodiment A magneto-optical recording device equipped with an optical pickup using a two-beam semiconductor array laser as a light source is prepared. A magneto-optical disk is set in this apparatus, and recording is performed on a land track and a groove track of this disk with a magneto-optical mark, and crosstalk is measured. A conceptual diagram of the optical system of this magneto-optical recording / reproducing apparatus is shown in FIG.

The two beams are adjusted so as to be focused on the land and the groove of the magneto-optical disk, respectively. The reflected beam from the land has a phase difference of + 5 °, and the reflected beam from the groove has a phase difference. Adjust to -5 °. Both wavelengths of the light source are 680 nm, NA of the objective lens is 0.55, and vignetting coefficient D
/ W 0.8, the polarization state is linearly polarized light, and its direction is parallel to the groove. The magneto-optical disk has a track pitch = land width = groove width = 0.8 μm and a groove depth of 67.2 nm.

When CT _L and CT _G were obtained in exactly the same manner as in Example 1, the results were CT _L = -56.3 dB, CT _G = -56.0.
It was dB.

[0041]

COMPARATIVE EXAMPLE 3 As a conventional example, a land reproducing beam having a phase difference of + 5 ° was focused on the groove and the same measurement was performed. As a result, CT _L = -56.1 dB and CT _G = -48.5 dB, resulting in a large increase in CT _G. From this result and the result of the third embodiment, by using beams having different phase differences in the land reproduction and the groove reproduction, the crosstalk is 7 to 8 d.
It can be seen that B can also be made smaller and data can be reproduced at low crosstalk levels for both land and groove.

[0042]

Fourth Embodiment A magneto-optical recording device is prepared. This device is of the same type as was previously used.
It is equipped with one beam optical pickup. A magneto-optical disk is set in this apparatus, and recording is performed on a land track and a groove track of this disk with a magneto-optical mark, and crosstalk is measured. FIG. 4 shows a conceptual diagram of an optical system of the conventional magneto-optical recording / reproducing apparatus. The wavelength of the light source of the optical pickup is 680 nm, the NA of the objective lens
0.55, vignetting coefficient D / W 0.8, polarization state is linearly polarized light, and its direction is parallel to the groove.

The magneto-optical disk has a track pitch = land width = groove width = 0.8 μm and a groove depth of 67.2 nm. The substrate is optically distorted, and the phase difference of the substrate carrier is + 5.2 ° at the land and −4.3 ° at the groove. When CT _L and CT _G were obtained in exactly the same manner as in Example 1, the results were CT _L = -56.4 dB and CT _G = -56.5 dB.

[0044]

Comparative Example 4 As a conventional example, a magneto-optical disk having no optical distortion, that is, one having no difference in phase difference between the land portion and the groove portion was used as the substrate. As a result CT
_L = -56.2 dB, CT _G = -48.5 dB, and CT _G increased significantly. From this result and the result of Example 4, the crosstalk can be reduced by 7 to 8 dB by using the magneto-optical disk manufactured by the substrate in which the land portion and the groove portion have different phase differences, and the crosstalk is low in both the land and the groove. You can see that the data can be reproduced at the level.

[0045]

Fifth Embodiment A magneto-optical recording device is prepared. This device is of the same type as was previously used.
It is equipped with one beam optical pickup. A magneto-optical disk is set in this apparatus, and recording is performed on a land track and a groove track of this disk with a magneto-optical mark, and crosstalk is measured. FIG. 4 shows a conceptual diagram of an optical system of the conventional magneto-optical recording / reproducing apparatus. The wavelength of the light source of the optical pickup is 680 nm, the NA of the objective lens
0.55, vignetting coefficient D / W 0.8, polarization state is linearly polarized light, and its direction is parallel to the groove.

The magneto-optical disk has a track pitch = land width = groove width = 0.8 μm and a groove depth of 67.2 nm. The recording film has different structures in the land portion and the groove portion, and the Kerr ellipticity angle χ _K in the land portion is +0.12.
°, the Kerr ellipticity angle χ _K in the groove is −0.12 °. Since the Kerr rotation angle θ _K of this recording film is + 0.8 °, the phase difference is tan ⁻¹ (χ _K / θ _K )
8.53 °, −8.53 ° at the groove.

When CT _L and CT _G were obtained in exactly the same manner as in Example 1, the results were CT _L = -55.6 dB and CT _G = -55.7.
It was dB.

[0048]

Comparative Example 5 As a conventional example, a magneto-optical disk in which the structure of the recording film is not changed between the land portion and the groove portion, that is, a magneto-optical disk having no difference in phase difference between the land portion and the groove portion is used. As a result, CT _L = -55.7 dB, CT _G = -47.9 dB
And CT _G increased significantly.

From this result and the result of Example 5, crosstalk is 7 to 8 by using a magneto-optical disk having a medium structure in which the phase difference is different between the land portion and the groove portion.
It can be seen that the dB can be reduced and the data can be reproduced at a low crosstalk level for both the land and the groove.

[0050]

As described above, according to the present invention, it is possible to provide the reproducing method, reproducing apparatus and optical disk of the land / groove recording system which can obtain the condition that crosstalk is free even in magneto-optical recording.

[Brief description of drawings]

FIG. 1 is a conceptual diagram illustrating an optical system of a reproducing method and a reproducing apparatus according to an embodiment of the present invention.

FIG. 2 is a conceptual diagram illustrating an optical system of a reproducing method and a reproducing apparatus according to an embodiment of the present invention.

FIG. 3 is a conceptual diagram illustrating an optical system of a reproducing method and a reproducing apparatus according to an embodiment of the present invention.

FIG. 4 is a conceptual diagram illustrating an optical system of a conventional reproducing method and reproducing apparatus.

[Explanation of symbols]

 1 ... 1/2 wave plate 2 ... Laser diode 3 ... Photo detector 4 ... Beam splitter 5 ... Babinet Soleil phase compensator 6 ... Objective lens 7 ... Reflection mirror 8 ... ..Pockels cell 9 ... Polarizing beam splitter 10 ... Condensing lens 11 ... Collimator lens 12 ... Semiconductor laser 13 ... Two-beam array laser D ... Magneto-optical disk

Claims (12)

[Claims] 1. A reproducing method of an optical disc for recording information on both a land and a groove, wherein a phase difference φ when reproducing a land track and a phase difference φ ′ when reproducing a groove track are different. How to play an optical disc. 2. An optical disc reproducing method for recording information on both a land and a groove, wherein a phase difference φ of an optical system when reproducing a land track and a phase difference φ ′ of an optical system when reproducing a groove track. A method for reproducing an optical disc, characterized in that 3. The optical disk reproducing method according to claim 2, wherein an optical system for reproducing a land track and an optical system for reproducing a groove track are separate. 4. The method of reproducing an optical disc according to claim 1, wherein φ = −φ ′ is substantially satisfied. 5. An optical disk reproducing apparatus for recording information on both a land and a groove, wherein a phase difference φ when reproducing a land track and a phase difference φ ′ when reproducing a groove track are set to different values. An optical disk reproducing apparatus characterized by the above. 6. An optical disk reproducing apparatus for recording information on both a land and a groove, having an optical system for reproducing a land track and an optical system for reproducing a groove track, and reproducing the land track. An optical disc reproducing apparatus characterized in that a phase difference φ of an optical system for reproducing and a phase difference φ ′ of an optical system for reproducing the groove track are different. 7. The optical disk reproducing apparatus according to claim 5, wherein φ = −φ ′ is substantially satisfied. 8. An optical disc for recording information on both a land and a groove, wherein the in-plane birefringence direction of the substrate in the land and the in-plane birefringence direction of the substrate in the groove are different. 9. An optical disc for recording information on both a land and a groove, wherein the phase difference φ at the land and the phase difference φ ′ at the groove are different. 10. The optical disc according to claim 9, wherein the phase difference φ of the substrate in the land and the phase difference φ ′ of the substrate in the groove are different. 11. A phase difference φ of a recording film on a land,
The optical disc according to claim 9, wherein the recording films in the grooves have different phase differences φ ′. 12. An optical disk reproducing apparatus according to claim 9, wherein: φ = −φ ′.