JPH05282705A - Optical disk - Google Patents

Abstract

PURPOSE:To provide the optical disk on which an information signal can be recorded and reproduced with high density without providing any special optical system nor signal processing circuit. CONSTITUTION:User recording pits are formed both at land parts 2, 3, and 4 and in guide grooves 5 and 6. The groove depth of the guide grooves is set to >=1/7+n/2 and <=5/14+n/2. Even when the signal is recorded both in the guide grooves and at the land parts, diffraction by adjacent user recording pits 8 and 9 is reduced and reproduction crosstalk is small. The recording density can, therefore, be doubled and the signal which is recorded as the recording pits can excellently be reproduced. Further, address pits 12, 13, and 14 and address pits 15 and 16 are mutually shifted not to adjoin to each other, so the crosstalk between address signals is reduced and address signals can excellently be reproduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk, and more particularly to an optical disk in which signals are recorded both in a guide groove and between guide grooves.

[0002]

2. Description of the Related Art In recent years, an optical disk device capable of recording and reproducing information signals such as video or audio signals has been actively developed. In a recordable optical disc, a guide groove is previously formed on a disc substrate to form a track. Information signals are recorded or reproduced by focusing the laser light between the guide grooves or in the guide grooves. In a general optical disk currently on the market, an information signal is usually recorded only in one of the guide grooves or in the guide groove, and the other is a guard band for separating adjacent tracks.

FIG. 4 is an enlarged perspective view of such a conventional optical disc. In the figure, 101 is a recording layer,
For example, it is formed of a phase change material. Reference numeral 102 is a recording pit, and 103 is a focused spot of laser light. Reference numeral 104 is a guide groove, and 105 is an area between the guide grooves, which is hereinafter referred to as a land portion. The land portion 105 is wider than the guide groove 104. As shown in the figure, the land portion 105 has a convex shape and the guide groove 104 has a concave shape when viewed from the laser light incident side. Further, in the figure, a transparent disk substrate through which incident light is transmitted is omitted.

The recording / reproducing operation of such a conventional optical disc will be described below. At the time of recording, the laser light from the optical head is focused on the recording layer 101 of the land portion 105 by the objective lens, and the recording layer 101 is heated. A phase change occurs in the process of cooling the heated portion, and the recording pit 102 is formed. The recording pit 102 is formed only on the land portion 105 as shown in FIG.
They are spaced apart from each other by a width of 4.

During reproduction, when the focused spot 103 irradiates each pit row in the track direction, it is reflected and diffracted by the recording pit 102. The information signal is reproduced by the optical head detecting the change in the intensity of the reflected light. The track pitch, that is, the period of the guide groove 104 is set to about the same as the size of the focused spot 103, here, 1.6 μm. The depth d ₁ of the guide groove 104 is about ⅛ of the wavelength of the reproduction light in terms of optical length. This is for stabilizing the tracking control by the push-pull method, which is the depth at which the push-pull signal from the light reflected by the grooved disk becomes maximum.

In order to increase the recording capacity of such an optical disk, conventionally, the width of the guide groove 104 is narrowed to close the track interval. However, if the track interval is narrowed, the diffraction angle of the reflected light by the guide groove 104 becomes large, so that there is a problem that the tracking error signal for accurately causing the focused spot 103 to follow the track is lowered. In addition, the width of the land portion 105 must be narrowed because there is a limit in narrowing the track interval only by the width of the guide groove 104. This causes a problem that the amplitude of the reproduction signal is lowered because the recording pit width is also narrowed.

On the other hand, as disclosed in Japanese Patent Publication No. Sho 63-57859, there is a technique of recording an information signal both between the guide grooves and in the guide grooves to increase the track density.

FIG. 5 is an enlarged perspective view of such an optical disc. In the figure, 111 is a recording layer, which is made of, for example, a phase change material. 112 is a recording pit, 1
Reference numeral 13 is a focused spot of laser light. Reference numeral 114 is a guide groove, and 115 is a land portion. As shown in the figure, the widths of the guide groove 114 and the land portion 115 are substantially equal.
Further, the period of the guide groove 114 is about 1.6 μm as in the optical disc of FIG. 4, and the depth d ₂ of the guide groove 114 is also about ⅛ of the wavelength of the reproduction light in terms of optical length.

In this optical disc, recording pit 1
12 is a guide groove 114 and a land portion 11 as shown in FIG.
5, the period of the guide groove 114 is equal to that of the guide groove 104 of the optical disk of FIG. 4, but the interval of the pit row is one half of that of the optical disk of FIG. The recording / reproducing operation is basically performed in the same manner as the optical disc shown in FIG.

[0010]

However, in the technique described above, the distance between the pit rows is half the diameter of the focused spot, so that the focused spot overlaps the pit row next to the pit row to be reproduced. Therefore, there is a problem that crosstalk during reproduction becomes large and reproduction S / N deteriorates. To reduce this crosstalk, for example,
"" High track density magn
eto-optical recording usi
ng a crosscanceller "S
PIE Vol. 1316 Optical Data
Storage (1990) P.I. 35 ”, the optical disk reproducing apparatus is provided with a special optical system and a crosstalk cancel circuit, but there is a problem that the optical system and the signal processing system of the apparatus become complicated.

The present invention is intended to solve the above problems, and an object thereof is to provide an optical disk capable of reducing reproduction crosstalk without providing a special optical system or a signal processing circuit.

[0012]

In order to achieve the above object, the optical disc of the present invention is arranged such that the widths of the guide grooves of the tracks provided on the disc and the widths between the guide grooves are substantially equal to each other, and the guide groove is inside the guide groove. An optical disc in which a signal is recorded on both sides of a groove by utilizing a change in a local optical constant or a physical shape due to irradiation of a light beam, and the depth of a guide groove is recorded and / or recorded.
Or 1/7 + n / 2 or more of the wavelength of reproduction light and 5/14 + n
The optical path length is equal to or less than / 2 (n is 0 or a positive integer).

[0013]

With the above structure, the optical disc of the present invention has
The guide groove is 1/7 + n / 2 or more of the reproduction light wavelength and 5/14 +
It is formed to a depth of n / 2 or less (n is 0 or a positive integer). Therefore, the optical phases of the reflected light from the target pit row and the reflected light from the adjacent pit row are substantially inverted.
As a result, the two are offset, and the influence of the adjacent pit train on the reproduction signal is reduced.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical disk according to an embodiment of the present invention will be described below with reference to the drawings. In the present embodiment, a case where a phase-change (PC) recording material that records by changing the actual reflectance is used as a recordable / reproducible optical disk will be described.

FIG. 1 is an enlarged perspective view for explaining the structure of the optical disc of this embodiment. In the figure, reference numeral 1 denotes a recording layer, which is formed of, for example, a phase change material, and a signal is recorded by utilizing the property that the actual reflectance of the surface is different between the crystalline state and the amorphous state. 2, 3 and 4 are land portions formed on the disk, 5 and 6 are guide grooves, and the widths of both are substantially equal. Here, it is assumed that light is incident from above in the drawing. Reference numerals 7, 8, 9, 10 and 11 are user recording pits written in the lands 2, 3, 4 and the guide grooves 5, 6. It should be noted that the user recording pit is a region where the recording layer 1 is made amorphous by the laser light and information is recorded. 12, 1
Reference numerals 3 and 14 are address pits, which are formed in advance in the land portions 2, 3 and 4 at the time of manufacturing the disk and indicate the positional information on the disk, and are composed of recesses having some appropriate depths. 15
Address pits 16 and 16 are also formed in the guide grooves 5 and 6. Also, when viewed in the track direction, the land portion 2,
Reference numerals 3 and 4 are divided into a user data portion 17 and a first address portion 18, respectively, and guide grooves 5 and 6 are also divided into a user data portion 17 and a second address portion 19. Moreover, the address pits of the first address portion 18 and the address pits of the second address portion 19 are arranged in the track direction so as not to be adjacent to each other in the disk radial direction. Reference numeral 20 is a focused spot. The most characteristic point of this embodiment is that the depth d of the guide grooves 5 and 6 is 1/7 + n / 2 or more of the wavelength of the reproduction light in terms of optical length and 5/14 + n.
/ 2 or less (n is 0 or a positive integer).

The principle of the reason why the crosstalk component in the reproduced signal can be removed by the above structure will be described below. For simplification of explanation, the intensity distribution of the laser light before being narrowed down by the objective lens is uniform in the pupil. Also, description will be given by using a one-dimensional model only in the radial direction of the disk.

FIG. 2 is a diagram for explaining the principle of the present invention.
(A) is a cross-sectional view of the section AA 'in FIG. 1 and the intensity distribution of the focused spot focused on the recording surface by the objective lens, and (b) shows the diffracted light from the disc surface returned to the objective lens. FIG. 6 is a distribution diagram of diffracted light immediately after passing through an exit pupil. In the figure (a), 21 is the intensity distribution of the focused spot narrowed down by the objective lens on the recording surface, 2, 3
Numerals 4 and 4 are land portions, and numerals 5 and 6 are guide grooves, where the track pitch is p, the land width is w = p / 2, and the groove depth is d. The beam diameter of the focused spot is assumed to be substantially equal to p, as set in a normal optical disk device.
Here, the beam diameter is 1 / e of the central intensity of the focused spot.
^The diameter is ² . In addition, the condensing spot is the land part 3
The following assumptions are made in order to consider crosstalk in the case where information is reproduced by irradiating along the line. That is,
Assuming that the actual reflectance changes depending on the user recording pit,
The actual reflectances in the guide grooves 5 and 6 are r ₁ and r ₃ , respectively, and the actual reflectances of the land portions 2, 3 and 4 are r ₂ . And
The effect on the total amount of light on the detection surface when r ₃ changes with r ₁ and r ₂ kept constant is calculated. Therefore, the period of the sectional shape is 2p, and the beam diameter is p as described above.
If so, out of the diffracted light due to the periodic structure, 0th to 3rd order light passes through the exit pupil of the objective lens. Figure 2
(B) depicts the situation, and the seven circles are -3rd order to +
It represents the third-order reflected diffracted light, and the thick solid circle also serves as the exit pupil of the objective lens. The total sum (intensity) of interference of all diffracted light that enters the circle of the exit pupil becomes the reproduction signal. The reflectivities of the lands 2, 3 and 4 are set to be equal to each other because the influence of the change in the reflectivity of the lands 2 and 4 on the reproduced signal is practically small and the model has periodicity.

The coordinate on the exit pupil of the objective lens is represented by x, the amount of deviation between the center of the track, that is, the land portion 3 and the center of the focused spot is represented by u, and the pupil function of the objective lens is represented by f.
(X), where m and m ′ are orders of reflected diffracted light, the light intensity distribution I (x) on the exit pupil plane of the objective lens is

[0019]

[Equation 1]

[0020] However, R (m) is a complex Fourier reflection coefficient, and the reflectance at the position ξ on the disk is R (ξ)
Then,

[0021]

[Equation 2]

Is calculated by Also, * represents a complex conjugate. From the model of FIG. 2 (a), R (ξ) is

[0023]

[Equation 3]

It is φ is the phase difference due to the groove depth d, where λ is the laser wavelength and n is the refractive index of the disk substrate.

[0025]

[Equation 4]

It can be obtained by The total reproducing light amount I is u
Since it is obtained by substituting = 0 (corresponding to no off-track) and further integrating in the range corresponding to the exit pupil of the objective lens,

[0027]

[Equation 5]

[0028] However, s represents the exit pupil of the integration range.

Here, if f (x) is standardized by the peak value of the incident light and x is further standardized by the exit pupil radius, the integral term of (Equation 5),

[0030]

[Equation 6]

Is equal to the area of the exit pupil, the circle having the center of m / 2p and the radius of 1 and the circle of the center of m ′ / 2p and the radius of 1, which is simpler than that of FIG. 2 (b). Be asked for. The derivation of these equations is done, for example, by "" Diffratio
n theory of laser read-ou
t systems for optical vid
eo discs "J. Opt. Soc. Am., Vo
l. 69. No. 1, January 1979 ”.

The complex Fourier reflection coefficients up to the third order are given by (Equation 2), (Equation 3) and (Equation 4)

[0033]

[Equation 7]

[0034]

[Equation 8]

[0035]

[Equation 9]

[0036]

[Equation 10]

It is Substituting (Equation 7) to (Equation 10) into (Equation 5), and summarizing for each term of the reflectances r ₁ , r ₂ , and r ₃ ,

[0038]

[Equation 11]

It becomes In (Equation 11), the first term is a signal component, the second and third terms are crosstalk components that do not depend on the groove depth, and the fourth term is a term that depends on φ. From this equation, it can be seen that the amount of crosstalk is reduced by optimizing φ, that is, the groove depth. Also, from the cosine term, it can be seen that the amount of crosstalk changes in a cycle of φ = 2π, that is, d = λ / 2.

The above is the calculation result in the simplified model as shown in FIG. 2, but the simulation calculation result in the model closer to the actual optical disk will be described. That is, considering the two-dimensional expansion of the disk recording surface, the shape of the user recording pit is assumed to be an oval shape that is close to the actual size, and the incident light from the light source to the objective lens is assumed to be Gaussian distribution. λ =
780 nm, NA = 0.45, n = 1.585, p =
1.6 μm, pit length = 3.3 μm, and the actual reflectance of the pit is ½ of the reflectance outside the pit. FIG. 3 is a graph showing the relationship between the amount of crosstalk and the groove depth calculated under the above conditions. However, the intensity ratio between the crosstalk signal component due to the user recording pits formed in the guide groove 6 and the main reproduction signal due to the user recording pits formed in the land portion 3 is defined as the crosstalk amount, and the vertical axis indicates decibels. displayed. The groove depth on the horizontal axis is converted into the optical path length at the substrate refractive index n. Therefore, hereinafter, the groove depth d is all represented by the optical path length. Normally, the allowable crosstalk amount for a reproduced signal is about -20 dB, so that according to the figure, the groove depth is 0.11 μm (λ / 7) to 0.29 μm (5λ / 1
It is desirable to set within the range of 4). More preferably, the amount of crosstalk can be minimized by setting the groove depth to around 0.16 μm (that is, λ / 5) or 0.24 μm (that is, 3λ / 10).

Based on the above principle, the recording / reproducing operation of the optical disk of this embodiment will be described below. Since the recording operation is the same as the operation described in the description of the conventional optical disk, the description thereof will be omitted and the reproducing operation will be described.

First, the case of reproducing the user data section 17 will be described. The laser light emitted from the light emitting element of the optical head is condensed on the land portion 3 on the disk by the objective lens and reflected and diffracted by the user recording pit 9. The reflected light is again guided to the detection element through the objective lens and converted into an electric signal. At this time, the guide grooves 5 and 6
Groove depth is λ / 7 + nλ / 2 or more 5λ / 14 + nλ / 2
Since it is set as follows, the influence of the adjacent user recording pits 8 and 10 on the diffracted and reflected light is small as described above. Also, when the focused spot 20 traces on the guide groove 5, the user recording pit 8 similarly reflects and diffracts the light. Also at this time, the influence of the user recording pits 7 and 9 on both sides on the reflected light is small.

On the other hand, address pits 12, 13, 14,
Since 15 and 16 utilize the imaginary reflectance due to the depression, that is, the change in phase, the influence on the adjacent track reproduction is larger than that of the user recording pit. In the optical disk of this embodiment, no other address pits are arranged in the guide grooves on both sides of the address pit 13, so that the address pit at the shortest distance is the address pit 12 of the next land portion 2 and 4. It is 14. Therefore, when the laser beam irradiates the address pits 13, the address pits 1 on both sides are
The effects from 2 and 14 are small. Moreover, since the ratio of the normal address area to the entire disk area is small,
Even if a blank area is provided next to the area where the address pits are engraved as in the present embodiment, the decrease in recording capacity is small.

As described above, in the optical disk of this embodiment, the groove depth of the guide grooves 5 and 6 is λ / 7 + nλ / 2 or more and 5λ / 1.
Since it is set to 4 + nλ / 2 or less, the crosstalk from the adjacent user recording pits 8 and 9 is small even though recording is performed in both the guide groove and the land. Therefore, even if the recording density is doubled as compared with the conventional one, it is possible to excellently reproduce the signal recorded as the user recording pit.

Further, the land portions 2, 3, 4 and the guide grooves 5, 6
By making the widths of the two substantially equal, the diffraction state becomes the same when the focused spot 20 is on the guide groove and when it is on the land. As a result, the characteristics of the signal obtained from the reflected light do not change between the two, and recording or reproduction can be performed stably.

Further, address pits 12, 13 and 1
4 and the address pits 15 and 16 are alternately shifted so as not to be adjacent to each other, so that crosstalk between the address signals is reduced and the address signals can be reproduced well.

In this embodiment, the groove depth is λ / 7.
Although it is set to + nλ / 2 or more and 5λ / 14 + nλ / 2 or less, it is more preferable to set it to approximately λ / 5. In this case, the amount of crosstalk is minimized as described above, and reproduction can be performed most favorably.

Further, preferably, the depth of the guide groove is approximately 3λ.
It may be / 10. Even in this case, as is clear from FIG. 3, the crosstalk amount can be minimized. Further, since the recording film material is laminated from above the disc during the manufacture of the optical disc, if the groove depth is increased, the recording layer formed on the wall surface becomes thinner. As a result, heat conduction between the land portion and the guide groove is suppressed, and thermal crosstalk during recording can be reduced. Therefore, there is an effect that the shape of the user recording pit becomes uniform and the quality of the reproduced signal is improved.

Furthermore, as is clear from (Equation 11),
The total reproduction light amount changes at a period of 2π with respect to the phase difference φ due to the groove depth d. Therefore, it can be considered that the amount of crosstalk also has the same periodicity with respect to the groove depth. Therefore, the guide groove may be deeper than the groove depth of the optical discs of the first and second embodiments by a phase difference of 2π, that is, a positive integer multiple of λ / 2.

Although the phase change material is used as the recording layer in the above embodiments, any method may be used as long as it is a method of recording a signal by utilizing the change of the optical constant. Alternatively, the disk substrate may be preliminarily formed with pits by ruggedness.

[0051]

As described above in detail, in the optical disc of the present invention, the depth of the guide groove is set to 1/7 + n / the wavelength of the reproducing light.
2 or more and 5/14 + n / 2 or less (n is 0 or a positive integer)
By setting the optical path length of, the diffraction due to the adjacent pit rows can be reduced and the crosstalk component in the reproduced signal can be reduced. Therefore, even if signals are given both between the guide grooves and inside the guide grooves, the recorded signals can be reproduced well, and an optical disc having a high recording density can be realized.

More preferably, the groove depth should be approximately λ / 5. In this case, the amount of crosstalk becomes extremely small, and reproduction can be performed best.

Preferably, the depth of the guide groove is approximately 3λ /
It may be 10. Also in this case, it is possible to minimize the amount of crosstalk. Moreover, since it is deeper than λ / 5, heat conduction between the land portion and the guide groove is suppressed, and thermal crosstalk during recording can be reduced. Therefore, there is an effect that the shape of the user recording pit becomes uniform and the quality of the reproduced signal is improved.

Further, by making the widths of the guide grooves and the widths between the guide grooves substantially equal, the characteristics of the signal obtained from the reflected light do not change between the two, and recording or reproduction can be performed stably.

The first groove provided in the guide groove of the truck
Since the address information part and the second address information part provided between the guide grooves are arranged so as not to be adjacent to each other in the radial direction, the address information can be reproduced well with low crosstalk.

[Brief description of drawings]

FIG. 1 is an enlarged perspective view for explaining a configuration of an optical disc according to an embodiment of the present invention.

FIG. 2 is a schematic diagram for explaining the principle of the embodiment.

FIG. 3 is a graph showing the relationship between crosstalk amount and groove depth in the example.

FIG. 4 is an enlarged perspective view for explaining the configuration of a conventional general optical disc.

FIG. 5 is an enlarged perspective view for explaining the configuration of a conventional optical disc that records information signals both between the guide grooves and in the guide grooves.

[Explanation of symbols]

 1 recording layer 2,3,4 land part 5,6 guide groove 7,8,9,10,11 user recording pit 12,13,14,15,16 address pit 17 user data part 18 first address part 19 second Address part

Claims (5)

[Claims] 1. An optical disc for recording a signal in a guide groove provided on a disc and between the guide grooves by utilizing a change in a local optical constant or a physical shape due to irradiation of a light beam. , The depth of the guide groove is 1/7 + n / 2 or more of the wavelength of the recording and / or reproducing light and 5/14 + n /
An optical disc having an optical path length of 2 or less (n is 0 or a positive integer). 2. The optical disk according to claim 1, wherein the depth of the guide groove forms an optical path length of about ⅕ of the wavelength of the recording and / or reproducing light. 3. The optical disk according to claim 1, wherein the depth of the guide groove forms an optical path length of approximately 3/10 of the wavelength of the recording and / or reproducing light. 4. The optical disk according to claim 1, 2 or 3, wherein the width of the guide groove and the width between the guide grooves are substantially equal to each other. 5. A first address information portion provided in the guide groove and having positional information on the disc recorded therein, and a second address information portion provided between the guide grooves and having positional information on the disc recorded therein. 5. The optical disk according to claim 1, wherein the first address information section and the second address information section are arranged so as not to be adjacent to each other in the radial direction.