JPH03104021A - Optical recording medium and recording and reproducing method thereof - Google Patents

Abstract

PURPOSE:To diminish inter-track spacings to about the half value of the diameter of a light spot and to increase a recording density by alternately disposing grooves of different depths so as to incorporate the two grooves within the spot and recording information pits on the plane between grooves. CONSTITUTION:The recessed shallow grooves 24 and the deep grooves 25 are alternately disposed in the direction perpendicular to the progressing direction in such a manner that the two grooves are contained within the light spot on the disk 3 surface consisting of a PbTeFe recording film, etc., on a disk substrate 29. The information pits 36 to 38 are recorded on planes 26 to 28 between the grooves. The depths of the grooves 24, 25 are preferably set at lambda/8, 3lambda/8 and are also preferably set at lambda/8, 2.5lambda/8. The information is preferably reproduced by detecting the change in the intensity of the interference region of zero order and third order on the groove 24 side.

Description

[Detailed description of the invention]

[Industrial Application Field 1] The present invention relates to an optical recording medium and a recording and reproducing method thereof,
In particular, the present invention relates to an optical recording medium suitable for improving recording density and a recording/reproducing method thereof. The present invention is capable of recording by utilizing local characteristic changes (for example, reflectance changes, transmittance changes, depth changes, etc.) caused by irradiation with a light spot.
Once or Erasable
) is particularly suitable for use in optical disc devices. [Conventional Techniques] For example, in the conventional recording and reproducing method of an optical disc for files, grooves of a certain depth are provided in a spiral shape on the disc surface, and a plurality of grooves are arranged at equal intervals in the radial direction of the disc. A light spot is irradiated along the grooves or between the grooves to record, reproduce, or erase information along the center of the grooves or between the grooves. This groove acts as a guide for making the light spot follow the track. In order to reduce noise during recording and playback, @
It is desirable that the (track spacing) be smaller than the diameter of the recording pits that are recorded as information on the disk. but,
As described above, there are two problems with the purpose of increasing the density by making the distance between tracks in the radial direction of the disk smaller than the diameter of the optical beam spot. The first problem is tracking. In general, the radial positional deviation of the light spot with respect to the center of the track (
As a method for detecting track deviation), a well-known so-called "push-pull method" is used. That is, the groove structure arranged periodically in the radial direction of the disk acts as a diffraction grating for the optical spot. For the purpose of increasing the density of storage capacity, reducing the track spacing, or groove spacing, means that the radial spatial frequency of the disk (expressed as the reciprocal of the groove period) is reduced by the cut-off frequency of the reading optical system ( This is a problem in that it becomes difficult to detect the positional deviation of the light spot in the radial direction because the value is close to the reciprocal of the diameter of the light spot. The second problem is crosstalk caused by the mixing of unnecessary information from adjacent tracks. If the track spacing is made smaller than the optical spot diameter, even if the optical spot accurately follows the center of the target track, the optical spot will overlap adjacent tracks, causing W
．． Unnecessary information is mixed into the information of the desired target track. In other words, crosstalk increases. In order to solve the above-mentioned conventional problems,
In No. 582, as shown in Figure 3 (a), the cross-section of the disk is shaped into a ``V-shape'' or ``inverted ladder'' shape, and information pits are recorded and reproduced by aligning the light spot along the slope of the groove. ing. In this method, the groove period is the same as the conventional spacing, but the track spacing is halved. Therefore, the track following error can be detected, and the first problem is solved. Furthermore, since the information track surface is a slope, the distribution of the diffracted light is controlled by controlling the shape of the slope, so that only the diffracted light from the targeted information track 11 is distributed around the outer periphery of the exit pupil. The second problem is solved by reducing the influence of crosstalk from the information tracks 12 or l3 on both sides. On the other hand, in JP-A-61-192047, Fig. 3(b)
As shown in the figure, convex tracks l4 and concave tracks 15 are provided alternately in the radial direction in a spiral or concentric manner, and each track is further provided with a light guide groove 16 for tracking along the track. ing. The width of the optical guide groove 16 is smaller than the diameter of the recording pit 17, and the depth is (1/4 to 1/8) relative to the laser beam wavelength (λ).
It is λ. In the disk structure as described above, the recording density is improved by performing recording and reproduction on both the convex tracks 14 and the concave tracks 15. Also,
By performing tracking using the optical guide grooves 16 on each track, highly accurate tracking is possible and crosstalk can be reduced. Furthermore, in JP-A-54-136303, Fig. 3(c)
As shown in FIG. 2, information tracks 20 to 23 consisting of pits 18 and 19 with depths of λ/4 and λ/8 are arranged on the disk surface 3 in the radial direction of the disk. In this way, by making the depth of the information pits themselves different between adjacent ones, the distribution of diffracted light is controlled, and the information track 20 with a depth of λ/8,
22, the difference between the signals from each light-receiving surface of the two-split photodetector is recorded on the information track 21.22 with a depth of λ/4. In the reproduction of No. 23, a signal with small crosstalk is detected by detecting the sum of the signals from each light receiving surface of the two-split photodetector as a reproduction signal. Problem to be Solved by the Invention 1 As a problem of the above-mentioned prior art,
In 28%, the first method for manufacturing a disk master having a groove with a radial cross section of "V" or "inverted trapezoid" is to machine a metal plate using a diamond needle with a "V" or "R" tip. Use the formula cutting method. However, in order to form the surface of the groove slope that forms the recording pit into a highly accurate mirror surface, it is necessary to use the commonly used cutting method characterized by a fine structure, that is, to apply laser light to ultraviolet curing resin (photoresist). Expose and develop,
It is difficult to create the master disk by laser cutting to form grooves. Regarding JP-A-61-192047, mechanical cutting must be used to make the convex groove surface or concave groove surface that forms the recording pit into a mirror surface, as in the above-mentioned conventional example. Furthermore, if the optical guide groove 16 is formed in the center of each track, there is a problem in that the influence of noise due to the optical guide groove increases when reading the information pits 17. In Japanese Patent Laid-Open No. 54-13603, the depth of each information pit must be arranged differently in adjacent tracks. This is possible for media such as "read-only optical discs" in which the information bits of the disc are created in advance using high-precision process control, such as laser cutting equipment, but for media such as "optical discs for data files" For media in which information pits are recorded, reproduced, and erased using a simple device on the user's side, it is difficult to accurately record pits with different target depths for each track. SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to easily create a master disc not only by mechanical cutting but also by laser cutting, and while maintaining stable tracking control, the track spacing can be adjusted to match the optical spot diameter. The object of the present invention is to provide a recording medium that can double the recording density by reducing the density to about half its value, and a method for recording and reproducing the same. [Means for Solving the Problems] The optical recording medium of the present invention is an optical recording medium in which recording is performed using local characteristic changes caused by irradiation with a light spot, and includes:
Grooves with different depths extending in the traveling direction of the optical recording medium are arranged alternately and periodically in a direction perpendicular to the traveling direction so that two grooves are included in the optical spot, and the recording pits are formed between these grooves. It is characterized by recording on a plane between the groove and the groove. According to one feature of the invention, each groove of different depth is
Its depth is λ/8, 3λ/8. According to another feature of the invention, each groove of different depth is
Its depth is λ/8, 2.5λ/8. Furthermore, the recording and reproducing method of the present invention detects intensity changes in the zero-order and third-order interference regions on the shallow groove side of the reflected diffraction light distribution obtained by irradiating the optical recording medium with a light spot. It is characterized by playing back information. In addition, among the above-mentioned received reflected diffraction light distribution, ○ order and ±3
Intensity changes in the following two interference regions are detected, and the position of the optical spot is detected based on the difference or sum signal. Furthermore, the above reflected diffraction light distribution is obtained on a photodetector, and the detection surface of this detector is divided into two to detect the O-order and 3rd-order interference regions on the shallow groove side, and the signals detected in each are divided into two. It is characterized by switching depending on the position of the light spot.

[Effect]

According to the present invention, since two grooves are included in the light spot, the track pitch is twice that of the conventional method. In addition, since the information pits, which are data, are recorded on the flat areas between the grooves, spot control such as focus servo is stable, and there is little noise during playback. In addition, there is an optimum value for the groove depth, and when the groove depths are λ/8 and 3λ/8, the total amount of light received can be large, so it can be used even for recording films with large disk noise. S/N
High signal detection is possible. Also, the depth of each groove is λ
/8, 2.5λ/8, even if the recording film is large enough for the information pits to protrude into the grooves, changes in the diffracted light due to local characteristic changes within the grooves will only appear in a part of the received light distribution. Therefore, crosstalk can be reduced. In the recording and reproducing method of the present invention, in the received light distribution obtained when the light spot is positioned between the grooves, the O
In the interference region of the second and third-order diffracted lights, the diffracted lights from the information pits on the adjacent tracks are canceled, so that crosstalk can be reduced. Furthermore, even if the optical spot contains two grooves, the depths of these two grooves are different, so the difference in the grooves can be resolved, and even if the track pitch is doubled, the tracking signal will not change. Can be detected normally. Furthermore, the shallow groove side is determined by detecting the light intensity on the above light receiving distribution, and by switching the signal detection so that the change in light intensity on the shallow groove side is always detected as an information signal, grooves of different depths can be detected. Because it is built in a double helix shape, even when the shallow grooves are swapped left and right on the light reception distribution after the light spot goes around, it is always possible to detect information signals with low crosstalk. Therefore, according to the present invention, it is possible to detect tracking signals, detect signals with small crosstalk, and double the track pitch, thereby realizing an optical disk device that can double the recording density. be able to.

[Embodiments] Prior to describing embodiments of the present invention, the problems to be solved by the present invention and the principles for solving the problems will be explained in detail with reference to the drawings. Here, as shown in FIG. 2, a parallel beam bundle 1 from a Gaussian distribution is incident on a focusing lens 2 and
Due to the diffraction effect on the disk surface 3, the diffracted light 4 from the disk surface returns through the focusing lens 2, and the reflected intensity is reflected on the photodetector surface 5 provided on the exit pupil surface. A case where it is formed as a distribution will be explained. However, for the sake of simplicity, only the one-dimensional direction necessary for explaining the present invention, that is, the radial direction of the disk, will be shown here. On the surface of the diaphragm lens 2, the X axis is taken in the radial direction of the disk. In the Gaussian distribution of the light beam 1 incident on the focusing lens 2, (X) becomes τ(x)=exp(-δ/2·xZ) (1). Here, δ represents the intensity ratio between the center and the edge of the intensity distribution, and the spread radius of the beam, that is, the radius of the light spot, is proportional to λ/NA. Furthermore, if there is no focal shift or aberration in the aperture lens 2, the light beam distribution f(
x) coincides with τ(X). This light beam f(x) is Fourier transformed by a lens 2 and focused onto a disk surface 3. If the disk radial direction on the disk surface is taken as the U axis, the complex amplitude distribution F(u) at this time is F(u) = f(x)exp(i2πux)dx
(2), and the light distribution F(u) is diffracted on the disk surface 3. The effect of diffraction is expressed by the product F(u)·R(u) with the complex reflectance R(u) on the disk surface 3. The complex reflectance R(u) is R(u)=r(u)exp((iψ(U))(3). However, r(.u) represents the real reflectance distribution on the disk surface 3. , ψ(u) represents the phase shape of the disk.If the vertical undulation of the disk surface 3 is d(U), in the case of a reflective type, φ(u)=4 πnd (u)/L (4). Here, n is the refractive index of the disk substrate, and λ is the wavelength of the light source. Also, the coordinate U is at the suprapupil [x] with respect to the actual coordinate δ on the disk surface 3. It is converted by u=(NA/λ)δ. However, NA is the numerical aperture of the diaphragm lens. Complex amplitude distribution of reflected light from the disk surface F(u)・R(
The light beam u) passes through the diaphragm lens again and is received by the exit pupil, that is, by the photodetector 5. The complex amplitude distribution α(X) of the received and reflected light is given by inverse Fourier transform. a (x)= F(u)R(u)exp←i2 πu
x) dx(5) α(x)=:exp(-i27c(m/p)u)・Rm
4(x-n+/p) (8) In deriving the above equation, Fourier transform was used, but if the complex reflectance R(u) on the disk surface 3 is expressed in the U-axis direction, where p is the on-axis period, R(u)=Rveexp(i2π(m/p)u)(
6) It is expressed as. However, m is an integer, and Rm is an m-th order Fourier coefficient. The Fourier coefficient Rm is determined by the following equation. Rm=1/p R(u)・exp(-i2 π(m/
p)u)du(7) When formula (7) is used, the complex amplitude distribution α(X) of the reflected light within the exit pupil 5 is given by the sum of the diffracted light distributions of each order. U=O,
In other words, when the light spot is at the origin, the m-th order diffracted light αm
Equation (8) shows that the center of the distribution is located at m/p, the distribution spreads within ±1 around the center, and has a Fourier coefficient Rm as a complex amplitude. the result,
Since the center of the distribution of high-order diffracted light moves away from the origin, the diffracted light outside the exit pupil 5 shown by the dotted line is not received by the light receiving surface 6 corresponding to the exit pupil. In FIG. 2, only the light receiving surface 6 is shown two-dimensionally. Also, the ezp term in equation (8) is . The deviation of the light spot from the origin, that is, U
This shows how the phase of the diffracted light wave changes with respect to . Next, the reflected light intensity distribution 1(x) on the light-receiving surface 6 is determined as a result of the interference of each order of diffracted light contained within the light-receiving surface 5, given by equation (8). That is, I(x)=exp(-
i2 tc [(+-+m″)/plu)・R(m)R
(m')·f(x-m/p) f books (x-(m'/p)) (9) However, the subscript book represents a conjugate complex number. Furthermore, the amount of light actually detected by the photodetector 5 is given by the integral of the reflection intensity distribution on the light receiving surface. For example, when the light-receiving surface 6 is divided, the amount of light received in the divided light-receiving area D is determined by the following equation. I'=DI(x)dx (10) The conventional problems will be explained using the above equation. The disk surface 3 of the conventional optical disk for data files is
A constant depth d in the radial direction of the disk as shown in Figure 2.
, Il@w grooves were created at equal intervals. As an example, the wavelength λ = 0.83 μm, the numerical aperture NA of the diaphragm lens 2 = 0.5, d = λ/8, w = 0.4 μ, p =
When it is set to 1.6 μm, the diameter W of the light spot focused on the disk surface 3 is approximately λ/NA=1.6 μm. At this time, the m-order diffracted light distribution αm determined by equation (8) is 0-order, as shown in the figure? Oriko α. and ±1st-order diffracted light α+,
, α-1 is the exit pupil surface 5, that is, the light receiving surface 6.
It is reflected. Furthermore, the reflection intensity distribution I(x) is (9
) As can be seen from the equation, the deviation of the light spot in the U-axis direction,
That is, only the exp term changes as the disk radially shifts. Therefore, the 0th order diffracted light α. Only the ±1st-order diffracted light α±■ contribute to the reflection intensity I (x). Among them, the exp term takes a finite value and changes with the value of U in regions 7 and 8 where the O-th and +1st-order or 0th- and -1st-order diffracted lights interfere. Therefore, the light receiving surface 6 is changed to the light receiving surfaces 9 and 10.
The intensity of the reflected light is detected. In this way, it is possible to detect the deviation of the optical spot in the disk radial direction, that is, the track following error. In addition, when recording and reproducing information pits between the grooves in the figure, since the interval p between the groove tracks is approximately the diameter of the optical spot, the information bit l of the target groove track is
1, there is no influence of the leakage of reflected light from the information pits 12, l3 on the adjacent inter-groove tracks, that is, crosstalk. Here, a case will be described in which the track interval p is decreased in order to increase the density. As is clear from equation (8),
As p is made smaller, the ±1st-order diffracted lights are each shifted outward from the exit pupil 5. Therefore, the track spacing p is set to half the optical spot diameter, that is, λ/(2NA).
When the size is reduced to 0, the 0th order diffracted light α appears on the exit pupil 5. Therefore, the value inside { } of the exp term in equation (9) becomes zero, making it impossible to detect the track following error. This is the first problem with the conventional method. The second problem is that when the track interval p becomes 172, the optical spot plane includes about half of the information pits 12 and 13 of the adjacent tracks on both sides, increasing crosstalk and causing errors. Because of the first and second problems mentioned above, it has been difficult in the conventional system to double the recording density by halving the track spacing. Next, the reason why these two problems can be solved by the present invention will be explained. First, for the asymmetric groove structure of the present invention, the diffracted light distribution α and the reflected light intensity distribution I(x) are determined, and the reason why the track following error can be detected and the crosstalk can be reduced will be explained. Here, as shown in FIG. 1, the groove structure on the disk surface is a concave shape with a groove width of W for simplification, and a shallow groove 24 with a depth ds and a shallow groove 24 with a depth d D (d D> The deep grooves 25 of d s) are alternately arranged at intervals P (P>W) along the radial direction of the disk. In addition, when recording or reproducing information by irradiating a light spot along the center between the grooves, in order to take into account the influence of crosstalk, we distinguish the contribution of each area of the disc to the diffracted light distribution α. It can be so. Therefore, assuming that only the actual reflectance of the recording medium changes due to the formation of information pits, the actual reflectance of the information tracks, that is, the grooves 26, 27, and 28, is calculated as r.
Set ir2, r3, and the actual reflectance in the groove as r4. As a result, the length of the period on the disk surface 3 is 4P between the two dotted lines in the figure, with respect to the track interval p. A light beam having the distribution shown in equation (1) is irradiated onto such a periodic structure through the focusing lens 2, and each order diffracted light αm obtained on the exit pupil 5 after being diffracted is determined from equation (8). The interval P between the information tracks is half the optical spot diameter, P=λ
/(2NA), P=2, and the diffracted light up to the third order among the m orders has a distribution on the exit pupil. FIG. 1 shows the m-order diffraction light distribution αm in which the amplitude of each order diffraction light, that is, the Fourier coefficient Rm, is normalized by 1, and the two-dimensional distribution arrangement. From equation (7), the Fourier coefficients up to the third order are γ”V/Py
If we set φs=4πds/l, φd:4πdD/λ, then R
o"(1-"f)/4・(r.+2rz+r3)+
(rJ2) y (exp(iφs)+exp(iφD
)) (11) R±1=±i/π・
sin(π/4(1-y))(rx-rz)(l2) R±2=(r./π)cos(π/2-Y)
-1/2cos(π/2・γ)(r+r.)
(13)±(i/π)r4sin(π/訃γ)
(exp(iφS)−exp(iφD)) R±3=−,+i/(Lc)・sin(3π/4(1−
y))(rz−r6) (14). The reason why a track following error signal can be detected for the groove structure of the disk as shown in Fig. 1 is that even if the groove interval p is about half the optical spot diameter λ/(2NA), the reason why the track following error signal can be detected is that even if the groove interval p is about half the optical spot diameter, λ/(2NA), Since the groove spacing is doubled to 2p, the diffracted light other than the 0th-order light enters the exit pupil 5 as described above.
This is because the reflection intensity distribution on the exit pupil changes in response to a deviation of the light spot from the track, that is, a change in U, and by detecting this change, the tracking deviation can be detected. What actually contributes to the change in the reflection intensity distribution with respect to the change in U is the interference between the 0th-order diffracted light and the ±2nd-order diffracted light, and the degree of the change is (1
3) It mainly depends on the third term { } of the equation, that is, the difference in depth between the shallow groove 14 and the deep groove l5. Next, a method for reducing evening losstalk will be described. As can be seen from equation (9), the reflected light intensity distribution detected by placing a photodetector on the exit pupil 5 is the sum of the interference between the respective orders of diffracted light αm determined by equation (8), and It is also strongly influenced by the distribution of the light beam bundle 1 incident on 2. Therefore, if the exit pupil 5 is divided into regions where each order diffracted light αm interferes, the four regions D1 and D2 shown in FIG.
, D3, and D4 are obtained. The reflected intensity light amount is determined for each of these four regions. The obtained reflected light intensity is divided into two product terms of the actual reflection coefficients r2r3 and r4 for each region of the disk surface 3, as shown in the vertical lines in FIGS. 4(.) and (b). . Expressing this as a formula, ID(i)=kA(j.,m,m')・(k(Lml
m7)・(r2)” ±k(2, mym’) {rz r4) ±k(3, m, m’)・(r,)”+k(4, m
, m') - (r,)''+k(5, m, m')・
(r, r3)+k(6,m,m'){r1r2)"k
(7,ll+m')'('3r'2)+k(8,m,a
t')'(r1r4)+k(Lm+m')"(r3r*
)+k(10,+++,m'){r4)2)
(15) D(i) indicates each light receiving area where i=1 to 4. becomes. In equation (15), each coefficient k(1
, m, m') ~ k (10. m, m') are shown in Fig. 4(a),
As shown in the column next to (b), the interference intensity in the interference term (m, m') between each order diffracted light αm included in the exit pupil 5 is shown, and the groove width W, the groove spacing p, and the The groove depth is given by ds and dD. In addition, the proportionality constants displayed in the four corners of the frame in the horizontal column calculate the peak value of the incident beam f (x) by 1 for each area D(i) on the exit pupil 5.
f(x-m/p)・f*(x
-m'/p) and the average value A(i, m, m') averaged in the X direction within each region D(i). ? Regarding equation 15), the information track 27 is set as the target track for reproducing information, and its signal components and a certain amount of crosstalk noise from the information tracks 26 and 28 on both sides thereof are classified. From equation (15), the first and second terms in { } represent the signal component, and the third to ninth terms represent the crosstalk noise component,
It can be seen that the lOth term gives a certain amount of noise due to the groove. Also, as can be seen from Figure 4(.)(b),
The first and third to seventh terms do not depend on the depth of the groove, and γ=W/
P, that is, the ratio of the groove width W to the groove interval P, depends on the other terms 2, 8, 9, and 10 also depend on the groove depths ds and dD. As a result of the analysis of equation (15), a large value can be obtained for the first term of the signal portion by reducing the groove vergence W and increasing the width of the information track, that is, by decreasing r. On the other hand, the evening loss talk, terms 3 to 7, are in area D (2)
and D(3), and is hardly included in D(1) and D(4). This is information track 16 or l8
This is because changes in the diffracted light distribution due to changes in the actual reflectance r2 or r1 mainly occur in the regions D(2) and D(3). Next, the second, eighth, and tenth grooves strongly depend on the groove depths ds and dD.
Regarding the term, since the groove depths are different, the reflection intensity distribution is biased towards the D(1) and D(2) sides of the exit pupil 5. Among these, the depth of the groove can be optimized so that the value of the crosstalk noise, or the eighth and ninth terms, is minimized. From the above, in order to reduce the crosstalk noise as much as possible and increase the signal component, only the reflected intensity light amount ID(1) in the area D(1) is detected,
And the crosstalk noise components in this region, 8th and 9th
The groove depth may be optimized so that the second term becomes larger by a certain amount of the signal. Next, an example of an optical disc according to the present invention will be explained with reference to FIG. FIG. 5(a) shows the disk structure. A thin recording film 30 is attached to a disk substrate 29 that is optically transparent to the wavelength of a light source used for recording and reproduction. In this embodiment, the recording film 30 is melted or evaporated by light irradiation and removed from the irradiation area, exposing the disk substrate, etc., and recording information pits by changing the effective reflectance. A PbTeSe recording film, which is one of the so-called perforated recording media, was used. As the groove structure of the disk surface 3, concave shallow grooves 24 and deep grooves 25 shown in the principle diagram of FIG. 1 are alternately arranged in the disk radial direction ξ. The information tracks 26, 27, or 28, which are planes between the grooves, divide the disk circumference by several tenths of an area called a sector 31, which is a unit of information management area. One sector further includes a preformat section 32 and a data section 33. The preformat section 32 consists of information such as addresses that give the positions of sectors on the disk, and is an area that is created in advance on the disk at the time of disk creation. This region consists of a phase pit row 34 with a depth of λ/8 or a phase pit row 35 with a depth of λ/4,
The phase pit rows 34 and 35 are arranged alternately in the radial direction of the disk. However, no groove structure exists in the preformat area 32. These preformat sections 32
Further, the method for forming the shallow grooves 24 and the deep grooves 25 will be described later as a disk master preparation method. On the other hand, the data section 33 is an area where information is recorded by the user, and the information pit 36
, 37 or 38 columns. As in this example, in a perforated recording medium with a film thickness of about a few tenths of the wavelength λ of the light source, information pits are areas where the effective reflectance is locally reduced by light irradiation. be. As shown in FIG. 1l, the optical system used for recording and reproducing information is a general optical pickup, except for the photodetector 39 for data reproducing, and is composed of at least a light source, a collapsing lens, and a beam splitter. , automatic focus detection system and control system. As shown in FIG. 5(a), the light beam from the light source is servo-controlled by an automatic focus detection system, and is focused by the focusing lens 2 onto the recording film 30 on the disk 3 through the disk substrate 29. When reproducing data, the reflected light from the disk surface 3 passes through the condensing lens 2 again and is guided in a direction different from the light source by a beam splitter or the like. Therefore, a photodetector 39 is arranged on the exit pupil plane 5, and the light receiving planes 40, 41, 42, 43, 4
4 will be provided. The light receiving surfaces 40 and 41 are area D(1) in FIG.
or D(4), respectively, and the light receiving surface 44 is in the area D
(2) and area D(3). As shown in FIG. 5(a), when reproducing the information track 27, the signal of the data section 33 is detected on the light receiving surface 40 on the shallow groove side as described above. Next, as explained in Fig. 1 above, the groove shape is optimized to reduce crosstalk from information bits on adjacent tracks, and furthermore, the groove shape is optimized to reduce crosstalk from information pits to the optimal groove shape. Describe the effects of information reproduction. First, we will examine the effect of optimizing the groove shape when the wavelength of the light source is λ=0.
83 μm, NA (numerical aperture) of the aperture lens = 0.5, track spacing p = Q, 8 μm,
Shown in FIGS. 6 and 7. FIG. 6 is a diagram for optimizing the groove depth. However, the groove depth dS of the shallow groove 24 was set to ds=λ/8n (n is the refractive index of the disk substrate 29) to simplify the analysis. In this figure, the horizontal axis shows the deep groove 2.
The depth dD of 9 is normalized with (λ/n) as 1, and the vertical axis represents each term of the reflected light intensity ID(1) in the area D(1) obtained by equation (15). The second one depends on the depth.
, the values of terms 8 to 10, and for reference, the lth of the signal
The value of the sum of the first, second, and tenth terms is also shown as the amount excluding the crosstalk component of the terms, that is, the total light amount. As can be seen from this figure, the groove depth dD at which both the eighth and ninth terms of the crosstalk components are minimum is 2.5λ/8 n≦dD≦3λ/
8 n range. Also, in order to make the second term of the signal component as large as possible, a
It is desired that D=3λ/8n. With the above value, the total amount of light can be large, so that signal detection with a high S/N is possible even for a recording film with large disk noise. The above optimization is based on the premise that the information pit is of a size that does not protrude into the shallow groove 24 or the deep groove 25. If, as shown in FIG. 5(a), the information pits 36, 37, and 38 have diameters that exceed IN, the second term includes not only the signal component but also the crosstalk component, and the second term includes not only the signal component but also the crosstalk component. The fourth term also includes both a signal component and a crosstalk component in addition to a certain amount of noise caused by the groove. As an example of optimization in such a case, the second term and the tenth term are also considered as crosstalk components, and the depth clD of the deep groove 25 is determined so as to take a value as small as possible. As can be seen from FIG. 6, dD=2.5λ/8n is optimal. With the above values, the total light intensity is dD or 3λ/8
Although it is smaller than in the case of n, since the first term of the signal component takes a constant value without depending on dD, the degree of signal modulation can be substantially increased. Therefore, this is an advantageous setting value for a recording film with small disk noise. Next, optimization of the groove #W will be described using FIG. The horizontal axis shows the ratio of the groove width W to the groove interval p, γ (mi W/p), and the vertical axis shows the values of terms ↓ to 10. In order to reduce the crosstalk component as much as possible, pay attention to the 8th and 9th terms that have the minimum value among the evening losstalk components, and set 0.35≦y≦0.5, that is, p as the vicinity of the minimum value.
=0. From 8 μm, the groove width W is Q. 3μm≦ws0.
The thickness is preferably 4 μm. This value can be created by using a groove forming technique that is carried out in a certain process of making a master disc, which will be described later. Rewriting the groove shape obtained through the above optimization, the shallow groove 24
[Case 1] Groove depth dD of deep groove 25 = 3λ/8 n [Case 2] Deep groove 2
5 groove depth dD=2.5λ/8n groove @w=0.3μm to Q. 4 μm Next, experimental results regarding the crosstalk reduction effect with these groove shapes will be described. FIG. 5(b) shows the actual measurement result of the reflection intensity distribution in the disk radial direction ξ received by the photodetector 39. The horizontal axis indicates the radius of the light receiving surface normalized by l. The vertical axis indicates the distribution of the amount of reflected light received. The distribution in this figure shows three information pits 36 with a bit diameter φ=0.6 μm,
37. Observations were made for 8 combinations of presence/absence of 38. Further, although this distribution was measured for the above-mentioned [Case 1], a similar distribution can be obtained for [Case 2] as well. The distribution curve group 45 is the distribution when the information pit 37 does not exist, and the distribution curve group 46 is the distribution when the information pit 37 does not exist.
This is the distribution when 7 exists. As described in the above optimization means, if light is received only on the light receiving surface 40, the amount of received light changes only depending on the presence or absence of the information pit 37, which becomes a signal, regardless of the presence of the information pit 36 or 38, which causes crosstalk. However, it can be seen that the amount of change is also large compared to other light-receiving surfaces. Further quantitative results of the above effects are shown in FIGS. 8 and 9. Figure 8 shows the results obtained for [Case ↓], and Figure 9 shows the results obtained for [Case 2]. In each figure, the horizontal axis indicates the position of the optical spot in the track direction +η, with point A as the origin. The vertical axis is the partial light receiving surface 4
0 or the amount of light received on the entire light receiving surface 39, the information pit 36,
It shows the relative modulation degree normalized by the received light amounts P and T when 37 and 38 are not present, respectively. The amount of crosstalk is the modulation degree S at point A when only information pit 37 exists and A when information pits 36, 37, and 38 exist.
It is determined by the difference in modulation degree C at the point. In FIGS. 8 and 9, when only the information pits 37 are present, the modulation degrees on the entire light-receiving surface 39 are shown as 49 and 50, the modulation degrees on the partial light-receiving surface 40 are shown as 51 and 52, and the information pits 36 and 37 , 38 are present, the modulation degrees on the entire light-receiving surface are shown as 53 and 54, and the modulation degrees on the partial light-receiving surface 40 are shown as 55 and 56, respectively. In the case of [Case 1], (when receiving light on all light receiving surfaces 39) -13.1 dB (T=
47.5%) -19.6dB (P=24.6%) (When receiving light on partial light receiving surface 40) In case 2, (When receiving light on all light receiving surfaces 39) (When receiving light on partial light receiving surface 4o) ) -13. 8dB (T=32.0%) -21. 5dI3 (P=14.2%). As described above, it has been found that crosstalk noise is reduced by 6 dB or more by detecting a signal on the partial light receiving surface 40. Furthermore, in [Case 2], the amount of received light is halved compared to [Case 1], but the amount of crosstalk can be further reduced by 2 dB. So far, we have discussed the case where the groove shape is uneven, but ■
Even the groove shape can reduce crosstalk noise. An example of the actual measurement results is shown in FIG. FIG. 10(a) shows the disk structure, and FIG. 10(b) shows the disk structure.
The crosstalk reduction effect for the shape of is shown. [Case 3] The groove shape is shown below. Shallow groove depth ds=λ/8n Deep groove depth dD=3λ/8n The groove width W is 0.4 μm for both the shallow groove and the deep groove. (b) When calculating the amount of crosstalk noise from the figure, it is -13.6 dB (T = 44.
0%) (When receiving light on partial light receiving surface 40) -24.0dB (P=
11.5%) However, when only the information pit 37 exists, the entire light receiving surface 3
The modulation degree at 9 is 57, and the modulation degree at partial light receiving surface 40 is 5.
8, the modulation degree on the entire light receiving surface when information pits 36, 37, and 38 are present is 59, and the partial light receiving surface 4
The modulation degree at o is indicated by 60. 2.5 more than the above result
Can reduce dB crosstalk noise. As described above, by using the groove shapes and partial light-receiving surfaces of [Case 1] to [Case 3], it was possible to perform sufficiently reliable data reproduction with crosstalk noise of -20 dB or less. Next, a reading method from the preformat section 32 will be described. That is, in reproducing the prepit row 34, the light receiving surfaces 40 and 4
The difference in the amount of received light from 1 is used as a preformat reproduction signal,
In the reproduction of the pre-pit 35, data such as addresses could be detected stably by using the sum as the pre-format reproduction signal. Next, a tracking method will be described for the disk structure of [Case 3]. In FIG. 10, the light spot is D−}E→(:, −+
F −+ Amount of light received when crossing Q and track 61
．． 62 and its sum 63 are shown in FIG. In order to make the light spot follow the target track C, the sum 63 should be equal to the offset amount 64. That is, in the circuit shown in FIG. 13, a signal 65 obtained by subtracting the offset amount 64 from the sum 63 is used as a tracking error signal to control the galvanomirror 66 shown in the first upper diagram. However, in case 4 is to follow track D or G, as is clear from FIG. 12, the polarity inversion circuit 67 (see FIG. 13)
It is necessary to invert the polarity of the tracking error signal by Hereinafter, the track in which shallow 'a47 is located on the light-receiving surface 40 side will be referred to as an odd-numbered track 68, and the track located in the opposite direction will be referred to as an even-numbered track 69. Next, a method for detecting data regarding a disk structure in which shallow grooves 47 and deep grooves 48 are arranged in a double spiral as shown in FIG. 14 will be described. First, a method of sequentially reading out odd-numbered tracks 68 and even-numbered tracks 69, which are arranged alternately in the radial direction of the disk, will be described. A track jump timing signal is detected from a preformat section 32 or the like that is prepared in advance on the disk. Here, as an example, odd number track 68
A case will be described in which a spot follows a track 69 and jumps to an adjacent even-numbered track 69 on the outside in the radial direction. Information signal detection before the jump is performed using the light receiving surface 40 as described above.
is used. In this state, at the moment when the timing signal is detected after the disc has rotated, the offset in the jumping direction is added to the tracking signal, as shown in FIG. 13, and the optical spot is shifted in the direction of the adjacent track to be jumped. At the next moment, by reversing the polarity of the tracking error signal, it is possible to track the adjacent even-numbered track 69 on the outside. Next, the tracking error signal polarity recognition circuit 70
According to the polarity of the tracking error signal, the signal 71 from the light receiving surface 40 and the signal 72 from the light receiving surface 41 are
to the playback signal and follow even-numbered tracks. By repeating this operation, the tracks can be read out in order. The above operations are similarly performed when detecting a preformat playback signal as shown in FIG. Next, we will describe a method for continuously reading the same track on a disc with a double helix structure. As an example in FIG. 14, when the light spot follows the odd track 68, after the disc rotates, the light spot skips one even track and is located on the outer odd track. Here, in order to read the same track continuously, the above-mentioned track jump timing signal 7 is sent after the disk rotation.
3, the offset of the impulse in the direction of returning the light spot inward is added to the tracking error signal. In this case, there is no need to invert the polarity of the tracking error signal. The above method makes it possible to read out the same track continuously. FIG. 15 shows an example in which a disk master having the disk structure used in the embodiment is manufactured by a laser cutting method. A laser 74 used for exposure is split into two beams by a beam splitter 75, passes through optical modulators 76 and 77 so that the intensity can be modulated and deflected independently, passes through a polarizing prism 78 again, and passes through a focusing lens 79 to the master disk 8.
0 on the photoresist 81. The optical modulators 76 and 77 deflect the optical spot by the same amount in the radial direction using the deflection pulse signal 82, and the optical modulation signals 83 and 84
Light intensity modulation is performed corresponding to each. Now, the first beam 85 has a shallow groove 47 and a λ/8 prepit row 34, and the second beam 86 has a deep i'l 48 and a 3λ/8 prepit row 35.
to expose. As shown in FIG. 15(b), when exposing the shallow grooves 47 and the deep grooves 48, the light is irradiated with light intensity such that the respective target groove depths can be obtained without deflecting the light. next,
In the format unit 32, a deflection pulse signal 82 is applied to deflect the beams 85 and 86 outward, and optical modulation is performed to expose the prepits 34 and 35. However, in the example, the track pitch p=0.8 μm and the deflection amount p=0.87zm. Furthermore, by rotating the master disc and sending two beams 85 and 86 in the radial direction of the disc at a pitch of 2p=1.6 μm, the master disc having the double helix structure shown in FIG. 14 can be prepared. In the above embodiments, the type of groove shape is a concave groove or a V groove.
Although a U-shaped groove is used, the same effect can be obtained even if the groove shapes of the shallow groove and deep groove are different. Furthermore, the values shown in the examples have tolerance values for the groove depth and groove width. [Effects of the Invention] As described above, by using the present invention, the track pitch can be narrowed by about twice as much as compared to the conventional one, and the target value of the amount of crosstalk, which is normally required in an optical disc device, is -20 dB.
You can achieve the following, increasing storage capacity while
Data can be recorded and reproduced with high reliability.

[Brief explanation of drawings]

Fig. 1 is a diagram for explaining the principle of the present invention, Fig. 2 is a diagram for explaining the conventional disk structure and its data detection method, and Fig. 3 is a diagram for explaining the conventional method for reducing crosstalk. Figure 4 shows an analysis of the intensity distribution on the light-receiving surface of the photodetector according to the present invention, and Figure 5 shows the disk structure and the light-receiving distribution on the light-detecting surface of an embodiment of the present invention. diagram showing,
FIG. 6 is a diagram showing the relationship between the depth of the groove shape and the signal according to the present invention, FIG. 7 is a diagram showing the relationship between the groove width and the signal, and FIGS. 8 and 9 are diagrams showing the relationship between the groove shape depth and the signal according to the present invention. Figure 10 is a diagram showing the actual measurement value of talk noise. Figure 10 is a diagram showing the disk structure and its crosstalk noise amount when the groove is shaped like a letter. Figure 11 is an example of the optical system used in the invention. 12 is a diagram explaining the principle of tracking, FIG. 13 is a diagram of a circuit configuration for tracking control and reproduction signal detection, and FIG. 14 is a diagram showing an example of a disk with a double helix structure according to the present invention. , FIG. 15 is a diagram for explaining the creation of a master disk according to the present invention. Explanation of symbols 1: light beam, 2: diaphragm lens, 5: exit pupil,
24-shallow groove, 25-deep groove, 31-sector, 32-preformat section, 33-data section, 34, 35-pre-pit row, 36, 37, 38-information pit, 39-photodetector, 40, 41, 44 - light receiving surface, 68 - odd track, 69 - even track, 8o - master disk, 85 - first beam, 86 - second beam. Me 2 Diagram / Diagram A 3 Box (^) Crow b Diagram 7 Group i (=ψh name? Diagram Z Diagram light S tree ゜t I Jl-I<, ν Voice of Hell 3-1q・ML Kigo

Claims (1)

[Scope of Claims] 1. An optical recording medium in which recording is performed using local characteristic changes caused by irradiation of a light spot, wherein grooves of different depths extending in the traveling direction of the optical recording medium are An optical recording medium characterized in that two pits are arranged alternately and periodically in a direction perpendicular to the traveling direction so that two pits are included in a spot, and recording pits are recorded on a plane between these grooves. . 2. Each of the grooves with different depths has a depth of λ/8,
2. The optical recording medium according to claim 1, wherein the optical recording medium has a wavelength of 3λ/8. 3. Each of the grooves with different depths has a depth of λ/8,
2. The optical recording medium according to claim 1, wherein the optical recording medium has a wavelength of 2.5λ/8. 4. Intensity for the 0th and 3rd order interference regions on the shallow groove side of the reflected diffraction light distribution obtained by irradiating the optical recording medium according to any of claims 1 to 3 with a light spot. A recording and reproducing method characterized by detecting changes and reproducing information. 5. Intensity changes in two interference regions of 0th order and ±3rd order of the distribution are detected, and the position of the light spot is detected based on the difference or sum signal.
Recording and playback method described. 6. Obtaining the above reflected diffraction light distribution on a photodetector,
6. The detection surface of the detector is divided into two parts so as to detect zero-order and third-order interference regions on the shallow groove side, and the signals detected in each part are switched depending on the position of the optical spot. Recording and playback method.