JPS58155528A - Optical disc recording and reproducing system, optical disc and its manufacture - Google Patents

Abstract

PURPOSE:To attain the recording or reproduction of high density information, by recording sreviously tracking signals of different frequencies on the top and the bottom of a V-shaped or inverted trapezoidal grooves as pits in advance, and tracking the optical spot at the center of a tilt surface of the groove. CONSTITUTION:Grooves having V-shaped or trapezoidal radial cross section are provided on the optical disc, signals in frequency f1 are formed on the top and signals in frequency f2 are formed on the top as tracking pits, for example. Laser light is collected and irradiated on the optical disc, and when the distribution (b) of light intensity is obtained with a little shift from the center of the tilt surface to the top, the change in the amount of light in the frequency f2 is larger than that in the frequency f1, and when the optical beam is shifted to the bottom inversely (distribution c), the change in the amount of light in frequency f1 is larger. Thus, the tracking to the center of the tilt surface is executed by making the amplitude of the change in the amount of light changing in the two frequencies f1, f2 equal with each other.

Description

DETAILED DESCRIPTION OF THE INVENTION An object of the present invention is to provide an optical recording medium (disk) capable of high-density recording, a method for manufacturing the same, and an optical disk recording and reproducing system.

A method has been developed in which coherent light from a laser or other source is focused on a spot with a microscopic diameter and irradiated onto a disc on which information such as images and audio has been recorded in advance, and the information is reproduced. It's on sale now. This information is recorded as "hole bits" that form track rows on a flat disk, and the optical phase difference that occurs inside and outside the pit is detected and used as a signal.

In addition, for the above-mentioned read-only disc, a thin film of photosensitive recording material is provided on the disc, and by irradiation with a single light spot,
Research and development have been conducted on methods for recording desired information and reproducing it in a digital format, and its application as ``data files'' and next-generation [recording/playback video discs] is promising. Such recording material thin films include metal thin films such as To, Tl50)C
Low oxide thin films such as (o (x < 2)) and magneto-optical thin films such as MnB1 are known. Methods include local evaporation of a metal thin film, changes in the reflectance and transmittance of a 'reox film, and rotation of the polarization angle of light in the case of magneto-optical materials, depending on the energy of light irradiation.

In commercially available playback-only optical video discs,
Using a HeNe laser as a coherent light source, the information track spacing is 1.67 .mu.m, and a disk with a diameter of 30.alpha. is rotated at 1800 revolutions per minute, making it possible to reproduce a 30-minute video in the NTSC system.

However, in practice, a regeneration time of 30 minutes is insufficient, and a longer regeneration time has been desired. For this reason, several methods have recently been proposed to double the playback time by providing a new track between the information track and the track in a way that prevents crosstalk from becoming noticeable. For example, JP-A-54-12806゜ and I# JP-A-54-136303
Now, let's check the "hole pit" of the information signal in the trucks next to each other.
They have different depths. However, these optical discs are difficult to manufacture, and even if they could be manufactured, they would only be used for playback purposes.In real-time recording/playback discs, it is impossible to make drastic changes in the recording state between adjacent tracks. With the current technology, optical disks that can record and play back desired information have a diameter of 3oCrfL and can only record and play back 30 minutes of video. High-power semiconductor lasers that can also record have near-infrared wavelengthsf), H
It is not as narrow as the eNe laser (wavelength: 0.633 μm). It is possible to narrow down the laser by increasing the numerical aperture (N) of the lens, but there is also a limit to the large number ζ due to the effects of aberrations due to uneven thickness of the disk base material, etc. It is impossible to reduce the track pitch to 1 μm or less. Therefore, fundamental improvements are required to double the recording density of recording/reproducing disks.

Therefore, by using the slope of a groove whose radial cross section of the optical disk is approximately V-shaped or inverted trapezoidal as the information signal surface, the track pitch can be halved and the recording density can be increased to σ and σ. A method has been proposed to reduce crosstalk from matching tracks.

For example, JP-A-55-58144 proposes a method in which a laser beam is incident obliquely on a lens to irradiate the slope of a groove or an inverted trapezoidal groove as perpendicularly as possible. Generally, a light beam incident obliquely on a high NA lens cannot be sufficiently focused due to aberrations. In particular, with the lens above NAo, 6[, if the laser beam is incident at an angle of 2 to 3 degrees or more with respect to the optical axis, the influence of aberrations becomes significant, and the above method is completely impractical.

On the other hand, the present inventors have previously proposed a more specific method for increasing the recording density (Japanese Patent Application No. 56-18
0685). To summarize this method, we will explain the case where the groove has a V-shaped cross section and the reflected light from the optical disc is used for reproduction. This method can be applied not only to read-only optical discs but also to recording/reproducing optical discs.

First, the recording/reproducing disc will be described. FIG. 1 is a diagram illustrating an example of a disc on which a signal can be recorded using a laser beam and then reproduced using the same laser beam. In the figure, 1 is the base material of the disk, 2 is an ultraviolet curing resin (UV resin) layer provided on the base material and has grooves with an rVJ-shaped cross section, and 3 is a recording material thin film.
4 is a signal pit that was inserted into 3 by laser beam irradiation. The refractive index and optical density of this portion have changed, or the portion has been depressed into a hole shape due to evaporation. In Figure 1,
Information is recorded or reproduced by entering a laser beam from the base material 1 side. Therefore, in this case, the base material 1 and the UV
A transparent resin is used as the second resin.

However, recording or reproduction from the direction opposite to the base material side is also possible. A light beam spot is irradiated along one side of the TV-shaped slope, for example, along the 0 side in FIG. 1, and information pits 4 are recorded. 2P (Fig. 1) If the track pitch is set equal to the conventional track pitch, when playing back the 0th side, even with the playback optical system used for conventional playback-only video discs, the A side and the However, due to the doubling of the recording density, information is also recorded on the B side and D side. The cross-sectional shape of the groove was determined in order to reduce the crosstalk of the signal without deteriorating the signal quality, and a new recording and playback method related to it was proposed in Japanese Patent Application No. 180685-1985.
is completely described.

The light beam incident on the lens is focused onto the disk, and the disk acts as a two-dimensional diffraction grating, and the reflected light or transmitted light from the disk is separated into many diffracted lights. The case of reflected light will be explained using FIG. 2. 2 on the lens 6 surface, with the X axis in the radial direction of the disk,
The y-axis is perpendicular to the plane of the paper, that is, in the tangential direction of the disk circumference. Distribution 1A of the electric field of the optical beam IO incident on the lens 6
Let it be (X, Y). However, the radius of spread of the incident light beam is W, and x2+y2<w2. By setting the ξ and η axes on the disk surface parallel to the X and y axes, we can calculate the distribution of complex reflectance 'tR(ξ,
η). As a coordinate system for the reflected light on the lens 5 surface, the U axis and the y axis are set to coincide with the X axis and the y axis, respectively.

In such cases, the following can generally be said: The reflected light is separated into many diffracted lights, Kg (z==o.

±1. ±2. ) is the fourth-order diffracted light electric field in the U plane. The electric field of all diffracted light is equal to the electric field of incident light (
x, y) have the same spread radius W and similar intensity distribution. The distance between the respective diffracted lights on the U plane λf is -, and the situation is shown in FIG. Further, the amplitude and phase of each reflected diffracted light El are determined by the complex coefficients of the 7IJ series expansion of R (ξ, η) with a period of 2P in the ξ-axis direction. Generally, the complex reflectance distribution R (ξ, η) has a periodic structure also in the η-axis direction, and the diffracted light and complex coefficients also need to be treated in two dimensions. However, to explain the cross-sectional shape of the groove, the η-axis direction can be assumed to be uniform, and a one-dimensional treatment of only the ξ-axis direction is sufficient. Consider a "V-groove" o The inclination angle of the track slope is θ, and the track pitch is P. Also, the reflectance of the slope C with respect to the light intensity is lr,
+2, and the reflectance of slopes B and D is 1121. The reflectance for the amplitude of the optical electric field is generally a complex number, r and r2, respectively.
Twelve slopes are arranged alternately and periodically. Actually, slopes B and D contain different information. However, in reproducing the information of track slope C, other slopes, especially slope B
In order to consider minimizing the crosstalk between the information of and D,
It is sufficient to satisfy the condition that the reflectance of slopes B and D is the same and the influence of r2 is minimized.

This is because the disk rotates and the reflectance at the light beam spot changes over time according to the recorded information.

r and r2 are functions of time t.

In Fig. 2, the inclination angle θ of the "v groove" and the track pitch P,
When the relationship between the laser wavelength λ and the laser wavelength λ satisfies the following, that is, when the depth of the V groove is λ/4n, the following can be said. In this equation, 06 is the refractive index of the transparent medium on the incident side of the laser (wavelength λ) that the groove contacts. During reproduction along the slope C, the (-1)th order reflected diffraction light X-1 contains information of the reflectance r1 of the 0 surface, and the reflectance r of the B and D surfaces.
It does not depend on 2.

The O-th order light is affected to the same extent by both r and r2, and (
-2) The next indication also depends on both r and r2, but r2
The impact is small. Also, the (-1) order light has the same phase as the 0th order light, and the (+1) order light has a phase difference of 180 degrees from the 0th order light, and these diffracted lights interfere with each other. Thus, the reflected light intensity distribution on the Uv plane is formed. The integral value of this light intensity in a suitable region becomes the amount of received light.

FIG. 2 shows the waveforms (broken lines) of the intensity distribution of each diffracted light (solid line) and the reflected light passing through the lens at a uniform reflectance (r1=r, . . . ). That is, when formula (1) is satisfied,
(-1) The next instruction light contains only the information of slope C, and to reproduce slope C, (-1) If the next instruction light is received as the center, B
Crosstalk from the surface and the D surface can be reduced.

In order to further reduce crosstalk, the 0th order instruction should be set to B.
Since the information on the plane and the D plane is included, it is better not to interfere with the (-1) next instruction light and the 0th order instruction light when receiving light centered on the (-1) next instruction light. When zero weight of incident light is incident on the entire surface of the lens 5, the spread of the reflected light in each method is the same as that of the incident light, so all reflected diffracted light passing through the lens interferes with the zero weight reflected light. Therefore, the incident light I. If it is not made incident on the outer periphery of the lens, the zero-order reflected light will not pass through the outer periphery of the lens, and only the diffracted light reflected from the outer periphery of the lens will be received. Figures 2 and 3 show such a case. The reflected light from portions F and G in FIG. 2, ie, the portions where no incident light beam is present, contains only %(-2) of a slight crosstalk component in the next instruction light.

Specifically, a photodetector divided into at least two parts M and N as shown in FIG. Moreover, it is installed symmetrically to the center O of the projected image of the lens 6 onto the photodetector surface (broken line in FIG. 4). Moreover, at this time, the outer peripheral part of the lens projection image, that is, the above-mentioned slight (+2) next instruction light is included (+1)
The magnification of the reflected optical path is set so that next time only the pointing light will be incident on the photodetector M or N described above.

Information pit 4 in Figure 11 shows that the reflectance and transmittance have changed.
In the case of "shade pit", rl in Figure 2.

Both r2 can be real numbers. This is recording material thin film-3
This can be achieved by using a low tellurium oxide thin film and irradiating it with a laser light spot. (Japanese Patent Application No. 63-118468) When the information pit 4 is a "hole bit" that causes a phase difference in light inside and outside the pit, r in FIG.

r2 is expressed as a complex number. For example, the depth of the pit is d, and the reflectance inside and outside the pit is r. When , the complex reflectance is expressed as r = roexp (2ikd). (k=2π/λ) Such a "hole bit" is produced by using tellurium metal as the recording material thin film 3 and evaporating it by laser beam irradiation. It is also possible to make a read-only optical disc with the structure shown in Figure 6 by copying from the original application, which is also disclosed in the earlier application filed by the present inventors in 1806/1986.
The invention described in No. 85 can be applied. Up to now, the case of a V-shaped groove has been described, but the exact shapes of the tops of the crests and the bottoms of the valleys of the V-groove are not important. Therefore, the explanation up to now can also be applied to a substantially V-shaped groove in which the peaks and valleys have a slight curvature, or a transparent ladder-shaped groove in which the peaks and valleys are flat.

The recording density of an optical disc can be doubled by the method described above.

For example, in the case of a video disc, an optical disc with a diameter of 30 meters (30 m) rotates at a constant angular speed that allows trick play, and has 2 discs on both the front and back sides.
When rotating at equal linear speed over time, it is possible to play back 4 hours of video on both sides.

The above-mentioned premise requires that a light beam spot be irradiated along one slope of the V-groove, that is, tracking must be possible.

Tracking can be performed along the valley S or peak T of the V-groove in Fig. 2 for recording and playback (see No. 7).
figure). For example, this can be done by controlling the reflected light intensity distribution on the lens surface to be symmetrical with respect to the track direction, which is known as far-field tracking. ■Tracking to one slope of the groove is also controlled by intentionally shifting the tracking control from the valley S.

However, as shown in FIG. 8, when attempting to track to the 0 surface where the B surface has been recorded, the reflected light intensity distribution changes from when the B surface is unrecorded, and tracking to the center of the Ds 0 surface is not possible. Tracking of recording and reproduction on side 0 largely depends on the recording state of sides B and D, and tracking control becomes unstable.

The present invention aims to solve the above-mentioned problems and provides a means that enables stable tracking regardless of the state of recording signals in adjacent tracks.

The present invention will be explained in detail below.

■A "pit" with different optical properties is formed at the peak and valley of the groove or inverted trapezoidal groove at two different frequencies.The pit has a phase difference between the light inside and outside the pit. It may be a "hole pit" that gives a 100% change in reflectance or a "shaded pit" that has a changed reflectance or transmittance. The amount of reflected light from the disk changes at two types of frequencies, and by making the frequency components of each of the amplitudes of light amount changes equal, tracking is performed on a V-groove or an inverted + cedar slope.

This method will be explained with reference to FIG. 9 for the case of the groove. Tracking signals of frequency C are formed as pits in the valleys, and tracking signals of frequency f2 are formed in the peaks. 9th
The pit shown is an example of a "hole bit." a, b, and C
is the intensity distribution of the laser beam focused on the optical disk. When the light beam is irradiated slightly from the center of the slope to the mountain part, for example, when the light intensity distribution is like b, the frequency is f2.
A stronger light is emitted from the signal part of
The change in light amount at frequency f is larger than the change in light amount at frequency f. Also, if the light beam shifts toward the valley (when distribution C)
, conversely, the change in light amount at frequency f is larger than the change at frequency f2. That is, when the light beam is irradiated to the center of the slope, which is exactly in the middle of the peak and the valley (distribution &), the amplitudes of the light amount changes at frequencies f and f2 become equal. Therefore, fl
Tracking to the center of the slope can be achieved by equalizing the amplitude of the light amount change that changes at the two frequencies p f2 .

A similar method can also be applied to the case where the groove shape is an inverted trapezoid. The method of making a zero-order tracking pit, whose shape is shown in FIG. 10, will be described below. ■ Grooves or reverse trapezoidal grooves are
A mirror-like disc made of copper or the like with a V-shaped or trapezoidal tip. It can be exploded by mechanical cutting with a diamond needle.

When the tracking bit is a "shade pit", a base material having V grooves etc. formed thereon is made from the above-mentioned cut master through a standby process, a replica process, etc. On the substrate, a thin film of a low tellurium oxide recording material is deposited,
By irradiating laser light while tracking the peaks and valleys, "shade pits" are recorded. This makes it possible to track the slope using the method described above, and enables high-density recording of information. The situation is shown in Figure 11.%
Information is recorded on the C side.

Even if the tracking bit is a "hole pit", it can be made by evaporation by laser beam irradiation if tellurium metal is used as the thin film of the recording material, or by laser beam irradiation and etching if photoresist is used. At this time, the substrate on which the recording material is provided may be a copper thickness M, a standby, or a replica. In this way, a disk is produced in which tracking hole pits are formed in the peaks and valleys of the V-groove or inverted trapezoidal groove,
This time, a base material with a similar shape was made as the master for this f'L.
Ru.

A recording material is provided on the base material, and desired information can be recorded and reproduced by tracking the slope. When tellurium low oxide is used as the recording material, the information signal becomes a "shade bit", as shown in FIG. 12a.

Furthermore, if tellurium metal is used, the information signal becomes a "hole pit" similar to the tracking signal, as shown in FIG. 12b.

Now, if both the tracking bits and the information signal pits are "hole pits" as shown in FIG. 12, this disc itself is again duplicated as a master to create a high-density optical disc for reproduction only. However, such a read-only optical disc can be more easily produced by simultaneously recording information signals when creating tracking bits. (2) A recording material is provided on the substrate in which the grooves are formed, and Te metal, inorganic photoresist, etc. can be used as the material. Two recording light beams are made to be able to be modulated independently and are simultaneously irradiated onto the optical disk. One light beam records the tracking pitch If while tracking the peaks or valleys of the V-groove, and the other light beam records information signals.

The light source and optical system are arranged so that the distance between the irradiation positions of the two light beams on the optical disk is always kept constant.

The distance in the radial direction of the optical disc is an odd number multiple of one-fourth of the pitch between the peaks of the V-groove. Also, if the optical disc is irradiated at a distance of 2 to 3 times the wavelength of the laser in the circumferential direction of the optical disc, the light intensity of the overlapping part of the two light beams will be small and recorded. FIG. 13 shows the state on the optical disk when a light beam is used. This is an example of tracking the peak of the V groove with a light beam spot that records the tracking pit.
is an information signal recording light beam □, and is spaced apart by four minutes of the distance between the peaks in the disk radial direction (ξ direction).

As described above, by pre-recording tracking signals of different frequencies as pits on the peaks and valleys of the V-groove or the reverse trapezoidal groove, the slopes of the V-groove or the reverse trapezoidal groove can be tracked. The present invention provides a method for recording or reproducing information signals with high density.

[Brief explanation of the drawing]

Figure 1 is a cutaway perspective view showing the structure of an optical disc with V-shaped grooves, Figure 2 is a diagram showing the state of reflected light from the V-groove, and Figure 3 is a diagram showing the state of reflected diffracted light on the lens surface. Figure shown, 4th
Figure 5 is a plan view showing an example of a photodetector, Figure 5 is a cross-sectional view showing the recording state of a disc recorded by evaporation of a metal thin film, and Figure 6 is a diagram of an optical disc on which information is pre-recorded using hole bits. 7 and 8 are perspective views showing how recording is performed on the V-groove, FIG. 9 is an explanatory diagram of the means for tracking on the slope of the V-groove, and FIG. 10 is a diagram showing the provision of pits for tigers and kings. Figures 11 and 12 are diagrams showing recording on the shoulder of the V-groove, and Figure 13 is a diagram showing two light spots on the optical disc when creating tracking pits. It is. 1... Base material, 2... Ultraviolet curing resin,
3...Photosensitive recording material thin film, 4...Recording pits, 5...10. lens. Name of agent: Patent attorney Toshio Nakao (1st person)
WA L-Z'-! 361 Fig. 4 *sai Fig. 61g Fig. 7 4110 II @ Fig. 12 Fig. 13 □chi

Claims (1)

[Claims] (1) A brocade whose radial cross section is V-shaped or inverted trapezoidal is provided on the optical disk, and the groove is narrowed along each of the V-shaped or inverted trapezoidal inclined surfaces. In a recording/reproducing method in which information is recorded or reproduced by irradiating a sporatra with a light beam, groove and king bits are formed in advance at different frequencies on each of the peaks and valleys of the groove, and the reflected light from the optical disc is By making the signal amplitudes of the two types of frequency components equal among the signals generated from the temporal changes of An optical disk recording and reproducing method characterized by: (2) having a groove on the optical disk 2 whose radial pI surface is V-shaped or inverted trapezoidal; An optical disc in which tracking pits are formed at different frequencies. (3) The optical disc according to claim 2, wherein the tracking pits are comprised of pits with different reflectances. (4) The optical disc according to claim 2, wherein the racking pits are concave or convex pits that give a phase difference to the light inside and outside. (5) First and second light beams that can be modulated independently are focused and simultaneously irradiated onto an optical disk having a groove whose radial cross section is V-shaped or inverted trapezoid, and the first light beam spot is A method for manufacturing an optical disk, comprising forming tracking pits while tracking the peaks or valleys of the groove, and forming an information signal track on the slope of the groove using the second light beam spot.