JPS63144435A - Optical information recording medium and information reading method - Google Patents

Abstract

PURPOSE:To omit a track exclusive for follow-up and to improve the information recording density by forming a diffraction grating on each track surface and discriminating a relevant track to its adjacent tracks based on the difference of diffraction characteristics. CONSTITUTION:A recording tracks include the tracks 4 (4a, 4b) of a first attribute and the tracks 5 (5a, 5b) of a second attribute. Then a diffraction grating is formed with a diffraction constant (d) to each track 4 in the direction of +45 deg. to the track forming direction and also to each track 5 in the direction of -45 deg. to the track forming direction respectively. As a result, the different diffraction characteristics are secured between those tracks 4 and 5. Thus the diffracted beams have different emitting directions. Therefore all tracks can be used as recording tracks and the information pits are formed on all tracks. As a result, the information recording density is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical information recording medium and an information reading method, and particularly to an optical information recording medium of a type in which information pits are recorded along a track and an information reading method.

[Prior Art] In recent years, optical information recording media such as laser discs and optical information recording cards have become popular.

In such a medium, a plurality of tracks are provided on the medium, and information pits are formed along the tracks. If the medium is a disk, the tracks are provided concentrically; if the medium is a card, the tracks are provided in parallel lines. FIG. 4 shows how information pits are formed in a conventional optical information recording medium. FIG. 4(a) is a top view of this medium, and FIG. 4(b) is a sectional view of FIG. 4(a) taken along the cutting line X--X-. Recording tracks 1 and follow-up tracks 2 are alternately formed on this medium. In Figure 4,
Recording tracks la, lb, lc and following track 2a
, 2b are shown. The following track 2 is shown in Figure 4 (
It has a groove as shown in b).

By irradiating the tracking beam and observing the reflected light, the tracking track 2 is recognized as a recess. On the other hand, data is stored in information pit 3 on recording track 1.
It is recorded in the form of presence or absence. If the reading head is scanned along the follow-up track 2, this head will also move along the recording track 1, making it possible to perform correct tracking control, that is, read control.

[Problem that the invention seeks to solve]

However, conventional optical information recording media have a problem in that the information recording area is wasted.

As shown in Figure 4, in the conventional optical information recording medium,
In order to perform tracking control, a groove must be provided as the following track 2, and the area that can be used for actual information recording as the recording track 1 is 5 of the total area of the medium.
It will only be 0%.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an optical information recording medium that can further improve information recording density, and a method for reading information recorded thereon.

[Means for solving problems]

The present invention is characterized in that in an optical information recording medium having a plurality of tracks and optically readable information pits formed on the tracks, a diffraction grating is formed on each track surface, and When reading information from this optical information recording medium, the diffraction characteristics of the diffraction gratings formed on the tracks are different from each other, and the tracks are scanned while observing the diffracted light by the diffraction gratings formed on each track. It is designed to control the direction of the recording medium, thereby increasing the information recording density.

[For production]

As shown in FIG. 5, when light enters a certain diffraction grating surface at an incident angle θ, reflected light exits at a reflection angle θ', and diffracted light exits at a diffraction angle θ1. Here, the reflection angle θ゛ is equal to the incidence angle θ, but the diffraction angle θ1 is determined by the grating constant d of the diffraction grating and the wavelength λ of the light, and if the first-order diffraction angle is 01, then
The following formula holds.

λ-ad(sin θ+sin θ1) Therefore, if the wavelength λ of the light used for reading information and the lattice constant d are determined, the diffraction angle θ1 can be determined. Note that the above equation applies when the grating formation direction is perpendicular to the incident light, and the diffraction angle will also differ depending on the orientation of the grating formation direction. That is, the emission direction of the diffracted light is determined by the wavelength λ of the light, the grating constant d1, and the direction in which the grating is formed.

According to the present invention, diffraction gratings oriented in different directions are formed on adjacent track surfaces. Therefore, the directions of diffracted light differ between adjacent tracks. Therefore, by observing this diffracted light, it is possible to identify adjacent tracks, and tracking control can be performed without providing a separate track for tracking as in the past. Therefore, information recording density can be improved.

〔Example〕

The present invention will be described below based on illustrated embodiments. FIG. 1 is a top view of an optical information recording medium according to an embodiment of the present invention. FIG. 4(a) shows the state before information pits are recorded, and FIG. 2(b) shows the state after information pits are recorded. In the optical information recording medium according to the present invention, all tracks are recording tracks, and no following track is provided.

Therefore, as shown in FIG. 1(b), information pits 3 are formed in all tracks. In this embodiment, the recording tracks are provided with a track 4 having a first attribute and a track 5 having a second attribute. FIG. 1 shows tracks 4a and 4b of the first attribute and tracks 5a and 5b of the second attribute. Track 4 of the first attribute (
= is +4 with respect to the track formation direction (vertical direction in the figure)
5'' direction, and the track 5 of the second attribute has a lattice constant d in the direction of -45° with respect to the track forming direction.
A diffraction grating is formed. Therefore, the first attribute track 4 and the second attribute track 5 have different diffraction characteristics and different emission directions of diffracted light.

Now, as shown in FIG. 2, if the reading light is irradiated onto the recording medium at an angle θ, the diffracted light from the track 4 of the first attribute will be emitted at an angle θ1, and the diffracted light will be emitted from the track 5 of the second attribute. The diffracted light will be emitted at an angle θ2. Here θ
1≠02. Therefore, if the first photosensor 61 is provided at a position corresponding to the angle θ1 and the second photosensor 62 is provided at a position corresponding to the angle θ2, the first photosensor 61 can detect the light from the track 4 of the first attribute. The diffracted light from the second attribute track 5 can be observed by the second photosensor 62, respectively. The first photosensor 61 is moved by the track pitch P to positions LL, L2. When placed at L3° and L4, the output signal from this sensor will be at positions 1 and L3 as shown in Figure 3.
detected only in That is, only the diffracted light from the first attribute track 4 is observed. vice versa,
If the second photosensor 62 is moved by the track pitch P from the position L2- shown in FIG. 2, only the diffracted light from the second attribute track 5 will be observed.

Now, as mentioned above, in the optical information recording medium according to the present invention, all the tracks can be used as recording tracks, so information pits 3 are formed in all the tracks as shown in FIG. 1(b). be done. In other words, the information recording density is doubled compared to conventional optical information recording media.

Two examples will be given below as methods for reading information from such an optical information recording medium. Note that the resolution of the photosensor used for reading may be comparable to that of photosensors used in conventional reading devices.

First Information Reading Method This method is a method in which first all tracks 4 of the first attribute of the optical information recording medium are scanned, and then the tracks of the second attribute are scanned. For example, in FIG. 1(b), the first photosensor 61 is used as a read-only sensor, and the second photosensor 62 is used as a tracking-only sensor.

Both sensors are fixed to the readhead. The second photosensor 62 performs tracking control so that the output level of the diffracted light from the second attribute track 5a is constant. That is, the reading head moves along the track 5a of the second attribute. When the read head position deviates from its normal position, this can be recognized because the output signal level decreases, as shown in the graph of FIG. The control system controls the read head to restore the output signal level. By such tracking control, the first photosensor 61 moves along the track 4a of the first attribute, and the first photosensor 61 moves along the track 4a of the first attribute.
The information pits 3 formed thereon can be read correctly. After reading all the information on the track 4a, the reading head is moved by 2P and the photosensor 62 follows the track 5b. Thereby, the photosensor 61 can correctly read the information pit 3 formed on the track 4b. Hereinafter, in the same manner, the photosensor 61
information is read from all tracks of the first attribute.

Next, move the read head back to its starting position, and this time:
The photosensor 62 is used as a read-only sensor, the photosensor 61 is used as a tracking-only sensor, and the second
The information pits 3 on all tracks of the attribute are read. At this time, tracking is performed based on the track 4 having the first attribute. With such two buses, all information pits can be read.

Second Information Reading Method This method is a method in which tracks of the first attribute and tracks of the second attribute are alternately scanned. For example, in Figure 1 (b
), first, the first photosensor 61 is used as a reading sensor and the second photosensor 62 is used as a tracking sensor to read information on the track 4a. Next, the reading head position is left as is, and the information on the track 5a is read using the second photosensor 62 as a reading sensor and the first photosensor 61 as a tracking sensor. Next, the reading head is moved by 2P, and the information on the track 4b is read using the first photosensor 61 as a reading sensor and the second photosensor 62 as a tracking sensor. In this way, the information on each track is sequentially read while alternating the roles of the two photosensors. This method has the advantage that all the information can be read in one pass, but the role of the photosensor must be changed for each track readout.

Finally, two examples of the method for manufacturing an optical information recording medium according to the present invention are shown below.

First Manufacturing Method This method is a method in which a diffraction grating is formed on the surface of a recording medium using uneven relief, and a thin film is formed on the diffraction grating.

The uneven relief can be created by forming fine parallel lines using mechanical cutting or holographic techniques.

By using a press standber, it is possible to reproduce the relief of the original plate, and it is also suitable for mass production. A thin film is formed on the uneven relief by a method such as vacuum deposition. Information pits will be formed on this thin film. Since information pits are generally formed by thermal irradiation with laser light, materials with high laser light absorption properties are suitable for the thin film, such as metal thin films mainly made of Te, organic thin films such as phthalocyanine.

Since the thickness of the thin film is sufficiently small compared to the unevenness of the relief, the unevenness of the relief is not impaired even after the thin film is formed, and the diffraction effect is not affected. In addition, even after a part of the thin film is thermally erased by a laser and information pits are formed,
The unevenness of the relief is not impaired and the diffraction effect is not affected.

Second Manufacturing Method This method is a method in which a plane pattern is formed on a recording medium, and a thin film transparent to the wavelength of the reading beam is formed thereon. The planar pattern may be formed by forming a pattern with density differences such as black and white, and can be easily reproduced using photographic technology or the like.

A thin film made of the above-mentioned material with high laser light absorption property is formed on this. Furthermore, this thin film is made of a material that is transparent to the wavelength of the reading beam. Therefore, the reading beam can be diffracted without any problem by the diffraction grating, which is a planar pattern on the recording medium.

Although the present invention has been described above based on several embodiments, the present invention is not limited to the above embodiments. For example, in order to change the diffraction characteristics, the direction in which the grating is formed is changed in the above embodiment, but the grating constant may also be changed. Further, although the above-described embodiment shows an example in which reflective reading is performed, the present invention can also be applied to a case in which transmission reading is performed.

〔Effect of the invention〕

As described above, according to the present invention, a diffraction grating is formed on each track surface, and adjacent tracks are distinguished from each other based on the difference in diffraction characteristics.Therefore, there is no need to provide a track dedicated to tracking, and the information recording density can be reduced. You can improve your performance.

[Brief explanation of the drawing]

FIG. 1 is a partial top view of the optical information recording medium according to the present invention, FIG. 2 is a diagram showing the diffraction characteristics of the optical information recording medium shown in FIG. 1, and FIG. 3 is a diagram showing the diffraction characteristics of the optical information recording medium shown in FIG. A graph showing the output signal level when diffracted light from an optical information recording medium is observed by the first photosensor, FIG. 4(a) is a partial top view of a conventional optical information recording medium, and FIG. ) is a partial sectional view thereof, and FIG. 5 is a diagram showing the direction of diffracted light by the diffraction grating. 1...recording track, 2...following track, 3
...Information pit, 4...Track of first attribute, 5.
... Second attribute track, 61... First photosensor, 62... Second photosensor. Applicant's agent: Yu Sato (α) (b) Figure 1 Figure 29 1 Field Figure 4 Figure 5

Claims (1)

[Claims] 1. An optical information recording medium having a plurality of tracks on which optically readable information pits are formed, in which a diffraction grating is formed on each track surface, and An optical information recording medium characterized in that diffraction gratings formed on adjacent tracks have different diffraction characteristics. 2. The optical information recording medium according to claim 1, wherein the diffraction characteristics are varied by changing the grating formation direction of the diffraction grating. 3. A first attribute track in which a grating is formed in a first angular direction with respect to the track forming direction, and a second attribute track in which a grating is formed in a second angular direction with respect to the track forming direction. 3. The optical information recording medium according to claim 2, characterized in that these are arranged alternately. 4. The optical information recording medium according to claim 3, wherein the first angle is +45° and the second angle is -45°. 5. In an optical information reading method in which information pits formed on a plurality of tracks are scanned and read along a predetermined track, a diffraction grating whose grating characteristics are at least different from that of adjacent tracks is provided on each track surface. An optical information reading method characterized by controlling the scanning direction while observing diffracted light by the diffraction grating. 6. The optical information reading method according to claim 5, wherein the diffraction characteristics are varied by changing the grating formation direction of the diffraction grating. 7. A first attribute track in which a grating is formed in a first angular direction with respect to the track forming direction, and a second attribute track in which a grating is formed in a second angular direction with respect to the track forming direction An optical information reading method 8 according to claim 6, characterized in that an optical information recording medium is used in which the first angle is +45° and the second angle is -. 8. The optical information reading method according to claim 7, wherein the angle is 45°. 9. The optical information recording medium according to claim 7 or 8, characterized in that the tracks of the second attribute are scanned after all the tracks of the first attribute on the optical information recording medium are scanned. How to read information. 10. The optical information reading method according to claim 7 or 8, characterized in that tracks of the first attribute and tracks of the second attribute on the optical information recording medium are scanned alternately.