JPH1125456A - Multivalued information recording/reproducing method for optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multivalued information recording method for an optical recording medium, which is capable of performing high-density recording by multivaluing recording information by a simple recording method. SOLUTION: An optically rewritable optical recording medium (phase transition type optical disk) is irradiated with a laser light to form an initial recording pit 2, a part of the initial recording pit is erased by an erasing pit 3 based on multivalued information multivalued according to information to be recorded to form a secondary recording pit 4 and, by modulating the area of this secondary recording pit 2, the multivalued information is recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for recording multi-valued information on an optical recording medium for performing high-density recording by forming multi-valued recording pits on an optical recording medium such as an optical disk, and the multi-valued recording method. The present invention relates to a reproducing method for reproducing information.

[0002]

2. Description of the Related Art Conventionally, as a method for performing high-density recording by multi-valued recording information on a disc-shaped optical recording medium, a reproducing laser beam is applied to recording pits formed along recording tracks of the optical recording medium. A method that changes the area, shape, and structure of the recording pit so that the reflectivity becomes multi-step when irradiated, that is, a method of recognizing multi-valued information by the amount of reflected light, the shape and direction of the recording pit, There is known a method of defining a plurality of combinations of positions and arrangements and reading these two-dimensional arrangement information.

As an example of a method of recognizing multi-value information by the amount of reflected light, a technique of changing the width direction of a recording groove in a recording pit to multi-value information is disclosed in, for example,
As described in Japanese Patent No. 43839, the recording groove formed in the optical recording medium is displaced in the width direction (radial direction of the optical recording medium) so that the opposing edge has a multilevel level. It has been proposed to detect the amount of displacement to reproduce multi-valued information.

As described in JP-A-6-318325 and JP-A-7-21568, one unit is formed by a plurality of recording pits, and the number of recording pits in the unit and There is also a method of changing the arrangement method to multivalue.

As a method of transforming the shape of a recording pit into multi-valued data, as described in Japanese Patent Application Laid-Open No. 7-169102, multi-valued information is obtained by a combination of changes in the shape of the start and end of a mark. The multi-valued information is expressed, and the shape of the recording pit is identified by a multi-division sensor or the like, and the multi-valued information is reproduced.

[0006]

However, each of the above-described multi-value coding methods has the following problems. In other words, the method of multi-valued recording information by a three-dimensional structure in which the recording pit shape and the depth and width of the recording groove of the optical recording medium are changed can be used as a ROM recording medium, but can be used as a RAM recording medium. This is not a value recording method.

In the case where a plurality of recording pits are formed in one unit and the number and arrangement method of the recording pits are changed to obtain multi-valued data, when writing is performed using an optical method such as laser light. Since the size of each recording pit is limited to the minimum beam diameter of the laser beam, the size of each recording pit becomes large as a unit, and the recording density cannot be significantly improved.

In the case where the recording pit shape is deformed and multi-valued, the recording pit shape needs to be complicated in order to achieve multi-valued recording, making it difficult to use the recording pit as a RAM recording medium. Also, when used as a ROM recording medium,
There is a disadvantage that the recognition mechanism of the recording pit shape is complicated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and a method of recording and reproducing multi-valued information on an optical recording medium capable of multi-valued recording information by a simple recording method and enabling high-density recording. The purpose is to provide.

[0010]

In order to achieve the above object, a method for recording multi-valued information on an optical recording medium according to the present invention comprises the steps of: irradiating a laser beam onto an optically rewritable optical recording medium; Forming recording pits, erasing a part of the initial recording pits into recording pits corresponding to multi-valued information multi-valued according to the information to be recorded, and modulating the area of the recording pits The multi-valued information is recorded by the following. I do.

According to this recording method, a part of the initial recording pit by the laser beam (recording light) is erased in correspondence with the multi-value information, so that the area of the recording pit is modulated to convert the multi-value information. Since recording is performed, it is possible to form a recording pit having a smaller area than the laser beam of the recording light. Then, since the light intensity pattern of the reflected diffracted light when the reproduction light is irradiated changes depending on the area of the recording pit,
It becomes possible to record multi-valued information. Also, multi-valued information is recorded according to the area of each recording pit, and multi-valued recording information is achieved by one recording pit. Density recording becomes possible.

The method of reproducing multi-valued information on an optical recording medium according to the present invention is an optical recording method in which recording pits for recording multi-valued information are formed by erasing a part of initial recording pits and modulating the area thereof. A reproducing laser beam is applied to the medium, a light intensity pattern of the diffracted light reflected from the recording pit is optically detected, and the light intensity pattern is demodulated to reproduce the multi-valued information.

The recording pits are multi-valued (m value) by modulating the area, and a plurality of recording pits (n
If the recording unit is combined to form a single recording unit, multi-valued information of the m-th power can be recorded as the recording unit. If the light intensity pattern of the reflected diffracted light from the recording unit is detected, the multi-valued information can be recorded. Since (m-th power) information can be reproduced, further high-density recording and reproduction can be performed.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of an embodiment of a multilevel information recording method for an optical recording medium according to the present invention will be described with reference to the drawings. The optically rewritable optical recording medium used in the method of the present invention uses a phase change optical disk. A phase-change optical disk irradiates a high-power recording light (laser light) spot according to information to be recorded on a recording film, thereby locally increasing a recording temperature.
An amorphous recording pit formed in a recording film by low-power reproducing light (laser light) is recorded by causing a phase change between crystal and amorphous to be recorded, and a change in an optical constant (reflectance) accompanying the recording is caused. The reproduction is performed by detecting the difference in the intensity of the reflected light using the difference in the reflectance between the crystal structure and the crystal structure formed therearound.

For example, in a phase change optical disk using a recording film having a relatively slow crystallization time, the disk is rotated,
The recording film formed on the disk is irradiated with recording light, the temperature of the recording film is raised to a temperature equal to or higher than the melting point, and after the recording light passes, the portion is rapidly cooled to record the portion in an amorphous state (recording pits are formed). )doing. At the time of erasing the recording, the recording film is crystallized by maintaining the recording film temperature in a crystallization-possible temperature range from the crystallization temperature to the melting point and lower than the crystallization temperature for a time sufficient for crystallization to proceed.

In a phase change optical disk using an information recording film capable of high-speed crystallization, one laser beam (recording light) condensed in a circular shape is used. Conventionally known methods perform crystallization or amorphization by changing a laser beam between two levels. That is, by irradiating the recording film with laser light having a power capable of raising the temperature of the recording film to a temperature equal to or higher than the melting point, most of the recording film becomes amorphous upon cooling, while the recording film temperature is crystallized. A portion irradiated with a laser beam having a power that reaches a temperature higher than the temperature and lower than the melting point is in a crystalline state.

The recording film of the phase change type optical disk is made of a chalcogenide-based material such as GeSbTe-based or InSbTe-based.
System, InSe system, AsTeGe system, TeOx-GeSe
A system, TeSeSn system, SbSeBi system, BiSeGe system, etc. are used, and all are formed by a film forming method such as a resistance heating vacuum evaporation method, an electron beam vacuum evaporation method, and a sputtering method. The state of the recording film immediately after film formation is a kind of amorphous state, and in order to perform recording on this recording film and form an amorphous recording portion, an initialization process for making the entire recording film crystalline. Is performed. Therefore, recording of information is achieved by forming an amorphous portion in the crystallized state.

When recording is reproduced from a phase change optical disk, an amorphous recording portion (recording pit) formed on a recording film is used.
And a method utilizing the difference in reflectance between the crystal structure formed therearound. The phase-change optical disk 10
As shown in FIG. 2, a spiral recording track 13 is formed in the surface portion 11 of the disc-shaped recording medium with respect to the center hole 12, and the recording track 13 is located in the radial direction of the optical disc with respect to the surface portion 11. The recording groove is formed by a recording groove having a concave-convex cross section, and a recording pit converted into multi-value information is formed on the bottom surface of the recording groove.

Next, the principle of multi-value recording in the recording method of the present invention will be described with reference to FIG. First,
As shown in FIG. 1, a recording light (power) capable of increasing the temperature of the recording film to a melting point or higher on an optical recording medium (phase-change optical disk) on which a crystalline recording film is formed. A laser beam is irradiated to form a circular initial recording pit 2. It should be noted that reference numeral 1 in FIG.
3 is a recording track center line (reference line) 1.

Next, a laser beam having a power such that the temperature of the recording film reaches a temperature equal to or higher than the crystallization temperature and equal to or lower than the melting point is irradiated so as to overlap a part of the initial recording pits 2 as the erasing pits 3. The erasing pit 3 becomes a crystalline state (initial state), and the initial recording pit 2 and the erasing pit 3
, A crescent-shaped secondary recording pit 4 is formed.

More specifically, a recording apparatus for recording on an optical recording medium (phase-change optical disk 10) is shown in FIG.
As shown in FIG. 5, a laser light emitting element (laser generating means) 5 for emitting recording light (laser light) applied to the disk surface 5
1, a collimator lens (condensing lens) 52 that converts the emitted laser light into parallel light, and a pickup lens (objective lens) 53 that converts the parallel light into a spot beam. The phase change optical disk 10 is rotatably arranged with respect to the laser light emitting element 51, and a laser beam (recording film) from the laser light emitting element 51 is applied to a recording track which is spiral with respect to the center of the phase change optical disk 10. (Which has a power to raise the temperature above the melting point) to form the initial recording pits 2 on the reference line 1 of the recording track, and then rotate the phase-change optical disc 10 to erase. A low-power laser beam for forming the pits 3 (having a power for setting the temperature of the recording film to a temperature higher than the crystallization temperature and lower than the melting point) is irradiated so as to overlap a part of the initial recording pits 2. Second recording pit 4
To form The laser light for forming the erasing pit 3 is emitted by an element different from the laser light emitting element that emits the laser light for forming the initial recording pit 2 or by modulating the power by the same laser light generating means. This is done by:

Then, as shown in FIG. 4, if the area where the initial recording pit 2 and the erasing pit 3 overlap is changed in accordance with the multi-valued information multi-valued according to the information to be recorded, The area of the secondary recording pits 4 can be changed stepwise or continuously (secondary recording pits corresponding to multi-valued information can be formed), and multi-valued information can be recorded. In forming each of the secondary recording pits 4 on the phase-change optical disk 10, the initial recording pits 2 and the erasing pits 3 are formed alternately and sequentially in the respective recording areas 20 arranged continuously along the reference line 1. This is done by:

The position of the erasure pit 3 superimposed on the initial recording pit 2 is such that a crescent-shaped secondary recording pit 4 consisting of a difference is formed. The secondary recording pits 4 may be arranged at any peripheral position, for example, as shown in FIG. Further, as shown in FIG. 6, it is also possible to superimpose two or more erased pits on the initial recorded pit 2 and leave the remaining portions as the secondary recorded pits 4a, 4b, 4c.

Next, the case of reproducing multi-valued recording on a phase change optical disk will be described. As shown in FIG. 7, a reproducing optical system for performing recording / reproducing includes a laser light emitting element 101 such as a semiconductor laser for generating a reproducing laser light for irradiating the optical disk 10, and a reproducing laser light emitted from the laser light emitting element 101. Lens 102 for changing the optical path of the reflected light from the optical disk, a λ / 4 plate interposed in the optical path to bend the optical path of the reflected light at the beam splitter 103 at a right angle (A quarter-wave plate) 104; an objective lens 105 for obtaining a spot-shaped light beam on the surface of the optical disk; and a light detection device 107 for detecting the intensity of light reflected from the beam splitter 103.

The reproduction laser light generated by the laser light emitting element 101 is first converted into parallel light by a condenser lens 102 and guided to a beam splitter 103. Beam splitter 1
The reproduction laser light passing through the laser beam 03 passes through the λ / 4 plate 104, is converted into a minute spot by the objective lens 105, and is applied to the disk 10 on which information is recorded on the recording track.
Here, according to the shape of the recording groove (recording pit) (not shown), the reproduction laser light is reflected, passes through the λ / 4 plate 104 again, and is guided to the beam splitter 103. At this time, the reproduced laser light reflected by the effect of the λ / 4 plate 104 is guided to the photodetector 107 instead of the laser light emitting element 101 side. The multi-value information is reproduced by detecting the intensity of the reproduction laser beam with the light detection device 107.

At the time of reproducing multi-valued information, low power reproducing light (laser light) is irradiated to a fixed area area (each recording area 20) including the secondary recording pits 4 and the area of the crescent-shaped secondary recording pits 4 is increased. The level of the average reflectance based on the ratio is determined by the photodetector 1
07 to reproduce as multi-valued recording information. Further, as shown in FIG. 4, it is also possible to demodulate the multi-valued recording information by detecting the pit interval 21 between the adjacent secondary recording pits 4 and the position of the edge 22 of each secondary recording pit 4. It is possible.

Further, as shown in FIG. 8, even if the secondary recording pits 4 have the same area, the density of the multilevel information can be further increased by giving directionality to the formation position of the erasing pits 3. Can be. When detecting the secondary recording pits 4 having directivity, an image sensor or the like is used as the light detecting device 107 of the reproducing device for detecting the multi-valued recording information. That is, at the time of reproducing multi-valued information, low power reproducing light (laser light) is irradiated to a fixed area area (each recording area 20) including the secondary recording pits 4 to change the shape of the crescent-shaped secondary recording pits 4. By detecting with the image sensor, the multi-value recorded information is reproduced from the average reflectance level and the pit shape.

The formation of secondary recording pits in which the erasing pits are formed with directionality is performed by a recording apparatus as shown in FIG. This recording apparatus is different from the recording apparatus of FIG. 3 in that a spot beam generated by a pickup lens 53 is applied to a surface of an optical recording medium (phase-change optical disk 10) by a laser generating means (not shown) for forming an erase pit. A configuration that can be moved above is added. That is, the pickup lens 53 is configured such that the focal position can be moved by an actuator 201 including a piezo element or the like, and the actuator 201 is controlled by a signal from the control device 202. The focal position is centered on the standard focal position A, and the optical recording medium (the phase-change optical disk 1)
It is possible to move between the moving focal position B and the moving focal position C in a direction orthogonal to the rotation direction 0).

According to this apparatus, the position of the spot beam of the laser beam for forming the erasure pits can be moved in the direction orthogonal to the rotation direction of the optical recording medium (the phase-change type optical disk 10). By combining the rotation of the medium (the phase-change optical disk 10), the erase pit 3 can be formed at an arbitrary position with respect to the initial recording pit 2, as shown in FIGS. 6 (b) and (c) and FIG. Such secondary recording pits 4 can be formed.

Further, as shown in FIGS. 10A to 10D, a plurality of the above-described secondary recording pits 4 having different recording areas are arranged in combination (for example, the number of the secondary recording pits 4 is 4).
By configuring the recording unit 30 individually), it is possible to increase the density of the multi-valued information. That is,
By modulating the pitch of the secondary recording pits or combining secondary recording pits having different areas or secondary recording pits having different directions, multi-valued recording units can be achieved.

Further, instead of forming the crescent-shaped secondary recording pits 4 in each recording area 20, a plurality of secondary recording pits 4 are continuously arranged as shown in FIG. When the small secondary recording pits 4 are continuous, the entire recording unit can be made smaller, and the density inside the recording unit can be increased. In this case, on the recording / reproducing apparatus side, the shape, arrangement direction, and the like of each secondary recording pit in the recording unit can be detected by using an image sensor or the like that reads the entire recording unit.

For example, when a recording unit is composed of a plurality of (n) secondary recording pits 4, even if each secondary recording pit 4 is a simple secondary recording pit having no directivity, as shown in FIG. to, if 7 (m) kinds of information in the area difference of the secondary recording pit 4 is represented, 7 ⁴ values as a recording unit (m ⁿ
Value) can be expressed.

In the above-described examples of the recording method and the reproducing method of the optical multi-valued information, the phase change type optical disk is used as the optical recording medium. However, the present method is applicable to any optically rewritable optical recording medium. Since it can be realized even with a medium, there is an advantage that the optical recording / reproducing apparatus which has been conventionally used can be used as it is without any significant improvement.

[0034]

According to the method of the present invention, when a part of the initial recording pit is erased by the laser beam, the area of the recording pit is modulated by the area difference to be erased. Can be multi-valued,
Higher density can be achieved. Further, when a plurality of recording pits are used as one recording unit, further higher density can be achieved. Further, when the reproduction light is irradiated, the light intensity pattern of the reflected diffracted light changes according to the area of the recording pit, and this is detected to reproduce the multi-value information. Therefore, the recording and reproduction of the multi-value information can be performed by a simple device. It can be carried out.

[Brief description of the drawings]

FIG. 1 is an explanatory plan view of a recording pit illustrating a recording pit forming process for explaining the principle of a method for recording multi-valued information according to the present invention.

FIG. 2 is an explanatory plan view of an optical recording medium.

FIG. 3 is a schematic configuration explanatory view showing a main part of a recording optical system that performs recording on an optical recording medium.

FIG. 4 is an explanatory plan view of recording pits showing respective secondary recording pits when multi-leveling is performed by using secondary recording pits whose areas are modulated.

FIG. 5 is an explanatory plan view of a recording pit showing another example of a case where multi-level conversion is performed using secondary recording pits.

FIG. 6 is an explanatory plan view of a recording pit when a plurality of erasing pits are present with respect to an initial recording pit.

FIG. 7 is an explanatory plan view of a recording pit when a shape of a secondary recording pit is given a direction.

FIG. 8 is a block diagram showing the configuration of a recording apparatus for forming erasing pits having directivity.

FIG. 9 is an explanatory diagram of a configuration of a reproducing optical system for reproducing multi-valued recording recorded on an optical recording medium.

FIGS. 10A to 10D are unit plan explanatory views showing an example in which a recording unit is formed by a plurality of recording pits.

[Explanation of symbols]

1 ... recording track center line (reference line), 2 ... initial recording pit, 3 ... erasing pit, 4 ... secondary recording pit, 1
0: optical recording medium (phase-change optical disk), 20: recording area, 21: pit interval, 22: edge part, 30
... Recording unit, 51,101 ... Laser light emitting element

Claims (4)

[Claims] An optical recording medium, which is optically rewritable, is irradiated with a laser beam to form initial recording pits, and the pits are made to correspond to multi-valued information according to information to be recorded. A method of recording multi-valued information on an optical recording medium, wherein the multi-valued information is recorded by erasing part of the initial recording pits to form recording pits and modulating the area of the recording pits. 2. An optical recording medium having recording pits for recording multilevel information by erasing a part of the initial recording pits and modulating the area thereof is irradiated with a reproducing laser beam.
A method of reproducing multi-valued information on an optical recording medium, comprising: detecting a light intensity pattern of reflected diffraction light from the recording pit, demodulating the light intensity pattern, and reproducing the multi-valued information. 3. An optical recording medium which is optically rewritable, is irradiated with laser light to form initial recording pits, and is multi-valued (m-valued) according to information to be recorded. A part of the initial recording pits is erased to correspond to information to form recording pits, a plurality of (n) recording pits are combined to form one recording unit, and the recording is performed by a plurality of recording pits having modulated areas. A method for recording multivalued information on an optical recording medium, wherein multivalued information of m to the nth power is recorded as a unit. 4. A light in which a recording unit comprising a plurality of (n) recording pits for recording multilevel (m-value) information by erasing a part of the initial recording pits and modulating the area thereof is formed. Irradiating the recording medium with a reproduction laser beam, detecting the light intensity pattern of the reflected diffraction light from the recording unit,
A method of reproducing multi-valued information on an optical recording medium, wherein the light intensity pattern is demodulated to reproduce multi-valued (m-th power) information.