JP2959650B2 - Optical information recording medium and reproducing method therefor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical information recording medium and an optical information recording medium .
And its reproduction method .

[0002]

2. Description of the Related Art In recent years, as society has become more computerized, a higher-density recording / reproducing system has been desired for a larger-capacity external storage device. Conventionally, when information is recorded optically, the size of the recording pit can only be reduced to a spot size determined by the wavelength of light and the numerical aperture (NA) of the objective lens.
It has been difficult to reduce the size of the recording pits to achieve high density.

However, in a so-called magnetic field modulation recording, in which recording is performed by using a magneto-optical recording medium as a recording medium and changing the polarity of an externally applied magnetic field at a high speed while irradiating a high-intensity light beam, the above-described spot size is used. It is reported that it is possible to record a recording pit shorter than the recording pit. (Miyamoto et al., “Optical Memory Symposium, '88 Transactions,” p. 49-, 1988) The outline of the operation will be described with reference to FIG. In FIG.
Is used as a light source, and divergent light from the
The light is converted into a parallel light beam through a beam shaping prism 30 and a beam splitter 4, and is applied to an objective lens 3, where the light is condensed to form a spot on the recording medium surface of the disk 2, and the reflected light is converted into an objective lens. The light is returned to the beam splitter 4 via 3 and a part of the reflected light is separated and sent to the control optical system.

In the control optical system, the separated light beam is further separated by a separately prepared beam splitter 9, and one of the separated light beams is passed through a half-wave plate 10 and a condenser lens 11.
2 where it is further separated to photodetectors 13, 1
4 and the other to a photodetector 19 via a condenser lens 15, a beam splitter 16 and a photodetector 18 via a knife edge 17, whereby the servo signal and the information signal are separately detected. I have to do it.

[0005] Recording by the magnetic field modulation method is performed as follows using an optical head as described above. The laser light incident on the disk has a constant power without being modulated, and modulates the magnetic field from the magnetic head 1 according to information. A thermal bias is applied by a laser, and the temperature is raised to, for example, the Curie point temperature or higher, and the direction of the magnetic field from the magnetic head 1 is reversed according to the information while erasing the previously recorded domain. The domain is formed the moment it cools down.

At this time, since the light spot usually has a Gaussian light intensity distribution, the temperature distribution of the medium heated by the light spot also has a smooth temperature distribution reflecting the light amount distribution, and the isothermal curve of the Curie point temperature. The shape is not short. Therefore, it is known that the recorded domain is an arrow feather-shaped domain. Since the magnetic field modulation recording method is a method as described above, the size of the recording domain does not depend on the size of the light spot, and is determined by the scanning speed and the modulation frequency of the magnetic head. FIG. 9 shows a domain recorded by this method. Thus, it is possible to record a domain smaller than the size of the light spot in the scanning direction.

[0007]

However, in reproducing a recording domain smaller than the light spot size recorded as described above, when the transfer function of the optical system is higher than the spatial frequency determined by the size of the light spot, it is abrupt. ,
It was difficult to reproduce a signal with a good S / N value.

SUMMARY OF THE INVENTION The present invention has been made to improve such disadvantages of the prior art. By providing a transmittance control layer on the heat mode recording layer on the incident side of the recording light beam, the light spot size is reduced. Information recording medium capable of reproducing a fine pattern having a good S / N value
And a reproducing method thereof .

[0009]

That is, the present invention provides the following:
Transmittance control in which light absorption characteristics change with light having a wavelength
Layer and reproducible by light having a second wavelength
Optical having a heat mode recording layer storing information
In the dynamic information recording medium, the first wavelength is the second wavelength.
Wavelength, and the transmittance control layer is
When the light having the first wavelength is not irradiated,
Transmitting light having the first wavelength and having the first wavelength
Absorbs light having the second wavelength when irradiated with light
An optical information recording medium characterized in that the light absorption characteristics change as described above.

In the above optical information recording medium,
Preferably, the recording layer is a magneto-optical recording layer. In addition, the transmission
Preferably, the rate control layer is a photochromic layer.

Further , the present invention provides the above optical information recording medium.
A method for reproducing information recorded on a body, comprising:
A first light spot having a second wavelength and a second light spot having a second wavelength
The medium is scanned in a predetermined direction with a second light spot, and
When the first light spot is moved to the second light with respect to the predetermined direction,
A part of the second light spot located before and after the spot
And two light spots overlapping the second light spot.
Selectively detecting light reflected by the medium of the pot
A method for reproducing information by using
You.

In the above-mentioned reproducing method, a change is caused in the transmittance control layer as the wavelength of the first light source so as to decrease the transmittance of the transmittance control layer at the wavelength of the second light source. It is preferable to select such a wavelength as to cause the light to flow.

[0013]

According to the present invention, a heat mode recording layer,
A first light source and a second light source having different wavelengths, using an optical information recording medium having a transmittance control layer on the incident side of a recording light beam adjacent to the heat mode recording layer; Means for forming two spots adjacent to each other in the track direction from a first light source on a recording surface of a recording medium; and a second optical spot aligned with a virtual optical axis center formed by the first spot forming means. By using an optical information recording / reproducing apparatus provided with a means for forming a second spot from two light sources and a wavelength selection element in a detection optical system, a recording domain smaller than the size of the light spot can be recorded. -To provide a reproducible optical information recording medium.

[0015]

The present invention will be described more specifically with reference to the following examples.

Embodiment 1 First, an optical information recording medium used in the present invention will be described with reference to FIG. FIG. 2 is a partial schematic view showing one example of the optical information recording medium of the present invention. In the figure, 2a is a transparent substrate, 2b is a photochromic layer, 2c
Denotes a heat mode recording layer, and 2d denotes a protective film. In this embodiment, an example in which a magneto-optical recording layer is used as the heat mode recording layer will be described.

It is generally known that the photochromic layer 2b absorbs light of a specific wavelength and changes the spectral characteristics of light absorption. For example, FIG. 3 shows a compound represented by the following chemical formula 1.

[0018]

Embedded image 5 is a graph showing an absorption spectrum (thickness: 0.6 μm) of a photochromic spiropyran vapor deposition film in the vapor deposition film of FIG. In the figure, (a) is before light irradiation, (b) is after ultraviolet light (0.4 J / cm ² ) irradiation, (c) is visible light (7.2
J / cm ² ) after irradiation.

Therefore, by irradiating light of two different wavelengths, the spectral characteristics of light absorption can be reversibly changed. At this time, since the change of the state is made by the absorption of photons, it is considered that the change generally takes place on the order of the relaxation time of the electron transition, and the state can be changed very quickly.

When a photochromic layer is used as the transmittance control layer, when the light of the wavelength of the first light source is irradiated on the disk 2, the photochromic layer 2b is
Absorption of light of the wavelength of the light source becomes large, and the magneto-optical recording layer 2
When the amount of light reaching the first light source is significantly reduced and the light of the wavelength of the first light source is not irradiated, the first light source and the first light source are moved so that the light of the second light source almost reaches the magneto-optical recording layer 2c. It is preferable to select the wavelength of the second light source and the material of the photochromic layer.

As such a photochromic material,
Materials such as fulgide, spiropyran, viologen, dihydropyrene, thioindigo, viviridine, and aziridine are known. The first wavelength is often ultraviolet light (about 360 nm) and the second wavelength is often visible light (about 600 nm).

Next, a recording / reproducing method using the above-described optical information recording medium will be described. FIG.
1 is a configuration diagram of an optical head used in the present invention. In the figure, reference numeral 8 denotes a first light source, which is a light source for extracting second harmonic light from a semiconductor laser using a non-linear optical crystal, for example, a phase shift element 5, a polarization beam splitter 29, and a beam splitter. The light is incident on the objective lens 3 via the optical disk 4 and forms a first spot on the disk 2. Here, as shown in FIG. 4, the phase shift element 5 is provided in a region where the light beam is divided into two in the track direction.

[0023]

(Equation 1)

Are elements that mutually generate a phase of π. As a result, two spots are formed on the disk as shown in FIG.

On the other hand, at the same time, light from the semiconductor laser 32 as the second light source is made incident on the objective lens 3 via the collimator lens 31, the beam shaping prism 30, and the polarizing beam splitter 4, and the second light is Form spots.

The first and second layers formed as described above
FIG. 6 shows the state of the spot. FIG. 6 (a)
Shows the intensity distribution of the first and second spots, where the solid line corresponds to the first spot and the broken line corresponds to the second spot. FIG. 6B shows the shapes of the first and second spots, where 21a and 21b are the first spots.
21c corresponds to the second spot.

The recording and reproduction of the optical information reproducing apparatus configured as described above will be described below. The recording was performed by setting the output of the first light source 8 of the ultraviolet light source to zero, and setting the semiconductor laser 3
Only the second spot from No. 2 is irradiated, and recording is performed in the same manner as in the above-described conventional magnetic field modulation recording method.

Next, reproduction will be described. As shown in FIG. 6B, the first light source 8 of the ultraviolet light source and the semiconductor laser are formed so that the first spot (21a and 21b) and the second spot (21c) are formed on the disk. 32 is caused to emit light. Then, as described above, the photochromic layer 2b absorbs the light of the second spot, changes the light absorption distribution characteristic, and as shown in FIG. 7A, the second spot of the second spot overlapping the first spot. In the region 21e, the light of the second spot is largely absorbed, and as a result, only the region 21f excluding the region overlapping the second spot reaches the magneto-optical recording layer.

Therefore, by providing the wavelength selection element 20 in FIG. 1 so that only the reflected light of the second spot is detected by the reflected light detection system, the entire optical system can be configured as shown in FIG.
FIG. 9B shows that the reproduction system is constituted by an equivalently very thin linear light spot as shown by 21f in FIG. 9B, the transfer function of the optical system extends to a high range, and the S / N value is good. It is possible to reproduce a minute recording domain as shown in FIG.

In FIG. 1, the operation after the reflected light has passed through the wavelength selection element 20 is the same as in the conventional example. After reproduction, the photochromic layer may be returned to the original state for the next recording by irradiating the second spot with increased light intensity.

Embodiment 2 In this embodiment, an example in which a phase shift element is used in the optical path in the spot forming means of the first light source has been described, but the first light source has two array-like light sources. May be.

[0032]

As described above, according to the present invention,
An optical information recording medium having a photochromic layer as a transmittance control layer on the incident side of the recording light beam of the heat mode recording layer is irradiated with light of a first wavelength, and the irradiated portion is irradiated with a second light.
When the second spot was irradiated by changing the photochromic layer so that the wavelength of the light was almost absorbed, only the portion apparently not overlapping the first spot was irradiated on the heat mode recording layer. This has the effect that the transfer function of the optical system can be effectively extended to a high frequency range, and a fine pattern smaller than the light spot can be reproduced as a signal having a good S / N value.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical head used in the present invention.

FIG. 2 is a partial schematic diagram illustrating an example of the optical information recording medium of the present invention.

FIG. 3 is a graph showing characteristics of a photochromic material.

FIG. 4 is an external view of a phase shift element.

FIG. 5 is a diagram showing an operation of the phase shift element.

FIG. 6 is a diagram showing a light spot on a disk.

FIG. 7 is an explanatory diagram of a light spot during reproduction.

FIG. 8 is a configuration diagram of a conventional optical system.

FIG. 9 is an explanatory diagram showing a magnetic field modulation method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnetic head 2 Disk 2a Transparent substrate 2b Photochromic layer 2c Heat mode recording layer 2d Protective film 5 Phase shift element 8 First light source 20 Wavelength selection element 32 Semiconductor laser

Claims (4)

(57) [Claims] 1. A and transmittance control layer absorption characteristics by light having a first wavelength changes, heat mode that stores information as playable by light having a second wavelength
Oite the optical information recording medium having a recording layer, wherein the first wavelength be different from the second wavelength, is and the transmittance control layer not irradiated with light having the first wavelength Sometimes, the light having the second wavelength is transmitted, and when the light having the first wavelength is irradiated, the light absorption characteristics change so as to absorb the light having the second wavelength. Optical information recording medium. 2. A method according to claim wherein the recording layer is a magneto-optical recording layer
2. The optical information recording medium according to 1. 3. The optical information recording medium according to claim 1 , wherein said transmittance control layer is a photochromic layer. 4. The light according to claim 1, wherein:
Method for reproducing information recorded on a biological information recording medium.
A first light spot having the first wavelength and a second light spot having the first wavelength.
The medium in a predetermined direction with a second light spot having a wavelength of
, And at this time, the first light spot is moved in the predetermined direction.
With respect to the second light spot, and partially
It consists of two light spots that overlap with two light spots,
Selectively reflecting light of the second light spot by the medium
Information is reproduced by detecting the
Playback method.