JPH0772567A - Optical information recording medium and optical information recording and reproducing device - Google Patents

Abstract

PURPOSE:To effectively micronize a light spot and to record and reproduce information at a recording density below optical resolution by arranging a photochromic layer using a specified photochromic material on the light irradiation side of a recording and reproducing layer. CONSTITUTION:A disk 6 of the optical information recording medium and optical information recording and reproducing device consists of a replica substrate 6a, a photochromic layer 6b, a recording and reproducing layer 6c, a reflecting layer 6d and a protective layer 6e. The photochromic layer 6b of the photochromic material has a light transmissivity increased with increase in incident power or incident energy density and saturated is arranged close to the recording and reproducing layer 6c, and a light spot with the incident power density increased at the center and decreased at the periphery is passed through the photochromic layer 6b to irradiate the recording and reproducing layer 6c. Accordingly, the light spot is effectively micronized, and information is recorded and reproduced at a recording density below the optical resolution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording medium and an optical information recording / reproducing apparatus, and more particularly to an optical information recording medium and optical information recording / reproducing capable of recording / reproducing information at a recording density lower than the optical resolution. Regarding the device.

[0002]

2. Description of the Related Art As a first conventional example, "Technical Digest of Optical Data Storage Topical Meeting 1991 Volume 5 (Te
chnical Digest of Optical Data Storage 1991 Volume
5 pp. 112-115 and pp. 116-119 "is known. This uses a plurality of layers of magneto-optical recording film, and a "layer for masking surrounding information" is provided outside the information recording / reproducing layer. Information recorded information (bits) appears in the portion where the temperature rises due to the irradiation of the reproducing light, so that interference with adjacent bits is suppressed and the resolution is improved even when the recording density becomes high. .

A second conventional example is Japanese Patent Laid-Open No. 5-114.
The optical information recording medium disclosed in Japanese Patent Publication No. 06 is known. This uses a material whose optical constant changes with heat, a bleaching material, an optical bistable material, and a high-order nonlinear material, and obtains the same effect as that of the first conventional example.

[0004]

The first conventional example has a problem in that the optical information recording medium is limited to the magneto-optical disk. In the second conventional example, the effective spot becomes asymmetric when a material showing a time during which the optical constant changes with light irradiation, that is, a relaxation time, which cannot be ignored with respect to the data reading time is used. However, there is a problem that the reproduced signal is distorted. Therefore, it is a first object of the present invention to provide an optical information recording medium and an optical information recording / reproducing apparatus which are not limited to a magneto-optical disk and whose recording / reproducing resolution is effectively improved. A second object of the present invention is to provide an optical information recording medium and an optical information recording / reproducing apparatus which can make an effective spot symmetrical.

[0005]

The optical information recording medium of the present invention records information by causing a local optical characteristic change by strong light irradiation, and detects the presence or absence of the local optical characteristic change by weak light irradiation. In an optical information recording medium having a recording / reproducing layer for reproducing information, a photochromic layer using a photochromic material having a light transmission characteristic that the transmittance increases and saturates with an increase in incident power or incident energy density, is formed from the recording / reproducing layer. Is also characterized in that it is arranged on the light irradiation side. Further, in the optical information recording medium of the present invention, the recording / reproducing layer is composed of a mixture of a photochromic material and a binder having a relatively strong interaction and laminated in multiple layers, and the photochromic material is provided between the respective recording / reproducing layers. Is characterized in that a photochromic layer composed of a mixture with a binder having a relatively weak interaction is interposed.

The optical information recording / reproducing apparatus of the present invention is characterized in that at least the latter half of the reproducing light spot or the recording light spot is overlapped and the initialization light spot is simultaneously irradiated. The optical information recording / reproducing apparatus of the present invention is characterized by irradiating the reproducing light or the recording light with a short pulse.

[0007]

In the photochromic material, the complex refractive index (particularly the absorption term) is governed by the incident power or the incident energy density, a photoisomerization reaction occurs, and the structure reversibly changes by irradiation with light having different wavelengths. Then, due to this structural change, the light transmission characteristics also change. For example, by irradiating light of a certain wavelength λ1 to reduce the transmittance for the wavelength λ2 and irradiating light of the wavelength λ2 in this state, the wavelength λ2
When the incident energy density of the light is low, photo-isomerization does not occur, and thus the transmittance remains low, but when the incident energy density increases, photo-isomerization occurs and the transmittance for the light of wavelength λ2 itself increases. That is, it is possible to cause a difference in transmittance between a portion having a small incident energy density and a portion having a large incident energy density, and to provide a nonlinear light transmission characteristic. Therefore, a photochromic layer made of this photochromic material is arranged in the vicinity of the recording / reproducing layer, and a light spot having a large incident power density in the central portion and a small incident power density distribution in the peripheral portion is irradiated to the recording / reproducing layer through the photochromic layer. To do.
Then, since the light spot is effectively miniaturized, information can be recorded / reproduced at a recording density lower than the optical resolution.
And this is not limited to magneto-optical disks.

When the optical information recording medium is scanned with the light spot, the incident energy density is higher in the latter half part than in the first half part of the light spot, and the incident energy density becomes asymmetric in the scanning direction. Therefore, the effective light spot also becomes asymmetric. However, in the optical information recording medium of the present invention, a recording / reproducing layer is constituted by a mixture of a photochromic material and a binder having a relatively strong interaction, and the recording / reproducing layer is laminated in multiple layers. Since a photochromic layer made of a mixture with a binder having a weak interaction is interposed, it is possible to suppress an increase in transmittance due to temperature characteristics and to make an effective light spot symmetrical. Further, in the optical information recording / reproducing apparatus of the present invention, since at least the latter half of the reproducing light spot or the recording light spot is overlapped and the initialization light spot is simultaneously irradiated, the transmittance becomes high in the latter half of the light spot. Is suppressed, and the effective light spot can be made symmetrical. Further, in the optical information recording / reproducing apparatus of the present invention, since the reproduction light or the recording light is irradiated with a short pulse, it is possible to prevent the incident energy density from increasing in the latter half of the light spot, and to make the effective light spot symmetrical. .

[0009]

The present invention will be further described below with reference to the embodiments shown in the drawings. The present invention is not limited to this.

First Example FIG. 1 shows structural changes and transmission spectra before and after photoisomerization (in this case, a ring-closing reaction and a ring-opening reaction) of the diarylethene derivative A. In the ring-opened state, as shown in the transmission spectrum curve 1, there is no absorption at a wavelength of 550 nm or more. Then, in the ring-opened state, 420 to 480
When it is irradiated with light in the wavelength band of nm, it changes to a closed ring state.
In the ring-closed state, as shown in the transmission spectrum curve 2,
It has an absorption peak near 00 nm. Then, in the ring-closed state, irradiation with light of 550 nm to 700 nm changes the ring-opened state.

FIG. 2 shows the transmittance characteristics when a film of the ring-closed diarylethene derivative A is irradiated with light having a wavelength of 630 nm. Closed ring state (state of incident energy density 0)
The transmittance at 26 is 26%. When the incident energy density is small, ring-opening does not occur so much, and thus the transmittance is small. Since ring-opening progresses as the incident energy density increases, the transmittance increases almost linearly and saturates.

FIG. 3 shows the transmission power characteristics when a film of the ring-closed diarylethene derivative A is irradiated with light having a wavelength of 630 nm. Due to the transmittance characteristic of FIG. 2, the transmission power characteristic curve becomes non-linear. The straight line indicated by the broken line is
A saturated transmission power characteristic is shown. Therefore, when an incident light spot having a two-dimensional Gaussian distribution is incident on the film of the diarylethene derivative A in the ring-closed state, the transmitted light spot has a higher transmission power density in the central portion and a closer peripheral portion. The transmitted power density becomes low,
The distribution becomes steep.

FIG. 4 shows the distributions of the light intensities of the incident light spot and the transmitted light spot in a standardized and overlapping manner. The half-width and spot diameter of the transmitted light spot are smaller than that of the incident light spot, and the effect of spot miniaturization is obtained. In order to efficiently perform the spot miniaturization, the peak power density value of the incident light spot should be matched with the incident power density value at the intersection of the transmission power characteristic curve and the straight line (saturated transmission power characteristic) in FIG. , Can be set.

FIG. 5 shows a disk 6 and an optical system of a first embodiment of the optical information recording medium and the optical information recording / reproducing apparatus of the present invention. The disc 6 includes a replica substrate 6a, a photochromic layer 6b, a recording / reproducing layer 6c, a reflecting layer 6d, and a protective layer 6e. The disk 6 is manufactured as follows. Make a stamper disk. The polycarbonate replica substrate 6a is manufactured by the 2P method or the injection method. Replica substrate 6a
Has a thickness of 1.2 mm. Powder of diarylethene derivative A which is a photochromic material is mixed with polyvinyl butyral resin which is a binder at 10 wt%, dissolved in anone solvent and spin-coated on the replica substrate 6a to form a photochromic layer 6b having a film thickness of 100 nm. Form. The binder is PMM.
A, cellulose diacetate, polymethacrylic acid, polystyrene or the like may be used. An InSe phase change film is sputtered on the photochromic layer 6b to form a recording / reproducing layer 6c having a film thickness of 75 nm. An Al film is sputtered on the recording / reproducing layer 6c,
The reflective layer 6d having a film thickness of 75 nm is formed. An ultraviolet curable resin, for example, is spin-coated on the reflective layer 6d and cured to form a protective layer 6e having a thickness of 200 nm.

The optical system comprises a reproducing optical system and an initializing optical system. The reproduction optical system narrows down the reproduction light having a wavelength of 630 nm from a semiconductor laser (not shown) through the diaphragm lens 14 and irradiates the disk 6 as a reproduction light spot 9. The initialization optical system is a halogen lamp 1.
Light from No. 5 is passed through the projection lens 17 and the wavelength selection filter 16 and irradiated onto the disk 6 as initialization light having a wavelength of 420 nm to 480 nm. The initialization light is positioned at the irradiation area in the area including the reproduction light spot 9 and is irradiated simultaneously with the reproduction light. Since the incident energy density of the reproducing light is higher than the incident energy density of the initializing light, there is no problem even if they are simultaneously irradiated.

It should be noted that the irradiation area of the initialization light is not limited to the position shown in FIG. 1 because the photochromic layer 6b may be initialized (ring closed) when or before the data is read by the reproduction light. Further, when the disc 6 is inserted into the optical information recording / reproducing apparatus, the entire face of the disc 6 may be scanned and initialized by the initialization light. Further, before reproducing a certain track, the track may be initialized by scanning it for one rotation with the initialization light.

The initialization optical system may be integrated with a recording / reproducing optical head (not shown) of the reproducing optical system. Further, an initialization optical system may be installed on the side of the disk 6 opposite to the recording / reproducing optical head (not shown) of the reproduction optical system so that the initialization light is emitted from the back side of the disk 6.

FIG. 6 shows the incident power density distribution 18 of the reproducing light spot 9, the incident energy density distribution 20 on the photochromic layer 6b when the reproducing light spot 9 scans the disk 6, and the reproducing light spot 9. Transmission power density distribution 21 from the photochromic layer 6b when scanning over the disk 6
And the reproduced light spot diameter cross section and the effective spot diameter cross section. Transmission power density distribution 2 from the photochromic layer 6b
Since 1 is governed by the incident energy density 20, when the reproduction light spot 9 scans the disk 6, the distribution becomes asymmetric. Therefore, the effective spot diameter cross section is also asymmetric.

FIG. 7 shows a reproduced signal 10 when the reproducing light spot 9 scans the disk 6 having marks. The reproduced signal 10 was somewhat asymmetric, but had a modulation factor that provided sufficient read characteristics. This modulation degree is smaller than the ideal reproduction signal 45, but higher than the conventional reproduction signal 12 (a disc without the photochromic layer 6b), and the optical resolution is improved. I understand. The reproduction signal 10 was obtained by detecting a change in the amount of reflected light. The tracking is performed by the push-pull method using the guide groove. Alternatively, JP-A-63-231
The sample servo method described in Japanese Patent Laid-Open No. 738 or Japanese Patent Laid-Open No. 01-195535 may be used. Defocus detection is performed, for example, in Japanese Patent Laid-Open No. 63-231738 and Japanese Patent Laid-Open No. 1-01.
The front-back differential detection method described in Japanese Patent No. 9535 is used.

The structure of the disk 6 is described in Japanese Patent Application No. 4-3936.
By adopting the multiple interference structure or the etalon structure as disclosed in Japanese Patent Publication No. 3, the gamma characteristic of the transmittance characteristic is emphasized and the optical resolution can be further improved.

-Second Embodiment-In the first embodiment, the regeneration is performed after the initialization to the closed state. On the other hand, in the second embodiment, the regeneration is performed after the initialization to the ring-opened state. The disk and the optical system of the second embodiment are the same as those in FIG. 5, except that the reproduction light uses the wavelength of 458 nm of the Ar + laser and the initialization light uses the wavelength selection filter 1.
6, a wavelength of 550 nm to 700 nm is used. The recording light uses a wavelength of 458 nm of an Ar + laser, and an intensity modulation is performed by an AO modulator or an EO modulator according to the presence or absence of data. Although the recording light and the reproducing light have the same wavelength, but the light intensity at the time of recording is about 5 times the light intensity at the time of reproducing, the transmittance of the photochromic layer 6b is close to 100%, and the effective spot at the time of recording is Becomes almost the same as the incident light spot. This second
Also in the example, the optical resolution could be improved as in the first example.

Third Embodiment FIG. 8 shows a disk 3 which is a third embodiment of the optical information recording medium of the present invention. This disk 3 is a replica substrate 3a
The photochromic layer 3b, the enhancement layer 3c, the recording / reproducing layer 3d, and the protective layer 3e. The replica substrate 3a is glass having a thickness of 1.2 mm. The photochromic layer 3b is formed by applying a mixture of the diarylethene derivative A and a binder to a film thickness of 100 nm. The enhancement layer 3c is SiN having a film thickness of 200 nm. The recording / reproducing layer 3d is a magneto-optical film of TbFeCo having a film thickness of 100 nm. The protective layer 3e is SiN having a film thickness of 100 nm. For example, when a reproduction signal was obtained by the polarization differential detection method described in Japanese Patent Laid-Open No. 57-88540, the optical resolution of this disk 3 could be improved as with the disk 6.

In the first to third embodiments, examples of the phase change film and the magneto-optical film are shown as the recording / reproducing layers 3d and 6c.
The present invention can be applied to a medium in which data is recorded in prepits such as a compact disc and a laser disc.
The structure of the optical information recording medium in this case is shown in FIG.

-Fourth Embodiment- In the first to third embodiments, only the reproducing light spot 9 is effectively miniaturized, but in the fourth embodiment, the recording light spot is also effectively miniaturized. , Forming minute marks.

FIG. 9 shows the structural change and the transmission spectrum of the diarylethene derivative B before and after the photoisomerization (called a ring-closing reaction and a ring-opening reaction). In addition, a transmission spectrum of the diarylethene derivative A is shown (curve 1 in FIG.
Same as 2.). In the ring-opened state, the diarylethene derivative B has no absorption at a wavelength of 550 nm or more as shown by the transmission spectrum curve 3. And, in the ring-opened state, 400
When it is irradiated with light in the wavelength band of ˜460 nm, it changes into a ring-closed state. The diarylethene derivative B is
As shown in the transmission spectrum curve 4, it has an absorption peak near 532 nm. And in the closed ring state, 465 nm
The ring-opening state is changed by irradiating light of ˜620 nm. The transmission spectrum curve 1 in the ring-opened state and the transmission spectrum curve 2 in the ring-closed state of the diarylethene derivative A are as described above with reference to FIG.

FIG. 10 shows a disk 4 and an optical system of a fourth embodiment of the optical information recording medium and the optical information recording / reproducing apparatus of the present invention. The disk 4 includes a replica substrate 4a,
The first photochromic layer 4b, the second photochromic layer 4c, the recording / reproducing layer 4d, the reflecting layer 4e, and the protective layer 4f. The replica substrate 4a is glass having a thickness of 1.2 mm. The first photochromic layer 4b is formed by applying a mixture of the diarylethene derivative A and a binder to a film thickness of 100 nm. The second photochromic layer 4c is formed by applying a mixture of the diarylethene derivative B and a binder to a film thickness of 100 nm. The recording / reproducing layer 4d has a film thickness of 75 nm.
InSe phase change film. The reflective layer 4e has a film thickness of 75n.
m Al reflection film. The protective layer 4f has a film thickness of 200 nm
Is an ultraviolet curable resin film.

The optical system comprises a recording / reproducing optical system and an initialization optical system. The recording / reproducing optical system is a recording light from a semiconductor laser having a wavelength of 630 nm or a second harmonic light source (SH
G: Second Harmonics Generator) wavelength 532n
The reproduction light of m is narrowed down through a narrowing lens and is irradiated onto the disk 4 as a recording light spot or a reproduction light spot 19. The initialization optical system irradiates the light from the halogen lamp 15 onto the disk 6 as initialization light having a wavelength of 450 nm to 460 nm through the projection lens 17 and the wavelength selection filter 16. Wavelength 450nm
Initialization light of ˜460 nm corresponds to diarylethene derivative A
And both the diarylethene derivative B are cyclized.

With respect to recording light having a wavelength of 630 nm, the first photochromic layer 4b acts as a non-linear light transmitting film by ring opening of the diarylethene derivative A. In addition, the second photochromic layer 4b has no absorption regardless of whether the diarylethene derivative B is in the ring-closed state or the ring-opened state, and can be ignored. Therefore, the first photochromic layer 4b effectively reduces the size of the recording light spot. On the other hand, wavelength 532n
For the reproduction light of m, the second photochromic layer 4c acts as a non-linear light transmission film by ring opening of the diarylethene derivative B. Further, the first photochromic layer 4b absorbs 50% when the diarylethene derivative A is in a ring closed state.
Since the reproducing light power is smaller than the recording light power, the ring-closed diarylethene derivative A acts merely as an attenuation filter. Here, the diarylethene derivative A
So that the absorption at the wavelength of 532 nm is as small as possible, and that the wavelength of 53 nm is less than the sensitivity for the wavelength of 630 nm.
When optimized and synthesized so that the sensitivity to 2 nm is greater, the reproduction at the wavelength of 532 nm is optimized even if the nonlinear transmission characteristic of the first photochromic layer 4b is optimized for the high power of the recording light at the wavelength of 630 nm. The diarylethene derivative A is sufficiently ring-opened with respect to the weak power of light, the transmittance of the first photochromic layer 4b is increased, and the reproduction light is sufficiently transmitted through the first photochromic layer 4b. Therefore, the second
The photochromic layer 4c effectively miniaturizes the reproduction light spot. It should be noted that the above-mentioned sensitivity is a change rate in which the transmittance changes with respect to the change in incident energy density, and
Corresponds to the slope of the transmittance characteristic curve of.

The diarylethene derivative A was prepared at a wavelength of 630.
By synthesizing so that the sensitivity for the wavelength of 532 nm is higher than the sensitivity for nm, the nonlinear transmission characteristic can be obtained for the reproduction light spot even in the first photochromic layer 4b. Therefore, it is possible to enhance the miniaturization of the reproduction light spot. In addition, the first photochromic layer 4
Since the recording light spot and the reproducing light spot can be miniaturized only by b, the second photochromic layer 4c can be omitted and the structure of the disk 4 can be simplified.

Changes in the complex refractive index of the diarylethene derivatives A and B with respect to the incident energy density and In
As a result of optimizing the multiple interference structure in consideration of the change in the complex refractive index of the Se phase change film before and after recording, the reflectance spectrum of the disk 4 and the recording / reproducing layer 4d as shown in FIG.
The absorption spectrum at was obtained. At the time of recording, in the region where the incident energy density is low, the absorptance of the recording light having the wavelength of 630 nm in the recording / reproducing layer 4d is low due to the absorptance (P low) 25 in FIG. On the other hand, in the region where the incident energy density is high, the recording absorption rate (Phigh) 26
As a result, the absorptance of the recording light of wavelength 630 nm in the recording / reproducing layer 4d is high. Therefore, the effective recording light spot became smaller than the incident light spot, and a minute mark could be recorded. At the time of reproduction, the reflected light from the unrecorded portion of the recording / reproducing layer 4d is high due to the unrecorded portion reflectance (Phigh) 27 and the unrecorded portion reflectance (Plow) 28 regardless of the incident energy density. Shows reflection. On the other hand, the reflected light from the recording portion of the recording / reproducing layer 4d shows low reflection when the incident energy density is large due to the recording portion reflectance (Phigh) 29, and the incident energy due to the recording portion reflectance (Plow) 30. It shows high reflection when the density is low. Further, spot miniaturization in the photochromic layers 4b and 4c is emphasized by the multiple interference effect. As a result, the reflected light changes only in the area where the peak intensity part of the miniaturized effective spot is applied to the mark part, and the reflected light from the unrecorded part and the reflected light at the skirt of the effective spot are about the same. done. As a result, the change in the amount of reflected light obtained when reproducing the mark row, that is, the degree of signal modulation can be increased.

In FIG. 10, the photochromic layers 4b and 4c are formed.
However, the same effect was obtained even if the diarylethene derivatives A and B were mixed in the same binder to form a single layer structure.

-Fifth Embodiment- In the fifth embodiment, the recording wavelength and the reproducing wavelength in the fourth embodiment are exchanged. That is, the wavelength of the recording light is 532 nm and the wavelength of the reproducing light is 630 nm. Even in this case,
Since the recording light with the wavelength of 532 nm is irradiated with higher power than the reproducing light with the wavelength of 630 nm, the diarylethene derivative A is completely ring-opened and the transmittance is increased. And
It was possible to improve the optical resolution.

-Sixth Embodiment-In the first to fifth embodiments, an initialization light source different from the recording light source and the reproduction light source is provided, but in the sixth embodiment, the recording light source is used for reproduction. It is used as the initialization light source, and the playback light source is used as the initialization light source during recording.

A photochromic material having a characteristic that the transmittance increases with irradiation of light having a ring-closing wavelength and the transmittance also increases with irradiation of light having a ring-opening wavelength, is used. One of the cyclization wavelengths is the wavelength of the recording light,
The other is the wavelength of the reproduction light. As a result, the recording light spot and the reproduction light spot can be effectively miniaturized without providing an initialization light source separate from the recording light source and the reproduction light source. For example, the medium is a diarylethene derivative A shown in FIG.
And a yellow semiconductor laser is used as a recording light source, and a ring-closing wavelength of 458 nm is used as a reproducing light wavelength, and an Ar laser is used as a reproducing light source. Further, for example, the diarylethene derivative C shown in FIG. 13 is used as the medium, the ring-opening wavelength of 680 nm is used as the recording light wavelength, the red semiconductor laser is used as the recording light source, and the ring-closing wavelength of 490 nm is used as the reproducing light wavelength. -Use a Group VI blue semiconductor laser as a reproducing light source.

FIG. 14 shows an optical system. A recording light spot 31 is used as a reproducing light spot 3 by using a known two-wavelength optical head.
It is arranged so that it is preceded by the same track 33 as the second track. For tracking, a known push-pull method was used for the wavelength of the recording light. As the defocus detection method, a known astigmatism method was used.

At the time of recording, the recording light is initialized by the reproduction light spot 32 in advance. At this time, the recording light power is set to a weak light enough to detect the servo signal. Since the reproducing light spot 32 for initialization is scanned after the recording light spot 31, discoloration due to the recording light spot 31 does not occur. Here, the reproducing light spot 32 has a spot diameter smaller than that of the recording light spot 31 by a wavelength ratio of 0.84. Therefore, in the irradiation area of the recording light spot 31, the radial direction not scanned by the reproduction light spot 32 is not sufficiently initialized. For this reason, the tracks before and after the track to be recorded are also scanned to complete the initialization. In this case, after waiting for three revolutions, the intensity of the recording light corresponding to the recording pulse is modulated, and recording is performed. As a result, even during recording, the recording light spot 31 can be effectively reduced, so that minute marks can be recorded stably.

In order to make the rotation waiting for initialization one rotation, as shown in FIG. 15, the reproduction light spot 32 is made into three spots in three adjacent tracks, and the tracks before and after the recording track are also scanned. . Since the diameter of the reproducing light spot 32 is larger than the track pitch 35 for narrowing the track, the irradiation positions of the three spots in the radial direction overlap each other, and the area of the recording light spot 31 can be completely initialized. The three spots are formed by using a diffraction grating or a three-beam array semiconductor laser. It should be noted that a crosstalk canceller, which is a narrow track narrowing technique for obtaining signals of a target track by calculating each signal of three spots (Japanese Patent Laid-Open No. 4-6).
9820).

The recording light spot 31 has a Gaussian distribution,
Since the energy is sufficiently small even when the skirt portion of the recording film is transmitted to the recording film, the influence of the skirt portion of the recording light spot 31 can be ignored when the recording mark has a temperature threshold value as in optical information recording. Therefore, it is not always necessary to scan the tracks before and after the track to be recorded. Therefore, in FIG.
As shown in FIG.
By setting 3 spots in 3 and initializing the recording light with the reproducing light spot 34 preceding the recording light spot 31, recording can be performed without waiting for rotation for initialization.

During reproduction, the read-out portion is the previously recorded portion, so the recording light has already been initialized to the reproduction light. Since the diameter of the reproduction light spot 32 is smaller than that of the recording light spot 31, the irradiation area of the reproduction light spot 32 is initialized. Therefore, normally, waiting for rotation at the time of reproduction is unnecessary. However, if the disk surface has been exposed to sunlight for a long time, it may be discolored.
Therefore, it is preferable to irradiate the recording light spot 31 having a weak power so as not to be re-recorded before the reproduction to initialize it. Even in this case, since the recording light spot 31 scans the disk surface prior to the reproducing light spot 32, waiting for rotation is unnecessary. However, there is a possibility that the initialization is not sufficient with a single irradiation of the recording light spot 31 having a weak power. Therefore, it is necessary to wait for the rotation, but it is preferable to completely initialize the recording light spot 31 with a weak power several times.

-Seventh Example- The transmission spectrum of the photochromic material in the ring-opened state and the transmission spectrum in the ring-closed state are the intensities when the light of the ring-closing wavelength and the light of the ring-opening wavelength are simultaneously irradiated. It depends on the ratio. Therefore, when the initialization light can be emitted simultaneously with the recording light and the reproducing light, the transmission characteristics of the photochromic layer can be controlled by it. That is, the sensitivity can be optimized. For example, the transmission power characteristic curve in FIG. 3 shifts in the horizontal axis direction by irradiating the reproduction light and the initialization light with appropriate power at the same time. As a result, by irradiating the initialization light with an appropriate power at the same time, the power of the reproduction light deviates from the non-linear characteristics of the photochromic material, or the wavelength of the light source drifts due to temperature fluctuations like a semiconductor laser. Even if it happens, the spot miniaturization can be optimized.

-Eighth Embodiment- FIG. 17 shows a case where a reproducing light spot having a reproducing wavelength of 532 nm and a diaphragm lens numerical aperture of 0.55 is constantly irradiated at a linear velocity of 10 m / s and a reproducing power setting of 1.65 mW. 6 shows a reproduction light incident power density distribution 38 in the scanning direction and a steady energy density distribution 41 by the reproduction light spot at the moment when the reproduction light spot is at the position of x = 2 μm.
The stationary energy density distribution 42 due to the initialization light will be described later. Similarly, FIG. 18 shows the stationary energy density distributions 41-1 and 41-2 in the radial direction. The stationary energy density distribution 41-1 is a radial cross section at a position of x = 1 μm, and the stationary energy density distribution 41-2 is x = 2 μm.
It is a radial cross section in the position of. FIG. 19 shows the power density distribution 38 s of the incident spot and the power density distribution 37 s of the outgoing light spot that has passed through the diarylethene derivative B during steady irradiation. However, both are standardized for comparison. Further, the power density distribution 82 of the emitted light spot in which the coordinates are matched with the power density distribution 38s of the incident spot is shown. The energy density distribution 44 due to the emitted light spot when the initialization light is simultaneously irradiated will be described later.

Regarding the scanning direction, as can be seen from the energy density distribution 41 of FIG. 17, in the rear of the spot,
Higher energy density. Therefore, as can be seen from the power density distributions 37s and 82 of the emitted light spot in FIG. 19, the miniaturization of the spot becomes small and the shape becomes asymmetrical behind the spot. For the radial direction, see FIG.
The distribution is symmetrical, as can be seen from the energy density distribution of.

In the eighth embodiment, the effective spot is miniaturized even behind the spot in the scanning direction to make the spot shape symmetrical.

FIG. 20 shows a spot arrangement diagram of the eighth embodiment. An initialization light spot 40 having a wavelength of 458 nm is arranged so as to overlap the latter half of the reproduction light spot 39 having a wavelength of 532 nm. Then, the irradiation power of the initialization light is set so that the ring opening due to the high energy density of the reproduction wavelength behind the reproduction light spot 39 does not proceed.
Reference numeral 42 in FIG. 17 shows an energy density distribution by the initialization light spot 40.

FIG. 21 shows a transmittance distribution 83 by irradiation of the reproducing light spot 39, a transmittance distribution 84 by irradiation of the initialization light spot 40, and a transmittance distribution 43 by simultaneous irradiation of both. Since the reproducing light spot 39 and the initializing light spot 40 are simultaneously irradiated behind the reproducing light spot 39, the transmittance distribution 43 is obtained, and the spot can be miniaturized even behind the reproducing light spot 39. In addition, the spot shape can be made symmetrical. Reference numeral 44 in FIG. 19 shows the energy density distribution of the emission spot when the reproduction light spot 39 and the initialization light spot 40 are simultaneously irradiated,
It can be seen that the spot shape is symmetrical. As a result of the above, a reproduction signal close to the ideal reproduction signal waveform 45 shown in FIG. 7 was obtained.

The focus position deviation signal and the track position deviation signal may be detected by the initialization light.

-Ninth Embodiment- In the ninth embodiment, the spot is further miniaturized by using an optical super-resolution spot. In FIG. 22, by masking the skirt portion of the reproduction light spot 47 with the initialization light bimodal spot 46, an increase in transmittance at the skirt portion of the reproduction light spot 47 is suppressed, and the reproduction light is transmitted only in the central portion. To make the spot smaller. Initialization Kosobu spot 46
Is obtained by inserting a matrix-shaped bimodal spot spatial filter (phase filter) 48 as shown in the figure into the optical path of the initialization light as described in Japanese Patent Publication No. 3-65012. In the ninth example, the effective spot could be made 20% smaller than that in the eighth example.

-Tenth Embodiment- In the tenth embodiment, as shown in FIG. 23, a super-resolution spot spatial filter 49 for shielding the center of the luminous flux of the reproduction light is inserted and the reproduction light spot 50 is super-solved. Form on the image spot. When the reproduction light spot 50 is formed as a super-resolution spot, the spot diameter of the main lobe 51 becomes small, but the increase of the side lobe 52 poses a problem during reproduction.
Therefore, the influence of the side lobe 52 is canceled by the initialization light bimodal spot 46 so that the transmittance of the irradiated portion of the side lobe 52 does not increase. In the tenth example, the effective spot could be made 20% smaller than that in the ninth example.

-Eleventh Embodiment- An eleventh embodiment is a parallel recording / reproducing system (special feature) in which a plurality of recording / reproducing light beams are provided and each light spot is positioned on a plurality of tracks to record / reproduce a plurality of information simultaneously. The present invention is applied to KAISHO 63-231738).

FIG. 24 shows a 2-beam parallel recording / reproducing system. As the disc, the disc 6 shown in FIG. 5 is used. In order for the initialization light spot 40 to include the two recording / reproducing light spots 53, the diameter of the initialization light beam having a wavelength of 458 nm is made smaller than the diameter of the reproduction light beam having a wavelength of 630 nm, thereby reducing the effective aperture. There is. That is, the effective numerical aperture of the initialization light is 0.45 with respect to the numerical aperture of 0.55 of the reproduction light.
I am trying. As a result, the two recording / reproducing light spots 5
The area scanned by 3 can be initialized at the same time.

Further, by simultaneously irradiating the initialization light at the time of recording / reproducing, it is possible to enhance the spot miniaturization. That is, at the time of reproducing by irradiating the reproducing light with low power, the initialization light is set to a weak power to satisfy the condition that the spot is miniaturized, and at the time of recording of irradiating the recording light with high power, The initialization light is set to a high power to satisfy the condition that the spot is miniaturized, and the spot is miniaturized both during recording and reproduction.

-Twelfth Embodiment- In the twelfth embodiment, the light shielding plate 54 shown in FIG. 25 is inserted into the initialization light beam shown in FIG. 24 to initialize the super-resolution spot as shown in FIG. The spots 40 'are formed on the disc in the radial direction. The two valleys 55 of the initialization light spot 40 'are respectively formed into two recording / reproducing light spots 5
By positioning it at 3, the effective spot in the radial direction can be further miniaturized and a narrower track can be realized.

Incidentally, also in the three reproducing light spot system shown in FIG. 15, the reproducing light spot can be miniaturized by using the initialization light spot of the super-resolution spot. Also, regarding the recording light spot, a minute mark can be formed by using the initialization light spot of the super-resolution spot.

-Thirteenth Example- At the time of recording or reproduction, at the modulation data detection point, at a time sufficiently smaller than the time obtained by converting the size of the irradiation spot into time with respect to the spot scanning speed, that is, the linear velocity, Modulates the irradiation power. The irradiation energy density distribution formed by such short-pulse irradiation becomes almost the same as the incident power density distribution.
It is possible to obtain a miniaturized spot similar to the miniaturized spot in the stationary state as shown in FIG.

FIG. 27 shows a thirteenth embodiment. Recording light,
The wavelengths of the reproduction light and the initialization light and the medium structure are the same as those in the eighth embodiment. A known sample servo format was used for the disk format. Data recording / reproduction is performed discretely at the recording / reproduction timing detected in advance in the sample area 56, that is, at the position of the grid point 57. In FIG. 27, a known NRZ (Non-Return-to Zero) is used.
The case where a modulation code is used is shown.

At the time of recording, the mark 58 is recorded at the lattice point corresponding to "1" of the modulation data. During reproduction, pulse irradiation is performed with the drive pulse 59 at the grid point. The pulse irradiation conditions are: irradiation power 1.65 mW, pulse width 20
ns. Under this pulse irradiation condition, the energy applied to the recording film is sufficiently smaller than the recording condition, the mark is not destroyed, and the mark is not formed. On the other hand, the irradiation energy density distribution 60 on the photochromic material is almost similar to the incident spot distributions 61 and 61 ′ and shows a symmetrical shape. Here, assume that data detection during reproduction is performed at the rear edge position of the grid point pulse. At this time, the effective miniaturized spot distribution 63 after passing through the photochromic material film at the trailing edge portion 62 of the irradiation pulse is sufficiently miniaturized (× 0.7) and symmetrical with respect to the presence or absence of a mark. It became a distribution.

The discrete value 65 of the obtained reproduced signal 64 is at a level at which the amplitude can be sufficiently discriminated. Then, the level is discriminated by the slice level 66, and the detection data 67 is obtained with high reliability.

The method is not limited to the photochromic material, but a medium exhibiting a normal third-order nonlinear optical effect (that is, a medium having a nonlinear refractive index term whose refractive index changes in proportion to the light intensity, for example, , An absorption saturated medium such as a dye CuPc (copper-phthalocyanine) and fine particles CdSe). This is because it takes a relaxation time for the phenomenon of absorption saturation to occur in a medium exhibiting a general third-order nonlinear optical effect, and therefore, within the relaxation time, the nonlinear light transmission to the light irradiation energy density is similar to that of the photochromic material. This is because the phenomenon is dominated.

Further, in order to increase the density, the eighth
The embodiment, the ninth embodiment and the tenth embodiment may be used together. For example, as shown in FIG. 23, initialization light bimodal spot 4
By overlapping 6 with the reproduction light spot 50 of the super-resolution spot and irradiating the initialization light bimodal spot 46 with the initialization light drive pulse 68 as shown in FIG. 27, the peripheral portion of the reproduction light spot 50. Can have a low transmittance (closed ring) and only the central part can have a significantly high transmittance, so the effective spot is further miniaturized.
A reproduced signal with high resolution was obtained.

The sample area 56 is composed of sample pits 69 for track position deviation detection signals, clock pits for extracting data recording / reproducing timing, and pre-pits in which address pits for address information are built in advance. ing. The pre-pit interval is set to be wider than the mark interval determined by the density of the data area. By setting in this way, it is preferable that the above three signals can be surely detected even when the effective spot is not miniaturized.

-Fourteenth Example-The fourteenth example utilizes the temperature dependence of the photoisomerization reaction of the photochromic material to optimize the spot miniaturization, enhance the miniaturization of the effective light spot, and the spot shape. Is to be symmetric.

As described in the publicly known "Optical Memory Symposium '92 Irie, Photochromic Optical Information Recording Medium-Trial of Nondestructive Readout", the ring-closing reaction of the diarylethene derivative D shown in FIG. 28 is caused by the interaction with the binder. Affected by. For example, when polymethacrylic acid is used as the binder, the cyclization reaction is promoted as the temperature rises, as shown in FIG. Especially when the temperature is 12
Above 0 ° C, the phase transition temperature Tg of polymethacrylic acid
And the interaction is reduced to accelerate the ring closure reaction. This indicates that there is a temperature threshold in the nonlinear light transmission characteristic.

The structure of the 14th embodiment is the same as that of FIG. 5, but polymethacrylic acid is used as the binder. Also,
The recording / reproducing light has a wavelength of 458 nm of Ar + laser, and the initialization light has a wavelength of 500 nm by the wavelength selection filter 16.
630 nm is used.

The temperature distribution in the portion irradiated with the recording / reproducing light spot almost reflects the energy density distribution.
Therefore, the non-linear light transmission characteristic has an energy density threshold value 70 as shown in FIG. 30, as compared with the case where the temperature dependence shown in FIG. 2 is not exhibited, and the change of the magnetic permeability with respect to the energy density ( The gradient (in FIG. 30) can be increased. As a result, the effective spot can be further miniaturized.

-Fifteenth Embodiment- A fifteenth embodiment is a combination of the eighth embodiment with temperature dependence. The structure of the fifteenth embodiment is similar to that of FIG. 20, but polymethacrylic acid is used as the binder. The reproduction light has a wavelength of 532 nm, and the initialization light has a wavelength of 458 nm by the wavelength selection filter 16. As a result, as shown in FIG. 31, since there is a threshold value for cyclization due to temperature, the gradient 71 of change in transmittance at the trailing edge of the reproduction light spot becomes large, and the miniaturization of the spot is enhanced.

-Sixteenth Embodiment- In the sixteenth embodiment, initialization is performed without using light. Known "Darcy, PJ et al, J.Cmemical.Societ
y. As shown in "Perkin Ι, 1981, 202", some photochromic materials have a ring-closing reaction caused by heat and a ring-opening reaction caused by light. For example, in the fulgide derivative shown in FIG. 32, the ring-closing reaction is caused by heat of 120 ° C. or higher, and the ring-opening reaction is caused by light.

Therefore, in the sixteenth embodiment, the ring-closed state, which is a colored state, is used as the initial state, and the reproduction light having a wavelength of 532 nm necessary for the ring-opening reaction, that is, fading is used. The energy density distributions during steady spot irradiation are shown in FIGS.
It becomes the same as 9. However, instead of the energy density distribution 42 due to the initialization light in FIG. 17, a temperature distribution 72 of the reproduction light itself is considered as shown in FIG. The energy density distribution 41 by the reproduction light spot governs the fading of the photochromic material, and the temperature distribution 72 of the reproduction light itself governs the coloring. That is, the central fading area 74 of the reproduction light incident spot distribution 73 is fading, but the coloring area 75 behind the reproduction light spot is colored again because the temperature exceeds the temperature threshold value 83. Therefore, the effective spot is miniaturized. Also, the area after the scanning of the reproduction light spot is in a colored state, that is, the initialization state, so that the initialization after the second time is not necessary, and if it is initialized at the time of shipment of the disc, the initialization is performed at the time of reproducing the target track. No need to wait for rotation.

As shown in FIG. 34, the temperature distribution is controlled by making the recording / reproducing layer absorb the reproducing light and utilizing the heat generated in the recording / reproducing layer to the photochromic layer. Good. By doing so, it is possible to perform initialization by scanning the reproduction light spot without performing initialization when shipping the disc.

-Seventeenth Example- A photochromic material can be used for the recording generation layer. For example, the closed state of the photochromic material is the recorded portion and the opened state is the unrecorded portion. At the time of reproduction, the reproduction light of the ring-opening wavelength is used to detect a change in the transmittance or the reflectance of the recorded portion and the unrecorded portion. In this case, the recording light is ring-opened by the reproduction light and the data is destroyed. Therefore, the recording light for cyclization is also irradiated with weak power at the same time, and the fact that the recording light is absorbed only in the recording part by irradiation with the reproducing light of strong power is used to simultaneously cyclize the recording light by the heat generated thereby. Allow it to occur and prevent data corruption (ie, regenerate data in light steady state). At the time of recording, only the recording light is strongly irradiated. At the time of erasing, only the reproduction light is strongly irradiated. For the photochromic layer as the non-linear light transmitting layer, a photochromic material is used in which the cyclization is not performed by the irradiation of the recording light or the quantum yield of the cyclization is smaller than that of the recording / reproducing layer even if the temperature rises.
As described above, by using the photochromic material for the recording / reproducing layer, the data can be read without destroying the data, the effective spot can be miniaturized, and the recording / reproducing with high resolution becomes possible.

-Eighteenth Embodiment- An eighteenth embodiment is based on the above-mentioned seventeenth embodiment of the two-wavelength multiplex recording / reproducing system.
The example is applied. FIG. 35 shows the structure of the eighteenth embodiment. The disk 350 includes a substrate 351 and a first
A photochromic layer 771, a first recording generation layer 761,
The intermediate layer 352, the second photochromic layer 772, the second recording generation layer 762, and the reflective layer 353 are included. In order to provide the recording generation layers 761 and 762 with a high temperature threshold value that prevents data destruction, polymethacrylic acid, which has a large interaction with the diarylethene derivative and has a high phase transition temperature Tg, is used as a binder, and the diarylethene derivative C, Each of the diarylethene derivatives A was used. Photochromic layers 771, 77 as non-linear light transmitting layers
For No. 2, diarylethene derivatives C and A were used, respectively, with polystyrene having a smaller interaction (smaller temperature dependence) with the diarylethene derivative than in the recording / reproducing layers 761 and 762 as a binder.

FIG. 36 shows the absorption spectrum. The absorption spectra of the ring-opened states of the diarylethene derivatives C and A are absorption spectra 76 having substantially the same shape. Therefore, the recording / reproducing layers 761 and 762 have a wavelength of 458 nm.
Recording and initialization of the photochromic layers 771 and 772 can be performed. A wavelength of 680 nm was used as the reproduction wavelength of the first recording / reproducing layer 761 and a wavelength of 630 nm was used as the reproducing wavelength of the second recording / reproducing layer 762. Therefore, the absorption spectrum of the recording portion of the recording / reproducing layer 761 during reproduction using the above-mentioned optical steady state is the absorption spectrum 80. In addition, the absorption spectrum of the recording portion of the recording / reproducing layer 762 during reproduction using the above-mentioned optical steady state is the absorption spectrum 81.

At the time of recording, recording light is focused on the target recording / reproducing layer 761 or 762 by focusing and irradiated with strong power to perform recording. FIG. 35 shows a state where recording is performed on the first recording / reproducing layer 761. Since the first recording / reproducing layer 761 and the second recording / reproducing layer 762 are sufficiently apart from the depth of focus of the focusing lens 354, the second recording / reproducing layer 762 is irradiated with diffused light and is erroneously recorded. It will not be done. In addition, the second photochromic layer 772
As a result, light with low irradiation intensity has a low transmittance and is blocked, so that the first recording / reproducing layer 761 and the second recording / reproducing layer 76 are shielded.
The recording light is cut off during the period between 2 and this also prevents the data from being destroyed.

During reproduction, the target recording / reproducing layer 76 to be reproduced.
The focal point is positioned at 1 or 762, and light steady irradiation reproduction is performed by simultaneous irradiation of reproduction light and recording light. In this case, in the photochromic layers 771 and 772, the temperature dependence of the cyclization is small even in the high temperature portion due to the reproduction light, so the cyclization is superior to the cyclization and the spot is miniaturized. In FIG. 37,
The state where the reproduction light spot is miniaturized is shown. In addition,
Here, the short pulse irradiation shown in the thirteenth embodiment is also used.

Since reproduction light and recording light are simultaneously irradiated during reproduction, it is not necessary to initialize the photochromic layers 771 and 772. However, initialization was also performed here. For initialization, recording light is positioned on the photochromic layers 771 and 772, and irradiation is performed with a power sufficiently weaker than during recording. The photochromic layers 771 and 772 are regions where the film temperature is low,
Since the quantum yield of cyclization is larger than that of the recording / reproducing layers 761 and 762, the recording / reproducing layers 761 and 762 can be initialized without recording. The photochromic layer 77
Since 1 and 772 are within the depth of focus with the recording and reproducing layers 761 and 762, the focus position may be adjusted to either the recording and reproducing layers 761 and 762 or the photochromic layers 771 and 772.

The two recording / reproducing layers 761 and 762 are shown in FIG.
As shown in FIG. 6, since they have absorption for the reproduction wavelengths of each other, when the target recording / reproducing layer is reproduced, leakage of reflected light or transmitted light from the marks of other recording / reproducing layers (that is, Interlayer crosstalk) may cause a data read error. However, since the distance between the recording / reproducing layers 761 and 762 is sufficiently larger than the depth of focus, the photochromic layer prevents light from leaking in, as shown in FIG. Therefore, interlayer crosstalk could be reduced.

At the time of erasing, only the reproduction light may be strongly irradiated.

As described above, in the two-wavelength multiplex recording / reproducing system, the spots can be miniaturized and the high density recording / reproducing can be performed. Further, it was possible to prevent the data destruction of the other recording / reproducing layer which is a problem during recording. Furthermore, it was possible to reduce interlayer crosstalk, which is a problem during playback.

-Nineteenth Embodiment- A nineteenth embodiment has a function of learning so as to obtain an optimum minute spot during recording and reproduction. Figure 38
FIG. 14 shows a schematic block diagram of the recording / reproducing system of the nineteenth embodiment. The structure of this recording / reproducing system corresponds to that of the 16th embodiment. However, for reference, a configuration including an external initialization light source is also added to the drawing. Light fluxes emitted from the respective light sources 381 and 382 are spatial filters 383 for forming super-resolution.
After passing through 383, it becomes one light beam by the beam splitter 384, and is irradiated onto the disk through the galvano mirror and the focusing lens. Here, when the light source is a semiconductor laser, the light flux is made into parallel light by a coupling lens and made into a circular light flux by a beam shaping prism. When the light source is an Ar laser or an SHG laser, intensity modulation is applied by an external signal using an intensity modulator such as an AO modulator.

The reflected light from the disk is guided to the light receiving system by the polarization beam splitter 385, and the recording light and the reproducing light are recorded light AF, TR detection 386, reproducing light AF,
It is guided to the TR detection 387, the learning signal differential detection system 388, and the data signal differential detection system 389. The interference filter is
The transmission wavelength is limited so that the recording light and the reproducing light do not leak into other systems.

The signal differential detection system 388, 389 is a differential detection system so that it can detect a magneto-optical signal as well, and outputs the difference signal and the sum signal as electric signals.

FIG. 39 shows a schematic flow chart of the operation at the time of recording / reproducing in the 19th embodiment. When the user inserts the disc, the focus servo and tracking servo are activated. At this point, recording / playback learning in a specific area is performed as the first learning (391). As the specific area, for example, an area outside the user area of the innermost circumference or the outermost circumference of the disc can be used. Here, even if the address cannot be detected in these areas, they can be positioned by an external scale or the like, so that learning can be surely performed. next,
After the address is detected, it is positioned on the track for recording or reproduction, and as the second learning, learning on the track is performed (392). As an example of the learning area, as shown in FIG. 40, in the sector format of the continuous servo system which is the 5-inch optical disk ISO format, it is provided, for example, in the head area of the DATA portion, part of or before the VFO area. Both the first learning and the second learning may be performed, or only one may be performed.

Then, recording is performed based on the optimum spot miniaturization condition at the time of recording / reproduction obtained as a result of learning (393).
Alternatively, reproduction (394) is performed. In the recording (393), the actual recording is actually written in the recording / reproducing layer by the known “recording trial writing” to set the final recording condition. Also,
After recording, read-after-write is performed to verify.

When the next data is recorded on another track in response to a command from the host, the learning is performed again on the track (392). On the other hand, the recording / reproducing condition that changes depending on the linear velocity may be obtained in advance, the linear velocity may be obtained from the track address, and the setting of the recording / reproducing condition may be changed accordingly (396).

FIG. 41 shows an outline of learning contents and recording / reproducing conditions. Further, FIG. 42 shows a flow chart of the learning operation. The contents of the first learning and the second learning are learning 1
And learning 2. Learning 1 is a measurement of the change in the transmittance of the photochromic layer (non-linear light-transmitting film) by the reflectance measurement (411). Learning 2 is measurement of the modulation of the reproduced signal (412). It may also include spot spacing measurements (421). The recording or reproducing conditions obtained by learning are the initialization power (413) and the recording or reproducing power (414). When the initialization light is focused on the disk through the focusing lens as in the recording / reproducing light as in the fourth to tenth embodiments, the spot interval measurement (421) is performed and the known multiple spot alignment is performed. By using the method (Japanese Patent Laid-Open No. 63-231738), the optimum spot interval is set (415). Also,
As shown in the thirteenth embodiment, when short pulse irradiation is performed during recording or reproduction, spot interval measurement (421) is performed and pulse irradiation timings of two light spots, that is, pulse positions and widths are set (416). . As a result of learning,
Set the conditions for high resolution playback. Further, the optimum miniaturization condition of the effective recording light spot is set.

Next, in the specific area or learning area, it is checked whether or not the photochromic layer has a nonlinear transmission characteristic sufficient for spot miniaturization, and the optimum powers of the initialization light, the recording light, and the reproduction light are determined. Explain the principle of learning. FIG. 43 shows the principle of learning 1. An unrecorded portion reflected signal amplitude level 431 after initialization and an unrecorded portion reflected signal amplitude level 43 after reproduction which has been discolored by irradiation of reproducing light.
2 is over the preset upper limit level 433 and lower limit level 434, or the modulation level of the amplitude level standardized by the reproduction light power is
It is checked that the lower limit 435 of the modulation factor is exceeded.

FIG. 47 shows a time chart for learning when spot miniaturization is performed during reproduction. In the first rotation of the disk rotation, the reproduction power is increased by the step function, the reproduction power at the time when the reproduction signal of the reproduction light reaches the lower limit value is held, and the learning area is opened. On lap two,
The initialization pulse 470 is increased by a step function to perform initialization (ring closure), and the initialized portion is irradiated with reproduction light,
The initialization state is monitored by detecting the reflection intensity with respect to the reproduction light. The position of the monitor pulse 471 shifts the time difference τ in consideration of the interval between the initialization light spot and the reproduction light spot. As the initialization power increases, the ring closure progresses. Then, when the upper limit is exceeded, it is determined that this disc has the non-linear transmission characteristic required for spot miniaturization.

FIG. 46 shows an example of the learning circuit. The auto gain control amplifier 461 standardizes the detection signal with respect to the reproduction light power. Sample hold circuit 462
Holds the reflection detection signal C when the ring closure is saturated. Using the hold value of the sample hold circuit 462 as a reference value, the reproduction light is increased stepwise to check the ring opening state. The divider 463 outputs the rate of change with respect to the amount of reflected light in the closed state. If this rate of change is greater than the rate of change limit 472, the target spot size can be reduced, so the reproducing power at this time is set. Learning 1 makes it possible to set the optimum initialization power and reproduction power even if the photochromic layer of the disc to be reproduced deteriorates with the increase in the number of times of reproduction and the nonlinear optical transmission characteristics shown in FIG. Became possible.

Also, when the recording spot is made minute during recording, learning is performed in the same manner as described above. However, with the exception of the ROM disk as shown in FIG. 8B, in recording / reproducing media, marks are recorded when the recording power is learned, so an external magnetic field is not applied unlike the magneto-optical film. And the property that the mark is not recorded is used. Further, in the learning area, only the aluminum reflection film may be built in without attaching the recording film.

44 and 45 show the principle of modulation degree measurement in learning 2. FIG. 44 shows a case where the degree of miniaturization of the spot is examined by measuring the modulation degree of the original waveform of the reproduction signal. In the learning area, a mark row 440 whose mark pitch changes is formed in advance by the uneven pits. The initialization power and the reproduction (recording) power are alternately changed to hold the modulation degree A of the sparsest mark row as shown in FIG. 46, and the modulation degree B / A of the closet mark row to this hold value is divided. In step 464, the set value whose value is larger than or larger than the limit 465 of the allowable mark modulation degree is calculated. Thereby, the effective spot can be minimized.

FIG. 45 shows a case where the modulation degree of the differential signal is measured in order to check the degree of spot miniaturization by measuring the rising or falling gradient of the reproduction signal of the isolated mark. As another means for investigating the miniaturization of the effective spot, the optimum setting power is the inclination of the reproduction signal when the spot scans the mark (that is, when the amplitude of the first-order differential signal exceeds the slice level 451). I want it.

As the detection signal necessary for learning, in the magneto-optical system shown in FIG. 38, the sum signal is used in the reflectance measurement and the difference signal is used in the learning by the modulation signal. However, read-only memory (RO) using phase pits other than magneto-optical
M), phase change disks, punched disks, etc., use the sum signal.

[0092]

According to the optical information recording medium and the optical information recording / reproducing apparatus of the present invention, since the light spot is effectively miniaturized, information can be recorded / reproduced at a recording density lower than the optical resolution. Further, it is not limited to the magneto-optical disk. Furthermore, the effective light spot can be made symmetrical.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a structural change and a transmission spectrum of a diarylethene derivative A before and after photoisomerization.

FIG. 2 is a transmittance characteristic diagram when a film of a diarylethene derivative A in a ring-closed state is irradiated with light having a wavelength of 630 nm.

FIG. 3 is a transmission power characteristic diagram when a film of a diarylethene derivative A in a ring-closed state is irradiated with light having a wavelength of 630 nm.

FIG. 4 is an explanatory diagram in which the light intensity distributions of an incident light spot and a transmitted light spot are normalized and overlapped.

FIG. 5 is a configuration diagram of a disc and an optical system of a first embodiment of an optical information recording medium and an optical information recording / reproducing apparatus of the present invention.

FIG. 6 is an explanatory diagram showing an incident power density distribution of a reproduction light spot, an incident energy density distribution on a photochromic layer, a transmission power density distribution from the photochromic layer, a reproduction light spot diameter cross section, and an effective spot diameter cross section. .

FIG. 7 is a view showing an example of a reproduction signal when a disc with marks is scanned by a reproduction light spot.

FIG. 8 is a configuration diagram of a disk and a ROM structure disk which are a third embodiment of the optical information recording medium of the present invention.

FIG. 9 is an explanatory diagram of a structural change and a transmission spectrum of a diarylethene derivative B before and after photoisomerization.

FIG. 10 is a configuration diagram of a disc and an optical system of a fourth embodiment of the optical information recording medium and the optical information recording / reproducing apparatus of the present invention.

FIG. 11 is an explanatory diagram of a reflectance spectrum and an absorptance spectrum of a recording / reproducing layer of the disc of the fourth example.

FIG. 12 is an explanatory diagram of transmission spectra before and after photoisomerization of the diarylethene derivative A.

FIG. 13 is an explanatory diagram of a structural change and a transmission spectrum of a diarylethene derivative C before and after photoisomerization.

FIG. 14 is a first configuration diagram of the optical system of the sixth embodiment.

FIG. 15 is a second configuration diagram of the optical system according to the sixth embodiment.

FIG. 16 is a third configuration diagram of the optical system of the sixth embodiment.

FIG. 17 is an explanatory diagram of a reproduction light incident power density distribution in the scanning direction and a steady energy density distribution by a reproduction light spot in the eighth embodiment.

FIG. 18 is an explanatory diagram of a stationary energy density distribution due to a reproducing light spot in a radial direction in an eighth example.

FIG. 19 is an explanatory diagram of the power density distribution of the incident spot and the power density distribution of the emitted light spot during steady irradiation in the eighth example.

FIG. 20 is a spot arrangement diagram of an eighth embodiment.

FIG. 21 is an explanatory diagram showing a transmittance distribution by irradiation of a reproduction light spot, a transmittance distribution by irradiation of an initialization light spot, and a transmittance distribution by simultaneous irradiation of both in the eighth embodiment.

FIG. 22 is a diagram illustrating the principle of the ninth embodiment.

FIG. 23 is a diagram illustrating the principle of the tenth embodiment.

FIG. 24 is an explanatory diagram of a 2-beam parallel recording / reproducing system.

FIG. 25 is an explanatory diagram of a light shielding plate.

FIG. 26 is an explanatory diagram of a super-resolution spot by a light shielding plate.

FIG. 27 is a principle view of the thirteenth embodiment.

FIG. 28 is an explanatory diagram of a structural change and a transmission spectrum of a diarylethene derivative D before and after photoisomerization.

FIG. 29 is a temperature characteristic diagram of a cyclization reaction of a diarylethene derivative D.

FIG. 30 is an explanatory diagram of a threshold value of energy density according to temperature.

FIG. 31 is an explanatory diagram of a threshold value for cyclization by temperature.

FIG. 32 is an explanatory diagram of a structural change and a transmission spectrum before and after photoisomerization of a fulgide derivative.

FIG. 33 is an explanatory diagram of a temperature distribution of reproduction light itself.

FIG. 34 is an explanatory diagram of heat conduction of heat generated in the recording / reproducing layer to the photochromic layer.

FIG. 35 is a configuration diagram of the eighteenth embodiment.

FIG. 36 is an explanatory diagram of absorption spectra according to the eighteenth example.

FIG. 37 is an explanatory diagram showing a state in which the reproduction light spot is miniaturized.

FIG. 38 is a schematic block diagram of a recording / reproducing system in a nineteenth embodiment.

FIG. 39 is a schematic flow chart of operations during recording / reproduction in the nineteenth embodiment.

FIG. 40 is a sector format diagram of a continuous servo system.

FIG. 41 is a schematic explanatory diagram of learning contents and recording / reproducing conditions.

FIG. 42 is a flowchart of a learning operation.

FIG. 43 is a principle diagram of Learning 1.

FIG. 44 is a principle diagram of modulation degree measurement in learning 2.

45 is another principle diagram of modulation degree measurement in learning 2. FIG.

FIG. 46 is a configuration diagram of a learning circuit after signal detection.

FIG. 47 is a time chart diagram of a signal of each circuit element for learning 1.

[Explanation of symbols]

 3 disc 3a replica substrate 3b photochromic layer 3c enhance layer 3d recording / reproducing layer 3e protective layer 4 disc 4a replica substrate 4b, 4c photochromic layer 4d recording / reproducing layer 4e reflective layer 4f protective layer 6 disc 6a replica substrate 6b photochromic layer 6c Recording / reproducing layer 6d Reflective layer 6e Protective layer 9 Reproducing light spot 10 Reproducing signal 12 Conventional reproducing signal 14 Focusing lens 15 Halogen lamp 16 Wavelength selection filter 17 Projection lens 19 Recording light spot or reproducing light spot 20 Incident energy density distribution 31 Recording light Spot 32 Reproducing light spot 33 Track 34 Pre-reproducing light spot 39 Recording / reproducing light spot 40 Initializing light spot 45 Ideal reproducing signal 46 Double peak spot 47 Reproducing light spot 48 Spatial filter for double peak spot 4 Spatial filter for super-resolution spot 53 Recording / reproducing light spot 54 Light-shielding plate 350 Disc 352 Intermediate layer 353 Reflective layer 354 Focusing lens 761 First recording / reproducing layer 762 Second recording / reproducing layer 771 First photochromic layer 772 Second Photochromic layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koichiro Wakabayashi 1-280, Higashi Koigokubo, Kokubunji, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. (72) Inventor, Akira Arimoto 7-1, 1-1, Mika-cho, Hitachi-shi, Ibaraki Prefecture Hitachi Ltd., Hitachi Research Laboratory (72) Inventor Shuji Imaseki 7-1-1 Omika-cho, Hitachi City, Ibaraki Prefecture Hitachi Ltd. Hitachi Research Laboratory (72) Inventor Setsuro Kobayashi 7, Omika-cho, Hitachi City, Ibaraki Prefecture No. 1 in Hitachi, Ltd. Hitachi Research Laboratory

Claims (18)

[Claims] 1. An optical information recording medium having a recording / reproducing layer for reproducing information by detecting the presence or absence of the local optical characteristic change by weak light irradiation to cause a local optical characteristic change by strong light irradiation to record information. In, the photochromic layer using a photochromic material having a light transmission characteristic in which the transmittance increases and is saturated with an increase in incident power or incident energy density is arranged on the light irradiation side of the recording / reproducing layer. Optical information recording medium. 2. The optical information recording medium according to claim 1, wherein the photochromic material has a wavelength λ with an increase in incident power or incident energy density of light having a wavelength λ1.
The first light transmission characteristic in which the transmittance for the light of wavelength 1 increases while the transmittance for the light of wavelength λ2 decreases.
And a second light transmission characteristic in which the transmittance for the light of wavelength λ2 increases with the increase of the incident power or the incident energy density of the light of wavelength 2 and at the same time the transmittance for the light of wavelength λ1 decreases. Optical information recording medium. 3. The optical information recording medium according to claim 1 or 2, wherein the photochromic material is a diarylethene derivative or a fulgide derivative. 4. The optical information recording medium according to claim 3, wherein the binder forming the photochromic layer by mixing with the photochromic material is polyvinyl butyral resin, PMMA, cellulose diacetate, polymethacrylic acid,
An optical information recording medium, which is one of polystyrene. 5. The optical information recording medium according to claim 1, wherein the recording / reproducing layer is a phase change film. 6. An optical information recording medium according to claim 1, wherein the recording / reproducing layer is a magneto-optical film. 7. The optical information recording medium according to any one of claims 1 to 4, wherein the recording / reproducing layer is made of a mixed material of a photochromic material and polymethacrylic acid. recoding media. 8. The optical information recording medium according to any one of claims 1 to 4, wherein the recording / reproducing layer is composed of a mixture of a photochromic material and a binder having a relatively strong interaction, and has a multi-layer structure. An optical information recording medium, characterized in that a photochromic layer made of a mixture of a photochromic material and a binder having a relatively weak interaction is interposed between the recording and reproducing layers. 9. The optical information recording medium according to claim 1, wherein at least one of the photochromic layer and the recording / reproducing layer transmits light in order to set optimum recording or reproducing conditions. An optical information recording medium having a learning area for learning characteristics. 10. An optical information recording / reproducing apparatus for recording / reproducing information on / from the optical information recording medium according to claim 1, wherein reproduction is performed on the optical information recording medium during reproduction. An optical information recording / reproducing apparatus, wherein a peak value of an incident power density distribution of light or recording light at the time of recording is set near a saturation point of a light transmission characteristic of the photochromic layer. 11. An optical information recording / reproducing apparatus for recording / reproducing information on / from the optical information recording medium according to claim 1, or the optical information recording / reproducing apparatus according to claim 10. An optical information recording / reproducing apparatus comprising an initialization optical system for irradiating the photochromic layer with initialization light that reduces the transmittance of reproduction light or recording light. 12. The optical information recording / reproducing apparatus according to claim 11, wherein the initialization light for the recording light is reproduction light,
An optical information recording / reproducing apparatus, wherein the initialization light for the reproduction light is recording light. 13. The optical information recording / reproducing apparatus according to claim 11 or 12, wherein the initialization light spot is irradiated prior to the reproducing light spot or the recording light spot. . 14. The optical information recording / reproducing apparatus according to claim 11 or 12, wherein at least the latter half of the reproducing light spot or the recording light spot is overlapped and the initialization light spot is simultaneously irradiated. Optical information recording / reproducing device. 15. An optical information recording / reproducing apparatus for recording / reproducing information on / from the optical information recording medium according to claim 1, or the optical information according to any one of claims 10 to 14. An optical information recording / reproducing apparatus, wherein a bimodal spot spatial filter is inserted in the optical path of the initialization light. 16. An optical information recording / reproducing apparatus according to claim 15, wherein a super-resolution spot spatial filter is inserted in an optical path of the reproducing light or the recording light. 17. An optical information recording / reproducing apparatus for recording / reproducing information on / from the optical information recording medium according to claim 1, or the optical information according to any one of claims 10 to 16. An optical information recording / reproducing apparatus, which is a recording / reproducing apparatus for irradiating reproducing light or recording light with a short pulse. 18. An optical information recording / reproducing apparatus for recording / reproducing information on / from the optical information recording medium according to any one of claims 1 to 9 or the optical information according to any one of claims 10 to 17. An optical information recording device, comprising a learning means for learning the light transmission characteristics of at least one of the photochromic layer and the recording / reproducing layer in order to set an optimum condition for recording or reproducing. Playback device.