JP3155636B2 - Optical recording medium and optical recording / reproducing system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium and an optical recording / reproducing system comprising a combination of an optical recording medium and an optical head, and more particularly to a technique for improving a recording density.

[0002]

2. Description of the Related Art FIG. 4 shows an example of a conventionally known optical recording / reproducing system.
And an optical head 3 having at least an objective lens 2. As shown in the figure, the optical recording medium 1
On one surface of a transparent substrate 4, a recording film or reflection film 5, a first protective film 6, and a second protective film 7 are sequentially laminated. The recording film is formed on a write-once or rewritable optical recording medium, and the reflection film is formed on a read-only optical recording medium.
The objective lens 2 focuses a light beam 8 such as a laser beam on a recording film or a reflection film 5, and applies a high-energy light beam to a write-once or rewritable optical recording medium. To record information by causing thermal deformation of the recording film due to the energy of the recording track. Also, a light beam of a low energy level that does not affect the transparent substrate 4 and the films 5 to 7 is applied to the recording track. And information is reproduced by detecting the reflected light. On the other hand, a read-only optical recording medium is irradiated along a recording track with a light beam of a low energy level that does not affect the transparent substrate 4 and the reflective film, and the reflected light is detected. Reproduce information.

As described above, the optical recording medium 1 includes the objective lens 2
Since information is recorded and reproduced by the light beam 8 irradiated from the light source, the recording density is greatly affected by the diameter (spot diameter) D of the light beam spot focused on the recording film or the reflection film 5. That is, when the recording sensitivity of the recording film and the intensity of the light beam are constant, a smaller diameter or width of the recording domain can be formed as the spot diameter D is reduced, and information is collected in the track direction and the track pitch direction. Since recording can be performed, the recording density of the optical recording medium can be increased.

[0004] The spot diameter D emitted from the objective lens 2 and focused on the recording film or the reflection film 5 has a wavelength of light of λ,
Assuming that the numerical aperture of the objective lens 2 is NA and the coefficient determined by the distribution of incidence on the objective lens 2 is α, DＮＡαλ / NA. From this equation, it is possible to reduce the spot diameter as the wavelength λ of the light is shorter, the numerical aperture NA of the objective lens 2 is larger, and the coefficient α is smaller. However, the shortening of the wavelength λ requires the development of a new laser light source and the like, so that it is difficult to put it to practical use immediately.
When the lens numerical aperture NA is increased, another technical inconvenience occurs such that the focal depth of the light spot becomes shallow and the load on the automatic focusing mechanism increases. Therefore, it is practically difficult at present to greatly reduce the spot diameter by changing the optical element.

On the other hand, for example, INTERNATIONAL SYMPOSIU
M ON OPTICAL MEMORY 1991,2D-1, 「MULTI-LAYERED MAGN
ETO-OPTICAL DISK FOR MAGNETICALLY INDUCED SUPER RE
SO-LUTION ”, the MSR (Magneti
2. Description of the Related Art A means for improving the recording density of a magneto-optical recording medium called a "cally induced super solution" method has been known. This method uses a temperature distribution smaller than the spot diameter on the magneto-optical recording film to realize super-resolution with the temperature distribution and the magnetic exchange auxiliary layer. However, this method can be applied only to a magneto-optical recording medium, and has a drawback that the signal amplitude obtained from the magneto-optical recording medium is reduced because the center of the temperature distribution is shifted from the center of the intensity of the light beam. .

[0006]

In the field of optical recording media, it is possible to improve the recording density of all known optical recording media regardless of the type of recording system or recording film.
Increasing recording capacity is one of the most important technical issues. Such a technical problem can be achieved by reducing the spot diameter of the light beam applied to the recording film or the reflection film of the optical recording medium. However, the drastic reduction of the spot diameter by changing the optical element is described above. It is difficult to achieve it as soon as possible. Further, depending on the MSR method, it cannot be applied to optical recording media other than the magneto-optical recording medium. Therefore, the spot diameter must be reduced by a method other than the above-described methods.

The present invention has been made to solve the above problems, and an object of the present invention is to provide an optical recording medium and an optical recording / reproducing system capable of high-density recording.

[0008]

According to the present invention, in order to achieve the above object, a recording film or a reflection film is carried on one surface of a transparent substrate, and the recording film or the reflection film is irradiated with a light beam. An optical recording medium that records and reproduces information by using a semiconductor or a fine powder of a metal or a metal compound between the transparent substrate and the recording film or the reflection film. A light control film having a light transmittance characteristic that has a low transmittance and a high light transmittance with respect to a light beam with high illuminance is provided.

As the light control film, a fine powder of a semiconductor or a metal or a metal compound is dispersed in a transparent dielectric or a transparent resin, or a layer of the fine powder and a layer of a transparent dielectric or a transparent resin are laminated. What was done can be used. Here, as the semiconductor, cadmium sulfide or cadmium selenide, or a solid solution thereof can be used, and as the metal or metal compound, gold, platinum, copper, any of copper chloride, or a mixture thereof. Mixtures can be used. The average particle size of the fine powder,
About 1 nm to 20 nm is particularly preferable. As the transparent dielectric, silicon dioxide, silicon nitride, yttrium oxide,
Alumina, lithium nitride, tantalum oxide, any of niobium oxide, or a mixture thereof can be used, and as the transparent resin, butyl acetate, polyvinyl alcohol, polyvinyl butyral, any of ultraviolet curable acrylic resin, or These mixtures can be used.

On the other hand, with respect to an optical recording / reproducing system, an optical recording / reproducing system comprising an optical recording medium and an optical head having an objective lens for focusing a light beam on a recording film or a reflection film of the optical recording medium. In the system, the optical recording medium according to claim 1 is used as the optical recording medium,
As the optical head, a mask is applied to a center portion of the objective lens, and a half-width width of a light spot focused on the recording film or the reflection film is reduced.
Alternatively, the half value width of the light spot focused on the recording film or the reflection film by making the phase distribution of the light transmitted through the central part of the objective lens earlier than the phase distribution of the light transmitted through the peripheral part of the objective lens Means such as using an optical head configured to reduce the diameter is used.

[0011]

The recording / reproducing light beam applied to the optical recording medium is generally a laser beam. The intensity distribution of the laser beam has a Gaussian distribution with respect to a plane perpendicular to the optical axis, and is strong at the center and weaker toward the periphery. A light beam having such an intensity distribution,
When the optical recording medium provided with the light control film having the non-linear light transmittance characteristic between the transparent substrate and the recording film or the reflection film is irradiated from the transparent substrate side, the light beam of low illuminance in the peripheral portion is subjected to light control. Only the light beam of high illuminance at the center reaches the recording film or the reflection film without being reached by the film and reaching the recording film or the reflection film.
Therefore, the spot diameter of the light beam applied to the recording film or the reflection film is reduced, and the recording density is increased. Such an effect can be obtained irrespective of the type of the recording film or the reflective film, so that the recording density of all optical recording media can be increased. Further, since the center of the beam always coincides with the center of the signal reading, a decrease in the reproduction signal level can be minimized.

In the case where a fine powder of a semiconductor or a metal or a metal compound is dispersed in a transparent dielectric or a transparent resin, etc.
Because of its excellent chemical stability, it can withstand long-term storage and use. Further, when the average particle diameter of the fine powder is adjusted to a value close to the bore diameter of an exciton formed from electrons or holes or both, at least one of the electrons and holes is caused by the quantum size effect of the fine powder. Since one is confined in the light control film, light absorption is suppressed, and a non-linear transmission characteristic is obtained. Since the bore diameter of electrons, holes or excitons of the fine powder material is about 1 nm to 20 nm, fine powder having an average particle diameter of this value is used.
Of course, when using a light control film material having a hole diameter of electrons, holes, or excitons outside this range, a fine powder having an average particle size corresponding to the diameter is used. In addition, as a light control film material having a non-linear light transmittance characteristic, in addition to a material obtained by dispersing a semiconductor or a fine powder of a metal or a metal compound in a transparent dielectric or a transparent resin, for example, a phthalocyanine dye or the like There are also organic dye materials. Organic dye materials have relatively strong third-order nonlinear characteristics with respect to the electric field of light.

If the center of the objective lens is masked or the phase of light passing through the center of the objective lens is made earlier than the phase of light passing through the peripheral portion of the objective lens, the recording film or the reflection film By irradiating an optical recording medium having the light control film with a light beam having a reduced diameter, the half-width width of the light beam focused on the recording film or the reflective film can be reduced. It is possible to further reduce the diameter of the spot irradiated thereon. If the central portion of the objective lens is masked or the phase of light transmitted through the central portion of the objective lens is made earlier than the phase of light transmitted through the peripheral portion of the objective lens, the periphery of the reduced main beam is reduced. However, since the light intensity of the side fringes is much smaller than the light intensity of the main beam, the light fringes are blocked by the light control film and do not reach the recording film or the reflective film. Has no adverse effect on

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a first embodiment of the optical recording / reproducing system according to the present invention will be described with reference to FIGS. FIG. 1 is an explanatory diagram of an optical recording / reproducing system according to the present embodiment, and FIG. 2 is a graph qualitatively showing light transmittance characteristics of a light control film.

As shown in FIG. 1, the optical recording / reproducing system of this embodiment comprises an optical recording medium 11 and an optical head 3 having at least an objective lens 2. As shown in the figure, the optical recording medium 11 has a non-linear structure on one surface of the transparent substrate 4 where the light transmittance is low for a light beam with low illuminance and the light transmittance is high for a light beam with high illuminance. A light control film 12 having the following light transmittance characteristics, a recording film or a reflective film 5,
Of the protective film 6 and the second protective film 7 are sequentially laminated.

The transparent substrate 4 is formed in a desired shape such as a disk shape or a card shape using a transparent ceramic such as glass or a transparent resin material such as polycarbonate, polymethyl methacrylate, polymethyl pentene or epoxy. Is done. On one side of the transparent substrate 4,
Normally, guide grooves for guiding a preformat signal and a light beam are formed in fine irregularities, but their arrangement and forming method are well-known and not the gist of the present invention. Is omitted.

The light control film 12 is formed of a film having a light transmittance characteristic such that the light transmittance is low for a light beam of low illuminance and the light transmittance is high for a light beam of high illuminance. . FIG. 2 shows an example of the light transmittance characteristic. As shown in the figure, the light control film 12 of this example, the characteristics that the light intensity is low transmittance of less of the light beam I _b, the light intensity is the light transmittance increases for I _b or more light beams Having. As the light control film 12 having such characteristics, a film formed by dispersing a fine powder of a semiconductor or a metal or a metal compound excited by light having a wavelength to be used in a transparent dielectric or a transparent resin, or a semiconductor or metal Alternatively, a film formed of a laminate of a metal compound fine powder layer and a transparent dielectric layer or a transparent resin layer can be used. Of the former, a light control film in which fine powder is dispersed in a transparent dielectric,
The light control film, which can be formed by a sputtering method using a fine powder material and a dielectric material as targets, and in which the fine powder is dispersed in a transparent resin, is formed by coating the transparent resin in which the fine powder is dispersed with the transparent substrate 4.
It can be formed by spin coating on top. The latter can be formed by laminating fine powder on the transparent substrate 4 using a plasma CVD method or the like.

As the transparent dielectric, silicon dioxide, silicon nitride, yttrium oxide, alumina, lithium nitride,
Any of tantalum oxide, niobium oxide, or a mixture thereof can be used, and as the transparent resin, butyl acetate, polyvinyl alcohol, polyvinyl butyral, any of an ultraviolet curable acrylic resin, or a mixture thereof can be used. it can. Further, as the semiconductor,
Cadmium sulfide or cadmium selenide, or a solid solution thereof can be used. As the metal or metal compound, any of gold, platinum, copper, copper chloride, or a mixture thereof can be used. The semiconductor, metal, or metal compound fine powder has a non-linear light transmission characteristic, and thus has an average particle diameter of an excitation formed from electrons or holes or both of the semiconductor, metal, or metal compound. It is adjusted to a value close to the bore diameter of the child. In general, the bore diameter of electrons, holes, or excitons of the fine powder material is about 1 nm to 20 nm, so that the average particle diameter of the fine powder is also adjusted to this value. Of course, for a light control film material having a hole diameter of electrons, holes, or excitons outside this range, a fine powder having an average particle size corresponding to the diameter is used.

The recording film is formed as an information recording layer of a write-once or rewritable optical recording medium, and may be made of any known material. On the other hand, the reflective film is formed as an information recording layer of a read-only optical recording medium, and may be made of any known material. In FIG. 1, the recording film or the reflection film 5 is shown as a single layer, but a film obtained by laminating a plurality of thin films made of the same or different materials in any order as necessary is used. You can also.

The first protective film 6 and the second protective film 7 protect the recording film or the reflective film 5 from mechanical and chemical influences, and include inorganic materials such as SiO ₂ , SiN, and AlN. Organic materials such as ultraviolet curable resin, aluminum,
It can be formed of a metal material such as gold or silver. In addition,
In this example, the first and second protective films 6 and 7 are provided, but either one of the protective films may be omitted.

As the optical head 3, the one which is provided with a semiconductor laser as a light source and is applied to a conventional system is applied as it is. The optical head 3 is provided with an actuator for autofocus, and is configured to always focus the light beam 8 emitted from the objective lens 2 on the recording film or the reflection film 5.

The operation and effect of the optical recording / reproducing system according to this embodiment will be described below. The laser beam 8 narrowed down to the diffraction limit by the objective lens 2
The laser beam is focused on the recording film or the reflection film 5 through the recording medium 2. As described above, the laser beam is directed to a plane perpendicular to the optical axis.
Since the Gaussian distribution has a strong central portion and becomes weaker toward the peripheral portion, a portion where the light intensity of the peripheral portion is equal to or less than _Ib is absorbed by the light control film 12 and is applied to the recording film or the reflective film 5. Do not reach. On the other hand, the light intensity at the center is I
The portion _b or more passes through the light control film 12 and reaches the recording film or the reflection film 5. Therefore, as shown in FIG, as compared with the spot diameter D ₁ of the case having no light control film 12, the spot diameter D ₂ of the laser beam is reduced in diameter to reach the recording film or reflective film 5. As described above, when the spot diameter of the laser beam reaching the recording film or the reflection film 5 is reduced, the recording domain (recording pits in a perforated optical recording medium, or magnetization domains in a magneto-optical recording medium, etc.) can be reduced in size. Therefore, information can be recorded in the track direction and the track pitch direction, and high-density recording can be performed. Even for a read-only optical recording medium, recording can be performed with the pit interval reduced, so that high-density recording is achieved. Such an effect can be obtained irrespective of the type of the recording film or the reflection film, so that the recording density can be increased for all known optical recording media. In addition, since the beam center always coincides with the signal reading center, it is possible to avoid the inconvenience that the reproduction signal level is reduced.

Next, a second example of the optical recording / reproducing system according to the present invention will be described with reference to FIG. FIG. 3 is an explanatory diagram of the optical recording / reproducing system according to the present embodiment. In the figure, reference numeral 13 denotes a mask, and the same reference numerals are shown in portions corresponding to those in FIG.

The optical recording / reproducing system of this embodiment is characterized in that an opaque mask 13 is provided at the central portion of the objective lens 2 on the light incident side. Otherwise, the configuration is exactly the same as that of the system of the first embodiment.

As described above, when the opaque mask 13 is attached to the center of the objective lens 2 and the laser beam passing through the opaque mask 13 is cut off, the mask 13 is not provided as shown by the solid line in FIG. A main beam 8a having a smaller spot diameter than that of the main beam 8a (shown by a broken line in FIG. 3) is irradiated on an optical axis passing through the center of the objective lens 2, and is surrounded by the main beam 8a.
Side fringes 8b and 8c having light intensity smaller than a are generated. Therefore, by providing the optical recording medium 11 with the light control film 12 having a threshold value lower than the peak value of the main beam 8a and higher than the peak values of the side fringes 8b and 8c, The diameter of the irradiated spot can be further reduced, and the recording density can be further improved as compared with the system of the first embodiment.

It is to be noted that the same effect as in the second embodiment can be obtained by changing the light shielding characteristic of the objective lens continuously or stepwise, instead of masking only the central portion of the objective lens. Second, the phase distribution of the central portion of the light beam 8 can be made earlier than that of the peripheral portion.
The same effect as that of the embodiment can be obtained.

[0027]

As described above, according to the present invention,
Light transmittance between the transparent substrate of the optical recording medium and the recording film or the reflection film, where the light transmittance is low for light beams with low illuminance and high for light beams with high illuminance Since a light control film having characteristics is provided, the recording film or the reflection film is irradiated by irradiating a light beam having an intensity distribution from the transparent substrate side such that the central part is strong and becomes weak toward the peripheral part. The spot diameter of the light beam to be emitted can be made smaller than the diffraction limit of the objective lens, and the recording density can be increased. Further, by adopting a means for reducing the half-width diameter of the light beam on the optical head side, higher density recording can be realized. Furthermore, as a light control film material, a material obtained by dispersing a fine powder of a semiconductor or a metal or a metal compound in a transparent dielectric or a transparent resin or the like is used, so that it has excellent chemical stability and is suitable for long-term storage and use. I can stand it.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an optical recording / reproducing system according to a first embodiment.

FIG. 2 is a graph qualitatively showing a light transmittance characteristic of a light control film.

FIG. 3 is an explanatory diagram of an optical recording / reproducing system according to a second embodiment.

FIG. 4 is an explanatory diagram of an optical recording / reproducing system according to a conventional example.

[Explanation of symbols]

 2 Objective lens 3 Optical head 4 Transparent substrate 5 Reflective film 6 First protective film 7 Second protective film 8 Laser beam 11 Optical recording medium 12 Light control film 13 Mask

Continued on the front page (72) Inventor Masashi Suenaga 1-1-88 Ushitora, Ibaraki-shi, Osaka Hitachi Maxell, Inc. (72) Inventor Hisamitsu Kamezaki 1-188 Ushitora, Ibaraki-shi, Osaka In-house Hitachi Maxell (72) Inventor Akira Arimoto 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Takeshi Nakao 1-280, Higashi Koikebo, Kokubunji City, Tokyo Within Central Research Laboratory, Hitachi, Ltd. (72) Inventor Kuki Sugiyama 1-280 Higashi Koikekubo, Kokubunji-shi, Tokyo Hitachi, Ltd. Central Research Laboratory (72) Inventor Jichi Miyamoto 1-280 Higashi Koikekubo, Kokubunji-shi, Tokyo Hitachi Central Research Laboratory, Ltd. Inventor Kimio Nakamura 1-280 Higashi Koikebo, Kokubunji-shi, Tokyo Central Research Laboratory, Hitachi, Ltd. (56) References JP-A-6-28713 (JP, A) JP-A-2-96926 (JP, A) JP-A Heisei 4-109438 JP, A) JP flat 2-12625 (JP, A) (58 ) investigated the field (Int.Cl. ^7, DB name) G11B 7/24 G11B 7/135

Claims (10)

(57) [Claims] 1. An optical recording medium comprising a transparent substrate carrying a recording film or a reflective film on one side thereof and recording or reproducing information by irradiating the recording film or the reflective film with a light beam. And between the recording film or the reflective film, contains a fine powder of a semiconductor or a metal or a metal compound, has a low light transmittance for a light beam of low illuminance, and a light transmittance for a light beam of high illuminance. An optical recording medium comprising a light control film having a light transmittance characteristic of increasing the light transmittance. 2. The optical recording medium according to claim 1, wherein the light control film is formed by dispersing a fine powder of a semiconductor or a metal or a metal compound in a transparent dielectric or a transparent resin. 3. The optical recording medium according to claim 1, wherein the light control film comprises a laminate of a fine powder layer of a semiconductor or a metal or a metal compound and a transparent dielectric layer or a transparent resin layer. 4. The semiconductor device according to claim 1, wherein:
An optical recording medium using cadmium sulfide or cadmium selenide, or a solid solution thereof. 5. The optical recording medium according to claim 1, wherein any one of gold, platinum, copper, copper chloride, or a mixture thereof is used as said metal or metal compound. 6. The optical recording medium according to claim 1, wherein the fine powder has an average particle size of 1 nm to 20 nm. 7. The method according to claim 2, wherein any one of silicon dioxide, silicon nitride, yttrium oxide, alumina, lithium nitride, tantalum oxide, and niobium oxide, or a mixture thereof is used as the transparent dielectric. An optical recording medium characterized by the following. 8. The method according to claim 2, wherein the transparent resin is any one of butyl acetate, polyvinyl alcohol, polyvinyl butyral, and an ultraviolet curable acrylic resin.
Or an optical recording medium using a mixture thereof. 9. An optical recording / reproducing system comprising: an optical recording medium; and an optical head having an objective lens for focusing a light beam on a recording film or a reflection film of the optical recording medium. The optical recording medium according to claim 1, wherein a mask is applied to a center portion of the objective lens as the optical head, and a half-width width of a light spot focused on the recording film or the reflection film. An optical recording / reproducing system using an optical head configured so as to reduce the size. 10. An optical recording / reproducing system comprising: an optical recording medium; and an optical head having an objective lens for focusing a light beam on a recording film or a reflection film of the optical recording medium. The optical recording medium according to claim 1 is used, and as the optical head, the phase distribution of light transmitted through a central portion of the objective lens is made larger than the phase distribution of light transmitted through a peripheral portion of the objective lens. An optical recording / reproducing system using an optical head configured so that the half-width of a light spot focused on the recording film or the reflective film is reduced as soon as possible.