JP2002298439A - Optical recording medium and reproducing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology by which a super-resolution effect can fully be obtained. SOLUTION: An optical recording medium 1 is detachably or undetachably mounted on a reproducing device which uses light converged by a focus lens for reproduction of information, and is provided with a layered structure having a thin film recording part 4 and a super-resolution film 3 in which an optical constant changes according to irradiated light intensity, and a substrate 2 to support the layered structure. The film thickness Ts of the super-resolution film 3, light wavelength λ and the numerical aperture NA of the focus lens satisfy a relation illustrated in the inequality: Ts>0.5×(λ/NA<2> ).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical recording medium and a reproducing method, and more particularly to an optical recording medium having a super-resolution film and a reproducing method for reproducing information recorded on such an optical recording medium.

[0002]

2. Description of the Related Art An optical disk memory that reproduces, records, and reproduces information by irradiating a light beam has excellent features such as a large capacity, high-speed access, and a removable optical disk. It has features. As such, such memories store audio, images,
It has been put to practical use as a storage device for storing various data such as computer data, and is expected to become more popular in the future.

Techniques for increasing the density of an optical disk include shortening the wavelength of a gas laser used for cutting a master, shortening the wavelength of a semiconductor laser as an operating light source, and increasing the numerical aperture of an objective lens. Increasing the height and making the light incident side substrate of the optical disk thinner have been considered. Further, for an optical disk capable of recording as well as reproduction, various approaches such as mark length recording and land / groove recording have been considered.

[0004] In addition to these high-density technologies, a super-resolution technology using a super-resolution film has been proposed as a technology capable of effectively realizing high-density. This super-resolution film is basically made of a material whose optical constant changes non-linearly and reversibly according to the intensity of irradiation light, and is provided on the light incident side with respect to the recording surface of the optical disk.

For example, when the optical response of an optical disc having a super-resolution film is designed so that low-intensity light is not transmitted and high-intensity light is transmitted, when a Gaussian beam is used as incident light, the beam becomes Since the peripheral portion of the beam has low intensity, it does not reach the recording surface, and only the central portion of the high intensity beam reaches the recording surface and contributes to recording and reproduction of information. This means that the beam spot diameter on the recording surface is smaller than the beam diameter of the incident light. Therefore, according to the super-resolution technique, it is possible to form a recording mark having a size smaller than the diffraction limit and to read out information recorded as a mark having such a size.

Several disclosures have been made in connection with the above-described super-resolution technique. For example, JP-A-11-273148
In general, Japanese Patent Application Laid-Open Publication No. H11-163873 discloses that an optical recording medium having a super-resolution film designed to obtain a high super-resolution effect at the time of recording has a significantly different beam intensity between at the time of recording and at the time of reproduction. Resolution effect cannot be obtained,
Addressing the problem of having to use separate optical systems for recording and playback to achieve high resolution during playback. Japanese Patent Application Laid-Open No. H11-273148 has been proposed to solve such a problem by providing two or more types of super-resolution films having different sensitivities on an optical recording medium so that a recording mark having a size smaller than a diffraction limit can be obtained with the same optical system. And that information recorded as a mark of such a size can be read.

The super-resolution technology can be roughly classified into a heat mode system and a photon mode system. Of the photon mode systems, those using a photochromic film as a super-resolution film generally have a single wavelength. Operation is not possible. Japanese Patent Application Laid-Open No. 10-320857 discloses a semiconductor fine particle dispersed film that realizes a nonlinear optical response by utilizing an absorption saturation phenomenon caused by electronic excitation from a full band to an exciton level or a conduction band. When this semiconductor fine particle dispersed film is used as a super-resolution film, basically operation at a single wavelength is possible.

[0008]

As described above, the prior art is to improve the material constituting the super-resolution film itself,
It is aimed at obtaining a high super-resolution effect both at the time of recording and at the time of reproduction using the same optical system. However, these techniques alone do not always provide a sufficient super-resolution effect.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a technique capable of sufficiently extracting a super-resolution effect. Another object of the present invention is to provide a technique capable of easily and sufficiently extracting a super-resolution effect.

[0010]

In order to solve the above-mentioned problems, the present invention relates to an optical recording medium mounted on a reproducing apparatus that uses light focused by a focus lens for reproducing information,
Comprising a substrate supporting the laminated structure and the laminated structure of the super-resolution film whose optical constant changes according to the irradiation light intensity and a thin film recording unit, wherein the wavelength of the thickness T _s of the super-resolution film the light An optical recording medium is provided, wherein λ and the numerical aperture NA of the focus lens satisfy a relationship represented by the following inequality: T _s > 0.5 × (λ / NA ² ).

Further, the present invention relates to a laminated structure of a thin-film recording portion and a super-resolution film whose optical constant changes according to the intensity of irradiation light, and an optical recording medium comprising a substrate supporting the laminated structure. Reading information recorded in the thin film recording unit by irradiating light focused by a focusing lens from the resolution film side toward the thin film recording unit and detecting reflected light from the optical recording medium. The reading of the information is performed according to an inequality: T _s > 0.5 × (λ / NA ² ) where the thickness T _s of the super-resolution film, the wavelength λ of the light, and the numerical aperture NA of the focusing lens. A reproduction method characterized in that the reproduction is performed under a condition satisfying the relationship shown below.

The optical recording medium of the present invention may be a read-only type, or a recordable type capable of performing both reproduction and recording. In the former case, the thin-film recording section is usually a reflective film provided with pits corresponding to information. On the other hand, in the latter case, the thin-film recording section is usually configured with a laminated structure in which at least a recording film and a reflective film are laminated.

When the optical recording medium of the present invention is a recordable type, it is a rewritable type optical recording medium capable of repeatedly recording and erasing information, such as a phase change recording medium and a magneto-optical recording medium. Alternatively, an optical recording medium of a single recording / erasable type that can record information only once, such as a dye-based optical recording medium, may be used.

In general, there are several standards in optical recording technology. In these standards, the reflectance, size, and shape of an optical recording medium, the wavelength of light used for recording and / or reproduction, the numerical aperture NA of a focus lens, and the like are clearly defined. Are designed based on these standards. For example, for a CD, the numerical aperture NA of the focusing lens is 0.45, and the wavelength λ of the laser beam used is set to 780 nm. For DVDs, the numerical aperture NA of the focusing lens
Is 0.6 and the wavelength λ of the laser beam used is 6
It is set to 50 nm. Further, in the HD-RAM, the numerical aperture NA of the focusing lens is 0.8 and the wavelength λ of the laser beam used is set to around 400 nm.

This cannot occur in a recording / reproducing apparatus or a reproducing apparatus to which an optical recording medium cannot be attached / detached, but in a recording / reproducing apparatus or a reproducing apparatus to which an optical recording medium can be attached / detached, an optical recording medium of various standards is loaded. May be Therefore,
The optical recording medium has recorded therein identification information for identifying which standard it corresponds to, and a recording / reproducing apparatus or reproducing apparatus capable of detaching the medium is recorded on the optical recording medium. From the identification information, it is identified which standard the loaded optical recording medium is based on. The “identification information” here is not limited to information recorded in the form of a recording mark such as a pit provided on a reflective film, but includes the reflectance of the optical recording medium, the size of the optical recording medium, and the optical recording medium. It also includes the shape characteristics of the medium.

As will be described in detail later, the present invention relates to the wavelength λ of the irradiation light and the numerical aperture NA of the focusing lens and a part of the optical recording medium which are derived from such identification information or actually used in the apparatus. constituting and makes it possible achieve a high super-resolution effect in a very simple method that satisfies the relationship represented by the inequality in the thickness T _s of the super-resolution film. That is, according to the present invention, it is possible to easily and sufficiently bring out the super-resolution effect.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to the drawings. In each figure,
The same or similar components are denoted by the same reference numerals, and redundant description will be omitted.

First, the basic principle of the super-resolution technique will be described. FIG. 1 is a graph showing an ideal relationship between the irradiation light intensity and the optical constant of the super-resolution film. In the figure, the horizontal axis indicates the irradiation light intensity P, and the vertical axis indicates the transmittance Tr of the super-resolution film. The data shown in FIG. 1 is based on the assumption that a light beam having a uniform intensity distribution is used as the irradiation light.

As shown in FIG. 1, for example, as shown in FIG. 1, when the irradiation light intensity is less than the critical power _Pc , the transmittance Tr
When the irradiation light intensity is higher than the critical power _Pc , the thin film has a high transmittance Tr. The critical power P
_c corresponds to the melting point when the super-resolution film is made of a material such as Sb, Te, and GeSbTe, and corresponds to the decomposition temperature when the super-resolution film is made of AgO _x , When the resolution film is composed of a leuco dye, it corresponds to the thermal fading temperature. When the super-resolution film is a photochromic film, the critical power P _c corresponds to, for example, the number of photons at which the ring-opening reaction sufficiently proceeds, and when the super-resolution film is a semiconductor fine particle dispersed film, the critical power P _c is equal to the absorption power. It corresponds to the number of photons that reach saturation.

FIG. 2 is a graph showing the intensity distribution of a Gaussian light beam before and after transmission into the super-resolution film showing the optical change shown in FIG. In the figure, the horizontal axis represents the distance r from the center of the light beam, and the vertical axis represents the light intensity P.
Curve 51 indicates the intensity distribution of the light beam before entering the super-resolution film, and curve 52 indicates the intensity distribution of the light beam after passing through the super-resolution film.

As shown in FIG. 2, when is incident Gaussian light beam in the super-resolution film, while the light beam propagates a super-resolution film, light intensity is less than the critical power P _c The beam periphery is cut off, and only the central portion of the light beam whose light intensity is equal to or higher than the critical power _Pc is selectively transmitted. That is, the beam diameter after passing through the super-resolution film is reduced as compared to before the beam enters the super-resolution film. This is the basic principle of super-resolution technology.

Next, the principle of the present invention will be described. FIG. 3 is a diagram schematically showing a state in which light focused by a focusing lens in a region where the optical constant is constant propagates. In the figure, w ₀ denotes the beam diameter at the focal position, D _f denotes the focal depth. The depth of focus D _f is the distance between the position where the peak power is 80% of the peak power at the focal position and the focal position. Using the numerical aperture NA of the focal lens and the wavelength λ of light, Formula: D _f = 0.5 × λ / NA ² The beam diameter at the position separated a distance D _f from the focus position is about 1.2 × w _0.

As shown in FIG. 3, the beam diameter of the focused beam propagating in the z direction decreases toward the focal point position, the minimum value w ₀ becomes the focal position, then increases. The rate of change of the beam diameter is a little in the focal position vicinity very large at a distance from the focal point distance or more D _f.

In the prior art, the interface between the super-resolution film and the thin film recording section is adjusted to the focal position, and the film thickness of the super-resolution film is determined by the depth of focus D
It was set thinner than _f . That is, in the prior art,
A light beam, the beam diameter was made incident on the super resolution film in a state of reduced to near w _0. In contrast, the present invention is to provide thicker than the focal depth D _f of the super resolution film, when combined interface with super-resolution film and the thin film recording unit to the focal position, near the focal position In addition, the super-resolution film is provided not only at a position where the rate of change of the beam diameter is large, but also a specific phenomenon obtained by using the super-resolution film can be used.

FIG. 4 is a sectional view schematically showing an optical recording medium according to one embodiment of the present invention. The optical recording medium 1 shown in FIG. 4 has a transparent substrate 2, a super-resolution film 3 provided on the transparent substrate 2, and a thin-film recording section 4 provided on the super-resolution film 3.

FIG. 4 shows the thickness of the super-resolution film 3 of the optical recording medium 1 and the light beam 11 used for recording information on the optical recording medium 1 or reproducing information recorded on the optical recording medium 1. Shows the relationship. However, FIG. 4 does not accurately show a state in which the light beam 11 is actually irradiated on the optical recording medium 1. That is, in FIG. 4, the effect of reducing the beam diameter provided by the super-resolution film 3 is not considered.

As shown in FIG. 4, the thickness T _s of the super-resolution film 3
Is larger than the depth of focus D _f , if the focal position of the light beam 11 is adjusted to the interface between the super-resolution film 3 and the thin film recording unit 4 or in the vicinity thereof, the beam diameter w ₀ of the light beam 11 at the focal position is obtained. The beam diameter w _i of the light beam 11 at the interface position between the transparent substrate 2 and the super-resolution film 3 and the beam diameter w of the light beam 11 at the interface position between the super-resolution film 3 and the thin film recording unit 4
The _r, the _{inequality: w 0 ≦ w r ≦ 1.12} × w 0 w r < to satisfy the relationship shown in w _i. Based on the above facts, effects obtained by the present invention will be described with reference to FIGS.

FIG. 5 is a graph schematically showing an example of the effect obtained by the present invention. In the figure, the horizontal axis is light beam 1
1 indicates the distance r from the center, and the vertical axis indicates the light intensity P. A curve 53 is an intensity distribution profile of the light beam 11 at an interface position between the transparent substrate 2 and the super-resolution film 3, and a curve 54 is a light intensity distribution profile of the light beam 11 at the interface position between the super-resolution film 3 and the thin film recording unit. It is an intensity distribution profile.
When the critical power P _c of the super-resolution film 3 is set lower than the peak power at the focal position, the light beam 11 having a power less than the critical power P _c while the light beam 11 propagates through the super-resolution film 3
Is blocked. On the other hand, the central portion of the light beam 11 having the critical power _Pc or more passes through the super-resolution film 3 and converges while propagating through the super-resolution film 3 as is clear from FIG. That is, if you set larger than the thickness T _s of the focal depth D _f of the super-resolution film 3, a transparent substrate 2 and the super-resolution film 3
Only the central part of the diameter φ ₁ of the light beam 11 at the interface position with the light beam is transmitted, and this central part of the light beam is focused on the diameter φ ₁ ′ and exits the super-resolution film 3.

[0029] In contrast, when the thickness T _s of the super-resolution film 3 is less than the focal depth D _f, as is clear from the description relating to FIG. 3, the light beam 11 super-resolution film 3 without the focused almost To propagate. Therefore, in this case, the intensity distribution profile of the light beam 11 at the interface position between the transparent substrate 2 and the super-resolution film 3 is different from the intensity distribution profile of the light beam 11 at the interface position between the super-resolution film 3 and the thin film recording section. Almost equal. Therefore, in this case, the light beam 11 is
While the peripheral portion of which the power is less than the critical power P _c is blocked while propagating, the diameter φ _{2 of the} central part of the light beam emitted from the super-resolution film 3 is compared with the diameter φ ₁ ′ realized by the present invention. And much larger.

As described above, according to the present invention, a much larger beam diameter reduction effect can be obtained as compared with the related art. Note that the above-described principle assumes that the optical response of the super-resolution film 3 to the light beam 11 is an ideal step function type, and that the beam profile of the beam profile while the light beam 11 propagates through the super-resolution film 3. Although it is based on model discussions, such as not considering changes very much, it explains the phenomena actually observed with sufficiently high accuracy.

FIG. 6 is a graph schematically showing another example of the effect obtained by the present invention. FIG. 6 shows a laminated structure of a super-resolution film (critical power P _c1 ) having a higher sensitivity and a super-resolution film (critical power P _c2 ) having a lower sensitivity as the super-resolution film 3. The beam diameter reduction effect obtained when the super-resolution film with sensitivity is disposed on the transparent substrate 2 side and the super-resolution film with lower sensitivity is disposed on the thin film recording unit 4 side is shown. As in FIG. 5, also in FIG. 6, the horizontal axis represents the distance from the center of the light beam 11, and the vertical axis represents the light intensity.

As described above, of the light beam 11 at the interface between the transparent substrate 2 and the super-resolution film 3, only the central portion of the diameter φ ₁ passes through the super-resolution film 3, and this light beam central portion Diameter φ
It is focused to a ₁ 'emits a super-resolution film 3. However, in reality, the transmittance of the super-resolution film 3 for light having a power less than the critical power _Pc is higher than 0%, and the thickness of the super-resolution film 3 is finite. In addition, since the light intensity increases as the light beam is focused, the beam diameter is largely changed in the super-resolution film 3 by the focusing of the light beam 11. Critical power P _c1 when incident
Even when the intensity is _lower than the above, a part of the super-resolution film 3 may be higher than the critical power P _c1 when the super-resolution film 3 is emitted.
That is, when the super-resolution film 3 is irradiated with the light beam 11,
In practice, the beam edge is not completely obstructed.

On the other hand, when the above-described laminated structure is employed, the peripheral portion of the light beam that has passed through the high-sensitivity super-resolution film having the critical power of P _c1 even if the intensity is increased by focusing. , Can be blocked by a low-sensitivity super-resolution film having a higher critical power P _c2 . That is, in this case,
The intensity distribution profile of the transmitted light can be made sharper. Such an effect can be obtained even when a laminated structure in which three or more super-resolution films are sequentially laminated from the light incident side to the light exit side so as to have low sensitivity is adopted. Further, the above effect can be obtained even when the sensitivity of the super-resolution film is inclined so as to continuously decrease from the light incident side to the light exit side.

Next, a more detailed structure and components of the optical recording medium 1 will be described. The optical recording medium 1 may be a read-only type or a recordable type capable of performing both reproduction and recording. That is, in the optical recording medium 1, the thin film recording section 4
Information recording may be possible, or a reflection film provided with pits as recording marks on the surface on the super-resolution film 3 side may be used. The recordable optical recording medium 1
Are rewritable optical recording media capable of repeatedly recording and erasing information, such as phase change recording media and magneto-optical recording media, and recording information once, such as dye-based optical recording media. It includes an optical recording medium of a single recording / erasable type that can be performed only once.

As the material of the transparent substrate 2, polycarbonate, polymethyl methacrylate, polyolefin, photopolymer-coated glass, glass and the like can be used. When the optical recording medium 1 is a read-only type, by forming pits on the surface of the transparent substrate 2, the pits can be transferred as recording marks on the surface of the reflective film as the thin film recording section 4. On the other hand, when the optical recording medium is of a recordable type, pits as recording marks are not usually provided on the surface of the transparent substrate 2,
Pits, tracking grooves, and the like corresponding to the address information are provided.

The transparent substrate 2 provided with pits and tracking grooves can be obtained, for example, by a mastering process described below. That is,
First, a resist film is formed on one main surface of a glass master. Next, using a gas laser cutting device, exposure is performed corresponding to the pits and tracking grooves on which the resist film is to be formed. After a resist pattern is formed by developing the resist film, a plating seed layer is sputtered on the surface of the glass master on which the resist pattern has been formed, and a plating process is further performed to obtain a stamper. After that, injection molding is performed using this stamper to obtain the transparent substrate 2 having pits and tracking grooves on the surface.

The transparent substrate 2 may provide a base for forming the super-resolution film 3 and the thin-film recording section 4, or the thin-film recording section 4 and the super-resolution film 3 may be sequentially provided. It may be a transparent cover layer arranged to face a formed substrate (not shown). In the latter case, the transparent substrate 2 need not always be provided.

In the optical recording medium 1, the super-resolution film 3
May be a heat mode type thin film or a photon mode type thin film.

As a thin film of the heat mode type, for example,
Examples of the thin film include a thin film containing a low-melting-point metal such as Sb and Te, a GeSbTe film having a high crystallization rate, a thermally decomposable AgO _x film, and a thin film containing a thermally decolorizable leuco dye. The super-resolution effect obtained in the heat mode system is that the super-resolution film 3 is heated by light irradiation, and at least a part of the constituent components undergoes some thermal change, and as a result, the optical constant changes nonlinearly. Based on For example, in the case of a thin film containing Sb or Te, a GeSbTe film, or the like, the optical constant changes nonlinearly when the super-resolution film is melted at the center of the beam spot where the light intensity is high. Further, in the AgO _x layer, AgO _x contained in the super-resolution film
Is thermally decomposed into Ag and O at the center of the beam spot, so that its optical constant changes nonlinearly. further,
The thin film containing the leuco dye is made transparent by thermally separating the dye and the color forming agent contained in the super-resolution film at the center of the beam spot.

On the other hand, as a photon mode type thin film,
Examples thereof include a photochromic film and a semiconductor fine particle dispersed film. In the photon mode system, a super-resolution effect is obtained by utilizing a chemical reaction by light or electronic excitation. For example, in order to obtain a super-resolution effect with a photochromic film, light having different wavelengths is irradiated between a ring opening reaction and a ring closing reaction of the photochromic material, or one of the reactions is thermally advanced. Therefore, when a photochromic film is used, it is generally impossible to operate at a single wavelength, and therefore, a complicated optical system is required for the device.
In the semiconductor fine particle dispersed film, an absorption saturation phenomenon by electronic excitation from a full band to an exciton level or a conduction band is used. When a semiconductor fine particle dispersed film is used as the super-resolution film,
At the center of the beam spot with high light intensity, the number of incident photons is sufficiently large, so that the number of excitable electrons is insufficient or the state of the upper level is saturated. As a result, the incident photons cannot be further absorbed. Shows a non-linear optical response. When using a semiconductor fine particle dispersed film, including the case where excitation or de-excitation of electrons occurs through a pure stable level,
Basically, operation at a single wavelength is possible.

Of the semiconductor fine particle dispersed film, a wavelength of 650 n
For example, CdSSe, Cu ₂ O,
AgTe, SrSe, SrTe, CaSi, ZnTe,
CdO, CdTe, GaSe, InS, AlSb, Sb
A thin film obtained by dispersing semiconductor fine particles such as Se, CuAlS, and ZnSiAs in an organic matrix can be used. Examples of the semiconductor fine particle dispersed film that can obtain a super-resolution effect when using light having a wavelength of 405 nm include ZnSSeTe, CuCl, and CuB.
r, AgCl, AgBr, AgI, ZnO, ZnSe,
GaS, AlSe, AlTe, InO, PbO, and T
A thin film obtained by dispersing semiconductor fine particles such as iO in an organic matrix can be used. Further, when light of a wavelength other than the above is used for recording or reproduction, a semiconductor material having a gap length close to the wavelength of the light to be used may be used as the material of the semiconductor fine particles.

The semiconductor fine particle dispersion film is formed, for example, by applying a coating liquid in which semiconductor fine particles are dispersed in a liquid organic matrix on one main surface of the substrate 2 by a spin coating method or the like, and curing the liquid organic matrix. Can be formed. In addition, such a coating liquid is, for example,
It can be prepared by mixing a solution of an organometallic compound containing each element constituting a semiconductor at a predetermined ratio and raising the temperature to an appropriate temperature. This coating solution can be used as a stock solution or after appropriately adjusting the concentration by adding a spin coating agent or the like. The thickness of the semiconductor fine particle dispersed film is
It can be controlled by the dilution degree of the coating liquid or the number of rotations of the substrate during spin coating.

When the particle size of the semiconductor fine particles is made smaller, the excitation lifetime is lengthened by the quantum size effect to easily cause absorption saturation, and the absorption of a level which is easily absorbed and saturated, for example, an exciton level, is reduced. It can be made more noticeable. The particle size and concentration of the semiconductor fine particles can be controlled by the concentration of the organometallic compound in the organometallic compound solution, the mixing ratio of the organometallic compound solution, the reaction temperature, and the like. Note that, under any conditions, if the generation of the fine particles progresses to some extent, the growth of the fine particles reaches saturation, so that particles having a uniform size can be obtained.

The sensitivity of the super-resolution film 3 may be set so that a super-resolution effect is obtained mainly during reproduction, or the sensitivity is set so that a super-resolution effect is obtained mainly during recording. You may. The sensitivity of the super-resolution film 3 can be adjusted by, for example, changing the melting point in the heat mode system, or by changing the electron transition energy in the photon mode system.

In the read-only optical recording medium 1, by setting the sensitivity of the super-resolution film 3 so as to obtain a super-resolution effect at the time of reproduction, recording marks (pits) smaller than the diffraction limit of the reproducing apparatus are obtained. Can be reproduced with high resolution even if the distance between the recording marks is reduced. That is, the recording density can be significantly improved.

In the optical recording medium 1 capable of both recording and reproduction, that is, of the recordable type, for example, the super-resolution film 3 is mainly used so as to obtain a super-resolution effect mainly at the time of reproduction.
When the sensitivity is set, it is difficult to significantly reduce the size of the recording mark. However, even if the recording is performed with the interval between the recording marks narrowed, it is possible to reproduce with high resolution.

Further, in the recordable optical recording medium 1, for example, when the sensitivity of the super-resolution film 3 is set so that the super-resolution effect is mainly obtained at the time of recording, the size of the recording mark is significantly reduced. It is possible to perform both recording and recording by narrowing the interval between recording marks. In this case, it is difficult to reproduce at a high resolution with the same optical system used for recording, so an optical system with a smaller beam diameter may be prepared separately from the optical system used for recording. .

When the optical recording medium 1 is a recordable type, as described above, by providing two or more super-resolution films having different sensitivities on the optical recording medium 1, diffraction by the same optical system is achieved. It is possible to form a recording mark of a size smaller than the limit and read out information recorded as a mark of such a size. In this case, both the high-sensitivity super-resolution film and the low-sensitivity super-resolution film can be arranged on the light incident side with respect to the thin-film recording section 4. Alternatively, a high-sensitivity super-resolution film may be disposed on the light incident side with respect to the thin-film recording unit 4, and a low-sensitivity super-resolution film may be disposed between the recording film and the reflective film.

The latter case is more advantageous than the former in terms of suppressing light loss during reproduction. Since the thickness of the recording film is usually as thin as about 10 to 30 nm, most of the incident light is transmitted to the reflection film side, and this transmitted light is reflected by the reflection film and returns to the recording film side. Since the sensitivity of the recording film is greatly affected by the multiple interference effect caused by the interference film, when a low-sensitivity super-resolution film is arranged between the recording film and the reflection film,
The diameter of the light beam returning from the reflection film to the recording film can be reduced. Therefore, also in this case, similarly to the case where both the high-sensitivity super-resolution film and the low-sensitivity super-resolution film are arranged on the light incident side with respect to the thin-film recording section 4, the same optical system is used. Both recording and super-resolution reproduction can be realized.

[0050] When providing a laminated structure of a plurality of super-resolution film on the light incident side of the thin film recording portion as the former, the individual super-resolution film is not necessarily thicker than the focal depth D _f, the laminate the thickness of the structure may be thicker than the depth of focus D _f. On the other hand, in the latter case, the film thickness of the super-resolution film disposed on the light incident side of the thin film recording unit 4 may be thicker than the depth of focus D _f,
There is no particular limitation on the thickness of the super-resolution film disposed between the recording film and the reflection film. However, the thickness of the super-resolution film disposed between the recording film and the reflective film is preferably less than the depth of focus D _f.

When two types of super-resolution films having different sensitivities are provided on the optical recording medium 1 to realize both super-resolution recording and super-resolution reproduction as described above, a low-sensitivity super-resolution film is used. Is preferably several times or more the critical power of the high-sensitivity super-resolution film. This is because the recording power and the reproduction power are significantly different.

As described with reference to FIG. 6, the super-resolution film 3 has a laminated structure of a high-sensitivity super-resolution film and a low-sensitivity super-resolution film. When the super-resolution film having the sensitivity is disposed on the light incident side, the intensity distribution profile of the transmitted light can be sharpened. Such effects, if satisfied the relationship shown in inequality thickness T _s is above the stacked structure can be an optical recording medium 1 is obtained be either only type and a recordable reproduction .

As a laminated structure of a high-sensitivity super-resolution film and a low-sensitivity super-resolution film, for a heat mode system, for example, a Te film which is a high-sensitivity super-resolution film and a low-sensitivity super-resolution film are used. A stacked structure with a GeSbTe film as an image film can be used. When such a laminated structure is a heat mode system, it is preferable to provide a transparent dielectric thin film between the super-resolution films in order to prevent the materials constituting the super-resolution films from being mixed with each other.

For the photon mode system, the wavelength 405
As a laminated structure having a super-resolution effect with respect to light of nm, for example, a plurality of Z layers having different S contents and Te contents from each other are used.
A laminated structure of the nSSeTe fine particle dispersed film can be used. In this case, a ZnSSeTe fine particle dispersion film having a lower S content and a higher Te content is used as a high-sensitivity super-resolution film, and a ZnSSeTe fine particle dispersion film having a higher S content and a lower Te content is Used as a low-sensitivity super-resolution film. The energy gap (electron transition energy) of the ZnSSeTe fine particle dispersed film is
When the content of Te is large, the width becomes narrow, and when the content of S is large, the width becomes wide. Further, the absorption saturation can be generated at a lower power as the difference between the energy gap and the energy of the irradiation light is smaller. Therefore, the above-mentioned laminated structure can be obtained by adjusting the S content and the Te content as described above.

When the optical recording medium 1 is a CD,
The numerical aperture NA of the focusing lens is 0.5 and the wavelength λ of the laser beam used is 780 nm. Therefore,
In this case, it is possible to obtain the effects described above by thicker than 1.56μm thickness T _s of the super-resolution film 3.
When the optical recording medium 1 is an HD-RAM, the numerical aperture NA of the focusing lens is 0.8 and the wavelength λ of the laser beam used is 410 nm. Therefore, in this case, it is possible to obtain the effects described above by thicker than 0.32μm thickness T _s of the super-resolution film 3. Further, when the optical recording medium 1 is a DVD, the numerical aperture NA of the focusing lens is 0.6 and the wavelength λ of the laser beam used is 650 nm. Therefore, in this case, it is possible to obtain the effects described above by thicker than 0.90μm thickness T _s of the super-resolution film 3.

According to the above theory, the effect of the present invention becomes more remarkable as the thickness of the super-resolution film 3 increases. However,
In reality, the transmittance of the super-resolution film 3 for light having a critical power _Pc or more is less than 100%. In other words, even high-intensity light is attenuated by the super-resolution film 3. Normally, such attenuation differs depending on the material used for the super-resolution film 3, and thus the upper limit of the film thickness of the super-resolution film 3 is appropriately set according to the material used.

When the optical recording medium 1 is a read-only type, the thin film recording section 4 is a reflection film having pits as recording marks on the surface on the super-resolution film 3 side as described above.
As a material of the reflection film, a metal material such as an Al alloy or an Ag alloy can be used. When light having a wavelength of, for example, 650 nm is used as reproduction light, Cu, A
Metals such as u and TiN, ceramics, and the like can also be used. The reflection film can be formed by a sputtering method or the like. The thickness of the reflective film is usually 50
nm or more, and is often set to about 100 nm.

When the optical recording medium 1 is a recordable type, the thin film recording section 4 is a recording film such as a phase change recording film or a magneto-optical recording film, or a dye-based recording film capable of repeatedly recording information. There is no particular limitation as long as it has a recording film such as a film that can record information only once. GeSbTe or Ag is used as a material for the phase change recording film.
InSbTe is typical, and TbFeCo is typical as a material for the magneto-optical recording film. The super-resolution film 3 and the thin-film recording unit 4 are different from each other in that the optical change is basically maintained only while the light irradiation is continued.
The latter is different in that the optical change has a memory property.

When the thin film recording section 4 can record information, the thin film recording section 4 usually has a reflective film in addition to the recording film. The reflection film is disposed so that the recording film is interposed between the super-resolution film 3 and the reflection film. As the material of such a reflective film, those described for the read-only type can be used.

When the optical recording medium 1 is of a recordable type, a structure in which the recording film is sandwiched between a pair of interference films for the purpose of optimizing the optical characteristics of the thin film recording section 4 and protecting the recording film, and the like. It is preferable to employ it. As a material of such an interference film, when the recording film is a phase change recording film, Z
nS.SiO ₂ is generally used, and when the recording film is a magneto-optical recording film, SiN is generally used.

In the optical recording medium 1 described above, the reflectance at the interface between the transparent substrate 2 and the super-resolution film 3 is set lower than the reflectance at the interface between the super-resolution film 3 and the thin-film recording section 4. Is preferred. In this case, the focus position can be automatically adjusted to the interface between the super-resolution film 3 and the thin-film recording section 4 without any particular focus adjustment. Such adjustment of the reflectance may be performed by appropriately selecting a material used for each component, or by providing an antireflection film between the transparent substrate 2 and the super-resolution film 3. You may.

The antireflection film is made of a material having a refractive index of n _ar and is a transparent thin film having a thickness of about λ / 4n _ar . The antireflection film can be formed by a sputtering method or the like,
As the material, for example, ZnS.SiO ₂ , Si
Examples include N, SiO, AlN, AlO, and TiO. The anti-reflection film may have a single-layer structure, but a more remarkable anti-reflection effect can be obtained by forming a multilayer structure in which a plurality of thin films are stacked so that the refractive indices are different between adjacent films. Can be obtained.

[0063]

Embodiments of the present invention will be described below. In each of the embodiments described below, an optical recording medium having a heat mode type super-resolution film and an optical recording medium having a photon mode type super-resolution film are manufactured, and their dynamic evaluation is performed. Before describing each embodiment individually, first, a super-resolution film used in each embodiment will be described.

In the following examples, a Te film was used as the super-resolution film of the heat mode system. Examples of the photon mode super-resolution film include semiconductor fine particle dispersion films in which CdSSe fine particles are dispersed in an organic matrix and exhibit an optical response to light having a wavelength of 650 nm;
A semiconductor fine particle dispersion film in which eTe fine particles were dispersed in an organic matrix and which showed an optical response to light having a wavelength of 405 nm was used.

The Te film as a photon mode super-resolution film was formed by a sputtering method. More specifically, the Te film was formed as a crystalline thin film having a predetermined thickness by heating the substrate with an IR lamp during sputtering. It should be noted that this crystalline Te is melted by laser heating and its extinction coefficient decreases, so that the transmittance increases in the melted portion of the Te film. Further, since crystallization of Te proceeds rapidly, molten Te returns to crystalline Te as soon as heating is completed. The transmittance of the Te film can be reversibly changed by such a principle.

On the other hand, the above-mentioned semiconductor fine particle-dispersed film includes a preparation step of preparing a coating solution by an organic synthesis method using an organometallic compound as a raw material, and a coating step of spin-coating the coating solution on a substrate. It formed by performing it sequentially. When the semiconductor fine particle-dispersed film is irradiated with laser light, in the irradiated portion, the excitation level is saturated by electronic excitation and the transmittance increases. When the light irradiation is completed, the state returns to the original state by de-excitation. The transmittance of the semiconductor fine particle dispersed film can be reversibly changed based on such a principle.

The coating liquid used for forming the semiconductor fine particle dispersed film was prepared by mixing a solution of an organometallic compound containing each element constituting the semiconductor at a predetermined ratio, and raising the temperature to an appropriate temperature. According to such a method, a coating liquid in which semiconductor fine particles are dispersed in a liquid organic matrix can be obtained. The coating solution was used as a stock solution or after appropriately adjusting the concentration by adding a spin coating agent or the like. The thickness of the semiconductor fine particle dispersed film was controlled by the degree of dilution of the coating solution and the number of rotations of the substrate during spin coating.

Next, the characteristics of the super-resolution film used in each embodiment will be described. These characteristics were not obtained for a super-resolution film formed as a part of an optical recording medium, but were obtained for a super-resolution film sample in which only a super-resolution film was formed on a substrate. It is.

Semiconductor fine particle dispersed films were prepared as super-resolution films under the same conditions as in the following examples, and the average particle size and particle size distribution of the semiconductor fine particles were examined for each semiconductor fine particle dispersed film. As a result, Cd
In both cases of using SSe fine particles and ZnSSeTe fine particles, the average particle diameter of the semiconductor fine particles was about 3 nm, and the particle diameter dispersion was within 10%. In addition, when the film thickness of the above-mentioned heat mode system and photon mode super-resolution film was measured by both the palpation type film thickness meter and the optical film thickness meter, the result obtained by these film thickness meters was within 10%. With a precision of.

Next, the super-resolution characteristics of the super-resolution film sample were examined. That is, using a high-power gas laser system, the wavelength 6 at which the beam diameter is several 100 μm and the power density is uniform in the beam spot is formed on the super-resolution film sample.
The relationship between the irradiation power density and the transmittance was examined by irradiating a laser beam of 50 nm. 7 and 8 show the results.

FIG. 7 is a graph showing the relationship between the irradiation power density and the transmittance obtained for a 1 μm thick Te film. FIG. 8 is a graph showing the relationship between the irradiation power density and the transmittance obtained for a 1 μm-thick CdSSe film. 7 and 8, the horizontal axis indicates the irradiation power density P, and the vertical axis indicates the transmittance Tr.

As shown in FIG. 7, the transmittance change of the Te film is steep near the irradiation power density corresponding to the melting of Te. On the other hand, in the CdSSe film, the transmittance change was not as steep as that of the Te film, but a large transmittance change was confirmed. The same evaluation was performed on the Te film and the ZnSSeTe film using light having a wavelength of 405 nm. As a result, a relationship substantially equivalent to that shown in FIGS. 7 and 8 was obtained.

Next, each embodiment will be described sequentially. Embodiment 1 FIG. 9 is a sectional view schematically showing an optical disc according to Embodiment 1 of the present invention. The optical disc 1 shown in FIG. 9 is a read-only type, and has a structure in which a super-resolution film 3 and a reflection film 5 as a thin film recording section 4 are sequentially laminated on one main surface of a transparent substrate 2. .

In this embodiment, as will be described later, the dynamic evaluation described later is performed for each of the cases where the numerical aperture NA of the focusing lens is 0.65 and 0.85.
In the former case, a transparent substrate 2 having a thickness of 0.6 mm and having pits formed as recording information on the surface on which the super-resolution film 3 is provided is used. The optical disc 1 was obtained by sequentially forming the super-resolution film 3 and the reflection film 5 on the surface provided. On the other hand, in the latter case, a transparent substrate (not shown) having a thickness of 1.1 mm and having pits formed as recording information on one main surface is used. The reflective film 5 and the super-resolution film 3 were sequentially formed, and the optical disc 1 was obtained by disposing a transparent substrate 2 having a thickness of, for example, 0.1 mm on the super-resolution film 3.

In any case, the duty is based on the resolution of the optical system (／0.5×λ/NA).
A single frequency signal having a ratio of 50% was recorded by changing the pit pitch. In any case, the super-resolution film 3 was formed thicker than the focal depth D _f.

Next, dynamic evaluation of these optical disks 1 was performed by the following method. That is, first, the optical disk 1 manufactured by the above-described method is set in a general optical disk evaluation machine, and then, while the disk 1 is being rotated, the optical disk 1 is set at 0.
Focusing and tracking adjustment were performed with a reproduction power of about 5 mW. Next, by irradiating a light beam having a Gaussian intensity distribution to a track on which pits were formed at a pitch less than the resolution of the optical system while changing the power, a reproduction power having a maximum CNR value was selected.
By this operation, the reproducing power can be set such that the transmittance of the super-resolution film at the light irradiation portion is sufficiently low at the periphery of the beam spot and sufficiently high at the center of the beam spot. The information recorded on the optical disk 1 was reproduced with the reproduction power set in such a manner, and the relationship between the pit pitch and the CNR value was examined.

[0077] Incidentally, in Table 1 below, the optical disk 1 subjected to dynamic evaluation in this example, are summarized the material and its thickness T _s as well as the thickness of the transparent substrate 2 of the super-resolution film 3. Table 1 shows the wavelength λ of the reproduction light used for the dynamic evaluation of the optical disc 1, the numerical aperture NA of the focusing lens, and the depth of focus D.
_{f is} also shown.

[0078]

[Table 1]

FIG. 10 is a graph showing an example of the relationship between the pit length and the CNR value obtained for the optical disc 1 according to the first embodiment of the present invention. In the figure, the horizontal axis shows the pit length, and the vertical axis shows the CNR value. In the drawing, a curve 55 indicates data obtained for the disk (2) in Table 1 above, and a curve 56 indicates a film thickness of the super-resolution film 3 of 500 nm.
The curve 57 shows data obtained for an optical disk having the same structure as that of the disk (2) except that the super resolution film 3 was not provided. The curve 57 shows an optical disk having the same structure as that of the disk (2). The data obtained for are shown.

As is apparent from FIG. 10, the pit length is 5
When the thickness is less than 00 nm, the super-resolution film 3 having a thickness of 1.5 μm
Optical disk 1 provided with a super-resolution film 3 having a thickness of 500 nm
In any of the optical disks provided with the pits, the pit length can be made shorter than that of the optical disk not having the super-resolution film 3. However, the effect is greatly different between the case where the thickness of the super-resolution film 3 is set to 1.5 μm and the case where the thickness is set to 500 nm. That is, the super-resolution film 3
It can be seen that the pit length can be significantly shortened by setting the film thickness of 1.5 μm.

Next, an optical disk 1 having the same structure as the disk (1) in Table 1 except that the thickness of the super-resolution film 3 was different was manufactured. These optical disc 1, the thickness T _s and the mark length of the super-resolution film 3 CNR values for pit string is the length of half the resolution of the optical system (CNR50)
And examined the relationship. The result is shown in FIG.

FIG. 11 shows an optical disk according to the first embodiment of the present invention.
Depth of focus D obtained for disc 1 _fSuper-resolution film for
Film thickness T of 3_sGraph showing an example of the relationship between the CNR value and the CNR ratio.
It is. In the figure, the horizontal axis is the ratio T_s/ D_fAnd the vertical axis
Indicates a CNR value (CNR50).

In general, the CNR needs to be about 40 dB or more. As is clear from FIG. 11, even when the mark length is half the resolution of the optical system, 40 dB can be obtained by setting the ratio T _s / D _f higher than 1.
Can be obtained. In particular, the ratio T _s / D _f
Is in the range of about 1.25 to about 2.5, CN
R50 showed a value as high as 50 dB or more.

Incidentally, the CNR 50 is such that the ratio T _s / D _f is 2.5
It becomes lower when it becomes above. This is due to the thickness T of the super-resolution film.
_{When s} is thicker, the optical path becomes longer and the light absorption at the center of the beam spot increases, and a part of the light component to be transmitted is attenuated in the process of propagating through the super-resolution film and becomes less than the critical power. It is because it becomes. Therefore, the ratio T _s / D _f is
It is preferably 5 or less, more preferably 3 or less, and most preferably 2 or less.

Next, the evaluations described above were also performed on the disks (1), (3) to (8) in Table 1 above. As a result, a tendency almost similar to that shown in FIGS. 10 and 11 was observed.

In the disk 1 manufactured in this embodiment, the reflectance at the interface between the transparent substrate 2 and the super-resolution film 3 is lower than the reflectance at the interface between the super-resolution film 3 and the reflection film 5. Therefore, the focal position could be automatically adjusted with respect to the interface between the super-resolution film 3 and the reflection film 5, that is, the recording surface. However, depending on the material used for the super-resolution film 3, the reflectance at the interface between the transparent substrate 2 and the super-resolution film 3 becomes excessively high.
In some cases, the focal position may be adjusted to the interface between the super-resolution film 3 and the super-resolution film 3. In this case as well, it is possible to adjust the focal position to the interface between the super-resolution film 3 and the reflection film 5 by performing the focusing offset adjustment, but the reflectance at the interface between the transparent substrate 2 and the super-resolution film 3 is reduced. It is preferable that the reflectance is set lower than the reflectance at the interface between the super-resolution film 3 and the reflection film 5.

(Embodiment 2) In this embodiment, the effect of the antireflection film will be mainly demonstrated, and the super-resolution effect of the optical disc 1 will be described in another embodiment.

FIG. 12 is a sectional view schematically showing an optical disk according to the second embodiment of the present invention. The optical disk 1 shown in FIG. 12 is a recordable type, and has an antireflection film 6, a super-resolution film 3, an interference film 7, a recording film 8, an interference film 9, and a reflection film on one main surface of a transparent substrate 2. It has a structure in which the films 5 are sequentially stacked. The interference film 7, the recording film 8, the interference film 9, and the reflection film 5 constitute the thin film recording unit 4. Usually, in the optical disc 1 having such a structure, the reflection film 5 is formed.
The thickness of the thin film recording unit 4 excluding the above is set to be less than the depth of focus.

In this embodiment, the super-resolution film 3 has a thickness of 1 μm.
The optical disk 1 shown in FIG. 12 was manufactured by using a Te film of m, a GeSbTe film as the recording film 8, and a ZnS.SiO ₂ film as the interference films 7 and 9. An optical disc 1 having the same structure except that the optical disc 1 did not have the antireflection film 6 was also manufactured.

The reflectance at the interface between the super-resolution film 3 and the thin film recording portion 4 is 20% when the recording film 8 is in a crystalline state.
And when it is in the amorphous state, it was adjusted to be approximately 0%. This is to obtain a high optical contrast between the recording mark forming portion and the non-forming portion. When the reflectances in the crystalline state and the amorphous state were set as described above, the average reflectance at the interface between the super-resolution film 3 and the thin-film recording portion 4 after recording was about 10%. In the optical disk 1 provided with the anti-reflection film 6, the reflectance at the interface between the transparent substrate 2 and the laminated structure including the anti-reflection film 6 and the super-resolution film 3 is about 3%. In the optical disc 1 not having the same, the reflectance at the interface between the super-resolution film 3 and the transparent substrate 2 was about 15%.

Next, the recording film 8 of the optical disk 1 was initially crystallized. Next, these optical discs 1 were evaluated by a method similar to that described in Embodiment 1 using an optical disc evaluator in which the wavelength λ of the irradiation light was 650 nm and the numerical aperture NA of the focusing lens was 0.65. Was.

As a result, in the optical disc 1 provided with the anti-reflection film 6, the focal position can be automatically adjusted with respect to the interface between the super-resolution film 3 and the thin film recording section 4 in both recording and reproduction. Was. On the other hand, with respect to the optical disk 1 having no antireflection film 6, the focal position could be automatically adjusted to the interface between the super-resolution film 3 and the thin film recording section 4 before recording. However, after recording, the transparent substrate 2
In some cases, the focal position is aligned with the interface between the super-resolution film 3 and the super-resolution film 3, making reproduction difficult.

Even if the optical disc 1 does not have the anti-reflection film 6, if the focus offset adjustment is performed to focus on the interface between the super-resolution film 3 and the thin-film recording section 4, the length of the recording mark can be reduced. A reproduced signal could be obtained with a high CNR even if the resolution was lower than the system resolution. However, in order to continue stable operation without such adjustment, it is necessary to provide an antireflection film 6 between the transparent substrate 2 and the thin film recording section 4.
Has been found to be preferable.

(Embodiment 3) In this embodiment, the effect obtained mainly when a plurality of super-resolution films having different sensitivities from each other will be demonstrated.

FIG. 13 is a sectional view schematically showing an optical disc according to Embodiment 3 of the present invention. The optical disc 1 shown in FIG. 13 is of a read-only type, and a reflective film 5, which is a thin film recording section 4, a first super-resolution film 3a, and a second super-resolution film are formed on one main surface of a transparent substrate 10. It has a structure in which the film 3b and the transparent substrate 2 are sequentially laminated. Note that the first super-resolution film 3a has lower sensitivity (or higher critical power) than the second super-resolution film. Although not shown, the transparent substrate 10
Pits are provided on the surface on the side of the reflective film 5 corresponding to the recorded information, and these pits are transferred to the surface of the reflective film 5 on the side of the transparent substrate 2.

In this example, a UV resin substrate having a thickness of 0.1 mm was used as the transparent substrate 2. This optical disc 1 has a structure suitable for operation under the condition that the numerical aperture NA of the focus lens is 0.85, and the reflective film 5 and the first Super-resolution film 3
a and the second super-resolution film 3b are sequentially formed, and the transparent substrate 2 is finally disposed.

In the present embodiment, the low-resolution super-resolution film 3 is used.
The ZnSSeTe fine particle dispersed film was used as a and the high-sensitivity super-resolution film 3b. The super-resolution films 3a and 3b
Was adjusted by making the S content higher and the Te content lower in the super-resolution film 3a than in the super-resolution film 3b. Further, a plurality of optical discs 1 having the same thickness as the super-resolution film 3a and the thickness of the super-resolution film 3b and having different thicknesses in a laminated structure formed by them were produced.

Next, with respect to these optical disks 1, the super-resolution films 3a, 3a,
The relationship between the film thickness of the laminated structure formed by 3b and CNR50 was examined. As a result, compared to the data shown in FIG. 11, the ratio T _s
/ D _f is CNR50 in the range of 2 or less is improved 2~3dB, CNR50 ratio T _s / D _f has maintained a value of more than 50dB up to about 1.1 to 3.5.

The reason why the CNR50 is improved is as follows.
The transmission effect is superimposed on the blocking effect of blocking the light beam periphery when propagating through the high-sensitivity super-resolution film, and the blocking effect of blocking the light beam periphery when propagating through the low-sensitivity super-resolution film. This is probably because the light intensity distribution profile could be made sharper. The reason why the upper limit of the ratio T _s / D _{f at which} the CNR 50 indicates a value of 50 dB or more is increased is that the power density at the central portion of the light beam at a position away from the focal point changes the optical constant of the super-resolution film. Since the power density is set higher than the power density, it can be considered that excessive light attenuation at a position away from the focal point is prevented.

(Embodiment 4) FIG. 14 shows Embodiment 4 of the present invention.
1 is a cross-sectional view schematically showing an optical disc according to the first embodiment. FIG.
The optical disk 1 shown in FIG.
A first super-resolution film 3a, an interference film 7, a recording film 8, an interference film 9, a second super-resolution film 3b, and a reflection film 5
Are sequentially laminated. The interference film 7,
The recording film 8, the interference film 9, and the reflection film 5 constitute the thin-film recording unit 4.

The structure shown in FIG. 14 is suitable when the numerical aperture NA of the focusing lens is about 0.65. When the numerical aperture NA of the focusing lens is about 0.85, the reflective film 5, the second super-resolution film 3b, the interference film 9, the recording film 8, the interference film 7, and the first It is preferable to employ a structure in which the super-resolution film 3a and the transparent substrate 2 are sequentially laminated.

In this embodiment, the structure shown in FIG. 14 was adopted, and a polycarbonate disk having address pits and tracking grooves formed by a mastering process was used as the transparent substrate 2. The thickness T _s as the super-resolution film 3a is 600 nm ZnSSe
A Te fine particle dispersed film is used, and the interference film 7 has a film thickness of 60
Use the nm of ZnS · SiO ₂ film, using a GeSbTe film having a thickness of 20nm as a recording film 8, using a ZnS · SiO ₂ film having a thickness of 15nm as an interference film 9, as a super-resolution film 3b Uses a ZnSSe fine particle dispersion film having a thickness of 200 nm, and the reflection film 5 has a thickness of 100 nm.
A PdCu film was used. Among these thin films, the super-resolution film 3
a and 3b were formed by sequentially performing the preparation of a coating solution by the above-mentioned organic synthesis method and coating by spin coating, and all other thin films were formed by a sputtering method. The optical disc 1 shown in FIG. 14 was manufactured as described above.

The sensitivity of the super-resolution films 3a and 3b can be adjusted so that the critical power of the super-resolution film 3a is 0.5 to 1 mW by changing the composition of the semiconductor fine particles and setting the energy gap to an appropriate value. To be within the range and the super-resolution film 3b
Was adjusted so that the critical power was within the range of 7 to 10 mW.

Next, a recording / reproducing test was performed on the optical disk 1 using an optical disk evaluation machine having a wavelength λ of the irradiation light of 405 nm and a numerical aperture NA of the focusing lens of 0.65. As a result, even when the recording mark pitch was 1/4 of the resolution (about 300 nm) of the optical system, a CNR value as high as 40 dB or more was obtained. Also,
A plurality of optical disks 1 having the same structure except that the thickness of the super-resolution film 3a was different were produced, and a recording / reproducing test was also performed on these optical disks. Based on the results obtained, the relationship between the CNR and the ratio T _s / D _f when the mark pitch was set to ４ of the resolution was obtained. The result was similar to that shown in FIG. was gotten.

(Embodiment 5) In this embodiment, an optical disc apparatus which can be used for reproducing information recorded on the optical disc 1 and recording information on the optical disc 1 manufactured in the above-described Embodiments 1 to 4 will be described. explain.

FIG. 15 is a diagram schematically showing an optical disk device according to Embodiment 5 of the present invention. An optical disk device 21 shown in FIG.
2, focus lens 23, half mirror 24, laser light source 2
5, photodetector 26, preamplifier 27, variable gain amplifier 2
8, A / D conversion circuit 29, linear equivalent circuit 30, data detection circuit 31, decoder 32, drive controller 3
3, a drive control system 34, an interface 35, a modulation circuit 36, and a laser driver 37. Incidentally, the optical disc device 21 usually requires a beam shaping prism and a half-wave plate, and when the optical disc 1 is a magneto-optical disc, a polarizer and an analyzer are necessary.
In FIG. 15, those members are omitted.

In the optical disk device 21 shown in FIG. 15, the optical disk 1 is of a read-only type or of a recordable type. Or irremovably supported. The optical disk 1 can be rotated at a predetermined rotation speed by controlling the rotation speed of the spindle motor 22.

[0108] Above the optical disk 1, a focus lens 23 constituting a part of the pickup system is arranged. The pickup system and the spindle motor 22 are driven by a drive controller 33 via a drive control system 34. With the driving mechanism configured as described above,
The number of rotations of the optical disc 1 and the focusing and tracking control can be performed.

[0109] In the optical disk device 21, the focal depth D _f of the optical system than the thickness T _s of the super-resolution film 3 of the optical disk 1 is short. That is, the wavelength λ of the laser beam emitted from the laser light source 25, the numerical aperture NA of the focusing lens 23, and the thickness T _s of the super-resolution film 3 of the optical disc 1 are inequalities: T _s >
The relationship shown by 0.5 × (λ / NA ² ) is satisfied.

The optical disk device 21 configured as described above
The information is recorded by the following method while controlling the rotation speed of the optical disc 1 and performing the focusing and tracking control as described above. That is, when recording information, under such control, first, the user data signal captured by the drive controller 33 via the interface 35 is transferred to the modulation circuit 36. The modulation circuit 36 converts the user data signal into a predetermined code bit string. The laser driver 37 drives the laser light source 25 in accordance with the code bit sequence, whereby the laser light source 25 emits a pulsed laser beam as recording light.

The recording light is transmitted through the half mirror 24, guided to the focus lens 23, and focused and irradiated on the optical disc 1. Thereby, a recording mark corresponding to the code bit string is formed on the recording film 8 of the optical disc 1. Recording of information in the optical disk device 21 shown in FIG. 15 is performed as described above. It is to be noted that in order to narrow the shortest mark pitch for recording, the output signal of the modulation circuit 36 or the drive control system 3
4 may be changed.

The reproduction of information in the optical disk device 21 is performed by the following method while controlling the rotation speed of the optical disk 1 and performing focusing and tracking control as described above. That is, when recording information, under such control, first, a laser beam having a reproduction power level is emitted from the laser light source 25 as reproduction light. The power level of the laser beam can be controlled by setting the output from the laser light source 25 to pulse light having a constant cycle and appropriately setting the cycle. The reproduction light emitted from the laser light source 25 is transmitted through the half mirror 24, guided to the focus lens 23, and is focused and irradiated on the optical disk 1. Light reflected from a recording track of the optical disc 1 is reflected by the half mirror 24 and guided to the photodetector 26, where it is converted into an electric signal.

The electric signal from the photodetector 26 is amplified by the preamplifier 37 and the variable gain amplifier 28,
The digital signal is converted by the / D conversion circuit 29. Next, this digital signal is filtered by the linear equalizer 30 to remove a jitter component caused by noise. The data detection circuit 31 is, for example, a signal processing circuit that estimates a code bit string by a maximum likelihood method for detecting data from a reproduced signal waveform equalized by a partial response, and is specifically a Viterbi decoder. The decoder 32 restores the code bit string detected by the data detection circuit 31 to the original recording data. The recording data restored in this way is output to the outside of the apparatus via the drive controller 33 and the interface 35. The reproduction of information in the optical disk device 21 shown in FIG. 15 is performed as described above.

The optical disk device 21 shown in FIG. 15 is a recordable type capable of both recording and reproduction. When the optical disk 21 is of a read-only type, the modulation circuit 36
Need not necessarily be provided. Further, the optical system other than the focus lens 23 and the light source 25 is not limited to the structure shown in FIG. 15, but can be variously modified.

[0115]

As described in the foregoing, in the present invention, by making thicker than the thickness T _s of the super-resolution film focal depth D _f, the interface the focal position of the super-resolution film and the thin film recording unit The super-resolution film exists not only near the focal position but also at a position where the rate of change of the beam diameter is large. for that reason,
According to the present invention, a remarkably large super-resolution effect can be obtained as compared with the related art. That is, according to the present invention,
There is provided a technique capable of sufficiently extracting a super-resolution effect. Further, according to the present invention, there is provided a technique capable of easily and sufficiently extracting a super-resolution effect.

[Brief description of the drawings]

FIG. 1 is a graph showing an ideal relationship between irradiation light intensity and an optical response of a super-resolution film.

FIG. 2 is a graph showing the intensity distribution of a Gaussian light beam before and after transmission into a super-resolution film showing the optical change shown in FIG.

FIG. 3 is a diagram schematically showing a state in which light focused by a focusing lens in a region where the optical constant is constant propagates.

FIG. 4 is a sectional view schematically showing an optical recording medium according to an embodiment of the present invention.

FIG. 5 is a graph schematically showing an example of an effect obtained by the present invention.

FIG. 6 is a graph schematically showing another example of the effect obtained by the present invention.

FIG. 7 is a graph showing the relationship between irradiation power density and transmittance obtained for a 1 μm-thick Te film.

FIG. 8 is a graph showing the relationship between irradiation power density and transmittance obtained for a 1 μm-thick CdSSe film.

FIG. 9 is a sectional view schematically showing the optical disc according to the first embodiment of the present invention.

FIG. 10 is a graph showing an example of a relationship between a pit length and a CNR value obtained for the optical disc according to the first embodiment of the present invention.

FIG. 11 is a graph showing an example of the relationship between the ratio of the thickness T _s of the super-resolution film to the depth of focus D _f and the CNR value obtained for the optical disc according to the first embodiment of the present invention.

FIG. 12 is a sectional view schematically showing an optical disc according to a second embodiment of the present invention.

FIG. 13 is a sectional view schematically showing an optical disc according to a third embodiment of the present invention.

FIG. 14 is a sectional view schematically showing an optical disc according to a fourth embodiment of the present invention.

FIG. 15 is a diagram schematically showing an optical disc device according to a fifth embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical recording medium; 2, 10 ... Transparent substrate; 3, 3a,
3b: super-resolution film; 4: thin film recording section; 5: reflection film;
... Anti-reflection film; 7, 9 ... Interference film; 8 ... Recording film;
... light beam; 21 ... optical disk drive; 22 ... spindle motor; 23 ... focus lens; 24 ... half mirror; 25 ... laser light source; 26 ... photodetector; 27 ... preamplifier; 28 ... variable gain amplifier; Conversion circuit; 30 linear equivalent circuit; 31 data detection circuit;
32: decoder; 33: drive controller; 3
4: Drive control system; 35: interface; 36:
Modulation circuit; 37 Laser driver; 51-57 Curve

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kenji Totori 1 Kosuka Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture Inside Toshiba R & D Center (72) Inventor Tadashi Kamiya 2-chome, Marunouchi, Chiyoda-ku, Tokyo No. 2 Mitsubishi Chemical Co., Ltd. (72) Inventor Kenichi Yoshie 2-5-2 Marunouchi, Chiyoda-ku, Tokyo F-term in Mitsubishi Chemical Co., Ltd. 5D029 MA39 5D090 AA01 BB04 BB10 BB12 CC05 DD01 EE02 FF11 KK03

Claims (5)

[Claims] An optical recording medium mounted on a reproducing apparatus that uses light focused by a focus lens for reproducing information, wherein a super-resolution in which an optical constant changes according to a thin-film recording portion and irradiation light intensity. comprising a substrate supporting the laminated structure and the laminated structure of the film, the film thickness T _s of the super-resolution film the light of the wavelength λ and the numerical aperture NA of the focusing lens is inequality: T _s> 0 optical recording medium which satisfies the relationship shown in ^{.5 × (λ / NA 2)} . 2. The optical recording medium according to claim 1, wherein said film thickness T _s is thicker than 0.32 μm. Wherein the thickness T _s is the optical recording medium according to claim 1, characterized in that greater than 0.90 .mu.m. 4. The optical recording medium according to claim 1, wherein said film thickness T _s is greater than 1.56 μm. 5. An optical recording medium comprising a laminated structure of a thin film recording section and a super-resolution film whose optical constant changes in accordance with the intensity of irradiation light, and an optical recording medium comprising a substrate supporting the laminated structure. Irradiating light focused by a focusing lens toward the thin-film recording unit from and detecting reflected light from the optical recording medium to read information recorded in the thin-film recording unit, For reading, the thickness T _s of the super-resolution film, the wavelength λ of the light, and the numerical aperture NA of the focusing lens satisfy the relationship represented by the following inequality: T _s > 0.5 × (λ / NA ² ). A reproduction method characterized in that the method is performed under the following conditions.