JP2001043568A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily and surely prevent the reflection of light at an interface regardlessly of material of a layer forming the interface by constructing an optical recording medium consisting of a multi-layered structure provided with a transparent substrate and a recording layer, and forming an antireflection structure on a surface of the transparent substrate or on at least one interface of each layer. SOLUTION: A hologram memory 1 as an optical recording medium is constituted of a recording layer 2 interposed by two sheet of transparent substrates 3 and 4. Each interface between the transparent substrates 3 and 4 and the recording layer 2 and each surface (interface between air and the transparent substrate 3 and 4) has each antireflection structure 5, 6, 7 and 8 formed by an integral forming as antireflection treatment. For example the antireflection structure 6 has a grid structure in which circular groove parts and circular higher parts concentric with the center of the transparent substrate 4 are alternately arranged at a prescribed period. The arranged period of ruggedness is specified to be one fourth of a wavelength of incident light or less, preferably one tenth of that or less, and an optical height for which a rugged part is effective is specified to be one fourth of the wavelength of the incident light (or an odd number times the value).

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 having a multilayer structure, and more particularly to an optical recording medium which has been subjected to an anti-reflection treatment for preventing light reflection at an interface or the like.

[0002]

2. Description of the Related Art An optical recording medium has at least a recording layer and a transparent substrate, and various layers such as a dielectric film, an adhesive layer and a reflective layer are provided according to a recording method and a material of the recording layer. It has a multilayer structure. In the case of such a multilayer structure, light reflection occurs at the interface due to the difference in the refractive index of each layer, but the light reflection at the interface causes a reduction in the S / N ratio.

Therefore, as a means for preventing reflection of light and improving the S / N ratio, an antireflection film (antireflection layer) is conventionally formed on the interface. For example, in the case of a structure in which a two-dimensional recording layer and a transparent substrate are directly laminated, as shown in FIG. 13A, an antireflection film 92 is formed on the surface of the transparent substrate 90 (interface with air). In addition, as shown in FIG. 13B, an antireflection film 93 is formed on the interface between the transparent substrate 90 and the two-dimensional recording layer 91. Also, prevention of these reflective films 92 and 93, have been formed by depositing or sputtering a SiO _X or MgF, etc. to the surface of the transparent substrate 90.

[0004]

By the way, the reflectivity of the above-described antireflection film is such that the optical film thickness (structural film thickness × refractive index) is one quarter of the wavelength of the incident light in the case of normal incidence. (Or an odd multiple thereof), and the refractive index n _{2 of the} antireflection film is n ₂ ² = n ₁ × n ₃ (none) with respect to the refractive indices n ₁ and n _{3 of} the upper and lower layers forming the interface. 0 when the reflection condition is satisfied. That is, the reflectance of the anti-reflection film depends on the relationship among the refractive indexes n ₂ , n ₁ , and n ₃ .
In order to minimize the reflectance, it is necessary to form the antireflection film with a material having a refractive index that satisfies the above-described non-reflection condition. In the case of the antireflection film 92 shown in FIG. 13A, the upper layer is air and the lower layer is the transparent substrate 90, whereas in the case of the antireflection film 93 shown in FIG. And the lower layer is the two-dimensional recording layer 91,
If the refractive indexes of the air, the transparent substrate 90 and the two-dimensional recording layer 91 are different, the two antireflection films 92 and 93 require different refractive indexes.

However, there are limitations on the materials that can be used for the optical storage medium as the antireflection film, and it is not easy to find a material having a refractive index that satisfies the above-described nonreflection condition.
For this reason, in the conventional optical storage medium, there is no suitable material having a refractive index satisfying the non-reflection condition depending on the combination of the refractive indices of the layers contacting at the interface, and some reflection has to be compromised. .

In recent years, research and development for further increasing the capacity and density of optical recording media have been carried out in response to the coming multimedia information age. For example, as shown in FIG. 14, the recording layer 101 laminated on the transparent substrate 103 is made thicker than the focal depth of the focused laser beam 102 and the focal position is shifted so that the recording layer 101 is shifted.
An optical recording medium (multi-layer optical memory) 100 of a multilayer recording system for performing three-dimensional recording in a depth direction inside the apparatus, and a signal beam 106 representing information such as light reflected from an object and signals as shown in FIG. By irradiating the signal beam 106 with the reference beam 107 in the recording layer 108 and gradually changing the incident angle of the reference beam 107, a plurality of holograms are formed at the same position in the recording layer 108. A three-dimensional optical recording medium, such as a hologram type optical recording medium (hologram memory) 105 for multiplex recording, has been developed.

In such a three-dimensional optical recording medium, the thickness of the recording layer is several tens to several hundreds μm, which is much larger than that of a conventional optical recording medium, and recording is performed three-dimensionally in the thickness direction of the recording layer. Therefore, prevention of reflection at the interface is more strictly required than in a conventional two-dimensional optical recording medium. For example, in the case of the hologram memory 105 described above, the signal beam 106 and the reference beam 1
The hologram is recorded by interference with the recording layer 108 at the interface (the interface with the air) or the interface between the recording layer 108 and the transparent substrate 109 on the incidence side, as shown in FIG. If reflected, the energy for recording the hologram may be insufficient, and
If the reflected light 111 reflected at the interface between the recording layer 108 and the transparent substrate 110 on the output side or the reflected light 112 reflected on the surface of the transparent substrate 110 on the output side (interface with air) is incident on the recording location, erroneous information is generated. There is a risk of being recorded.

The present invention has been made in view of the above problems, and provides an optical recording medium capable of easily and surely preventing light reflection at an interface irrespective of the material of a layer forming the interface. The purpose is to:

[0009]

In order to achieve the above object, an optical recording medium according to the present invention comprises an optical recording medium having a multilayer structure having at least a transparent substrate and a recording layer.
An anti-reflection structure is formed on at least one of the surface of the transparent substrate and the interface of each layer (claim 1).

Here, the anti-reflection structure is composed of irregularities arranged periodically and continuously, and one arrangement period of the irregularities is set to one quarter or less of the wavelength of the incident light. The effective optical height of the concavities and convexities is set to an odd multiple of approximately one quarter of the wavelength of the incident light, and the average refractive index at the interface is a non-reflection condition with respect to the refractive indexes of the layers on both sides contacting at the interface. It is preferable that the volume ratio between the concave portion and the convex portion of the unevenness is set so as to satisfy the condition (claim 2). In this specification, the term “incident light” refers to light that is irradiated onto an optical recording medium as recording and / or reproducing beam light and is incident on the optical recording medium, and “wavelength of incident light” Means the wavelength immediately before the incident light enters the antireflection structure.

Alternatively, the antireflection structure may be composed of a large number of convex portions or concave portions formed at random (claim 3). In this case, the arrangement interval of the convex portions or the arrangement interval of the concave portions is The wavelength is set to be equal to or less than a quarter of the wavelength of the incident light, and the effective optical height of the convex portion or the effective optical depth of the concave portion is an odd multiple of approximately a quarter of the wavelength of the incident light. It is preferable that the density of the above-mentioned convex portions or concave portions is set so that the average refractive index at the interface satisfies the antireflection condition with respect to the refractive indexes of the layers on both sides contacting at the interface. Item 4).

[0012] The recording layer may contain 90% by weight or more of synthetic resin, and may be configured to enable three-dimensional recording on the recording layer.
Furthermore, the recording layer may be sandwiched between a pair of transparent substrates directly or via another layer. Also,
When the transparent substrates are provided in pairs and the recording layer is provided sandwiched between the pair of transparent substrates, reflection occurs on at least one of the interfaces of the pair of transparent substrates in contact with the recording layer. Preferably, an anti-reflection structure is formed (claim 7), and more preferably, an anti-reflection structure is formed on at least one of the surfaces of the pair of transparent substrates (claim 8). Further, it is more preferable that the anti-reflection structure is integrally formed with the transparent substrate.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 7 show an optical recording medium according to an embodiment of the present invention. Here, the optical recording medium is configured as a hologram memory. As shown in FIG. 1, the hologram memory 1 is configured by sandwiching a recording layer 2 between two transparent substrates 3 and 4. The recording layer 2 has a thickness of several tens to several hundreds of micrometers, and is made of a synthetic resin, for example, a binder resin and a photopolymerizable monomer, or two kinds of photopolymerizable monomers having different polymerization rates as main materials (90%). % By weight or more). The transparent substrates 3 and 4 are formed in a disk shape by injection molding of a transparent resin, for example, a polycarbonate resin, an acrylic resin, a methacryl resin, a polystyrene resin, a vinyl chloride resin, an epoxy resin, a polyester resin, an amorphous polyolefin, or the like. Here, the term “transparent” means that at least the recording and / or reproducing beam light is transparent to the light beam applied to the optical recording medium.

Antireflection structures 5, 6, 7, and 8 are integrally formed on each interface of transparent substrates 3 and 4 with recording layer 2 and each surface (interface with air) as an antireflection treatment. Is formed. 2 and 3 are views showing an example of the configuration of the antireflection structure, and FIG. 4 is a view for explaining the operation. Hereinafter, the configuration and operation of the antireflection structure will be described with reference to FIGS. Here, a case where the antireflection structure 6 is formed at the interface with the recording layer 2 on the transparent substrate 4 will be described as an example.

As shown in FIGS. 2 and 3, the antireflection structure 6 has a lattice structure in which annular grooves 11 and peaks 10 concentric with the center of the transparent substrate 4 are alternately arranged at a predetermined period. The arrangement period Λ of the irregularities in the radial direction is の 一 or less, preferably 五 or less, more preferably 十分 or less of the wavelength λ of the incident light. The target height N ₂ × d is set to a quarter (or an odd multiple thereof) of the wavelength λ of the incident light. Here, d represents the geometric height (or depth) of the unevenness, and N ₂ represents the apparent antireflection layer 12 (hereinafter simply referred to as “antireflection layer 12”) formed by the antireflection structure 6 described later. (Which may be referred to as an effective refractive index). The wavelength λ of the incident light indicates the apparent wavelength of the incident light immediately before entering the antireflection layer 12,

(Equation 1) Is referred to as a non-reflection condition.

In FIG. 3, the peak 10 is formed integrally with the transparent substrate 4 and the resin for forming the recording layer 2 enters the groove 11, so that, when viewed from a minute portion, the anti-reflection structure 6 The refractive index becomes the refractive index N ₁ of the transparent substrate 4 at the peak portion 10 and becomes the refractive index N ₃ of the recording layer 2 at the groove portion 11.

However, if one arrangement period 凹凸 of the irregularities is equal to or less than a quarter of the wavelength λ of the incident light, when viewed from the incident light,
Crest 10, the difference in refractive index N _1, N ₃ in the groove 11 are averaged, as shown in FIG. 4, the uniform refractive index N ₂ layers 1
It will be reflected as 2. In other words, this is equivalent to the provision of the layer 12 having the refractive index N ₂ at the interface between the transparent substrate 4 and the recording layer 2.

Here, N ₁ , N ₂ and N ₃ are “effective refractive indices” in consideration of the influence of the incident angle, refraction angle and emission angle of incident light in addition to the refractive index inherent to the material forming each layer. (Hereinafter referred to as “effective refractive index”). For example, when the antireflection structure 6 is a single periodic structure shown in FIG.
As shown in ( ₁₎ , the refractive index of the material forming the transparent substrate 4 was measured as n ₁ , the refractive index of the material forming the recording layer 2 was measured as n ₃ , and the normal direction from the transparent substrate 4 to the antireflection layer 12 was measured. The incident angle is φ ₁ , the refraction angle at the anti-reflection layer 12 is φ ₂ , and the emission angle from the anti-reflection layer 12 to the recording layer 2 is φ _3.
Where F is the filling factor of ENGlytsisand TKGaylor, represented by a series of formulas represented by the following (1) or (2).
d, Applied Optics, 31 (22), 4459 (1992)].

(1) In the case of the TE mode K is a lattice vector parallel to the antireflection layer 12 and perpendicular to the groove of the antireflection structure 6, and E is an electric field vector of the incident light. E
Is perpendicular to K, that is, in the case of the TE mode, the apparent effective refractive index N ₂ of the antireflection layer 12 formed by the antireflection structure 6 is

(Equation 2) It is expressed as The effective refractive indices N ₁ and N ₃ of the transparent substrate 4 and the recording layer 2 are respectively

(Equation 3) It is expressed as

(2) In the case of TM mode In the case where H is the magnetic field vector of the incident light and H is perpendicular to the lattice vector K, that is, in the case of TM mode, the antireflection structure 6 is used.
The effective refractive index N _{2 of} the apparent antireflection layer 12 formed by
Is

(Equation 4) It is expressed as

The effective refractive indices N ₁ and N ₃ of the transparent substrate 4 and the recording layer 2 are respectively

(Equation 5) It is expressed as

When the wavelength of the light incident on the antireflection layer 12 is λ, the non-reflection condition (I) is satisfied when the following condition (3) or (4) is satisfied.

(3) In the case of TE mode The filling factor F and the geometric height d of the antireflection structure 6 are as follows:

(Equation 6)

(Equation 7) It is expressed as

(4) In the case of TM mode The filling factor F and the geometric height d of the antireflection structure 6 are as follows:

(Equation 8)

(Equation 9) here,

(Equation 10) It is expressed as

When the optical recording medium of the present invention is actually designed, irregularities satisfying the filling factor F and the geometric height (or depth) d satisfying these conditions may be formed. Note that even when the antireflection structure 6 is other than the single periodic structure shown in FIG. 5, ENGlytsis and T.K. Gaylord, Applied Opt
ics, 31 (22), 4459 (1992), by forming the antireflection structure 6 using an appropriate filling factor F and a geometric height d calculated according to the calculation method described in Similar effects can be obtained.

In the anti-reflection structure 6, the optical
Utilizing the properties, the refractive index N of the transparent substrate 4₁Of the recording layer 2
Folding rate N_Three, The effective refractive index N of the antireflection layer_TwoIs nothing
The volume ratio of the peak 10 and the groove 11 so as to satisfy the reflection condition
The rate is set. Also, other anti-reflection structures 5, 7, 8
The same applies to the case where the transparent substrate 4 is formed at the interface with the recording layer 2.
In the anti-reflection structure 5 thus formed, like the anti-reflection structure 6,
Refractive index N of bright substrate 3₁And the refractive index N of the recording layer 2_ThreeAnd according to
To form irregularities on the surface of the transparent substrates 3 and 4.
In the anti-irradiation structures 7 and 8, the refractive indices N of the transparent substrates 3 and 4₁When
Refractive index N of air ₀Thus, the unevenness is formed.

Optical recording medium 1 as one embodiment of the present invention
Is configured as described above, and has the following operation when recording a hologram. Hereinafter, the operation and effect of the optical recording medium 1 will be described with reference to FIG. As shown in FIG. 7, at the time of recording a hologram, the recording layer 2 is irradiated with a signal beam 16 and a reference beam 17 representing information such as light reflected from an object and a signal. Then, interference occurs at the intersection between the signal beam 16 and the reference beam 17, and the signal beam 16 and the reference beam 1
The refractive index of the recording layer 2 changes in accordance with the light intensity distribution due to the interference with the hologram 7, and a hologram is recorded. When the reference beam 17 is a plane wave, the irradiation angle is changed little by little (angle multiplex recording method). When the reference beam 17 is a spherical wave, the recording portion is slightly shifted. As a result (shift multiplex recording method), a plurality of holograms are multiplex-recorded at the same location.

At this time, the signal beam 16 and the reference beam 1
7 first enters the transparent substrate 3, transmits through the transparent substrate 3, and then enters the recording layer 2. Therefore, the signal beam 16 and the reference beam 17 are applied to the surface of the transparent substrate 3 (the interface with air). Then, it will hit the interface between the transparent substrate 3 and the recording layer 2. However, in the optical recording medium 1, since the antireflection structures 7, 5 having an effective refractive index satisfying the non-reflection condition are formed at each interface, the reflection of the signal beam 16 and the reference beam 17 at the interface is prevented. ,
Energy shortage for recording can be prevented. Further, even when the noise light 18 enters the recording layer 2,
Since the antireflection structures 6 and 8 having an average refractive index satisfying the non-reflection condition are formed at each interface of the transparent substrate 4 on the emission side, the noise light 18 is reflected from the transparent substrate 4 without being reflected at the interface. Emitted information can be prevented from being recorded due to the emitted noise light 18.

As described above, according to the present optical recording medium 1, the S / N ratio can be greatly improved by preventing the reflection of light at the interface by the anti-reflection structures 5, 6, 7, and 8. There is an advantage that three-dimensional recording in the thickness direction can be reliably performed. In addition, antireflection structures 5, 6,
Reference numerals 7 and 8 denote a material for each layer forming the interface because the reflectance at the interface can be minimized simply by setting the volume ratio between the groove and the peak according to the refractive index of each layer forming the interface. Regardless of this, there is an advantage that light reflection at the interface can be easily and reliably prevented.

Further, the antireflection structures 5, 6, 7, 8
There is also an advantage that it can be easily formed by injection molding together with the transparent substrates 3 and 4. Note that the present invention is not limited to the above-described embodiment, and can be implemented with various modifications without departing from the spirit of the present invention. For example, the grating structure of the anti-reflection structure is not limited to the one in which the peaks and the grooves are arranged in a ring shape as in the above-described embodiment. Depending on the polarization direction of the incident light, as shown in FIG. An anti-reflection structure 23 having a structure in which peaks 21 and grooves 22 are arranged radially from the center of the transparent substrate 20 may be used. As shown in FIG. 9, the anti-reflection structures 6 and 8 shown in FIG. An anti-reflection structure 24 having a structure obtained by combining the anti-reflection structure 23 shown in FIG. However,
Even in this case, the crest 21 and the groove 22 at any place
Is required to be equal to or less than a quarter of the wavelength of the incident light. Further, the anti-reflection structure 28 shown in FIG.
The rectangular projections 26 are formed in the portions surrounded by the grooves 27 by arranging the grooves 27 at a period equal to or less than one-fourth of the wavelength of the incident light in the orthogonal direction. Irregularities may be formed.

Further, instead of the antireflection structure having a regular structure as in the above-described respective configuration examples, the protrusions may be formed randomly on the transparent substrate. That is, in order to prevent reflection at the interface, the lattice structure does not need to be regularly arranged. The height of the unevenness (the height of the convex portion or the depth of the concave portion) is an odd multiple of approximately a quarter of the wavelength of the incident light, and the concave portion and the convex portion are effective at the interface. It is only necessary that the density of the convex portions or concave portions on the plane for which antireflection is required be set so that the refractive index of the layers on both sides of which the interface is in contact with the interface satisfies the non-reflection condition. Of course, a part where the antireflection structures are regularly arranged on the transparent substrate and a part where the antireflection structures are provided at random may be mixed.

Therefore, the shape of the grating structure is not limited to the rectangle as shown in each of the above configuration examples, and various shapes such as a triangular waveform, a staircase shape, and a sine curve shape can be used as long as the effective refractive index satisfies the nonreflection condition. Can be molded into, for example,
As in the anti-reflection structure 32 shown in FIG.
It is also possible to adopt a structure in which quadrangular pyramid-shaped projections 31 are continuously arranged on the upper side. Of course, as long as the effective refractive index satisfies the non-reflection condition, not only the case where each antireflection structure has the same or similar shape, but also a plurality of shapes are mixed or individually as illustrated in the drawings. It may have a completely different shape.

In the above embodiment, the case where the optical recording medium of the present invention is configured as a hologram memory has been described. However, the present invention can be applied to other three-dimensional optical storage media such as a multilayer memory. Of course, it is also possible to apply to a conventional two-dimensional optical storage medium. Further, the method of forming the antireflection structure is not limited to the integral molding with the transparent substrate by injection molding, as described above, and may be formed on the transparent substrate by a photoresist, etching, or the like,
Further, it may be formed using a photopolymer. In this case, however, as shown in FIG. 12, since the projection 35 forming the anti-reflection structure 38 is separate from the transparent substrate 36, the refractive index _Nd of the projection 35 and the surrounding medium of the projection 35 the effective refractive index N _b of the layer in which is determined by the refractive index N _a of 37,
Refractive index N _c of the refractive index N _a and the transparent substrate 36 of the surrounding medium 37
It is necessary that the volume ratio be such that the non-reflection condition is satisfied.

In the above embodiment, the recording layer is directly sandwiched between the pair of transparent substrates. However, another layer such as a moisture-permeable layer or an adhesive layer is provided between the transparent substrate and the recording layer. You may. And as an interface for forming an anti-reflection structure,
It is not limited to the interface where the transparent substrate contacts, but can be formed at any interface where reflection should be prevented. Further, in the above-described embodiment, the example in which the antireflection structure according to the present invention is provided on all interfaces and surfaces of the optical recording medium has been described. However, it is not always necessary to provide the antireflection structure on all interfaces and surfaces. Or a portion required according to the recording method.

Further, the shape of the present optical recording medium is not limited to the above-mentioned disk type, but may be applied to optical recording media of various shapes such as a card type optical recording medium such as a memory card. Can be.

[0036]

As described in detail above, according to the optical recording medium of the present invention (claims 1 to 9), the anti-reflection structure formed at the interface makes it possible to use the anti-reflection structure regardless of the material of each layer forming the interface. There is an advantage that light reflection at the interface can be easily and reliably prevented. In particular, in a three-dimensional recording medium in which recording is performed three-dimensionally also in the thickness direction of the recording layer, the S / N ratio can be greatly improved by reliably preventing reflection at the interface, and the third order in the thickness direction of the recording layer can be improved. There is an advantage that original recording can be reliably performed (claim 5).

Another advantage is that the antireflection structure can be easily formed by injection molding together with the transparent substrate (claim 9).

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of an optical recording medium according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a configuration example of an anti-reflection structure according to the optical recording medium as one embodiment of the present invention.

FIG. 3 is a partial cross-sectional view showing a configuration example of an antireflection structure according to an optical recording medium according to an embodiment of the present invention.

FIG. 4 is a diagram for explaining an operation of the antireflection structure according to the optical recording medium as one embodiment of the present invention.

FIG. 5 is a diagram illustrating a condition for satisfying a non-reflection condition of the antireflection structure according to the optical recording medium as one embodiment of the present invention.

FIG. 6 is a diagram for explaining conditions for satisfying a non-reflection condition of the antireflection structure according to the optical recording medium as one embodiment of the present invention.

FIG. 7 is a schematic diagram for explaining the operation and effect of the optical recording medium as one embodiment of the present invention.

FIG. 8 is a perspective view showing another configuration example of the antireflection structure according to the optical recording medium as one embodiment of the present invention.

FIG. 9 is a perspective view showing another configuration example of the antireflection structure according to the optical recording medium as one embodiment of the present invention.

FIG. 10 is a partial perspective view showing another configuration example of the antireflection structure according to the optical recording medium as one embodiment of the present invention.

FIG. 11 is a partial perspective view illustrating another configuration example of the antireflection structure according to the optical recording medium as one embodiment of the present invention.

FIG. 12 is a partial cross-sectional view showing another configuration example of the antireflection structure according to the optical recording medium as one embodiment of the present invention.

13A and 13B are partial cross-sectional views illustrating a configuration of a conventional optical recording medium, in which FIG. 13A illustrates a case where an antireflection film is formed on the surface of a transparent substrate (interface with air), and FIG. The case where an antireflection film is formed at the interface between the recording layer and the recording layer is shown.

FIG. 14 is a schematic diagram showing a configuration of a multiplex optical memory which is one of three-dimensional optical recording media.

FIG. 15 is a schematic diagram showing a configuration of a hologram memory which is one of the three-dimensional optical recording media.

FIG. 16 is a cross-sectional view for explaining a problem in a conventional hologram memory.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical recording medium 2 Recording layer 3, 4 Transparent substrate 5-8 Antireflection structure 10 Mountain part (convex part) 11 Groove part (concave part) 12 Antireflection layer

Claims (9)

[Claims] 1. An optical recording medium having a multilayer structure including at least a transparent substrate and a recording layer, wherein an antireflection structure is formed on at least one of the surface of the transparent substrate or an interface between the layers. An optical recording medium. 2. The anti-reflection structure comprises irregularities arranged periodically and continuously, and one arrangement period of the irregularities is set to one quarter or less of the wavelength of incident light. The effective optical height is set to an odd multiple of approximately one quarter of the wavelength of the incident light, and the average refractive index at the interface satisfies the non-reflection condition with respect to the refractive indexes of the layers on both sides contacting at the interface. As described above, the volume ratio of the concave and convex portions of the irregularities is set,
The optical recording medium according to claim 1. 3. The optical recording medium according to claim 1, wherein the antireflection structure is constituted by a large number of convex portions or concave portions formed at random. 4. The arrangement interval of the convex portions or the arrangement interval of the concave portions is set to be equal to or less than a quarter of the wavelength of the incident light, and the effective optical height of the convex portions or the effective interval of the concave portions. The optical depth is set to an odd multiple of approximately a quarter of the wavelength of the incident light, and the average refractive index at the interface satisfies the non-reflection condition with respect to the refractive indexes of the layers on both sides contacting at the interface. 4. The optical recording medium according to claim 3, wherein the density of the convex portions or the concave portions is set. 5. The recording layer according to claim 1, wherein the recording layer contains 90% by weight or more of a synthetic resin, and the recording layer is configured to enable three-dimensional recording. 2. The optical recording medium according to 1. 6. The optical recording medium according to claim 5, wherein the recording layer is sandwiched between a pair of transparent substrates directly or via another layer. 7. The transparent substrate is provided as a pair, and the recording layer is provided sandwiched between the pair of transparent substrates, and at least one of an interface of the pair of transparent substrates in contact with the recording layer. 2. The optical recording medium according to claim 1, wherein an anti-reflection structure is formed on one of the sides. 8. The optical recording medium according to claim 7, wherein an antireflection structure is formed on at least one of the surfaces of said pair of transparent substrates. 9. The optical recording medium according to claim 7, wherein said anti-reflection structure is formed integrally with said transparent substrate.