JP2004087126A - Optical disk - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize recording, reproduction, and erasing with respect to a focusing recording layer by generating no diffracted light except the zero-order diffracted light and by reducing crosstalk generated from another recording layer from which reproduction is not performed. <P>SOLUTION: Recording layers 19 each constituted by arranging two layers, a first layer 17 and a second layer 18 adjacently, each of which has transmissivity changed by a difference in irradiated light intensity are held by transparent bodies 1. The plurality of recording layers 19 are layered by interposing the transparent bodies 11 while satisfying a condition: T1AxT2A=T1BxT2B wherein T1A is the transmissivity of the first layer 17 and T2A is the transmissivity of the second layer 18 with respect to the irradiated light intensity A, and T1B is the transmissivity of the first layer 17 and T2B is the transmissivity of the second layer 18 with respect to another irradiated light intensity B. Thus, the generation of the diffracted light except the zero-order diffracted light is eliminated, the crosstalk generated from the other recording layer from which reproduction is not performed is reduced and recording, reproduction, and erasing with respect to the focusing recording layer is realized. <P>COPYRIGHT: (C)2004,JPO

Description

The present invention relates to an optical disc for optically recording or reproducing information on an optical disc as a recording medium.

The following describes the conventional optical disk and optical disk device.

As shown in FIG. 17, the radiated light of the semiconductor laser 1 is converted into 0-order and ± 1st-order diffracted light by the diffraction grating 2, reflected by the beam splitter 3, and recorded on the optical disk 5 by the objective lens 4. The light spot 7 is formed by being narrowed down on the layer 6.

Next, the light beam 8 reflected by the optical disk 5 passes through the objective lens 4 and reaches the beam splitter 3, and the transmitted light beam 8 enters the photodetector 9. From the photodetector 9a divided into four parts, a focus error signal is detected together with the reproduced signal by the astigmatism method. The tracking error signal is obtained by a three-beam method for detecting the difference in the amount of light of the ± first-order diffraction return light incident on the photodetectors 9b and 9c. The reproduced signal is obtained as the sum of the amounts of light received by the photodetector 9a divided into four parts. In such a conventional optical disk device, there is only one recording layer 6 per surface of the optical disk.

In recent years, attempts have been made to increase the density of optical disk devices, such as shortening the wavelength and narrowing the track. In addition to the improvement of the density in the recording surface, the recording density can be improved by increasing the density in the vertical direction of the recording surface, that is, by increasing the number of surfaces by stacking the recording layers in the thickness direction. However, such a laminated structure has an effect of reflected light and transmitted light of recording layers other than the reproduction recording layer, and due to this drawback, the laminated structure is not employed. Looking at the configuration of the conventional optical disk device, the number of recording surfaces provided on the optical disk 5 is only one on each side, and the number of recording surfaces provided on one optical disk 5 is up to two.

(4) If the recording layers are stacked in the thickness direction of the optical disc so as to increase the recording density as described above, there is a problem that the recording layers are affected by the interference light from the recording layers that are not recorded or reproduced.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems, and eliminates the generation of diffracted light other than the 0th order, suppresses signal mixing due to the influence of interference light from a recording layer that is not a target of recording and reproduction, and provides a good reproduced signal. It is an object of the present invention to provide an optical disk which can obtain a high recording density and further has a greatly improved recording density.

According to the first invention of the present invention, the transmittance of the first and second layers is T1A and T2A for the irradiation light intensity A, and the transmittance of the first and second layers is for the irradiation light intensity B. The recording layer composed of the first layer and the second layer having transmittances of T1B and T2B is T1A × T2A = T1B × T2B.
This is an optical disc that satisfies the following condition and is stacked in plural with a transparent body interposed.

{Circle around (4)} This eliminates the generation of diffracted light other than the 0th order, so that there is almost no crosstalk from other recording layers that do not reproduce, and recording / reproduction / erasing of the focused recording layer becomes possible.

Further, a second invention of the present invention is directed to a recording medium comprising a recording layer and a transparent body, which are composed of first and second layers and an intermediate transparent body sandwiched between the first and second layers, which are alternately laminated and irradiated. When the transmittance of the first and second layers becomes T1A and T2A for the light intensity A, and the transmittance of the first and second layers becomes T1B and T2B for the irradiation light intensity B,
T1A × T2A = T1B × T2B
An optical disc which satisfies the following condition, has a substantially equal refractive index between the intermediate transparent body and the transparent body, and sets the distance between the recording layers at least 10 times the wavelength used.

{Circle over (2)} This makes it possible to suppress signal mixing due to the influence of interference light from a recording layer that is not a target of recording and reproduction, and obtain a good reproduced signal.

Further, according to a third aspect of the present invention, the first and second layers have thicknesses of H1 and H2, and the refractive indexes of the first and second layers are N1A and N2A with respect to the irradiation light intensity A, For the irradiation light intensity B, the first and second layers have a refractive index of N1B and N2B, and the recording layer composed of the first layer and the second layer has N1A × H1 + N2A × H2 = N1B × H1 + N2B × H2
This is an optical disc that satisfies the following condition and is stacked in plural with a transparent body interposed.

Thereby, a good reproduced signal can be obtained.

The fourth invention of the present invention compares the reflectance at the interface between the first layer and the transparent body and the reflectance at the interface between the first layer and the second layer with respect to the irradiation light intensity A. Then, when the former is small, the refractive index of the first layer with respect to the irradiation light intensity A and the refractive index of the second layer with respect to the irradiation light intensity B are made substantially equal to the refractive index of the transparent body, and when the latter is small, An optical disc according to a third aspect of the present invention, wherein the refractive indexes of the opposite layers are made equal to the refractive index of the transparent body.

(4) As a result, even in an optical disk having recording layers with different reflectivities, it is possible to prevent a decrease in the amount of reflected light and obtain a good reproduction signal.

In a fifth aspect of the present invention, a recording layer and a transparent body composed of a first and a second layer and an intermediate transparent body sandwiched between the first and the second layers are alternately laminated. 1, the thickness of the second layer is H1 and H2, the first and second layers have a refractive index of N1A and N2A for the irradiation light intensity A, and the first and second refractive indexes of the second layer have the irradiation light intensity B. When the refractive index of the second layer is N1B and N2B, N1A × H1 + N2A × H2 = N1B × H1 + N2B × H2
An optical disc which satisfies the following condition, the refractive index of the intermediate transparent body and the refractive index of the transparent body are substantially equal, and the interval between the recording layers is 10 times or more of the used wavelength.

{Circle over (2)} This makes it possible to suppress signal mixing due to the influence of interference light from a recording layer that is not a target of recording and reproduction, and obtain a good reproduced signal.

Further, the sixth invention of the present invention compares the reflectance at the interface between the first layer and the transparent body and the reflectance at the interface between the second layer and the intermediate transparent body with respect to the irradiation light intensity A. When the former is small, the refractive index of the first layer with respect to the irradiation light intensity A and the refractive index of the second layer with respect to the irradiation light intensity B are made substantially equal to the refractive indices of the transparent body and the intermediate transparent body, The optical disk according to the fifth invention, wherein when the latter is small, the refractive indexes of the opposite layers are made equal to the refractive indexes of the transparent body and the intermediate transparent body.

Thereby, a better reproduction signal can be obtained.

The optical disk of the present invention can suppress signal mixing due to the influence of interference light from a recording layer that is not a target of recording and reproduction, can obtain a good reproduction signal, and can stack recording layers, and It is possible to realize an optical disk having an improved recording density.

The best mode for carrying out the present invention will be described below with reference to the drawings. Note that the present invention is not limited by the present embodiment. Further, in the description of the present embodiment, portions having the same configuration and operation and effect will be denoted by the same reference numerals, without redundant description.

(Reference Example 1)
As shown in FIGS. 1 and 2, in this embodiment, the optical disk 5 described in the conventional example is an optical disk 12 in which a plurality of recording layers 10 are stacked with a transparent body 11 interposed therebetween. That is, the optical disk 12 has a plurality of recording layers 10 stacked and separated from each other by a sufficiently long stacking interval L with respect to the wavelength of the light beam 8. After the light beam 8 has passed through some of the non-focused recording layers 10b of the recording layer 10, the light beam 8 is narrowed down to the focused recording layer 10a to be recorded / reproduced. It is configured to follow the reverse optical path, pass through the beam splitter 3 and enter the photodetector 9. In the drawing, reference numeral 13 denotes a recording pit, and d denotes a depth from the surface of the optical disc 12 to the focused recording layer 10a as viewed from the objective lens 4 side.

The operation of the optical disk device configured as described above will be described below.

In the optical disc 12 of the present embodiment, when transmitted through the recording layer 10, the first or higher order diffracted light by the recording pits 13 is not generated, and the transmitted light beam 8 is substantially only the 0th order diffracted light. Here, the 0th-order diffracted light means transmitted light that does not change its traveling direction due to diffraction during transmission. By doing so, it is possible to suppress signal mixing from the recording layers 10b, 10c, etc., which are not to be recorded / reproduced. This will be described below. First, an adverse effect when the transmitted light includes first-order or higher diffraction light will be described. The problem is the effect of the diffracted light when the light beam 8 passes through the out-of-focus recording layer 10b before the focal point shown in FIG. Since the recording pit is on the track, the recording pit acts as a diffraction grating having a pitch between tracks. Therefore, as shown in FIG. 3, all the diffracted lights are focused on the focus recording layer 10a, and the light spot 0s by the 0th-order diffracted light, the light spot 1s by the 1st-order diffracted light, the light spot -1s by the -1st-order diffracted light, etc. The light spots 1s, -1s, etc., of the first order or higher other than the light spot 0s, irradiate recording pits at positions not related to recording pits to be recorded / reproduced. Part of this reflected light enters the photodetector 9 and mixes with the signal. This signal contains a reproduced signal of a recording pit that should not be recorded and reproduced, and its output is more than that of the original reproduced signal. Since the image is reproduced in the in-focus state, it becomes so large that it cannot be ignored. This is a state where simultaneous reproduction is performed with multiple light spots such as 0 s, 1 s, and -1 s, and a signal originally required is buried in a multi-spot reproduction signal, which is a problem. As described above, when the transmitted light has high-order diffracted light, normal reproduction is impossible, and in order to perform normal reproduction, strictly speaking, there is no higher-order diffracted light in transmitted light. Is a necessary condition. In practice, it is difficult to completely eliminate high-order diffracted light. However, it is desirable that at least 10% or more of first-order or higher-order diffracted light is 0% or less of 0th-order diffracted light, and if 1% or less, it is practical It can be said that there is almost no problem. It is also possible to produce an optical disk of 1% or less.

Therefore, the following describes the existence of other adverse effects under the condition that there is no higher-order diffracted light in the transmitted light.

First, in the case of transmission through the recording layer 10, neither the transmitted light on the outward path nor the transmitted light on the return path generates first-order or higher diffracted light. Since there is no pit 13, there is no problem and there is no problem.

Next, the reflected light from the recording layer 10 will be described. The reproduction signal on the optical disk 12 is detected as a change in the amount of light received by the photodetector 9. When the light spot 0s irradiates the recording pit 13 on the focusing recording layer 10a, the reflected light beam 8 is diffracted by the recording pit 13 and a part of the high-order diffracted light does not enter the objective lens 4, so that the objective lens 4 4, the total amount of incident light decreases, and the decrease in the amount of light is detected, and a reproduction signal is obtained. Therefore, if a light amount fluctuation occurs for some reason other than the light amount fluctuation described above, this becomes an interference signal. First, consider an interference signal caused by reflected light br reflected by the out-of-focus recording layer 10b in the defocused state shown in FIG.

(4) Reflection diffraction occurs due to the recording pits 13 on the out-of-focus recording layer 10b, and this causes fluctuations in the amount of incident light on the objective lens 4 and becomes an interference signal. However, as schematically shown in FIG. 2B, if the lamination interval L of the recording layer 10 is set to be sufficiently large with respect to the wavelength of the light beam 8 and the size of the recording pit 13, the light beam 8 When irradiating the out-of-focus recording layer 10b, the size of the light beam 8 becomes sufficiently larger than the size of the recording pits 13, so that a large number of recording pits 13 in a wide range on the out-of-focus recording layer 10b are formed. It will be irradiated. For this reason, even if the number of irradiated recording pits 13 fluctuates somewhat, the number of irradiated recording pits 13 can be considered to be almost always constant, because the number of irradiated recording pits 13 is small compared to the number of irradiated recording pits. Therefore, the amount of light br reflected by the out-of-focus recording layer 10b and entering the objective lens 4 is usually almost uniform, so that the effect on the detection signal is not substantially large.

For example, if the objective lens NA is 0.5, the track pitch and the pit pitch are standard values of 1.6 μm, and the lamination interval L of the recording layers 10 is 10 μm, the light beam irradiating the non-focused recording layer 10 b The diameter G of 8 becomes (Equation 1), and approximately 44 recording pits 13 are included in the circle of the diameter G.

Here, for example, if there is a change corresponding to one recording pit, the change is 1/44 = 2.3% with respect to the whole, which is not a serious problem in practical use. When the lamination interval L of the recording layer 10 is longer than this value, the value further decreases. When the lamination interval L is 30 μm,
2.3 × (10/30) ² = 2.3 × 0.11 = 0.25%
And there is almost no problem.

上限 The upper limit of the stacking interval L of the recording layer 10 is limited to about 0.8 mm because if the stacking interval L is too large, the effect of stacking is reduced.

Next, the effect of the multiple reflected light of the reflected light ar by the focused recording layer 10a, which should become the original signal, will be described. As an example, a light beam am traveling toward the objective lens 4 after being reflected between the unfocused recording layer 10b and the focused recording layer 10a will be described. Since the light beam ar irradiates the out-of-focus recording layer 10b in a spread state, and then irradiates the in-focus recording layer 10a in a further spread state, the averaging similar to that described above has a substantial effect. Not. The same applies to other multiple reflections. The same applies to the light beam cr that passes through the focused recording layer 10a, is reflected by the unfocused recording layer 10c, and travels toward the objective lens 4.

As described above, if the transmitted light can be made only the 0th order, it is possible to substantially eliminate the influence of the recording pits 13 on the non-focused recording layer 10b where the light beam 8 is not recorded or reproduced. By focusing on a predetermined recording layer 10, recording and reproduction can be performed without being affected by other recording layers 10.

Next, the relationship with the performance of the objective lens 4 will be described. In the optical disc 12 of the present embodiment, as the lamination interval L of the recording layers 10 is wider, the signal mixing from the other recording layers 10 is reduced, which is advantageous. The depth d changes depending on the difference of the recording layer 10 to be focused. The objective lens 4 is designed to have a predetermined thickness (about 1.2 mm) of the optical disk 12 and exhibits satisfactory performance when the thickness is changed. The problem of not being able to do it arises. This is because the spherical aberration increases, and if the spherical aberration can be suppressed, it is possible to prevent the aperture stop performance from deteriorating. Since the spherical aberration is mainly caused by the difference in the optical path length of the light beam passing through the central part and the peripheral part of the optical axis of the light beam 8, for example, as shown in FIG. If the light beam 8 is formed into a ring shape, for example, and the light beam 8 is passed only to the peripheral portion, or if the light amount in the peripheral portion is increased, the optical system composed of the objective lens 4 and the optical disk 12 in this ring region The difference in the optical path length is significantly reduced, and the aperture performance can be improved. Since this method is a super-resolution method, the diameter of the convergent spot can be shortened at the same time.

と し て Also, as another method, as shown in FIG. 5, an optical path length changing means 15 can be used. The optical path length changing means 15 is, for example, disposed between the objective lens 4 and the optical disk 12 and has two wedge-shaped glasses having the same refractive index, with the slopes facing each other. If the focus lens is moved, the thickness w of the optical path length changing means 15 can be changed, so that the change in the depth d due to the change in the focus recording layer 10a can be corrected. Deterioration can be prevented. The optical path length changing means 15 may be provided anywhere as long as the light beam 8 is non-parallel, and is not limited to the space between the objective lens 4 and the optical disk 12. For example, FIG. As shown in the figure, in an optical system in which the emitted light of the semiconductor laser 1 is converted into a parallel or almost parallel light beam 8 using a collimator lens 16, an optical path length changing means 15 is provided between the semiconductor laser 1 and the collimator lens 16. The same effect can be obtained by disposing.

As described above, in the present embodiment, since there is no first-order or higher-order diffracted light with respect to the light transmitted by the recording pit 13, it is possible to reduce the influence from the recording layer 10 other than the reproducing layer. The problem of the laminated structure can be solved. As a method for improving the recording density based on a concept similar to that of this embodiment, there is a wavelength multiplexing method. The wavelength division multiplexing method is to superimpose and record a large number of different wavelengths on a recording material formed of only one layer, and reproduce the same at different wavelengths, whereby a reproduced signal can be obtained independently for each wavelength. There is a possibility that the density can be increased by the number of wavelengths used, and a method using an organic dye as a recording material, a chemical hole burning method, and the like have been studied. In addition, as a multiplex recording method, a method has been proposed in which recording and reproduction are performed by changing the direction of deflection of light. In contrast to these methods, the present embodiment uses a multi-layer recording layer 10 and can be used even if the wavelength of the light beam 8 is constant or the light deflection direction is constant. With this configuration, the recording density can be improved.

The optical disk 12 of the first embodiment is characterized in that only the 0th-order diffracted light of the pit diffracted light of the light beam 8 is transmitted. Next, the optical disk 12 that realizes this will be described.

(Reference Example 2)
Hereinafter, a read-only optical disk using a light absorber as a recording layer will be described.

As shown in FIG. 7, the thickness of the recording layer 10 is made constant so that the transmittance of the recording layer 10 becomes constant over the entire surface, and further, the refractive indexes of the transparent bodies 11 on both sides of the recording layer 10 are made substantially equal. Set. The recording pits 13 are produced by providing the recording layer 10 with irregularities. Thus, looking at the phase difference between the transmitted light TP in the portion of the recording layer 10 where the recording pits 13 are located and the transmitted light TL in the portion where the recording pit 13 is not located, the two are equal in the optical path length comparison from the plane U1 to the plane U2. No phase difference occurs. Further, since the transmittance is constant, the amplitude of the transmitted light is also constant. Diffraction of the transmitted light occurs when either the amplitude or phase of the light changes due to transmission, but in this reference example, since there is no change in both the transmitted light TP and TL, no light diffraction occurs, and the transmitted light is zero. Only the second-order diffracted light is obtained. Therefore, the transmitted light does not sense the presence or absence of the recording pit 13, which is similar to the absence of the recording pit 13. On the other hand, the optical path length of the reflected light differs by twice the depth V of the recording pit 13 between the reflected light RP at the portion of the recording pit 13 and the reflected light RL at the portion without the recording pit 13, so that the phase changes, and the primary or higher order. Is generated, and the recorded pit information of the diffracted light is included, and pit information can be obtained. The recording layer 10 can be formed by vapor deposition, sputtering, or the like, using a metal such as aluminum as the light absorber so as to have a film thickness with an appropriate transmittance.

(Reference Example 3)
Hereinafter, a read-only optical disk using a dielectric as a recording layer will be described.

As shown in FIG. 7, light is reflected at interfaces S1 and S2 between the recording layer 10 and the transparent body 11 due to a difference in refractive index. When the thickness a of the recording layer 10 is reduced to about the wavelength of light, it takes advantage of the multiple interference effect of reflected light at the interfaces s1 and s2, and is relatively large by the same principle as a well-known antireflection film, multilayer filter, or the like. The reflectance can be obtained. Here, the conditions are such that the thickness a of the recording layer 10 and the refractive index of the transparent body 11 sandwiching the recording layer 10 are constant in any portion. The reflectance and the transmittance of the recording layer 10 using the dielectric are related to the refractive indexes on both sides of the interfaces S1 and S2. In the case of this reference example, the refractive index of the portion of the recording pit 13 and the portion without the recording pit 13 is Since the transmitted light TP and the transmitted light TL have the same amplitude and phase, the diffraction by the recording pits 13 does not occur, and the transmitted light is only the 0th-order diffracted light as in the above-described reference example 2. Thus, the same effect as in Reference Example 2 can be obtained. Further, as for the reflected light, there is a difference in optical path length depending on the depth v of the recording pit 13 as in the case of the reference example 2, and recording pit information can be obtained. Since the reflectance and the transmittance are determined by the refractive index and the thickness of the recording layer 10 and the transparent body 11, when the medium on both sides of the recording layer 10, that is, the transparent body 11 has the same refractive index, the recording layer 10 and the transparent body 11 are different. If the refractive indices are different, reflection occurs. The more the refractive index of the recording layer 10 is different from the refractive index of the transparent body 11, the greater the reflectance. In this embodiment, it is desirable that the refractive index is about 5% or more. Is 1.1 times or more or 0.9 times or less. As a dielectric material satisfying this, for example, there are TiO ₂ , ZnS, CeO ₂ , ZrO _{2 and the} like. In the above description, the recording layer 10 has a single dielectric, but the same effect can be obtained with a plurality of layers, and the degree of freedom in design is further increased.

(Embodiment 1)
The recording / erasing type optical disk will be described.

As shown in FIG. 8A, a recording layer 19 in which a first layer 17 and a second layer 18 whose transmittance changes depending on a difference in irradiation light intensity is disposed close to each other is sandwiched by a transparent body 11. This is the configuration. For the irradiation light intensity A, the transmittance of the first layer 17 is T1A, the transmittance of the second layer 18 is T2A, and for the other irradiation light intensity B, the transmission of the first layer 17 is T1A. An optical disc having a configuration in which the transmittance is T1B and the transmittance of the second layer 18 is T2B is such that when the portion indicated by P is irradiated with the irradiation light intensity A and the portion indicated by Q is irradiated with the irradiation light intensity B, the portion of P The transmittances of the first and second layers 17 and 18 are T1A and T2A, and the transmittances of the first and second layers 17 and 18 of the portion Q are T1B and T2B. Here, the reflectance for the light irradiation light intensities A and B at the interfaces S1 and S2 is R1a, R2a, R1b, and R2b. For example, if R1a> R2a and R1b <R2b, the reflection at the portion P is transparent 11 At the interface S1 between the first layer 17 and the second layer 18 and at the interface Q between the first layer 17 and the second layer 18 (in the figure, the first layer 17 and the second The hatched portion has a higher reflectance than that of the layer 18). Regarding the reflected lights R1a and R2b, a step H1 of the reflection surface corresponding to the thickness of the first layer 17 is generated between the portion P and the portion Q, which has the same effect as the formation of the recording pit. Become. When the portion P is irradiated with the irradiation light intensity B, the previously formed step H1 disappears. Therefore, by changing the irradiation intensity, recording and erasing can be performed.

On the other hand, with respect to the transmitted light, assuming that the entire transmittance of the recording layer 19 in the P portion and the Q portion is TP, TL
TP = T1A × T2A
TL = T1B × T2B
T1A × T2A = T1B × T2B
In this condition, no diffracted light other than the 0th order is generated, and the transmitted light does not detect the step H1, so that there is almost no crosstalk from other recording layers that are not reproduced, and recording / reproduction / erasing of the focused recording layer is possible. It becomes.

(Embodiment 2)
A recording / erasing type optical disk using a dielectric as a recording layer will be described below.

The configuration of the second embodiment is the same as that of the first embodiment described with reference to FIG. 8A, and uses a dielectric material for the recording layer and a first layer 17 whose refractive index changes depending on the difference in irradiation light intensity. The recording layer 19 in which two layers of the second layer 18 are arranged close to each other is sandwiched by the transparent body 11. For the irradiation light intensity A, the refractive index of the first layer 17 is N1A, the refractive index of the second layer 18 is N2A, and for the other irradiation light intensity B, the first layer 17 In an optical disc having a configuration in which the refractive index of the second layer 18 is N1B and N2B, when the P portion is irradiated with the irradiation light intensity A and the Q portion is irradiated with the irradiation light intensity B, the first and second portions of the P portion are irradiated. The refractive indices of the layers 17 and 18 are N1A and N2A, and the refractive indices of the first and second layers 17 and 18 in the portion Q are N1B and N2B. Here, assuming that the reflectances of the interfaces S1, S2 with respect to the light irradiation intensities A, B are R1a, R2a, R1b, R2b, these are determined by the refractive index and the thickness on both sides of the interfaces S1, S2, S3. . If the relationship among R1a, R2a, R1b, and R2b is R1a> R2a, R1b <R2b as in the first embodiment, recording pit formation and recording erasure can be performed with a pair of R1a and R2b.

As for the transmitted light, the transmitted optical path lengths OPP and OPQ of the P portion and the Q portion are as follows: OPP = N1A × H1 + N2A × H2
OPQ = N1B × H1 + N2B × H2
So
OPP = OPQ
That is,
N1A × H1 + N2A × H2 = N1B × H1 + N2B × H2
Under the conditions shown in (1) and (2), the optical path lengths of the transmitted light in the P portion and the Q portion of the recording layer 19 become equal, so that there is no difference in the phase change between the two. For this reason, as in the first embodiment, the transmitted light does not sense the step between the interface S1 and the interface S2, so that there is no generation of ± 1 or more order diffracted light caused by the recording pits formed here.

Further, the refractive index N2A when the irradiation light intensity A of the second layer 18 in the P portion is equal to the refractive index N1B when the irradiation light intensity B in the first layer 17 in the Q portion is the refractive index of the transparent body 11. 8B, the interface S3 between the second layer 18 in the P portion and the transparent body 11 and the interface S1 between the first layer 17 in the Q portion and the transparent body 11 Since the light reflected by the interface S3 of the transmitted light TP at the portion P and the light R1b reflected by the interface S1 at the portion Q disappear, the noise component disappears and a better reproduction signal is obtained. be able to.

(Embodiment 3)
Hereinafter, a recording / erasing type optical disk in which an intermediate transparent body is provided between recording layers will be described.

As shown in FIG. 9A, in the third embodiment, an intermediate transparent body 20 made of a transparent substance is disposed between the first layer 17 and the second layer 18 in the configuration of the second embodiment. The configuration is a recording layer 21.

It is assumed that the transmittance of the first and second layers 17 and 18 changes as in the second embodiment due to the difference in irradiation light intensity, and that the optical characteristics of the intermediate transparent body 20 do not change. In the third embodiment, for example, the reflection at the portion P is large at the interface S1 between the transparent body 11 and the first layer 17, and at the portion Q, the interface S3 between the intermediate transparent body 20 and the second layer 18 is large. To increase. Thus, the recording pit of the step H3 can be formed. In the third embodiment, by providing the intermediate transparent body 20, the interdependence between the depth of the recording pit and the thicknesses of the first and second recording layers 17 and 18 can be eliminated. The degree of freedom in setting the thicknesses of the first and second recording layers 17 and 18 can be increased. When recording pits are formed by using the difference in transmittance, the condition of the transmittance of the first and second layers 17 and 18 is N1A × H1 + N2A × H2 = N1B × H1 + N2B × H2.
It becomes. The conditions for forming the first and second layers 17 and 18 using a dielectric are as described above in OPP = OPQ.
It becomes. 8B, the refractive index N2A of the second layer 18 in the portion of P and the refractive index N1B of the first layer 17 in the portion of Q are set to If the refractive index of the intermediate transparent body 20 is made equal, as shown in FIG. 9B, the interface between the second layer 18 of the P portion and the transparent body 11 and the intermediate transparent body 20 and the first portion of the Q portion Since the interface between the layer 17 and the transparent body 11 and the intermediate transparent body 20 is not optically present, the reflected light from this portion disappears, and a better reproduction signal can be obtained.

(Embodiment 4)
Hereinafter, an optical disc having a recording layer with different reflectivity will be described.

As shown in FIG. 10, assuming that the light beam 8 is incident on the optical disk 22 from below, the first to the recording layer 23a, the second to the recording layer 23b, and the third to the recording layer 23 in order from the incident side of the light beam 8. Is the recording layer 23c, the irradiation light amount t1 to the second recording layer 23b is reduced by the reflection light amount R1 and the absorption light amount at the first recording layer 23a, so that the reflection light amount R2 at the recording layer 23b is correspondingly reduced. And the amount of light returning to the photodetector also decreases. Similarly, the irradiation light amount t2 and the reflection light amount R3 to the third recording layer 23c decrease, and the decrease amount increases as the number of recording layers 23 increases. Further, after the light is reflected from the recording layer 23 and returns to the photodetector, the amount of light also decreases due to transmission through another recording layer 23. Therefore, the farther the recording layer 23 is from the semiconductor laser, the smaller the amount of light returned to the photodetector becomes. It will further decrease. Therefore, by adopting a configuration in which the reflectance is increased as the recording layer 23 is located farther from the semiconductor laser, a decrease in the amount of light returning to the photodetector can be prevented.

(Reference Example 4)
An optical disk using a magneto-optical material utilizing a magneto-optical effect as a recording layer will be described below.

As shown in FIG. 11, when the light beam 8 irradiates the out-of-focus recording layer 10b, the light beam 8 incident on the out-of-focus recording layer 10b is polarized in the direction indicated by the arrow A. Then, the polarization direction of the transmitted light in the unrecorded portion 24 does not change and remains in the direction indicated by the arrow A, but the polarization direction rotates and changes in the direction indicated by the arrow B in the portion of the recording pit 13. The difference between the recording pit 13 and the unrecorded portion 24 is only this polarization direction, and since there is no difference between the amplitude and the phase of the light beam 8, no light diffraction occurs. Also, as for the reflected light, similarly to the above-mentioned transmitted light, only the change in the polarization direction of the recording pit 13 occurs, and no light diffraction occurs. The polarization directions of the transmitted light and the reflected light as a whole change, and this is determined by the area ratio between the recording pit 13 and the unrecorded portion 24 and the intensity distribution of the irradiation light. If the number of recording pits 13 on the out-of-focus recording layer 10b irradiated with the light beam 8 is sufficiently increased by increasing the stacking interval between the recording layers 10, the number is large as described above. Therefore, the influence of the recording pits 13 on the polarization direction of the entire light beam 8 is averaged, and in practice, this polarization direction may always be regarded as constant. Thus, the polarization direction of the entire light beam 8 is directed to a specific direction between the polarization direction of the recorded portion and the polarization direction of the unrecorded portion 24. Since the reproduction signal is determined by the change of the entire light beam 8, a constant change in the polarization direction of the entire light beam 8 only involves a DC component on the reproduction signal, and does not affect the reproduction signal. . As described above, in the case of the recording layer of the magneto-optical material, if the lamination interval of the recording layer 10 is made sufficiently large with respect to the wavelength or the recording pit size, there is no diffraction by transmission and reflection of the out-of-focus recording layer 10b. In addition, the influence of the non-recording / reproducing layer on the reproduction signal can be suppressed, and the recording / reproducing density can be improved.

(Reference Example 5)
Hereinafter, an optical disc having a configuration in which a multilayer recording layer and a conventional recording layer are mixed and laminated will be described.

As shown in FIG. 12, when the optical disc 26 is formed by adding a conventional recording layer 25 that generates higher-order transmitted light to the recording layer 10, higher-order transmitted light is usually generated in the recording layer 25 having the conventional configuration. This becomes an interference signal for the reproduced signal. Therefore, if the multi-layered recording layer 10 is provided on the light beam 8 incident side and the conventional recording layer 25 is provided on the light beam 8 transmitting side, the transmitted light of the conventional recording layer 25 has an adverse effect. Therefore, both can be used together. However, only one conventional recording layer 25 is used, and a phase-change recording layer utilizing a state change between amorphous and crystal is used.

(Reference Example 6)
Hereinafter, a method for manufacturing an optical disk will be described. As described with reference to FIGS. 1 and 2 of Reference Example 1, the optical disc 12 has a configuration in which the recording layers 10 and the transparent bodies 11 are alternately laminated, and the lamination interval L between the recording layers 10 is about 10 μm to several hundreds. It is desirable that the thickness of the transparent body 11 be made uniform since the thickness is relatively thin, such as about μm, and the lamination interval L is preferably as constant as possible. Therefore, as shown in FIG. 13, a spacer 28 whose thickness is strictly defined is inserted between the recording layers 27, and the thickness L of the spacer 28 defines the lamination interval L of the recording layer 27. After that, the optical disk 30 is prepared by a method of pouring and solidifying the transparent body 29. As shown in FIG. 14, the spacers 28 may be arranged concentrically or radially.

Further, in order to define the lamination interval L between the recording layers 27, after the liquid resin is dropped on the recording layer 27, the optical disk 30 is rotated to apply the resin uniformly and thinly, that is, by so-called spin coating. There is also a method of forming the transparent body 29.

(Reference Example 7)
Hereinafter, reproduction of a double-sided bonded optical disk will be described.

As shown in FIG. 18, a conventional double-sided lamination type optical disk 31 has two single-sided disks 31A and 31B, each having a recording layer formed on one side thereof, and having both recording layers facing each other. When reproducing the recording layer of the single-sided disk 31A, a light beam is irradiated from the single-sided disk 31A side when reproducing the recording layer of the single-sided disk 31A, and when reproducing the recording layer of the single-sided disk 31B, the light beam is reproduced when reproducing the recording layer of the single-sided disk 31B. Since it is necessary to irradiate from the 31B side, it is necessary to reverse the optical disc 31 after reproducing one recording layer and then reproducing the other recording layer. Therefore, in order to continuously reproduce the two-sided recording layer without manual intervention, a head moving means for providing the guide 33 and transferring the optical head 32 to both sides of the optical disk 31 has been used. Further, as shown in FIG. 19, a double-sided head unit having optical heads 34 provided on both sides of the optical disk 31 is used.

In the optical disk of the present embodiment 7, for example, as shown in FIG. 15, the recording layers 35A and 35B are provided with irregularities to form recording pits, bonded by the bonding material 36, and sandwiched by the transparent body 11, Since the recording layer 8A can be reproduced even if it passes through the recording layer 35A in the middle, the recording layer 35A and the recording layer 35B can be reproduced even if the light beam 8 is irradiated from above. Therefore, in the conventional optical disk, it is possible to reproduce the recording layers 35A and 35B on both sides without the necessary reversal of the optical disk, and the double-sided arrangement head means and the head moving means are unnecessary as in the conventional example.

Further, as shown in FIGS. 16A and 16B, a recording layer 38 having a two-layer structure and a recording layer 39 using a magneto-optical material are bonded with a bonding material 36, respectively. The sandwiched optical disk 40 and optical disk 41 can be played back in the same manner as the above-described optical disk 37, and the same effect can be obtained. Note that the refractive index of the transparent body 11 and the refractive index of the bonding material 36 are substantially equal to each other in order to prevent higher-order transmitted light.

As is apparent from the above description, the present invention calculates the product of the transmittance of the first layer and the transmittance of the second layer for a certain irradiation light intensity, and the transmittance of the first layer for another irradiation light intensity. And the transmittance of the second layer are made equal to each other, so that an optical disc having a plurality of stacked layers sandwiching a transparent body eliminates the generation of diffracted light other than the 0th order, and prevents the cross from other recording layers that are not reproduced from crossing. With a small amount of talk, it is possible to record / reproduce / delete the focused recording layer, suppress signal mixing due to the influence of interference light from the recording layer that is not the target of recording / reproduction, and achieve a large recording density that can provide a good reproduced signal. An improved and superior optical disk can be realized.

Schematic configuration diagram of the optical disc device of Reference Example 1. Explanatory diagram of light transmission and reflection in the recording layer of the optical disc device Illustration of diffraction by recording pits on the recording layer Schematic configuration diagram of an optical disc device provided with a beam conversion unit of the reference example Schematic configuration diagram of an optical disc device provided with an optical path length changing unit of the reference example Configuration diagram of main parts of another reference example of an optical disc device provided with the same optical path length changing means Schematic cross section of the configuration of the optical disc of Reference Example 2. 1 is a schematic cross-sectional view of a configuration of an optical disc according to a first embodiment of the present invention. 3 is a schematic sectional view of a configuration of an optical disc according to a third embodiment of the present invention. Explanatory drawing of light transmission and reflection in the recording layer of the optical disc according to the fourth embodiment of the present invention. Explanatory drawing of the polarization of the recording pit of the optical disk of Reference Example 4. Schematic cross-sectional view of the configuration of the optical disc of Reference Example 5 Sectional schematic view showing the arrangement state of the spacers in the method of manufacturing the optical disc of Reference Example 6. Sectional view of main part showing another arrangement state of the spacer Configuration schematic diagram of optical disk of Reference Example 7 Sectional schematic view of another optical disc of Reference Example 7 Schematic configuration diagram of a conventional optical disk device Configuration diagram of main parts of optical disk device used for conventional double-sided bonded optical disk Configuration diagram of main parts of another optical disk device used for the same optical disk

Explanation of reference numerals

1 semiconductor laser (light source)
4 Objective lens 9 Photodetector (detection means)
DESCRIPTION OF SYMBOLS 10, 19 Recording layer 11 Transparent body 12 Optical disk 14 Beam conversion means 15 Optical path length changing means 17 First layer 18 Second layer 20 Intermediate transparent body 28 Spacer

Claims (6)

For the irradiation light intensity A, the transmittance of the first and second layers becomes T1A and T2A, and for the irradiation light intensity B, the transmittance of the first and second layers becomes T1B and T2B. The recording layer composed of the first layer and the second layer is T1A × T2A = T1B × T2B
An optical disc characterized by satisfying the following conditions and being stacked in plural with a transparent body interposed therebetween. A recording layer composed of a first and second layer and an intermediate transparent body sandwiched between the first and second layers and a transparent body are alternately laminated. When the transmittance of the second layer becomes T1A and T2A and the transmittance of the first and second layers becomes T1B and T2B with respect to the irradiation light intensity B,
T1A × T2A = T1B × T2B
An optical disk characterized by satisfying the following conditions, wherein the intermediate transparent body and the transparent body have substantially the same refractive index, and the interval between the recording layers is at least 10 times the wavelength used. When the thicknesses of the first and second layers are H1 and H2, the first and second layers have a refractive index of N1A and N2A for the irradiation light intensity A, and the first and second layers have the first and second refractive indexes for the irradiation light intensity B. The recording layer composed of the first layer and the second layer in which the refractive index of the second layer is N1B and N2B is N1A × H1 + N2A × H2 = N1B × H1 + N2B × H2
An optical disc characterized by satisfying the following conditions and being stacked in plural with a transparent body interposed therebetween. With respect to the irradiation light intensity A, the reflectance at the interface between the first layer and the transparent body and the reflectance at the interface between the first layer and the second layer are compared. The refractive index of the first layer with respect to A and the refractive index of the second layer with respect to the irradiation light intensity B are substantially equal to the refractive index of the transparent body. 4. The optical disc according to claim 3, wherein the refractive index is equal to the refractive index. A recording layer composed of a first and second layer and an intermediate transparent body sandwiched between the first and second layers and a transparent body are alternately laminated, and the thickness of the first and second layers is H1, At H2, the refractive indices of the first and second layers are N1A and N2A for the irradiation light intensity A, and the refractive indices of the first and second layers are N1B and N2B for the irradiation light intensity B. When there is N1A × H1 + N2A × H2 = N1B × H1 + N2B × H2
An optical disc characterized by satisfying the following conditions, wherein the intermediate transparent body and the transparent body have substantially the same refractive index, and the interval between the recording layers is at least 10 times the used wavelength. Compare the reflectance at the interface between the first layer and the transparent body and the reflectance at the interface between the second layer and the intermediate transparent body with respect to the irradiation light intensity A. And the refractive index of the second layer with respect to the irradiation light intensity B is substantially equal to the refractive index of the transparent body and the intermediate transparent body, and when the latter is small, the refractive indices of the opposite layers are respectively set. 6. The optical disk according to claim 5, wherein a refractive index is equal to a refractive index of the transparent body and the intermediate transparent body.

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