JPH0778353A - Optical disk and optical disk device - Google Patents

Abstract

PURPOSE:To suppress mixing of a signal and to improve recording density by laminating alternately a recording layer and a transparent material plurally, and distributing a majority of energy to diffracted light beams of 0 order out of transmitted diffracted light beams by a recording pit on a recording layer. CONSTITUTION:An optical disk 12 is constituted so that plural recording layers 10 are laminated in a transparent body 11. That is, the plural recording layers 10 laminated and arranged with lamination interval being sufficiently long for a wavelength of an light beam 8. After the beam 8 is passed through several non-focus recording layers 10b out of the recording layers 10, it is made incident on a focus recording layer 10a to be recorded and reproduced. The disk 12 has constitution in which diffracted light beams of one order or more due to a recording pit are not generated when a light beam is passed through the recording layer 10, only diffracted light beams of 0 order are transmitted. Thereby, mixing by signals from the recording layer 10b, 10c and the like which are not object of recording and reproducing can be suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk device for optically recording or reproducing information on an optical disk as a recording medium.

[0002]

2. Description of the Related Art A conventional optical disk and optical disk device will be described below.

As shown in FIG. 17, the emitted light of the semiconductor laser 1 is converted by the diffraction grating 2 into 0th order light and ± 1st order diffracted light, which is then reflected by the beam splitter 3 and then by the objective lens 4. The light spot 7 is narrowed down on the recording layer 6 of No. 5 to form a light spot 7. Next, the light beam 8 reflected by the optical disk 5 passes through the objective lens 4, reaches the beam splitter 3, and the light beam 8 that passes through this enters the photodetector 9. From the four-divided photodetector 9a, a focus error signal is detected together with the reproduction signal by the astigmatism method. The tracking error signal is detected by the photodetectors 9b and 9c.
To detect the difference in light quantity of the ± 1st-order diffracted return light that is incident on 3
Obtained by the beam method. The reproduction signal is obtained as the sum of the amount of light received by the photodetector 9a divided into four. In such a conventional optical disc device, there is only one recording layer 6 per one side of the optical disc.

In recent years, attempts have been actively made to increase the density of optical disc devices, such as shortening the wavelength and narrowing the track. In addition to improving 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 recording layers by laminating the recording layers in the thickness direction. However, such a laminated structure is affected by reflected light and transmitted light of recording layers other than the reproduction recording layer, and due to this drawback, the laminated structure is not adopted. 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.

[0005]

If the recording layers 6 are stacked in the thickness direction of the optical disk 5 so as to increase the recording density as described above, the recording layer 6 is affected by the interference light from the recording layer 6 which does not record or reproduce. I had a problem.

The present invention solves the above-mentioned conventional problems, and suppresses signal mixing due to the influence of interference light from a recording layer that is not the target of recording / reproduction, and thus an optical disc and an optical disc apparatus having a significantly improved recording density. The purpose is to provide.

[0007]

In order to achieve this object, the present invention provides a light source, a recording layer and a transparent body which are alternately laminated, and which is the 0th order of the transmitted diffracted light by the recording pit on the recording layer. Equipped with an optical disc in which approximately energy is distributed to the folding light, an objective lens that converges a light beam from a light source onto the optical disc, and a detection unit that receives reflected light from the optical disc and detects information recorded on the optical disc. It is a thing.

[0008]

In this structure, it is possible to suppress signal mixing from the recording layer which is not the object of recording / reproducing, and it is possible to stack the recording layers, and the recording density is dramatically improved.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

In the embodiment of the present invention, the same parts as those described in the above-mentioned conventional example are designated by the same reference numerals, and the description thereof will be omitted.

(Embodiment 1) As shown in FIGS. 1 and 2, the feature of this embodiment is that the optical disk 5 described in the conventional example is laminated with a plurality of recording layers 10 sandwiched by a transparent body 11. The point is that the optical disk 12 is used. That is,
In the optical disc 12, a plurality of recording layers 10 are laminated and arranged at a laminating distance L sufficiently long with respect to the wavelength of the light beam 8. The light beam 8 passes through some of the non-focus recording layers 10b of the recording layers 10 and is then focused on the focused recording layer 10a to be recorded / reproduced. The light beam 8 reflected here is referred to as the outward path. It is configured to follow the reverse optical path, pass through the beam splitter 3, and enter the photodetector 9.
In the figure, 13 is a recording pit, and d is the 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 this embodiment, when the recording pit 1 is transmitted through the recording layer 10,
The diffracted light of the first and higher orders due to 3 is not generated, and the transmitted light beam 8 is almost only the 0th order diffracted light.
The 0th-order diffracted light referred to here means transmitted light that does not change its traveling direction due to diffraction during transmission. By doing so, the recording layer 1 that is not the target of recording and reproduction
It is possible to suppress signal mixing from 0b, 10c, etc., which will be described below. First, a description will be given of adverse effects when the transmitted light includes diffracted light of the first order or higher.
The problem is the influence of the diffracted light when passing through the non-focus recording layer 10b in front of the focus shown in FIG. 3 when the light beam 8 travels toward the optical disk 12.
Since the recording pit is on the track, it has the function of a diffraction grating with the track interval as the pitch. Therefore, as shown in FIG. 3, all the diffracted light is in the focused state on the focused recording layer 10a, a light spot 0s by the 0th order diffracted light, a light spot 1s by the 1st order diffracted light, and a light spot -1s by the -1st order diffracted light.
Etc., and the first or higher-order light spots 1s, −1s, etc. other than the light spot 0s irradiate the recording pits at positions unrelated to the recording pits to be recorded / reproduced. A part of this reflected light enters the photodetector 9 and is mixed with the signal. However, this signal includes a reproduction signal of a recording pit that should not be recorded / reproduced, and its output is better than the original reproduction signal. Since it is reproduced in a focused state, it becomes large so that it cannot be ignored. This is a state in which simultaneous reproduction is performed with multi-light spots such as 0s, 1s, and -1s, and a signal originally required is buried in the multi-spot reproduction signal, which is a problem. In this way, normal reproduction is impossible if there is a high-order diffracted light in the transmitted light, and in order to perform normal reproduction,
Strictly speaking, it is a necessary condition that transmitted light does not have high-order diffracted light. Actually, it is difficult to completely eliminate the high-order diffracted light, but it is desirable that the high-order diffracted light of 1st order or more is at least 10% or less with respect to the 0th order diffracted light.
If it is less than%, it can be said that there is practically no problem. Also, 1
It is also possible to create an optical disk of less than%.

Therefore, next, the presence or absence of other adverse effects will be described under the condition that the transmitted light does not include high-order diffracted light.

First, in the case of passing through the recording layer 10, neither the transmitted light in the forward path nor the transmitted light in the return path generate the diffracted light of the first order or more, and therefore, the information of the recording pits 13 of the recording layer 10 is multiplied. No recording pit 13 is the same, so there is no effect and there is no problem.

Next, the reflected light of 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 focused 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 the objective lens The total amount of light incident on the beam No. 4 decreases, and this decrease in the amount of light is detected to obtain a reproduction signal. Therefore, if the light amount variation occurs due to some cause other than the light amount variation described above, this becomes an interference signal. First, consider a disturbing signal due to the reflected light br reflected by the defocused recording layer 10b in the defocused state shown in FIG. 2A and traveling toward the objective lens 4.

Reflection diffraction occurs due to the recording pits 13 on the non-focus recording layer 10b, which causes fluctuations in the amount of light incident on the objective lens 4 and becomes an interference signal. However, FIG.
As schematically shown in (b), if the lamination interval L of the recording layers 10 is set sufficiently large with respect to the wavelength of the light beam 8 and the size of the recording pit 13, the light beam 8 is out of focus. When irradiating the recording layer 10b, the size of the light beam 8 becomes sufficiently larger than the size of the recording pits 13, and a large number of recording pits 13 in a wide range on the non-focus recording layer 10b are irradiated. Become. For this reason, even if the number of irradiated recording pits 13 varies to some extent, it is insignificant compared to the number of irradiated recording pits 13. Therefore, the number of irradiated recording pits 13 can be considered to be almost constant at all times. Therefore, the amount of the reflected light br reflected by the non-focused recording layer 10b entering the objective lens 4 is usually substantially uniform, and the influence on the detection signal is not so large substantially.

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 stacking interval L of the recording layers 10 is 10 μm, the non-focus recording layer 10b is irradiated. The diameter G of the light beam 8 to be generated becomes (Equation 1), and the recording pit 13 is formed in the circle of this diameter G.
Is about 44 pieces.

[0018]

[Equation 1]

Here, for example, if there is a change of one recording pit, 1/44 = 2.3 to the whole.
%, Which is not a serious problem for practical use. If the stacking interval L of the recording layer 10 is made larger than this, this value becomes smaller, and if the stacking interval L is 30 μm, 2.3 × (10/30) ² = 2.3 × 0.11 = 0. Two
It becomes 5%, and there is almost no problem.

The upper limit of the stacking interval L of the recording layer 10 is 0.8 mm because the effect of stacking is diminished if this is set too large.
The degree is the limit.

Next, the focusing recording layer 1 to be the original signal
The influence of multiple reflection light of the reflection light ar due to 0a will be described. As an example, the non-focus recording layer 10b and the focus recording layer 1
Consider the light beam am that is directed to the objective lens 4 after being reflected between 0a. The unfocused recording layer 10b is used as a light beam ar.
Is irradiated in a spread state, and then the focused recording layer 10a is irradiated in a further spread state, and therefore, averaging similar to that described above has no substantial effect. 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 non-focused recording layer 10c, and travels toward the objective lens 4.

As described above, if the transmitted light can be only the 0th order, the influence of the recording pits 13 on the non-focus recording layer 10b, which is not the target of the recording / reproduction of the light beam 8, can be substantially eliminated. It becomes possible, and 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, the wider the lamination interval L of the recording layers 10 is, the less signals are mixed from other recording layers 10, which is advantageous.
The depth d from the surface of No. 2 to the focused recording layer 10a changes depending on the difference of the focused recording layer 10. The objective lens 4 is designed in accordance with a predetermined thickness (about 1.2 mm) of the optical disk 12, and exhibits satisfactory performance at this thickness, but when the thickness changes, the light beam 8 is sufficiently narrowed. There is a problem that you can not put it. This is because the spherical aberration becomes large, and if the spherical aberration can be suppressed, it is possible to prevent deterioration of the focusing performance. Since the spherical aberration is mainly caused by the difference in the optical path length of the light beam passing through the central portion and the peripheral portion of the optical beam 8, the beam converting means 14 using a prism is provided as shown in FIG. 4, for example. Light beam 8
If, for example, is made into a ring shape and the light beam 8 is passed through only the peripheral portion, or if the amount of light in the peripheral portion is increased, the optical path length difference between the optical system composed of the objective lens 4 and the optical disk 12 in this ring area is It becomes significantly smaller and the narrowing 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.

As another method, as shown in FIG.
The optical path length changing means 15 can also be used. The optical path length changing means 15 is, for example, disposed between the objective lens 4 and the optical disk 12, and is constituted by two wedge-shaped glasses having the same refractive index with their slope sides facing each other, and one glass is provided along the slope. If the optical path length changing means 15 is moved, the thickness w
It is possible to correct the change of the depth d due to the change of the focus recording layer 10a, and it is possible to prevent the deterioration of the narrowing performance of the objective lens 4 because it can be changed.
Further, the optical path length changing means 15 may be disposed anywhere as long as the light beam 8 is a non-parallel portion, and is not limited to between the objective lens 4 and the optical disk 12, and for example, as shown in FIG.
As shown in FIG. 3, the emitted light of the semiconductor laser 1 is converted into a parallel or nearly parallel light beam 8 by using a collimator lens 16.
With respect to the optical system described above, the same effect can be obtained by disposing the optical path length changing means 15 between the semiconductor laser 1 and the collimator lens 16.

As described above, in this embodiment, the recording pit 13
By adopting a configuration in which there is no diffracted light of the first or higher order with respect to the transmitted light, it is possible to reduce the influence from the recording layer 10 other than the reproducing layer, and solve the problem of the laminated structure. A wavelength multiplexing method is a method for improving the recording density with a concept similar to that of the present embodiment. The wavelength division multiplexing method is that when a recording material formed of only one layer is overlaid with a number of different wavelengths and then recorded at different wavelengths, a reproduced signal can be obtained independently for each wavelength. Yes,
It is possible to increase the density for the number of wavelengths used, and as a recording material,
Methods such as organic hole dyeing and chemical hole burning are being studied. In addition, as a multiplex recording method, a method of recording / reproducing by changing the deflection direction of light has been proposed. In contrast to these methods, the present embodiment uses the multi-layer recording layer 10, and it is possible even if the wavelength of the light beam 8 is constant or the light deflection direction is constant, which is simple. The structure can improve the recording density.

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, an embodiment of the optical disk 12 which realizes this will be described.

(Embodiment 2) A read-only optical disc using a light absorber as a recording layer will be described below.

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 the refractive indexes of the transparent bodies 11 on both sides of the recording layer 10 are almost the same. Set to be equal. Recording pit 13
Is produced by giving unevenness to the recording layer 10. Thus, the transmitted light T of the recording pit 13 of the recording layer 10
Looking at the phase difference between P and the transmitted light TL in the portion where the recording pit 13 is not present, the two are the same in the comparison of the optical path lengths from the plane U1 to the plane U2, and therefore no phase difference occurs. Also, since the transmittance is constant, the amplitude of transmitted light is also constant. Diffraction of transmitted light occurs if either the amplitude or the phase of the light changes due to the transmission, but in this embodiment,
Since there is no change in both the transmitted light TP and TL, the light is not diffracted, and the transmitted light is only the 0th order diffracted light. Therefore, the transmitted light does not detect the presence or absence of the recording pit 13, and the recording pit 1
Similar to the lack of 3. 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 of the recording pit 13 and the reflected light RL of the portion without the recording pit 13, so that the phase changes, Diffracted light of
The recording pit information of this diffracted light is included, and the pit information can be obtained. As a method for producing the recording layer 10, a metal such as aluminum may be formed as a light absorber by vapor deposition, sputtering, or the like so as to have a film thickness capable of obtaining an appropriate transmittance.

(Embodiment 3) A read-only type optical disc using a dielectric as a recording layer will be described below.

As shown in FIG. 7, the recording layer 10 and the transparent body 1
At the interfaces S1 and S2 of No. 1, light is reflected due to the difference in refractive index. When the thickness a of the recording layer 10 is reduced to about the wavelength of light, the multiple interference effect of the reflected light at the interfaces s1 and s2 is utilized to make it relatively large due to the same principle as that of well-known antireflection films, multilayer filters, and the like. The reflectance can be obtained. Here, the condition is 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 part. The reflectance and the transmittance of the recording layer 10 using a dielectric material are related to the refractive indices on both sides of the interfaces S1 and S2. In this embodiment, the refractive index of the recording pit 13 and the portion without the recording pit 13 is Since it is the same, transmitted light TP and transmitted light TL
Has the same amplitude and phase, so recording pit 13
Diffraction due to is not generated, and the transmitted light can be only the 0th-order diffracted light as in the above-described second embodiment, and the same effect as in the second embodiment can be obtained. Further, regarding the reflected light, an optical path length difference due to the depth v of the recording pit 13 is generated as in the second embodiment,
The 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 as in the present embodiment, recording is performed. If the layer 10 and the transparent body 11 have different refractive indices, reflection occurs. Recording layer 10
The refractive index of the transparent body 11 increases as the refractive index of the transparent body 11 differs from that of the transparent body 11, and in the present embodiment, about 5% or more is desirable. To achieve this, the refractive index of the recording layer 10 is 1. It is preferably 1 time or more or 0.9 times or less. Examples of dielectrics satisfying this are TiO ₂ , ZnS, and Ce.
O ₂ , ZrO _{2 and the} like. In the above description, the recording layer 10 has one dielectric layer, but the same effect can be obtained even if the recording layer 10 has a plurality of layers, and the degree of freedom in design is further increased.

(Embodiment 4) A recording / erasing type optical disk will be described below.

As shown in FIG. 8A, the first layer 17 and the second layer 18 whose transmittance changes depending on the difference in irradiation light intensity.
The recording layer 19 in which the two layers are arranged close to each other is sandwiched between the transparent bodies 11. For the irradiation light intensity A, the transmittance of the first layer 17 is T1A and the transmittance of the second layer 18 is T2.
A, and for other irradiation light intensities B, the first layer 17
Of the optical disk having a transmittance of T1B and a transmittance of the second layer 18 of T2B.
When the portion indicated by Q is irradiated with the irradiation light intensity B, the transmittances of the first and second layers 17 and 18 in the portion P are T1A and T1.
2A, and the transmittances of the first and second layers 17 and 18 in the Q portion are T1B and T2B. Here, the interfaces S1 and S2
The reflectance for the light irradiation light intensities A and B at R1a and R2
a, R1b, R2b, for example, R1a> R2a, R1
If b <R2b, the reflection at the P portion is large at the interface S1 between the transparent body 11 and the first layer 17, and at the Q portion, the first reflection occurs.
It becomes larger at the interface S2 between the layer 17 and the second layer 18.
(Note that, in the drawing, the first layer 17 and the second layer 18 are compared and the one with the higher reflectance is shaded.) Reflected light R1
Regarding a and R2b, a step H1 of the reflecting surface corresponding to the thickness of the first layer 17 is generated in the P portion and the Q portion,
This has the same effect as the formation of the recording pit. Further, when the P portion is irradiated with the irradiation light intensity B,
Since the step H1 previously formed disappears, it is possible to erase the recording by changing the irradiation intensity.

On the other hand, regarding the transmitted light to this, P
The total transmittance of the recording layer 19 in the portions of and is TP,
If TL, TP = T1A × T2A TL = T1B × T2B Therefore, under the condition of T1A × T2A = T1B × T2B, no diffracted light other than the 0th order is generated,
Since the step H1 is not sensed by the transmitted light, there is almost no crosstalk from other recording layers that do not reproduce, and recording / reproduction / erasure of the focused recording layer becomes possible.

(Embodiment 5) A recording / erasing type optical disk using a dielectric as a recording layer will be described below.

The structure of this embodiment is the same as that of the embodiment 4 described with reference to FIG. 8A, and a dielectric is used for the recording layer, and the first layer 17 whose refractive index changes depending on the difference in irradiation light intensity. Second
The recording layer 19 in which the two layers 18 of 18 are disposed close to each other is sandwiched between the transparent bodies 11. For the irradiation light intensity A, the refractive index of the first layer 17 is N1A, and the refractive index of the second layer 18 is N2A. For the other irradiation light intensity B, the first layer 17, In the optical disc having a structure in which the refractive index of the second layer 18 is N1B and N2B, the P portion is irradiated with the irradiation light intensity A.
When the Q portion is irradiated with the irradiation light intensity B, the refractive index of the first and second layers 17 and 18 of the P portion becomes N1A and N2A, and the first and second layers 17 and 18 of the Q portion are The refractive indexes of 18 are N1B and N2B. Here, the reflectances of the interfaces S1 and S2 with respect to the light irradiation intensities A and B are R1a, R2a, and R1.
b and R2b are determined by the refractive index and the thickness on both sides of the interfaces S1, S2 and S3. R1a, R
The relationship between 2a, R1b, and R2b is R1a as in the fourth embodiment.
When> R2a and R1b <R2b, recording pits can be formed and recording / erasing can be performed with a pair of R1a and R2b.

Regarding the transmitted light, the transmitted light path lengths OPP and OPQ of the P portion and the Q portion are OPP = N1A × H1 + N2A × H2 OPQ = N1B × H1 + N2B × H2, so OPP = OPQ, that is, N1A × H1 + N2A × H2 = N1B × H1 + N2B ×
Under the condition indicated by H2, the optical path lengths of the transmitted light in the P portion and the Q portion of the recording layer 19 are equal, and therefore the difference in phase change between the two does not occur. For this reason, as in the case of the fourth embodiment, since the transmitted light does not sense the step between the interface S1 and the interface S2, there is no generation of diffracted light of ± 1st order or more caused by the recording pits formed here.

Further, the refractive index N2A at the irradiation light intensity A of the second layer 18 in the P portion and the refractive index N1B at the irradiation light intensity B of the first layer 17 in the Q portion are set to the transparent body 11. 8B, the interface S3 between the second layer 18 at the P portion and the transparent body 11 and the interface between the first layer 17 at the Q portion and the transparent body 11 as shown in FIG. 8B. Since S1 does not exist optically, the reflected light by the interface S3 of the transmitted light TP in the P portion and the reflected light R1b by the interface S1 in the Q portion disappear, so that the noise component due to this disappears and better reproduction is achieved. You can get a signal.

(Embodiment 6) A recording / erasing type optical disc having an intermediate transparent body disposed between recording layers will be described below.

In this embodiment, as shown in FIG. 9A, an intermediate transparent body 20 made of a transparent material is arranged between the first layer 17 and the second layer 18 of the construction of the above-mentioned fifth embodiment. The recording layer 21 is provided.

It is assumed that the transmittances of the first and second layers 17 and 18 are changed by the difference in the irradiation light intensity as in the case of Example 5,
It is assumed that there is no change in the optical characteristics of the intermediate transparent body 20. In this 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 is large at the interface S3 between the intermediate transparent body 20 and the second layer 18. To do. In this way, the recording pit with the step H3 can be formed. In this embodiment, by providing the intermediate transparent body 20, the depth of the recording pit and the first and second recording layers 17 and 18 are
Of the recording pits and the thickness of the first and second recording layers 17 and 18 can be set more freely. When the recording pit is formed using the difference in transmittance, the conditions for the transmittance of the first and second layers 17 and 18 are N1A × H1 + N2A × H2 = N1B × H1 + N2B ×
It becomes H2. The condition for forming the first and second layers 17 and 18 using a dielectric material is OPP = OPQ described above. In addition, as in Example 5 described in FIG. 8B, the refractive index N2A of the second layer 18 in the P portion and the refractive index N1B of the first layer 17 in the Q portion are set to the transparent body 11 and the intermediate portion. If it is made equal to the refractive index of the transparent body 20, as shown in FIG. 9B, the interface between the second layer 18 in the P portion and the transparent body 11 and the intermediate transparent body 20, and the first portion in the Q portion. Since the interface between the layer 17 and the transparent body 11 and the intermediate transparent body 20 is optically eliminated, the reflected light at this portion disappears and a better reproduced signal can be obtained.

(Embodiment 7) An optical disk having recording layers having different reflectances will be described below.

As shown in FIG. 10, it is assumed that the light beam 8 is incident on the optical disc 22 from below, and the first recording layer 23a is arranged on the recording layer 23 in order from the incident side of the light beam 8.
If the second recording layer 23b and the third recording layer 23c are used, the irradiation light amount t1 to the second recording layer 23b is reduced by the reflected light amount R1 and the absorbed light amount at the first recording layer 23a. The amount R2 of reflected light at 23b is also reduced by this amount, and the amount of light returning to the photodetector is also reduced. Similarly, the amount t2 of irradiation light and the amount R3 of reflected light to the third recording layer 23c also decrease, and the amount of decrease increases as the number of recording layers 23 increases. In addition, since the amount of light also decreases due to the transmission of the other recording layer 23 in the process of returning to the photodetector after being reflected from the recording layer 23, the amount of light returning to the photodetector increases as the recording layer 23 is farther from the semiconductor laser. It will be further reduced. Therefore, by decreasing the reflectance of the recording layer 23 at a position farther from the semiconductor laser, the amount of light returning to the photodetector can be prevented from decreasing.

(Embodiment 8) An optical disk using a magneto-optical material utilizing the magneto-optical effect as a recording layer will be described below.

As shown in FIG. 11, when the light beam 8 irradiates the unfocused recording layer 10b, the light beam 8 incident on the unfocused recording layer 10b is polarized in the direction indicated by the arrow A. If so, the polarization direction of the transmitted light of the unrecorded portion 24 does not change and remains in the direction indicated by the arrow A, but the polarization direction of the recording pit 13 is rotationally changed in the direction indicated by the arrow B. . The only difference between the recording pit 13 and the unrecorded portion 24 is this polarization direction.
Since there is no difference in amplitude and phase between the two, light diffraction does not occur. Further, as for the reflected light, only the change in the polarization direction of the recording pit 13 is caused as in the case of the transmitted light, and the light is not diffracted. The polarization directions of the transmitted light and the reflected light are changed as a whole, and this is determined by the area ratio of the recording pit 13 and the unrecorded portion 24 and the intensity distribution of the irradiation light. Here, if the number of recording pits 13 on the non-focus recording layer 10b irradiated with the light beam 8 is made sufficiently large by increasing the stacking interval between the recording layers 10, as described above, the number is large. 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 can be regarded as always constant. Thus, the polarization direction of the entire light beam 8 is the same as the polarization direction of the recorded portion and the unrecorded portion 24.
Will be oriented in a certain direction between the polarization directions of. Since the reproduction signal is determined by the change in the entire light beam 8, a constant change in the polarization direction of the entire light beam 8 causes a DC change in the reproduction signal.
Since only the component is added, it does not affect the reproduced signal and is not a problem. As described above, in the case of the recording layer made of the magneto-optical material, the non-focus recording layer 10b can be obtained by setting the lamination interval of the recording layers 10 sufficiently large with respect to the wavelength or the recording pit size.
Since there is no diffraction due to transmission or reflection, the influence of the non-recording / reproducing layer on the reproduction signal can be suppressed and the recording / reproducing density can be improved.

(Embodiment 9) An optical disc having a structure in which multiple recording layers and conventional recording layers are mixed and laminated will be described below.

As shown in FIG. 12, when an optical disk 26 is formed by adding a conventional recording layer 25 for generating high-order transmitted light to the recording layer 10, a high-order transmitted light is normally generated in the recording layer 25 having the conventional structure. Occurs, which becomes an interfering signal with respect to the reproduced signal. Therefore, the multilayer recording layer 1 is provided on the incident side of the light beam 8.
0 is provided, and the conventional recording layer 25 is provided on the transmission side of the light beam 8.
By disposing the above, since the transmitted light of the conventional recording layer 25 does not have an adverse effect, both can be used together. However, only one conventional recording layer 25 is used,
A phase change recording layer or the like that utilizes the state change between amorphous and crystal is used.

(Embodiment 10) An optical disk manufacturing method will be described below. As described in FIGS. 1 and 2 of the above-described embodiment, the optical disc 12 includes the recording layer 10 and the transparent body 1.
In the configuration in which the recording layers 10 are alternately laminated, the lamination interval L between the recording layers 10 is relatively thin, about 10 μm to several hundreds μm, and the lamination interval L is preferably as constant as possible. It is important to make the thickness of the transparent body 11 uniform. Therefore, as shown in FIG. 13, a spacer 28 having a strictly defined thickness is sandwiched between the recording layers 27, and the stacking interval L of the recording layers 27 is defined by the thickness of the spacer 28. Then, the optical disk 30 is prepared by a method of pouring the transparent body 29 and hardening it. Note that FIG.
There is also a method of arranging the spacers 28 concentrically or radially as shown in FIG.

In order to define the stacking interval L between the recording layers 27, after the liquid resin is dropped on the recording layer 27, the optical disc 30 is rotated to apply the resin uniformly and thinly. There is also a method of forming the transparent body 29 by spin coating.

(Embodiment 11) The reproduction of a double-sided bonded type optical disc will be described below.

As shown in FIG. 18, the conventional double-sided bonding type optical disc 31 includes two single-sided discs 31A and 31A.
The optical disc 3 has a structure in which recording layers are formed on one side of B, and two recording layers are laminated by facing both recording layers.
In the reproduction of No. 1, the light beam must be emitted from the single-sided disc 31A side when reproducing the recording layer of the single-sided disc 31A, and the light beam must be emitted from the single-sided disc 31B side when reproducing the recording layer of the single-sided disc 31B. Therefore, it is necessary to invert the optical disc 31 to reproduce the other recording layer after reproducing the one recording layer. Therefore, in order to continuously reproduce the double-sided recording layer without human intervention, the guide 33 is provided and the optical disc 31 is provided.
Head moving means for moving the optical head 32 to both sides of the above was used. Further, as shown in FIG. 19, a double-sided arrangement head means in which optical heads 34 are provided on both sides of the optical disc 31 is used.

As shown in FIG. 15, the optical disc 37 of the present embodiment, for example, an optical disc 37 in which recording layers 35A and 35B are provided with irregularities to form recording pits, which are bonded by a bonding material 36 and sandwiched by the transparent body 11, The recording layer 3 where the light beam 8 is in the middle
Even if it passes through 5A, it can be reproduced, so
The recording layer 35A and the recording layer 35B can be reproduced by irradiating. Therefore, in the conventional optical disc,
Recording layers 35 on both sides without reversing the required optical disk
It becomes possible to reproduce A and 35B, and the double-sided arrangement head means and head moving means are not required unlike the conventional example.

As shown in FIGS. 16 (a) and 16 (b), a recording layer 38 having a two-layer structure and a recording layer 39 made of a magneto-optical material are adhered with a bonding material 36, respectively, and are transparent. The optical disc 40 and the optical disc 41 sandwiched by the body 11 can be reproduced in the same manner as the optical disc 37 described above, and the same effect can be obtained. The transparent body 11 and the bonding material 36 have substantially the same refractive index in order to prevent higher-order transmitted light.

[0053]

As is apparent from the above description, the present invention generally uses a light source, a recording layer and a transparent body alternately laminated, and is generally a 0th-order diffracted light among the transmitted diffracted light by the recording pits on the recording layer. Of the optical disc, the objective lens that converges the light beam from the light source onto the optical disc, and the detection means that receives the reflected light from the optical disc and detects the information recorded on the optical disc. It is possible to realize an excellent optical disc and optical disc device in which signals are prevented from being mixed due to the influence of interference light from a recording layer that is not a target of recording / reproduction and a large recording density is improved.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an optical disk device according to a first embodiment of the present invention.

FIG. 2 shows transmission of light through a recording layer of the optical disc device,
Illustration of reflection

FIG. 3 is an explanatory diagram of diffraction by recording pits on the recording layer.

FIG. 4 is a schematic configuration diagram of an optical disk device provided with a beam converting means of the embodiment.

FIG. 5 is a schematic configuration diagram of an optical disk device provided with an optical path length changing unit of the same embodiment.

FIG. 6 is a configuration diagram of a main part of another embodiment of an optical disc device provided with the optical path length changing means.

FIG. 7 is a schematic sectional view of the configuration of an optical disc according to a second embodiment of the present invention.

FIG. 8 is a schematic sectional view showing the configuration of an optical disc according to Example 4 of the present invention.

FIG. 9 is a schematic sectional view showing the configuration of an optical disc according to Example 6 of the present invention.

FIG. 10 is an explanatory diagram of light transmission and reflection in the recording layer of the optical disc of Example 7 of the present invention.

FIG. 11 is an explanatory diagram of polarization of recording pits of the optical disc of Example 8 of the present invention.

FIG. 12 is a schematic sectional view showing the configuration of an optical disc according to Example 9 of the present invention.

FIG. 13 is a schematic cross-sectional view showing the arrangement state of spacers in the optical disc manufacturing method according to example 10 of the present invention.

FIG. 14 is a sectional view of an essential part showing another arrangement state of the spacer.

FIG. 15 is a schematic sectional view showing the structure of an optical disc according to Example 11 of the present invention.

FIG. 16 is a schematic sectional view of another optical disc in the same example.

FIG. 17 is a schematic configuration diagram of a conventional optical disc device.

FIG. 18 is a configuration diagram of main parts of a conventional optical disk device used for a double-sided bonded optical disk.

FIG. 19 is a configuration diagram of a main part of another optical disk device used for the optical disk.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 semiconductor laser (light source) 4 objective lens 9 photodetector (detection means) 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

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kenichi Nishiuchi, 1006, Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (25)

[Claims] 1. A 0-th order diffracted light of a transmitted diffracted light by a recording pit of the recording layer recorded by the amplitude or phase change of light, having a plurality of recording layers in which recording layers and transparent bodies are alternately arranged. An optical disc characterized in that almost all energy is distributed. 2. The optical disc according to claim 1, wherein the recording layer located farther from the incident direction of the light beam irradiating the optical disc has a higher reflectance. 3. The optical disk according to claim 1, further comprising a spacer that defines a mutual distance between the recording layers. 4. The optical disc according to claim 1, further comprising a recording layer having a high-order diffracted light by recording pits at a position farthest from the incident direction of the light beam for irradiating the optical disc. 5. The optical disc according to claim 4, wherein the recording layer on which the high-order diffracted light due to the recording pit is present is a phase change recording layer. 6. A recording layer made of a magneto-optical material and a transparent body having a substantially uniform refractive index are alternately laminated, and the distance between the recording layers is 10 times or more the wavelength used. Optical disc. 7. A recording pit is formed by providing projections and depressions, and a recording layer and a transparent body in which the transmittance of the recording pit portion and the portion without the recording pit are substantially equal are alternately laminated, and the recording layer is formed. An optical disk characterized in that the transparent bodies on both sides of the sandwich are made substantially equal in refractive index, and the distance between the recording layers is 10 times or more the wavelength used. 8. The optical disc according to claim 7, further comprising a recording layer formed of a light absorber having a constant transmittance. 9. The optical disk according to claim 7, further comprising a recording layer formed of a dielectric having a refractive index different from that of the transparent body. 10. The refractive index of the recording layer is 0.
The optical disc according to claim 9, which is 9 times or less or 1.1 times or more. 11. The optical disc according to claim 9, further comprising a recording layer formed by laminating a plurality of dielectrics. 12. The transmittances of the first and second layers are T1A and T2A for the irradiation light intensity A, and the transmittances of the first and second layers are T1B for the irradiation light intensity B. , The recording layer composed of the first layer and the second layer of T2B satisfy the condition of T1A × T2A = T1B × T2B, and a plurality of layers are laminated with a transparent body sandwiched between them. Is an optical disc having a wavelength of 10 times or more. 13. A recording layer composed of first and second layers and an intermediate transparent body sandwiched between the first and second layers, and a transparent body are alternately laminated to obtain an irradiation light intensity A. When the transmittances of the first and second layers are T1A and T2A and the transmittances of the first and second layers are T1B and T2B for the irradiation light intensity B, T1A × T2A = T1B × An optical disk characterized in that the condition of T2B is satisfied, the refractive indexes of the intermediate transparent body and the transparent body are substantially equal to each other, and the distance between recording layers is 10 times or more the wavelength used. 14. The thickness of the first and second layers is H1 and H2, and the refractive index of the first and second layers is N1 with respect to the irradiation light intensity A.
A, N2A, and the first and second with respect to the irradiation light intensity B
The recording layer composed of the first layer and the second layer having the refractive indices of N1B and N2B is N1A × H1 + N2A × H2 = N1B × H1 + N2B ×
An optical disc, wherein a plurality of layers satisfying the condition of H2, are laminated with a transparent body sandwiched therebetween, and the distance between recording layers is 10 times or more the wavelength used. 15. Compared with 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, and the former is smaller. When the latter 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. The optical disk according to claim 14, wherein the index is equal to the refractive index of the transparent body. 16. A recording layer and a transparent body composed of first and second layers and an intermediate transparent body sandwiched between the first and second layers are alternately laminated to form first and second layers. Thickness is H1, H2
With respect to the irradiation light intensity A, the refractive indices of the first and second layers are N1A and N2A, and with respect to the irradiation light intensity B, the refractive indices of the first and second layers are N1B and N2B. When N1A × H1 + N2A × H2 = N1B × H1 + N2B ×
An optical disk, wherein the condition of H2 is satisfied, the refractive indices of the intermediate transparent body and the transparent body are substantially equal to each other, and the distance between the recording layers is 10 times or more the used wavelength. 17. When the former is small, the reflectance of the interface between the first layer and the transparent body and the reflectance of the interface between the second layer and the intermediate transparent body are compared with respect to the irradiation light intensity A. Makes the refractive index of the first layer for the irradiation light intensity A and the refractive index of the second layer for the irradiation light intensity B substantially equal to the refractive indexes of the transparent body and the intermediate transparent body, and when the latter is small, respectively. The optical disk according to claim 16, wherein the refractive index of the opposite layer is equal to the refractive index of the transparent body and the intermediate transparent body. 18. A light source, a recording layer and a transparent body are alternately laminated, and the 0th time of the transmitted diffraction light by the recording pit on the recording layer recorded by the change of the amplitude or phase of the light beam from the light source. An optical disc in which approximately energy is distributed to the folding light, an objective lens that converges a light beam from the light source onto the optical disc, and reflected light from the optical disc is received to detect information recorded on the optical disc. An optical disc device comprising: 19. A light source, an optical disc in which recording layers and transparent bodies are alternately laminated, an objective lens for converging a light beam from the light source onto the optical disc, and an optical path for changing a transmission optical path length of the light beam. A length changing means and a detecting means for receiving reflected light from the optical disc to detect information recorded on the optical disc, wherein the optical path length changing means is arranged in a non-parallel portion of the light beam. Characteristic optical disk device. 20. The optical disk device according to claim 19, wherein the optical path length changing means is arranged between the objective lens and the optical disk. 21. An optical path length changing structure in which two wedge-shaped transparent bodies are arranged so as to face each other with their slopes facing in opposite directions, and the transmission optical path length of a light beam is changed by shifting their positions. 20. The optical disk device according to claim 19, further comprising means. 22. A light source, an optical disk in which recording layers and transparent bodies are alternately laminated, beam conversion means for converting a light beam from the light source into a ring-shaped light beam, and the light beam on the optical disk. An optical disc apparatus comprising: an objective lens that converges to an optical disc; and a detection unit that receives reflected light from the optical disc and detects information recorded on the optical disc. 23. Two discs are bonded with a bonding material by forming a recording pit by providing unevenness on the light source and the recording layer, and making the transmittances of the recording pit portion and the portion without the recording pit of the recording layer approximately equal. Then, a double-sided bonding type optical disc having a structure in which the refractive index of the disc and the bonding material are substantially equal to each other, an objective lens for converging a light beam from the light source onto the optical disc, and a reflected light from the optical disc are received. do it,
An optical disk device comprising a detection means for detecting information recorded on the optical disk, and reproducing the two recording layers of the optical disk by irradiating a light beam in only one direction without inverting the optical disk. 24. An optical disk device according to claim 23, comprising the optical disk according to any one of claims 12, 13, 14, and 16. 25. The optical disk device according to claim 23, further comprising an optical disk using a magneto-optical material as a recording layer.