JP2004079101A - Optical recording and reproducing medium, and recording and reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical recording and reproducing medium and a recording and reproducing device for easily identifying each multilayered recording and reproducing layer. <P>SOLUTION: This optical recording and reproducing medium 10 is formed by laminating many optical recording and reproducing layers 12 on a substrate 11. Members 13 for layer identification are respectively and adjacently arranged on the respective optical recording and reproducing layers 12. A pair of electrodes 14 and 15 is arranged so as to insert each member13 for layer identification between them. An intermediate layer 16 is provided to separate respective laminated layers. The member 13 for layer identification is formed by sealing, for example, cholesteric liquid crystal with a thin plate-shaped transparent hollow member and arranged adjacently to or at a fixed distance from the optical recording and reproducing layers 12 to detect the member 13 for layer identification, thereby being able to identify the optical recording and reproducing layer 12 and to focus a focused luminous flux. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical recording / reproducing medium in which optical recording / reproducing layers are stacked in multiple layers, and a recording / reproducing apparatus for performing optical recording or reproduction on such a medium.
[0002]
[Prior art]
Reflecting the recent information society, the capacity of optical recording / reproducing media for optical recording and reproduction has been increased.
[0003]
In order to increase the capacity of an optical recording / reproducing medium, there is a method of laminating optical recording / reproducing layers to form a multilayer optical recording / reproducing medium. By laminating the optical recording / reproducing layers, the recording capacity of the optical recording / reproducing medium can be increased without increasing the recording capacity of each optical recording / reproducing layer.
[0004]
For example, a so-called photorefractive material which spatially selectively changes in refractive index by two-photon absorption is used as a medium, and fluorescence emission generated in a refractive index change portion by irradiation of a reproducing light beam is detected to perform three-dimensional optical recording. A method for realizing reproduction has been proposed.
[0005]
Alternatively, by stacking non-linear optical materials with high transmittance at the wavelength of the light source to be used for the medium and detecting the optical non-linear phenomenon that appears in any medium by the converged light flux, multiple media layers are realized. A way to do that has been proposed.
[0006]
Incidentally, in order to perform optical recording and reproduction using a multilayer optical recording and reproducing medium, it is necessary to identify an optical recording and reproducing layer related to recording or reproduction. For example, in a DVD having two recording / reproducing layers, the transmittance is allocated to the recording / reproducing layers so that light is reflected from each recording / reproducing layer. As a result, a so-called focus error signal based on the reflected light can be generated for each of the plurality of recording / reproducing layers, and the recording / reproducing layers are identified.
[0007]
[Problems to be solved by the invention]
However, in such a method of distributing the transmittance, when the number of recording / reproducing layers to be stacked increases, it is necessary to greatly reduce the light use efficiency in order to keep the intensity of light reaching each layer constant. In addition, adverse effects are caused by mutual interference of light between the recording and reproducing layers. For this reason, there is a limit to the increase in the number of recording / reproducing layers using transmittance distribution.
[0008]
The present invention has been made in view of such circumstances, and an object of the present invention is to provide an optical recording / reproducing medium and a recording / reproducing apparatus which can easily identify each of the multi-layered recording / reproducing layers.
[0009]
[Means for Solving the Problems]
(1) In order to solve the above-mentioned problems, an optical recording / reproducing medium according to a main aspect of the present invention includes at least two or more optical recording / reproducing layers and adjacent or predetermined distances from each of the optical recording / reproducing layers. And a layer identification member that selectively increases reflectance at a specific light wavelength.
[0010]
In the present invention, since the layer identifying member having a selectively high reflectance at a specific light wavelength is arranged adjacent to or separated from each optical recording / reproducing layer by a predetermined distance, each of the multi-layered recording / reproducing layers is used. Can be easily identified. For example, a focusing error signal can be detected in a state of high reflectance by focusing on a layer identification member corresponding to an optical recording / reproducing layer to be focused. Therefore, a stable focus error signal can be obtained. Then, for example, by adding or subtracting a constant bias signal, a recording or reproducing light beam can be accurately converged on the corresponding optical recording / reproducing layer.
[0011]
A cholesteric liquid crystal can be cited as an example of a layer identifying member having a high reflectance for a specific light wavelength. In the case of cholesteric liquid crystal, a pair of conductive materials (electrodes) are arranged so as to sandwich the layer identifying member, and the optical characteristics of the cholesteric liquid crystal are changed by applying or removing an electric field to these electrodes. In addition, an arbitrary layer identification member is made to exhibit light reflection characteristics different from those of the other layer identification members, thereby making it possible to specify an arbitrary layer identification member.
[0012]
Here, the cholesteric liquid crystal has a phase state in which a planar phase, a focal conic phase, and a homeotropic phase are reversibly changeable, and among these, the planar phase selectively shows high reflectance in a specific light wavelength region. The light wavelength region exhibiting the high reflectance can be easily set by controlling the pitch in the helical structure of the cholesteric liquid crystal.
[0013]
The change in state between the planar phase showing wavelength selective reflection and the homeotropic phase showing total transmission can be controlled by an applied electric field, and is applied to recording or reproduction by applying an electric field to a layer identification member other than the layer related to recording or reproduction. The layer to be identified can be specified by relatively increasing the reflectance of the layer on the layer identifying member and detecting the light reflected from this member.
[0014]
In that case, it is preferable that at least one of the conductive materials is arranged at a position corresponding to the recording / reproducing line in the optical recording / reproducing layer.
[0015]
Here, the recording / reproducing line is, for example, a groove or track spirally formed on a plane of a circular medium.
[0016]
Thereby, it is possible to cause a distribution of the reflected light intensity on the layer identification member, and it is also possible to obtain relative position information on the layer identification member by detecting this distribution. This information is, for example, a so-called pre-groove signal which is required as a position control signal of a signal sequence in a signal recording process, or an arbitrary positional relationship with the position of the reproduced signal is given to a partial arrangement of the electrodes to form the reproduced signal sequence. The position control signal may be used as a so-called tracking error signal.
[0017]
A means for constantly applying an electric field to the layer identification member may be provided.
[0018]
The relationship between the application of the electric field and the phase change can be reversed by providing a bias electric field which is always applied in the opposite direction to the electric field.
[0019]
In a preferred embodiment, the optical recording / reproducing layer is made of a member that generates light having different wavelengths when irradiated with recording / reproducing light.
[0020]
By selectively reflecting unnecessary fundamental wave light included in the reproduced signal light whose wavelength has changed and transmitting and detecting the reproduced signal light, a so-called optical filter that separates and removes the unnecessary fundamental light can be provided. . Of course, it is also possible to selectively reflect the reproduction signal light having the wavelength changed and transmitting the fundamental wave light to separate and remove the unnecessary fundamental light.
[0021]
Here, as an optical signal reproducing method whose wavelength changes in a recording / reproducing medium, for example, fluorescence detection for a fundamental wave light in an optical memory using two-photon absorption or fundamental light in a nonlinear optical memory using a nonlinear optical effect is used. And harmonic light detection.
(2) A recording / reproducing apparatus according to another aspect of the present invention includes at least two or more optical recording / reproducing layers, and is disposed adjacent to or at a predetermined distance from each of the optical recording / reproducing layers, and includes a cholesteric liquid crystal. A stage on which an optical recording / reproducing medium including a layer identification member and a pair of conductive materials arranged to sandwich each of the layer identification members is mounted, and each of the pair of conductive members It is characterized by comprising means for selectively applying a potential difference between materials, and means for converging a recording or reproducing light beam on the optical recording / reproducing layer.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Optical recording / reproducing medium)
FIG. 1 is a sectional view showing a configuration of an optical recording / reproducing medium according to one embodiment of the present invention.
[0023]
As shown in FIG. 1, an optical recording / reproducing medium 10 is configured by laminating a number of optical recording / reproducing layers 12 on a substrate 11. Each of the optical recording / reproducing layers 12 is provided with a layer identifying member 13 adjacent thereto. Further, a pair of electrodes 14 and 15 are arranged so as to sandwich each layer identification member 13. An intermediate layer 16 is provided to separate the stacked layers from each other.
[0024]
The number of layers of the optical recording / reproducing medium 10, the presence or absence of the substrate 11, and the thickness of the intermediate layer 16 can be arbitrarily set.
[0025]
The optical recording / reproducing layer 12 is made of, for example, a nonlinear optical crystal thin plate or a thin film of a non-linear optical material such as lithium niobate (LiNbO ₃ ), lithium iodate (LiIO ₃ ), KTP (KTiOPO ₄ ), or a methaocyanine complex salt, nitroaniline. Or thin films of organic nonlinear optical materials such as organic / nitropyridine-based organic crystals, polymers of azo dyes and polymers, or thin films or thin films of non-linear optical liquid crystal polymers with chirality (handiness). Can be It is also possible to use a thin plate or a thin film of a photorefractive optical crystal such as silica glass or lithium niobate (LiNbO ₃ ) as a photorefractive material, or a thin plate or a thin film of a photorefractive polymer. The material is not limited to these as long as it is in line with the material.
[0026]
For the substrate 11 and the intermediate layer 16, for example, an optical resin such as PMMA (polymethyl methacrylate) or PC (polycarbonate) can be used, provided that it is transparent at the wavelength of the luminous flux used in the application of the present invention. It is not limited to these.
[0027]
The layer discriminating member 13 is formed, for example, of a cholesteric liquid crystal sealed in a thin transparent hollow member. The layer discriminating member 13 is disposed adjacent to or separated from the optical recording / reproducing layer 12 by a certain distance. The detection of 13 enables identification of the optical recording / reproducing layer 12 and focusing of the convergent light beam on the layer.
(Phase change of cholesteric liquid crystal)
FIG. 2 is a diagram for explaining a phase change of the cholesteric liquid crystal.
[0028]
In the cholesteric liquid crystal, when no electric field E is applied, as shown in FIG. 2A, the cholesteric liquid crystal selectively reflects a circularly polarized light component having a wavelength corresponding to the helical structure of constituent molecules in a planar phase.
[0029]
By applying a weak electric field E ₁ in this state with a part of the light becomes a state of focal conic texture disappears wavelength selective reflection of what scattered as shown in FIG. 2 (b), after removal of the electric field molecular orientation That is, the phase state is maintained. Higher by the electric field E ₂ is applied FIG. 2 (c) in no wavelength-selective reflective similarly focal conic texture ready homeotropic phase as shown, the scattered light is reduced to further high transmittance. When the electric field is removed from this state, the state changes to the planar state. Therefore, it is possible to reversibly change the states of the cholesteric liquid crystal to the planar phase and homeotropic phase by applying or removing the electric field E _2, optionally wavelengths by layers identification member 13 is removed and the application of the electric field An optical switch function of transmitting or reflecting light can be realized.
[0030]
In addition to the means for applying an electric field, for example, a ferroelectric thin film in which an electric field in the direction opposite to the electric field application direction is disposed adjacently and a bias electric field is applied to the phase discriminating member 13 in advance It is also possible to reverse the relationship between the application of an electric field to the cholesteric liquid crystal and the change in phase state. In other words, the cholesteric liquid crystal becomes a homeotropic phase and is in a light transmitting state due to the presence of the bias electric field.However, when an electric field is applied against the bias electric field, the electric field applied to the cholesteric liquid crystal is removed, and the cholesteric liquid crystal is changed to a planar phase to select a wavelength. Can be in a reflective state.
(Configuration of electrode)
The electrodes 14 and 15 can use the luminous flux efficiently by using a transparent electrode such as ITO (Indium Tin Oxide) or ZnO (zinc oxide). Further, it may be provided on the entire area of the opposing surface of the layer identification member 13 on which the electrodes are provided, or may be provided on any part of the surface.
[0031]
FIG. 3 is a plan view showing an example in which the electrode 14 is arranged at a position corresponding to the recording / reproducing line in the optical recording / reproducing layer 12. A recording / reproducing line in the optical recording / reproducing layer 12 is, for example, a groove or a track spirally formed on the plane of the circular medium 10. As shown in FIG. Have been.
[0032]
Thus, a distribution of the reflected light intensity can be generated in the layer identification member 13, and relative position information in the layer identification member 13 can be obtained by detecting this distribution. This information is, for example, a so-called pre-groove signal which is required as a position control signal of a signal sequence in a signal recording process, or by giving an arbitrary positional relationship with a position of a reproduction signal to a partial arrangement of the electrodes to form a reproduction signal sequence. The position control signal may be used as a so-called tracking error signal.
[0033]
In this case, as shown in FIG. 4, it is preferable to provide a bias electric field layer 17 for constantly applying a bias electric field so as to be adjacent to the layer discriminating member 13. By changing the state to the planar phase, wavelength selective reflection occurs, and only the formation portion of the electrode 14 is identified. For example, by arbitrarily setting the position of the recording or reproduction signal line and the position of the electrode formation portion, the signal line can be used. Alignment of the converging spot of the luminous flux can be realized.
[0034]
Note that it is possible in principle to use the arrangement of the electrodes directly as the recording / reproducing signal instead of the optical recording / reproducing layer 12.
(Principle of layer identification)
5 and 6 are schematic diagrams illustrating the principle of layer identification according to the present invention. FIG. 5 shows a state where no layer identification has been performed, and FIG. 6 shows a state where layer identification has been performed.
[0035]
Here, the electrodes 14 and 15 of the laminated optical recording / reproducing medium 10 are applied with a power source 21 and an electric path switch 22 for selectively applying an electric field to the layer identification member 13 of each layer. It can be applied and removed.
[0036]
In the state of FIG. 5, since an electric field is applied to all the layers, the cholesteric liquid crystal, which is the layer identifying member 13 of each layer, has a homeotropic phase, and the incident light 23 to the optical recording / reproducing medium 10 remains unchanged. pass.
[0037]
In the state shown in FIG. 6, since the electric field is removed from any one of the layers, the cholesteric liquid crystal, which is the layer identifying member 13 of the layer from which the electric field has been removed, has a planar phase, and the wavelength of the incident light is selectively reflected by the cholesteric liquid crystal. When it is equal to the wavelength, the light is reflected as reflected light 24.
(Recording / reproducing device)
FIG. 7 is a schematic diagram showing a configuration of a recording / reproducing apparatus according to one embodiment of the present invention.
[0038]
As shown in FIG. 7, on the stage 43, the optical recording / reproducing medium 10 having the above configuration is mounted.
[0039]
Here, the light beam emitted from the light source 31 is condensed inside the optical recording / reproducing medium 10 via a collimator lens 32, an optical path branching component 36, and a condenser lens 33. Any one layer of the optical recording / reproducing medium has a planar phase in which the cholesteric liquid crystal of the layer identifying member 13 is selectively reflected with respect to the wavelength of the light flux from the light source. The reflected light flux 24 is reflected by the layer identification member 13, passes through the condenser lens 33, is reflected by the optical path branching component 36, and reaches the condenser lens 40 of the focus detection optical system. The light flux converged by the condenser lens 40 passes through a focus detection cylindrical lens 41 to generate astigmatism, and reaches a focus detection photodetector 42. The light detector 42 uses the fact that the light flux before and after the focal point becomes a focal line due to astigmatism of the incident light flux, and information that the light flux focused on the phase identification member 13 is separated from the focal position, A so-called focus error signal is generated.
[0040]
On the basis of the focus error signal thus obtained, the focal position can be controlled by, for example, moving the condenser lens 33 in the optical axis direction.
[0041]
However, the object on which the convergent light beam should be focused is the optical recording / reproducing layer 12 corresponding to the layer identifying member 13. Therefore, by superimposing a so-called bias signal according to the distance between the layer identifying member 13 and the optical recording / reproducing layer 12 on the focus error signal or the condenser lens driving signal, the optical recording / reproducing layer 12 relating to recording / reproducing is superimposed. Can be focused. That is, by removing the application of the electric field to the arbitrary layer discriminating member 13, a reflection surface for the light flux from the light source 31 appears in the optical recording / reproducing medium 10, and further detects the position information of the reflection surface. By controlling the focal position in this way, it becomes possible to identify the optical recording / reproducing layer 12 related to recording / reproducing and simultaneously form a focal spot on that layer.
[0042]
Here, after a focal spot is formed on the optical recording / reproducing layer 12, for example, the intensity of light emitted from the light source 31 is increased to be higher than the intensity required for signal recording on the optical recording / reproducing layer 12, so that recording / reproducing is performed. The signal can be recorded by specifying the optical recording / reproducing layer 12 according to the above. In this case, since the stacked optical recording / reproducing layers 12 are separated from each other by the intermediate layer 16, the transmission cross-sectional area of the recording / reproducing luminous flux in the optical recording / reproducing layer 12 which is not involved in recording / reproducing becomes large and the per unit area is increased. The light intensity is sufficiently lower than the value near the focal spot so that it does not exceed the threshold for signal recording.
(Example using nonlinear optical material for optical recording / reproducing layer)
FIG. 8 is a schematic diagram of a recording / reproducing apparatus using a nonlinear optical material for the optical recording / reproducing layer 12, and using detection of harmonic light for signal reproduction.
[0043]
Here, since the layer identification and the focus position control have already been described, the description will be omitted. In addition, the optical recording / reproducing medium 10 and the electric circuit switch 22 are schematically omitted.
[0044]
The light beam emitted from the light source 31 converges on the optical recording / reproducing layer 12 before being wavelength-selectively reflected by the layer identification member 13 from which the electric field has been removed.
[0045]
As the optical recording / reproducing layer 12, a thin plate or a thin film of a nonlinear optical material such as lithium niobate (LiNbO ₃ ) can be used. The nonlinear optical material generates a second harmonic in a light beam irradiated by the nonlinear optical effect with an intensity proportional to the square of the light intensity per unit area. In other words, a high-intensity second harmonic is generated near the focal point of the convergent light beam, but the second-harmonic generation intensity in the optical recording / reproducing layer 12 far from the focal point is sufficiently small, and is not involved in signal recording / reproduction. The influence of the second harmonic generated in the optical recording / reproducing layer 12 as a disturbance signal on the signal detection signal is small. Further, since the second harmonic generated in this manner has a wavelength that is half that of the irradiated recording / reproducing light source light, the second harmonic passes through the layer identification member 13 without being wavelength-selectively reflected, and is transmitted for detection. The objective lens 34 can be reached.
[0046]
The optical recording / reproducing layer 12 may be a thin plate or a thin film of a photorefractive optical material such as silica glass. After a region having a different refractive index is formed by the photorefractive effect, the region is irradiated with a light beam having a high light intensity density, thereby generating fluorescence having a wavelength longer than the wavelength of the irradiation light. The generated fluorescence intensity has a non-linear relationship with the light intensity density similarly to the generation of non-linear harmonic light, so that it can be used for signal detection in a multi-layered medium. On the other hand, since the wavelength has changed to a long wavelength, the light can pass through the layer identifying member 13 without being selectively reflected by the wavelength and reach the objective lens 34 for signal detection.
[0047]
Here, even a light beam that is wavelength-selectively reflected by the layer identification member 13 may be transmitted without being reflected depending on its polarization state. Therefore, a wavelength selection filter 37 may be further disposed. The arrangement can be omitted by adjusting the polarization state of the light beam incident on the layer identification member 13.
[0048]
The harmonic light beam that has passed through the objective lens 34 and the wavelength selection filter 37 becomes convergent light at the signal detection condenser lens 35 and reaches the optical signal detector 38. The optical signal of the second harmonic that has reached the detector 38 is photoelectrically converted into an electric signal.
[0049]
【The invention's effect】
As described above, according to the present invention, by using a layer identification member having a selectively high reflectance at a specific light wavelength, any layer related to recording / reproduction of an optical recording / reproduction layer laminated in multiple layers can be used. It is possible to specify a layer without recording / reproducing light being reflected or absorbed by a recording / reproducing layer not involved in recording / reproducing.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a configuration of an optical recording / reproducing medium according to an embodiment of the present invention.
FIG. 2 is an explanatory diagram of a phase change and an optical characteristic of the cholesteric liquid crystal material according to one embodiment of the present invention due to an applied electric field.
FIG. 3 is a plan view showing a configuration of an optical recording / reproducing medium according to another embodiment of the present invention.
FIG. 4 is a cross-sectional view illustrating a configuration of an optical recording / reproducing medium according to another embodiment of the present invention.
FIG. 5 is a schematic diagram showing passage of a light beam in a non-identification state in the phase identification method according to one embodiment of the present invention.
FIG. 6 is a schematic diagram showing reflection of a light beam in an identification state in a phase identification method according to an embodiment of the present invention.
FIG. 7 is a schematic diagram illustrating a configuration of a recording / reproducing apparatus according to an embodiment of the present invention.
FIG. 8 is a schematic diagram showing a configuration of a recording / reproducing apparatus according to an embodiment of the present invention, in which a non-linear optical material is used for an optical recording / reproducing layer.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Optical recording / reproducing medium 11 Substrate 12 Optical recording / reproducing layer 13 Layer identification member 14, 15 Electrode 16 Intermediate layer 17 Bias electric field layer 21 Electric field application power supply 22 Electric path switch 23 Light incident on recording / reproducing layer 24 Layer identification Light reflected from the member 31 Light source 32 Collimator lens 33 Condenser lens 34 Signal detection objective lens 35 Signal detection condenser lens 36 Optical path branching component 37 Wavelength selection filter 38 Optical signal detector 40 Focus detection condenser lens 41 Focus Detection cylindrical lens 42 Focus detection photodetector 43 Stage

Claims (7)

At least two or more optical recording / reproducing layers;
An optical recording / reproducing medium, comprising: a layer discriminating member disposed adjacent to or at a predetermined distance from each of the optical recording / reproducing layers and having a selectively high reflectance at a specific light wavelength. . The optical recording / reproducing medium according to claim 1,
An optical recording / reproducing medium, wherein the layer identification member is made of cholesteric liquid crystal. An optical recording / reproducing medium according to claim 2,
An optical recording / reproducing medium, comprising: a pair of conductive materials disposed so as to sandwich each of the layer identifying members. The optical recording / reproducing medium according to claim 3, wherein
An optical recording / reproducing medium, wherein at least one of the conductive materials is arranged at a position corresponding to a recording / reproducing line in the optical recording / reproducing layer. An optical recording / reproducing medium according to claim 2,
An optical recording / reproducing medium, further comprising means for constantly applying an electric field to the layer identifying member. The optical recording / reproducing medium according to claim 1,
The optical recording / reproducing medium, wherein the optical recording / reproducing layer is made of a member that generates light having different wavelengths by irradiation of the recording / reproducing light. At least two or more optical recording / reproducing layers, disposed adjacent to or separated by a predetermined distance from each of the optical recording / reproducing layers, sandwiching a layer identifying member made of cholesteric liquid crystal and each of the layer identifying members. A stage on which an optical recording / reproducing medium including a pair of conductive materials arranged as described above is mounted,
Means for selectively applying a potential difference between the pair of conductive materials,
Means for converging a recording or reproducing light beam on the optical recording / reproducing layer.

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