KR20090017387A - Holographic data storage medium, and apparatus and method for recording/reproducing holographic data on/from the same - Google Patents

Abstract

A holographic information storage medium to improve signal quality through the space layer interposed between the polarized beam reflective layer and the holographic recording layer, and a holographic information record/playback apparatus and method using the same are provided. A holographic information storage medium comprises a substrate(110), a cover layer(170) in which first and second beam having circular polarization meeting each other at right angle enter, a polarized beam reflective layer(140) which reflects the first beam with maintaining the polarization direction and transmits the second beam, a holographic recording layer(160) in which information is recorded in the dark fringe formed by the first beam reflected from the polarized beam reflective layer and the second beam which comes in the cover layer, and a space layer(150) is prepared between the polarized beam reflective layer and the holographic recording layer.

Description

Holographic data storage medium and holographic data recording / reproducing apparatus and method using the same

The present invention relates to a holographic information storage medium, and a holographic information recording / reproducing apparatus and method using the same. More particularly, the present invention relates to a single side method in which signal light and reference light are irradiated through the same plane, and thus can reduce noise during reproduction. A holographic information storage medium having a structure, and a holographic information recording / reproducing apparatus and method using the same.

Recently, information storage technology using holograms has attracted attention. Holograms store information in the form of optical interference fringes and store it in inorganic crystals or polymer materials that are sensitive to light. The optical interference fringe is formed by using two coherent laser beams. In other words, the interference fringe formed by the reference light and the signal light that cross different paths is recorded by causing a chemical or physical change in the photosensitive storage medium. In order to reproduce the information from the recorded interference pattern, reference light similar to the light at the time of recording is irradiated to the interference pattern recorded on the storage medium. This causes diffraction due to the interference pattern, whereby the information is reproduced while the signal light is restored.

Such hologram information storage technology uses a volume holography method for recording / reproducing pages by volume using volume holography and a micro-recording / reproducing method for single bits using micro holography. There is a holography method. Volume holography has the advantage of processing a large amount of information at the same time, but because the optical system has to be adjusted very precisely there is a problem that it is difficult to be commercialized as an information storage device for the general consumer.

On the other hand, the micro-holography method forms a fine interference pattern by interfering two focused light at the focal point, and moving the interference fringe on the storage medium plane to record a plurality of recording layers to form a recording layer. By superimposing and recording in the depth direction, information is recorded in three dimensions on the storage medium.

However, when the signal light and the reference light are incident separately on both sides of the storage medium for information recording, the optical system for the signal light and the optical system for the reference light should be provided separately on both sides of the storage medium, thereby increasing the size of the entire optical system. In order to solve this problem, a single side recording / reproducing method in which signal light and reference light are irradiated on the same side of the storage medium has been proposed. In this method, the signal light and the reference light are focused in the recording layer provided on the storage medium, and information is recorded by the interference fringe formed at the focus position. The information recorded in this way can be reproduced by injecting a reference light into the interference fringe.

However, in such a single side recording / reproducing method, there is a noise problem due to reflected light. In the case of a conventional optical information recording / reproducing apparatus, the noise caused by the reflected light increases the distance between the recording layer and the reflective film so that the reflected light can be removed by defocusing the reflected light from the photodetector. However, since the size of the reproduction signal is very small due to the characteristics of the hologram, it is difficult to apply such a method of removing noise by increasing the distance between the recording layer and the reflective film to the hologram information storage medium. The reflectivity, i.e., diffraction efficiency, varies according to the thickness of the hologram, the refractive index change of the storage medium, and the like. When the hologram is recorded in a local area such as a micro hologram, the reflectance is very low. In general, the amount of change in refractive index of a photo-polymer, which is frequently used as a material for a holographic recording layer, is about 0.01, and in this case, the reflectance of a micro-hologram recorded by an optical system having a numerical aperture of 0.85 is It is within 1%. In addition, when multi-layer recording is performed to increase the recording capacity, the reflectance is further reduced, and it is generally known to decrease in proportion to the square of the number of recording layers. For example, in the case of having more than 20 recording layers, the reflectance becomes very low such that 0.01% or less. Due to the characteristics of the hologram, increasing the distance between the recording layer and the reflective layer to reduce the reflection noise increases the aberration to be compensated between the signal light and the reference light and becomes vulnerable to tilt, making it difficult to construct an optical system.

The present invention provides a holographic information storage medium for storing information in a single side recording / reproducing method, and a holographic information recording / reproducing apparatus and method using the same, to prevent signal quality from being deteriorated by noise reflected during reproduction. For the purpose of

In order to achieve the above object, the holographic information storage medium according to the present invention, the substrate; A cover layer to which first and second light having circularly polarized light perpendicular to each other are incident; A polarization separation reflection layer provided between the substrate and the cover layer to reflect the first light while maintaining the polarization direction and to transmit the second light; A holographic recording layer provided between the polarization split reflection layer and the cover layer, the holographic recording layer recording information into an interference fringe formed by first light reflected from the polarization split reflection layer and second light incident from the cover layer; It is characterized by.

On the other hand, in order to achieve the above object, the holographic information recording / reproducing apparatus according to the present invention, the first light of the first and second light having a circular polarization orthogonal to each other, the first light is reflected while maintaining the polarization direction A device for recording / reproducing information on a holographic information storage medium in which a polarized light splitting reflection layer, a holographic recording layer, and a cover layer are sequentially stacked, wherein the first and second light are directed to the hole. An optical pickup that irradiates a graphic information storage medium and records information in an interference fringe formed at one focal point in the holographic recording layer by first light reflected by the polarization splitting reflection layer and second light incident on the cover layer; Characterized in that it comprises a.

In addition, in order to achieve the above object, the holographic information recording / reproducing apparatus according to the present invention, the first light of the first and second light having a circular polarization orthogonal to each other, the first light is reflected while maintaining the polarization direction A device for reproducing information in a holographic information storage medium comprising a polarization splitting reflection layer for transmitting a second light and transmitting a second light, a holographic recording layer in which information is recorded as an interference fringe, and a cover layer. And an optical pickup that irradiates an information storage medium and receives light reflected with a change in polarization direction at one focal point of the holographic recording layer in the second light, and transmits the holographic recording layer in the second light. The light may be blocked from being re-entered into the optical pickup by the polarization separation reflection layer.

On the other hand, in order to achieve the above object, in the holographic information recording / reproducing method according to the present invention, the first light of the first and second light having a circular polarization orthogonal to the substrate and the first light is kept in the polarization direction. A method of recording information on a holographic information storage medium in which a polarization splitting reflection layer for reflecting and transmitting a second light, a holographic recording layer, and a cover layer are sequentially stacked, and reproducing the recorded information. The signal light and the reference light having the second polarization perpendicular to the first polarized light are guided in the same optical path, but are different in the amount of refraction according to the polarization direction, so that any one of the signal light and the reference light is the holographic information storage medium. The focus layer is focused at one focal point within the recording layer, and the other of the signal light and the reference light passes through the cover layer and the recording layer of the holographic information storage medium. After the reflection is reflected by the polarization splitting reflection layer to focus on the focal point, an interference fringe is formed along the depth direction of the holographic information storage medium in the vicinity of the focal point to record information.

The holographic information storage medium according to the present invention and the holographic information recording / reproducing apparatus and method using the same by the problem solving means as described above prevent the signal quality from being deteriorated by the noise reflected during reproduction, thereby improving the signal quality. To improve.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the examples exemplified below are not intended to limit the scope of the present invention, but are provided to fully explain the present invention to those skilled in the art. In the drawings, like reference numerals refer to like elements, and the size of each element in the drawings may be exaggerated for clarity and convenience of description.

1 is a diagram schematically illustrating a configuration of a holographic information storage medium according to an embodiment of the present invention.

Referring to the drawings, the holographic information storage medium 100 of the present embodiment includes a substrate 110, a servo layer 120, a buffer layer 130, a polarization splitting reflection layer 140, a space layer 150 and The holographic recording layer 160 and the cover layer 170 are sequentially stacked. For convenience of description, the side on which the cover layer 170 is stacked based on the substrate 110 will be referred to as an upper side and the opposite side thereof as a lower side.

The substrate 110 may be formed of a polycarbonate resin, an acrylic resin, or the like as a support provided to maintain a shape of a storage medium such as a disk shape.

The cover layer 170 is to protect the holographic recording layer 160. When the material of the holographic recording layer 160 is not solid, the cover layer 170 also maintains the shape of the storage medium. An upper surface of the cover layer 170 may further include an antireflection layer (not shown) for suppressing surface reflection.

The holographic recording layer 160 is formed of a photoreactive material whose refractive index changes when it absorbs light. For example, the holographic recording layer 160 is formed of a photo polymer or a thermoplastic material. Such photoreactive materials generally have a refractive index that changes in proportion to the light intensity, and it is desirable to have a non-linear characteristic in which a reaction occurs only in light above a threshold with a predetermined threshold. This is because when the material of the holographic recording layer 160 has a non-linear characteristic when it is desired to increase the recording density by forming a plurality of different interference fringes overlapping at different focal positions in the depth direction of the holographic recording layer 160, This is because the farther away from the focal position, the weaker the intensity of the interference fringe is, so that the multi-layer recording can be performed densely.

The space layer 150 is a layer for securing a space between the holographic recording layer 160 and the polarization splitting layer 140, and the signal light reflected by the polarization splitting layer 140 is a holographic recording layer. When forming the focal point F in FIG. 160, the distance between the polarization split reflecting layer 140 and the focal point F where recording is made is ensured. The thickness of the space layer 150 varies depending on the performance of the holographic recording layer 160, and is formed to a thickness of approximately 0 to 100 μm. As the distance is secured between the polarization split reflection layer 140 and the focal point F, noise caused by light partially reflected from the polarization split reflection layer 140 may be reduced during reproduction. The relationship between the space layer 150 and noise reduction will be described later. The space layer 150 is not an essential layer in the present invention, and a portion of the holographic recording layer 160 may be replaced with a space layer without using it for recording.

The polarization split reflecting layer 140 is formed of a material that reflects light of the first circularly polarized light and transmits light of the second circularly polarized light with respect to the first and second circularly polarized light which are orthogonal to each other. Further, the polarization split reflection layer 140 maintains the polarization direction of the light of the first circularly polarized light as it is reflected. Hereinafter, the polarization split reflecting layer 140 reflects the light of the left circularly polarized light and transmits the light of the right circularly polarized light, and the reflected light of the left circularly polarized light will be described as an example. The polarization splitting reflection layer 140 may be formed of a cholesteric liquid crystal of a liquid crystal state or a cured liquid crystal film. A cholesteric liquid crystal is a structure in which the directors of liquid crystal molecules are twisted in a spiral shape. The cholesteric liquid crystal reflects light of circularly polarized light corresponding to the spiral and transmits light of circularly polarized light corresponding to the opposite direction of the spiral, thereby allowing two circles to be perpendicular to each other. It can be separated by polarization, and the reflected light is kept in the original circularly polarized state.

2 shows the optical characteristics of this cholesteric liquid crystal layer. In FIG. 2, the horizontal axis represents the polarization direction of light transmitted through the cholesteric liquid crystal layer, and the vertical axis represents the transmittance of incident light. Referring to FIG. 2, it can be seen that the light of R polarization is transmitted as it is, but hardly transmits L polarization. In the case of the cholesteric liquid crystal, the wavelength of the transmitted light may be adjusted according to the spiral period of the liquid crystal molecules. Furthermore, the polarization splitting reflection layer 140 may be formed of a laminate in which cholesteric liquid crystal layers made of liquid crystal molecules having different spiral periods are stacked in multiple layers, and by adjusting the spiral period or the number of stacking times of the cholesteric liquid crystal layer The light of a predetermined wavelength may be transmitted / reflected according to the polarization direction and the light of another wavelength may be transmitted. In the present embodiment, since the servo layer 120 is under the polarization separation reflection layer 140, the signal / reference light is transmitted / reflected according to the polarization direction, and the servo light is formed to transmit.

The buffer layer 150 is a layer interposed between the polarization separation reflection layer 140 and the servo layer 120, and may be formed of a transparent material or a material absorbing the wavelength of light for recording / reproducing. The buffer layer 150 fills the patterns of the servo information formed on the servo layer 120 so that the polarization split reflection layer 140 may be formed flat.

The servo layer 120 is a layer on which servo information is written and reflects servo light. In the present embodiment, the wavelength of the servo light is set differently from the wavelength of the light for recording / reproducing, and the layers on the servo layer 120, that is, the buffer layer 130, the polarization splitting reflection layer 140, and the space layer ( 150, the holographic recording layer 160, and the cover layer 170 are designed to transmit servo light.

Next, a method of recording information on a holographic information storage medium according to the present invention will be described with reference to FIGS. 3 to 5.

FIG. 3 is a diagram schematically illustrating an optical configuration in which a signal light and a reference light are irradiated to the holographic information storage medium of FIG. 1, and FIG. 4 is an enlarged view of region A of FIG. 3, and an interference fringe formed by the signal light and the reference light. Shows. 5 is a diagram illustrating polarization states of signal light and reference light incident on the holographic information storage medium of FIG. 1.

Referring to FIG. 3, the signal light L1 and the reference light L2 are incident on the holographic information storage medium 100 through the same objective lens 280. The signal light L1 is reflected by the polarization splitting reflection layer 140 to form a spot at one focal point A in the holographic recording layer 160, and the reference L2 light is incident on the cover layer 170 and immediately after the light is incident on the cover layer 170. Spots form at the focal point A. As the spots overlap the focal point A with the signal light L1 and the reference light L2 as described above, an interference fringe is formed. Since the shape of the interference fringe is changed depending on the modulated state of the signal light L1 or the modulated state of the signal light L1 and the reference light L2, information may be recorded by the interference fringe. 4 is an enlarged view of the vicinity of the focal point A of the signal light L1 and the reference light L2 in FIG. 3, and shows that an interference fringe is formed. These interference fringes are recorded along the track on the same plane to form a single-layered recording surface 165 in the holographic recording layer 160, and the interference fringes are changed while changing the focal position in the depth direction of the holographic recording layer 160. By superimposing, it can record in multiple layers. The holographic information storage medium of this embodiment is a micro holography method in which a single bit of information is contained in an interference fringe for each focal point A, but is not limited thereto. For example, a volume holography method in which the spot of the signal light L1 and the spot of the reference light L2 overlap at the focal point A and a three-dimensional interference pattern is formed to write a plurality of information simultaneously may be applied.

A process of forming an interference fringe considering polarization will be described with reference to FIG. 5. Referring to Fig. 5, the holographic information recording / reproducing apparatus includes a quarter wave plate 285 and an objective lens 280. The signal light L1 and the reference light L2 are incident on the quarter-wave plate 285 with different linear light. For example, the signal light L1 is incident on the quarter-wave plate 285 in an S-polarized state, and the reference light L2 is incident on the quarter-wave plate 285 in a P-polarized state. The quarter-wave plate 285 is an optical member that converts linearly polarized light into circularly polarized light and circularly polarized light into linearly polarized light. The signal light L1 changes the polarization state to the light of the left circularly polarized light L while passing through the quarter-wave plate 285, and the reference light L2 passes through the quarter-wave plate 285 to the right circularly polarized light R. The polarization state changes with the light of. The signal light L1, which is the left circularly polarized light L, is reflected by the polarization separation reflection layer 140 to maintain the left circularly polarized light. The signal light L1 of the reflected left circularly polarized light L is focused on the recording surface 165. On the other hand, the reference light L2, which is the right circularly polarized light R, focuses on the recording surface 165 and proceeds as it passes through the polarization separation reflection layer 140. Since the signal light L1 and the reference light L2 that meet the recording surface 165 proceed in the direction facing each other, the directions of the circularly polarized light are opposite, so that the electric field vector of the signal light L1 and the electric field vector of the reference light L2 are in the same direction. Rotates, thus causing interference in the recording surface 165. This interference causes information to be recorded in the holographic recording layer 160 of photoreactive material.

On the other hand, the reference light L2 of the right circularly polarized light R passing through the polarization split reflection layer 140 may be reflected by the servo layer 120 or other layers, but the reflection only changes the direction of the light, and the electric field vector Since the direction of rotation does not change, the reference light L2 reflected by the servo layer 120 or the like becomes left circularly polarized light R and cannot pass through the polarization splitting reflection layer 140 again.

6 and 7, a method of reproducing information recorded on a holographic information storage medium according to the present invention will be described.

6 is a diagram illustrating a polarization state of regenerated light incident on the holographic information storage medium of FIG. 1, and FIG. 7 is a graph illustrating noise according to a distance of a reflective film.

Referring to FIG. 6, the reproduction light having the same polarization direction as the reference light is irradiated to the holographic information storage medium 100 for reproduction. That is, the incident regenerated light L3i of the P-polarized light is in the right circularly polarized state R through the quarter-wave plate 285 and is incident on the holographic information storage medium 100 via the objective lens 280. Based on the recording surface 165, the light incident on the recording surface 165 is called incident reproduction light L3i, and the light reflected from the recording surface 165 is called reflection reproduction light L3r, and passes through the recording surface 165. One light is referred to as transmitted reproduction light L3t. The incident regenerated light L3i of the right circularly polarized light R is diffracted, ie reflected, from the recording surface 165 on which information is recorded by the interference fringe, and is directed back to the objective lens 280. The reflected reproduction light L3r reflected by the recording surface 165 only changes the traveling direction of the light, and does not change the rotation direction of the electric field vector, and thus becomes the left circularly polarized light L state. On the other hand, the transmitted reproduction light L3t transmitted through the recording surface 165 of the incident reproduction light L3i of the right circularly polarized light R passes through the polarization splitting reflection layer 140 as it is. The transmitted and regenerated light L3t may be reflected by the servo layer 120 or other layers, but the reflected and regenerated light L3t 'only changes the traveling direction of the light and does not change the rotation direction of the electric field vector. The transmitted and reproduced light L3t 'reflected by the layer 120 becomes the left circularly polarized light R and cannot pass through the polarization splitting reflection layer 140 again. If the reflected transmission light L3t 'is transmitted through the recording surface 165 as it is and re-entered into the objective lens 280, it will act as noise of the reproduction signal. However, as the transmitted and reproduced light L3t 'reflected as described above does not pass through the polarization split reflection layer 140, the noise caused by the reflected light may be reduced, and the signal quality may be improved. On the other hand, the conventional servo layer should be designed to suppress the reflection of the transmitted and reproduced light (L3t) as much as possible in order to reduce noise, in the case of the present invention, even if the transmitted and reproduced light (L3t) reflects the polarization separation reflection layer 140 Since it does not pass again, the required performance of the servo layer 120 is alleviated, thereby facilitating the manufacture of the holographic information storage medium 100.

The present embodiment presupposes that the transmitted and reproduced light L3t of the right circularly polarized light R passes through the polarization separation reflection layer 140 as it is, but in reality, a part of the transmitted and reproduced light L3t having the right circularly polarized light R is It may be reflected by the polarization split reflecting layer 140. In such a case, the reflectance of the incident regenerated light L3i of the right circularly polarized light R is reflected by the recording surface 165 is substantially very low, so that the noise L3n that is partially reflected by the polarization splitting reflection layer 140 may be a problem. There is a number. However, the noise L3n partially reflected by the polarization split reflection layer 140 can be suppressed by sufficiently reducing the distance between the recording surface 165 on which the recording is made and the polarization split reflection layer 140.

FIG. 7 is simulation data showing a relationship between the noise L3n and the reflection film distance in FIG. 6. In FIG. 7, the reflective film distance represents the distance between the polarization splitting reflection layer 140 and the recording surface 165 on which the actual recording is made. In this simulation, the reflectance at which the incident reproduction light L3i is reflected on the recording surface 165 is set to approximately 0.0135%, and the noise reflectance at which the transmitted reproduction light L3t of the right circularly polarized light R is reflected on the polarization separation reflection layer 140 is measured. Approximately 1%. As the distance between the recording surface 165 and the polarization separation reflection layer 140 increases, the transmitted and reproduced light L3t focused on the recording surface 165 is defocused in the polarization separation reflection layer 140, and thus, the polarization separation reflection layer The intensity of the noise reflected at 140 becomes small. Referring to FIG. 7, when the reflection film distance is 40 μm or more, the noise to signal (N / S) becomes smaller than 2.5%. Therefore, under the conditions of the simulation, in order to make N / S smaller than 2.5%, it is preferable to set the thickness d of the space layer 150 to at least 40 μm. More preferably, the thickness d of the space layer 150 can be made 50 µm or larger to make N / S 1.5% or less. However, the thickness of the space layer 150 may vary depending on optical design parameters such as reflectance at the recording surface 165 or noise reflectance at the polarization splitting reflection layer 140. Further, as described above, the holographic recording layer 160 is formed sufficiently thick in place of the space layer 150, and thus the distance between the recording surface 165 and the polarization splitting reflection layer 140 where recording is performed is, for example, It is possible to suppress the reflection noise in the polarization split reflecting layer 140 by securing it to 40 μm or more. Further, as described later, a pinhole member (295 in FIG. 12) is provided in front of the photodetector of the holographic information recording / reproducing apparatus to limit the detection of defocused light, thereby suppressing the reflection noise in the polarization splitting reflection layer 140. Can be.

In the above embodiment, the servo layer is interposed between the substrate 110 and the polarization split reflecting layer 140, but is not limited thereto. 8 to 10 show modifications with different positions of the servo layer.

Referring to FIG. 8, the holographic information storage medium 102 may have a structure in which the servo layer 122 is interposed between the polarization separation reflection layer 140 and the space layer 150. In this case, the servo layer 122 is formed of a material that transmits light for recording / reproducing, that is, signal light, reference light, and reproduction light. In such a configuration, the polarization split reflecting layer 140 is interposed between the holographic recording layer 160 and the substrate 110 as in the above-described embodiment, thereby transmitting noise through the holographic recording layer 160. Noise can be removed by blocking reproduction light back into the objective lens. The remaining components except for the servo layer 122 are substantially the same as the embodiments described with reference to FIGS. 1 to 6, and thus, detailed descriptions thereof will be omitted.

Referring to FIG. 9, the holographic information storage medium 104 may have a structure in which a servo layer 124 is interposed between the holographic recording layer 160 and the cover layer 170. Also in this case, the servo layer 122 is formed of a material that transmits light for recording / reproducing, that is, signal light, reference light, and reproduction light. In such a configuration, the polarization split reflecting layer 140 is interposed between the holographic recording layer 160 and the substrate 110 as in the above-described embodiment, thereby transmitting noise through the holographic recording layer 160. Noise can be removed by blocking reproduction light back into the objective lens. The remaining components except for the servo layer 124 are substantially the same as the embodiments described with reference to FIGS. 1 to 6, and thus, detailed descriptions thereof will be omitted.

Referring to FIG. 10, the holographic information storage medium 106 may have a structure in which the servo layer 126 is interposed in the recording layer 160. Also in this case, the servo layer 126 is formed of a material that transmits light for recording / reproducing, that is, signal light, reference light, and reproduction light. In such a configuration, the polarization split reflecting layer 140 is interposed between the holographic recording layer 160 and the substrate 110 as in the above-described embodiment, thereby transmitting noise through the holographic recording layer 160. Noise can be removed by blocking reproduction light back into the objective lens. The remaining components except for the servo layer 126 are substantially the same as the embodiments described with reference to FIGS. 1 to 6, and thus, detailed descriptions thereof will be omitted.

Furthermore, the above-described embodiment presupposes that the wavelength of the servo light is different from the wavelength of the light for recording / reproducing, but is not limited thereto. Referring to FIG. 11, the holographic information storage medium 108 uses the polarization separation reflection layer 145 as the servo layer without having a separate servo layer. In this case, the servo light may be separate from the light for recording / reproducing, but the present invention is not limited thereto, and the servo may be performed using the light for recording / reproducing. If the servo light uses a different light from the recording / reproducing light, the polarization splitting reflection layer 145 is designed to reflect the servo light, and when the servo is performed using the recording / reproducing light, the reflection is reflected. Servo is performed using the reproduced light.

12 schematically shows an optical configuration of a holographic information recording / reproducing apparatus according to an embodiment of the present invention.

Referring to FIG. 12, the holographic information recording / reproducing apparatus of the present embodiment is an apparatus for recording / reproducing information on the holographic information storage medium 100 of the present invention described above, and includes a circularly polarized signal light and a reference light ( And an optical pickup 200 for irradiating L1 and L2 to the holographic information storage medium 100 and a circuit unit (not shown) for driving control of the optical pickup 200 and processing signals.

The optical pickup 200 includes a light source 210, a first beam splitter 220, a 1/2 wavelength wave 230, a shutter 240, a second beam splitter 250, The third beam splitter 260, the mirror 225, the quarter-wave plate 285, the objective lens 280, and the photodetector 290 are included. The optical pickup 200 of the present exemplary embodiment may further include a signal light side and a reference light side focus control units 270 and 275 for varying a focus position so that information can be recorded / reproduced in a multi-layer, and a pinhole for blocking defocused noise light. The member 295 may be further included. In addition, it may further include a servo optical system (not shown) for the maintenance line.

The light source 210 mainly emits light of P-polarized light. For example, a blue semiconductor laser diode may be employed. The polarization direction of the emitted light is for convenience of description and the present invention is not limited thereto. Furthermore, the light source 210 itself may emit unpolarized light and select a predetermined linearly polarized light using a separate polarizing plate. The light source 210 may also be used as a servo light source, a separate servo light source may be provided. If a separate servo light source is provided, the wavelength of the servo light may be different from the wavelength of the light emitted from the light source 210.

The first to third beam splitters 220, 250, and 260 are examples of optical path separation units. The first and second beam splitters 220 and 250 function as half mirrors that split the light passing through the two optical paths. The light emitted from the light source 210 is split into the signal light L1 and the reference light L2 by the first beam splitter 220. The signal light L1 reflected and branched by the first beam splitter 220 is converted into S-polarized light by the half-wave plate 230 and passes through the second and third beam splitters 250 and 260. The shutter 230 is a member that blocks light in accordance with an electrical signal. The shutter 230 is disposed on an optical path of the signal light L1 and passes the signal light L1 during recording and blocks the reflected reproduction light L3r light during reproduction. . The reference path L2 transmitted through and branched from the first beam splitter 220 is converted to an optical path at the mirror 225 to face the third beam splitter 260. The third beam splitter 260 is a polarizing beam splitter. The third beam splitter 260 reflects the signal light L1 of S-polarized light and transmits the reference light L2 of P-polarized light. Therefore, the signal light L1 and the reference light L2 incident on the third beam splitter 260 in different paths are combined in the third beam splitter 260 to be directed to the quarter wave plate 285.

The signal light L1 incident on the quarter-wave plate 285 is converted into S-polarized left circularly polarized light, and the reference light L2 incident on the quarter-wave plate 285 is incident to right circularly polarized light from P-polarized light. . The signal light L1 and the reference light L2, which are converted to orthogonal circular polarizations, are incident on the holographic information storage medium 100 through the objective lens 280, and as described with reference to FIGS. Information will be recorded.

The signal light side and reference light side focus control units 270, 275 may include, for example, beam expanders of relay lens groups 271, 272, 276, 277 as shown. Such a focus control unit 270, 275 is provided so that at least one lens of the relay lens group 271, 272, 276, 277 is movable in the optical axis direction, and is driven by a driving unit (not shown). In this way, by moving at least one of the relay lens groups 271, 272, 276 and 277 along the optical axis direction, the focus control units 270 and 275 may change the focal position formed in the holographic information storage medium 100. Such focus control units 270 and 275 enable multi-layer recording in the holographic information storage medium 100. That is, as the signal light L1 and the reference light L2 condense at one focal point (F in FIG. 3) in the holographic information storage medium 100, one recording surface (165 in FIG. 3) is formed, and the focus control units 270 and 275 are provided. Since the recording surface is also changed as the focal positions of the signal light L1 and the reference light L2 are changed by?), Recording is performed in multiple layers. The focus control units 270 and 275 of the present embodiment have been described using beam expanders made of relay lens groups 271, 272, 276 and 277 as an example, but the present invention is not limited thereto. For example, the focus control units 270 and 275 may be implemented using liquid crystal lenses. Voltage is applied to the liquid crystal lens, and the light of predetermined polarization is refracted due to the alignment of the liquid crystal. Since the configuration of such a liquid crystal lens is well known in the art, detailed description thereof will be omitted. The liquid crystal lens may be disposed in place of the relay lens groups 271, 272, 276 and 277 in the optical paths of the signal light L1 and the reference light L2, and the focus may be changed by applying a voltage to the liquid crystal lens.

On the other hand, when the reproduction is to be performed, the incident reproduction light L3i emitted from the light source 210 is divided into the first beam splitter 220, the mirror 225, the third beam splitter 260, the quarter wave plate 285, and the like. The light enters the holographic information storage medium 100 through the objective lens 280. The incident reproduction light L3i is reflected on the recording surface 165 of FIG. 6 in which the information is recorded in the holographic information storage medium 100 in the form of an interference fringe, and is incident again on the objective lens 200. Since the incident reproduction light L3i passes through the same path as the reference light L2, the incident reproduction light L3i is incident on the holographic information storage medium 100 in a right circularly polarized state, and the reflected reproduction light L3i reflected from the recording surface 165 is It is converted to the left circularly polarized light and reincident to the objective lens 200. The reflected regenerated light L3r, which is the left circularly polarized light, is converted into the S polarized state through the quarter-wave plate 285, is reflected by the third beam splitter 260, and passes through the second beam splitter 250. It is detected by the detector 290. In this case, some of the reflected reproduction light L3r may be reflected by the second beam splitter 250, but some of the reflected reproduction light L3r reflected by the second beam splitter 250 is blocked by the shutter 240. do. On the other hand, when information is recorded in multiple layers in the holographic recording layer (160 in FIG. 6), the focus position of the incident reproduction light L3i is varied by using the reference light side focus control unit 275, so that the recording surface is read. The incident reproduction light L3i is focused.

The pinhole member 195 blocks light reflected outside the recording surface 165 to be read. The pinhole member 195 is a member having a limited aperture, that is, a pinhole 295a and a blocking film 295b that blocks light as shown in FIG. 13, and is disposed in front of the photodetector 290. do. The radius Rh of the pinhole 295a may be larger than the radius Rs of the beam spot S, and may be about twice the radius Rs of the beam spot S, for example. This pinhole member 195 blocks defocused light. Referring to FIG. 14, when the reproduction light is focused on the recording surface 165 to be read, the pinhole (295a in FIG. 13) of the pinhole member 295 is positioned at the position where the light reflected from the focused position is in focus again. When arranged, the light reflected in the other region, for example, the light partially reflected by the polarization separation reflection layer 140 (L3n in FIG. 6) is reflected in a defocused state, thereby blocking the blocking film of the pinhole member 295 ( It is mostly blocked by 295b) of FIG. Therefore, noise caused by light partially reflected by the polarization split reflection layer 140 (L3n of FIG. 6) may be suppressed using the pinhole member 295 together with the space layer 150 (FIG. 6) as described above.

In this reproduction process, the light transmitted through the holographic recording layer 160 of the reproduction light for reproducing the information recorded as described above with reference to FIG. 6 is simply transmitted by the polarization separation reflection layer 140, and once polarized The light transmitted through the separation reflection layer 140 is blocked by the polarization separation reflection layer 140 even though it is reflected by the servo layer 120. Furthermore, although some of the light is reflected by the polarization splitting reflection layer 140, the space layer 150 of the holographic information storage medium 100 or the pinhole member 295 of the holographic information recording / reproducing apparatus 200 are used. Noise can be suppressed.

The above-described embodiments have described holographic information storage media according to the present invention in various forms, and a holographic information recording / reproducing apparatus and method using the same. The present invention interposes a holographic recording layer and a substrate with a polarization separation reflection layer for selectively reflecting and transmitting circularly polarized light in order to suppress noise caused by reflected light. Its characteristic is that it eliminates noise by blocking reentry into the lens. Such a holographic information storage medium and a holographic information recording / reproducing apparatus and method using the same have been described with reference to the embodiments shown in the drawings for clarity of understanding, but these are merely exemplary and common knowledge in the art. Those skilled in the art will appreciate that various modifications and equivalent other embodiments are possible therefrom. Therefore, the true technical protection scope of the present invention will be defined by the appended claims.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a holographic storage technology, and in particular, it can be applied to a micro holographic holographic information storage medium storing a single bit of holographic information with high density, and a holographic information recording / reproducing apparatus and method using the same.

1 is a diagram schematically illustrating a configuration of a holographic information storage medium according to an embodiment of the present invention.

2 is a graph showing the optical characteristics of the polarization split reflecting layer.

3 is a diagram schematically illustrating an optical configuration in which a signal light and a reference light are irradiated to the holographic information storage medium of FIG. 1.

4 shows an interference fringe formed by signal light and reference light.

5 is a diagram illustrating polarization states of signal light and reference light incident on the holographic information storage medium of FIG. 1.

6 is a diagram illustrating a polarization state of reproduction light incident on the holographic information storage medium of FIG. 1.

7 is a graph illustrating noise according to a reflection film distance.

8 to 11 are modified examples of the holographic information storage medium of FIG. 1.

12 is a diagram showing a schematic configuration of a holographic information recording / reproducing apparatus according to an embodiment of the present invention.

13 is a view showing a schematic structure of a pinhole member.

14 is a diagram showing that defocused noise light is blocked by the pinhole member.

<Description of the symbols for the main parts of the drawings>

100, 102, 104, 106, 108 ... holographic information storage media

110 ... substrate 120, 122, 124, 126 ... servo layer

130 ... buffer layer 140, 145 ... polarization separation reflection layer

150 ... Space Layer 160 ... Holographic Recording Layer

160 ... recording position 170 ... cover layer

200 ... optical pickup 210 ... light source

220, 250, 260 ... beam splitter 225 ... mirror

230 ... 1/2 Wavelength 240 ... Shutter

270, 275 ... Focus control unit 280 ... Objective lens

285 ... 1/4 wavelength plate 290 ... Photodetector

295 ... Finhole member F ... Focus

L ... Right polarization R ... Right polarization

S ... S Polarization P ... P Polarization

L1 ... Signal light L2 ... Reference light

L3 ... reproducing light

Claims (24)

A substrate; A cover layer to which first and second light having circularly polarized light perpendicular to each other are incident; A polarization separation reflection layer provided between the substrate and the cover layer to reflect the first light while maintaining the polarization direction and to transmit the second light; A holographic recording layer provided between the polarization split reflection layer and the cover layer, the holographic recording layer recording information into an interference fringe formed by first light reflected from the polarization split reflection layer and second light incident from the cover layer; Holographic information storage medium, characterized in that. The method of claim 1, The polarization split reflecting layer is a holographic information storage medium, characterized in that formed of a cholesteric liquid crystal material. The method of claim 2, The polarization split reflecting layer is a holographic information storage medium, characterized in that made of a liquid crystal state or made of a cured liquid crystal film. The method of claim 2, The polarization split reflecting layer is a holographic information storage medium, characterized in that the liquid crystal layer of a single layer or a plurality of liquid crystal layers of different spiral periods of the liquid crystal molecules. The method of claim 1, And the holographic recording layer is formed of photo-polymer or thermoplastic resin. The method of claim 1, A servo layer in which servo information is recorded between any one of the substrate and the polarization separation reflection layer, between the polarization separation reflection layer and the holographic recording layer, inside the holographic recording layer, and between the holographic recording layer and the cover layer. Holographic information storage medium, characterized in that further provided. The method of claim 1, The holographic information storage medium, characterized in that the servo information is recorded in the polarization split reflection layer. The method of claim 1, The holographic information storage medium, characterized in that a space layer is further provided between the polarization separation reflection layer and the holographic recording layer. The method of claim 8, The thickness of the space layer is greater than at least 40μm holographic information storage medium. The method of claim 1, And the spacing between the polarization split reflecting layer and the recording surface on which the information in the holographic recording layer is written is at least a space layer larger than at least 40 μm. The method of claim 1, And a focal position of the first and second light in the depth direction of the holographic recording layer is varied so that information is recorded in multiple layers along the depth direction. The method of claim 1, And the information recorded in the interference fringe is recorded in a single bit. A polarization splitting reflection layer for reflecting the first light among the first and second light having the circular polarization perpendicular to each other and maintaining the polarization direction and transmitting the second light, the holographic recording layer, and the cover layer are sequentially A holographic information recording / reproducing apparatus for recording / reproducing information on a holographic information storage medium stacked in the form of: Irradiating the first and second light to the holographic information storage medium, and forming the focal point in the holographic recording layer by the first light reflected by the polarization splitting layer and the second light incident on the cover layer. And an optical pickup for recording information with the interference fringes. The method of claim 13, The optical pickup irradiates the holographic information storage medium with the second light to receive light reflected from the second light with the polarization direction changed in the holographic recording layer. And the light transmitted through the holographic recording layer among the second lights is blocked from being re-entered into the optical pickup by the polarization splitting reflection layer. Holographic recording in which information is recorded as an interference fringe, and a polarization splitting reflection layer for reflecting the first light of the first light and the second light having circular polarizations perpendicular to each other while maintaining the polarization direction, and transmitting the second light. A holographic information recording / reproducing apparatus for reproducing information in a holographic information storage medium comprising a layer and a cover layer, An optical pickup for irradiating the second light to the holographic information storage medium to receive light reflected from one focal point of the holographic recording layer with the polarization direction changed among the second light; And the light transmitted through the holographic recording layer among the second lights is blocked from being re-entered into the optical pickup by the polarization splitting reflection layer. The method according to any one of claims 13 to 15, And a focus variable unit configured to vary the focus along a depth direction of the holographic information storage medium. The method according to any one of claims 13 to 15, And the focal variable unit is a beam expander or a liquid crystal lens. The method according to any one of claims 13 to 15, And a pinhole member for blocking the light reflected outside the focal point. The method according to any one of claims 13 to 15, And the information recorded in the focal point is recorded in a single bit. Of the first and second light having a circular polarization perpendicular to each other, the first light is reflected while maintaining the polarization direction and the second light is transmitted, the holographic recording layer, and the cover layer are sequentially A holographic information recording / reproducing method for recording information on a holographic information storage medium stacked in a stack and reproducing the recorded information. The difference between the signal light having the first polarization and the reference light having the second polarization perpendicular to the first polarization is refracted in the polarization direction so that any one of the signal light and the reference light covers the holographic information storage medium. The light is focused at one focal point within the recording layer, and the other of the signal light and the reference light is reflected at the polarization separation layer through the cover layer and the recording layer of the holographic information storage medium and then focused at the focal point. And recording the information by forming an interference fringe along the depth direction of the holographic information storage medium in the vicinity of the focal point. The method of claim 20, In the recording mode, the holographic graphic information recording / reproducing method for converting light having a linear polarization component emitted from a first light source into light having a polarization component of the first and second polarizations. The method of claim 21, In the regeneration mode, the linearly polarized light emitted from the first light source is used as the regenerated light, And a polarization direction of the reproduction light is the same as the polarization direction of the reference light. The method of claim 20, And recording information by one bit at the focal point. The method of claim 20, And varying the one focal point along the depth direction of the holographic information storage medium to record information in multiple layers along the depth direction of the holographic information storage medium.

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