JP6667177B2 - Hologram recording / reproducing method and hologram recording / reproducing apparatus - Google Patents

Description

  The present invention relates to a hologram recording / reproducing method and a hologram recording / reproducing device. More specifically, a hologram recording / reproducing method and a hologram recording / reproducing method using a recording medium having a configuration effective for configuring a large-capacity optical memory by multiplexly recording a two-dimensional digital bit pattern as a hologram on a recording medium. Related to the device.

  2. Description of the Related Art Hitherto, a hologram recording / reproducing method for two-dimensionally recording / reproducing digital information using a hologram has been proposed. In this hologram recording / reproducing method, a recording medium having a recording layer made of a photoreactive monomer and a light transmitting layer is used, and when recording digital information, a spatial light modulator consisting of a plurality of pixels is used. A hologram is formed by causing a signal light carrying digital information (data information) modulated by the above and a reference light coherent with the signal light in a recording medium (recording layer) to form a hologram. Record as information. When reproducing digital information recorded on a recording medium, diffracted light is generated by irradiating the hologram with reference light used for recording, and the hologram is recorded as a hologram on a CCD (imaging device). An image of digital information is formed.

  In such a hologram recording / reproducing method, specific hologram recording methods include an angle multiplex recording method and a speckle reference beam multiplex recording method.

  In the hologram recording method based on the angle multiplex recording method, the irradiation angle of the reference light on the recording medium is changed little by little, and the hologram is multiplex-recorded on a certain area on the recording medium. When the thickness of the recording medium is large (specifically, 1 mm or more), the Bragg diffraction condition becomes angularly strict, and when the angle is about 0.1 °, the Bragg diffraction angle condition deviates and reading becomes impossible. . Using this principle, several hundred holograms are recorded (multiplexed) in the same area on a recording medium. In the angle multiplex recording method, multiplex recording is performed in book units. That is, after performing multiplex recording of a hologram in a certain area, the irradiation area of light (signal light and reference light) is changed, and multiplex recording of a new hologram is performed in another area that does not overlap with the one area. It is performed sequentially for each book.

  In the hologram recording method using the speckle reference light multiplex recording method, the reference light is modulated by a speckle pattern. The hologram is recorded by the interference between the reference light and the signal light modulated by the speckle pattern on the recording medium. For this reason, when reproducing the hologram recorded on the recording medium, reproduction can be performed only when the reference light has the same speckle pattern as at the time of recording. Thus, if the recording medium is shifted by a small distance (specifically, about 10 μm), the conformity of the speckle pattern (correlation of the speckle pattern) is broken, and the hologram cannot be reproduced. Using this principle, multiplex recording of a hologram is performed by shifting the recording medium. That is, a new hologram can be recorded by slightly shifting the recording medium, and shift multiplex recording can be repeated.

JP 2010-61750 A

  In the angle multiplexing recording method which has been conventionally studied, light propagating by a plane wave is used as reference light. In the angle multiplex recording method, when a reflection layer is provided on a recording medium, the plane wave reference light is reflected while maintaining the light intensity to irradiate an area other than the recording area in the recording layer. There is a problem that the number of multiplex recordings is limited by polymerization. For this reason, in the recording medium, the reflection layer is not used at present, and a mirror is installed on the opposite side of the recording medium by phase conjugate reproduction, the angle of the mirror is changed according to the angle change, and the optical path of the reference light In general, signal reproduction is performed by reversing. In this method, since each hologram is multiplex-recorded with a slight angle change, when reproducing each hologram, the reference light propagating in the opposite direction to the reference light at the time of recording is used for phase conjugate reproduction. Due to the necessity of irradiation, it is necessary to install a mirror having an angle adjusting function on the opposite side of the recording medium, which has a drawback that the configuration of the apparatus is complicated and that head access to an information position is difficult.

  On the other hand, in a speckle reference beam multiplex recording method which has been conventionally studied, a reflection layer is provided between a light transmission layer and a recording layer in a recording medium. In such a recording medium, the light intensity is concentrated due to the presence of the reflective layer at the condensing position of the signal light and the reference light, and the monomer in the recording layer is excessively consumed, thereby limiting the number of multiplex recordings. There is a disadvantage that. In this method, a reflection hologram formed by reference light propagating in the opposite direction to a so-called normal reference light is also formed at the same time due to interference between the reflected reference light and the signal light. Reflection holograms are more sensitive to tolerances caused by changes in the environment or light propagation conditions than transmission holograms, and have the drawback that stable reproduction is not performed. For this reason, the reproduction light of the reflection hologram fluctuates due to the influence of the tolerance, and the reproduction light amount easily fluctuates significantly as a whole. In addition, since unnecessary hologram recording is performed in addition to the transmission type, wasteful consumption of monomers occurs, and the number of multiplex recordings is greatly limited. Also, in this method, when the reflection layer is set apart from the light condensing position, the signal light and the reference light are reflected in the same direction. It becomes difficult and causes an increase in noise. This increase in noise also limits the number of recording multiplexes.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to increase the density of information recorded on a reflective recording medium and to stabilize a recorded hologram. It is an object of the present invention to provide a hologram recording / reproducing method and a hologram recording / reproducing apparatus which can perform simple reproduction and can simplify the configuration of the hologram recording / reproducing apparatus itself and can perform high-speed access.

The hologram recording / reproducing method of the present invention records an interference fringe between a signal light carrying data information and a reference light as a hologram on a recording medium and irradiates the hologram recorded on the recording medium with the reference light, thereby irradiating the hologram with the reference light. In a hologram recording / reproduction method for reproducing recorded data information,
As a recording medium, a hologram recording layer irradiated with signal light and reference light from one side, a light absorption layer laminated on the other surface of the hologram recording layer, and a light transmission layer on the other surface of the light absorption layer And a reflective layer that is laminated by using
A spherical wave is used as the reference light,
It is characterized in that spherical reference light shift multiplex recording is performed by moving one of an optical mechanism for irradiating the recording medium with signal light and reference light and one of the recording medium relative to the other.

  In the hologram recording / reproducing method of the present invention, when a plane perpendicular to a plane including the optical axis of the signal light incident on the recording medium and the optical axis of the reference light incident on the recording medium is set as the reference plane, On a track on the surface of the recording medium, after recording a shift multiplexed hologram sequence by performing spherical reference light shift multiplexed recording in only one direction, in the same region as the recording region where the shift multiplexed hologram sequence was recorded, It is preferable to perform multiplexed recording of a new multiplexed hologram array by performing spherical reference beam shift multiplexed recording while the surface of the recording medium is inclined at a predetermined angle with respect to the reference plane.

The hologram recording / reproducing apparatus of the present invention performs multiplex recording of interference fringes between a signal light carrying data information and a reference light as a hologram on a recording medium and irradiates the hologram recorded on the recording medium with the reference light to thereby perform the hologram recording. In a hologram hologram recording / reproducing apparatus for reproducing data information recorded on a hologram,
As a recording medium, a hologram recording layer irradiated with signal light and reference light from one side, a light absorption layer laminated on the other surface of the hologram recording layer, and a light transmission layer on the other surface of the light absorption layer And a reflective layer that is laminated by using
An optical mechanism that irradiates the recording medium with the signal light and the spherical reference light, and a moving mechanism that moves one of the optical mechanism and the recording medium relative to the other,
One of the optical mechanism and the recording medium is relatively moved in one direction along the surface of the recording medium with respect to the other, and shift multiplex recording is performed on the recording medium, so that a shift multiplex hologram sequence is recorded. It is characterized by the following.

In the hologram recording / reproducing apparatus of the present invention, when the plane perpendicular to the plane including the optical axis of the signal light incident on the recording medium and the optical axis of the reference light incident on the recording medium is set as the reference plane, the recording medium is rotated. It further comprises a recording medium tilt mechanism for inclining the surface of the recording medium with respect to the reference plane,
In the state where the surface of the recording medium is tilted with respect to the reference plane by the recording medium tilt mechanism, the spherical reference light shift multiplex recording in only one direction is performed, so that a new shift multiplexed hologram sequence is already recorded on the recording medium. It is preferable that multiplex recording is performed in the same area as the recording area of the shifted multiplexed hologram row.

  According to the hologram recording / reproducing method of the present invention, the hologram is multiplex-recorded by the spherical reference beam shift multiplex recording method on the reflection type recording medium in which the reflection layer is laminated on the hologram recording layer via the light transmission layer. Thereby, at the time of hologram recording, the influence of the reflected light of the signal light by the reflective layer and the reflected light of the reference light by the reflective layer on the recording of the hologram can be extremely reduced. Therefore, the density of the information to be recorded can be increased, and the recorded hologram can be stably reproduced. Further, the configuration of the hologram recording / reproducing apparatus itself can be simplified, and high-speed access is possible.

  When reproducing the hologram recorded on the recording medium, a reference light having a different polarization direction from the recording reference light at the time of recording the hologram is irradiated as reproduction reference light, and the recording reference light is used as a recording medium. The same effect can be obtained by using a reflective type having a reflective layer that transmits and reflects the reference light for reproduction.

  According to the hologram recording / reproducing apparatus of the present invention, by implementing the above-mentioned hologram recording / reproducing method, the density of information to be recorded is increased while the configuration of the apparatus itself is simplified. In addition, the recorded hologram can be stably reproduced, and the information can be easily accessed to increase the speed.

FIG. 2 is an explanatory diagram showing an example of a configuration of a recording medium used in a first hologram recording / reproducing method according to the present invention, together with a signal light focusing objective lens and a reference light focusing objective lens. FIG. 4 is an explanatory diagram showing another example of the configuration of the recording medium used in the first hologram recording / reproducing method according to the present invention. FIG. 11 is an explanatory diagram illustrating an example of a configuration of a recording medium used in a second hologram recording / reproducing method according to the present invention. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory schematic diagram illustrating an example of a configuration of a main part in a hologram recording / reproducing apparatus of the present invention together with a recording medium. FIG. 5 is a perspective view schematically showing a configuration example of a recording medium driving mechanism in the hologram recording / reproducing apparatus shown in FIG. 4. FIG. 5 is an explanatory schematic diagram showing another example of the configuration of the main part in the hologram recording / reproducing apparatus of the present invention, together with a recording medium.

Hereinafter, embodiments of the present invention will be described.
[First hologram recording / reproducing method]
The first hologram recording / reproducing method according to the present invention uses a spherical wave (hereinafter, referred to as a “spherical reference light”) as a reference light, irradiates a signal light and a spherical reference light, and a reflection type recording medium. By moving one relative to the other in one direction along the surface of the recording medium, a spherical reference light shift multiplex recording in only one direction is performed on the recording medium to record a shift multiplex hologram array. .

In the spherical reference light shift multiplex recording, when a plane perpendicular to a plane including the optical axis of the signal light and the optical axis of the spherical reference light with respect to the recording medium is set as a reference plane, for example, the surface is arranged along the reference plane. The recording is performed by shifting the recording medium in one direction along the surface thereof. As a result, a shift multiplexed hologram row in which a plurality of holograms are recorded so as to be arranged in one direction while partially overlapping each other is obtained. Here, one hologram has a substantially circular shape in plan view, and its size is, for example, a diameter (hologram diameter) of 50 μm. The shift amount of the hologram (the shift amount of the recording medium) is, for example, 10 μm or more, and thereby, it is possible to avoid crosstalk between adjacent holograms.
Such spherical reference light shift multiplex recording may be performed by moving an optical mechanism for irradiating the signal light and the reference light with respect to the recording medium.

FIG. 1 is an explanatory diagram showing an example of the configuration of a recording medium used in the first hologram recording / reproducing method according to the present invention, together with a signal light focusing objective lens and a reference light focusing objective lens.
The recording medium 10 includes a hologram recording layer 11 on which signal light Ls and spherical reference light Lr are irradiated from one side via a light transmitting substrate 14, and a light transmitting layer 12 laminated on the other surface of the recording layer 11. And a reflection layer 13 laminated on the other surface of the light transmission layer 12. Here, “light transmission (property)” means that the light transmittance of the signal light Ls and the spherical reference light Lr in the wavelength band is 80% or more.

The hologram recording layer 11 is made of a photoreactive monomer. The photoreactive monomer is converted into a polymer when irradiated with light, and as a result, a region having a different refractive index is formed, which becomes a hologram.
The thickness of the hologram recording layer 11 is preferably, for example, 0.3 to 2.0 mm, and more preferably 0.5 to 1.0 mm, from the viewpoint of recording / reproducing ability.
The light transmission layer 12 is a base layer for supporting the hologram recording layer 11. As the light transmitting layer 12, for example, a light transmitting substrate can be used.
The reflection layer 13 is made of a deposited film. As a material of the reflection layer 13, a material that can reflect at least reproduction light is used.

In the recording medium 10 described above, the signal light Ls condensed by the signal light condensing objective lens 38 and irradiated on the recording medium 10, and the signal light Ls condensed by the reference light condensing objective lens 43 and The hologram is formed by the interference of the irradiated spherical reference light Lr on the hologram recording layer 11 of the recording medium 10.
The hologram recorded on the recording medium 10 is irradiated with spherical reference light having a smaller output than the spherical reference light Lr used for recording the hologram, whereby data information recorded on the hologram is reproduced. You.

  Light irradiation conditions for the recording medium 10 during hologram recording are, for example, that the output of the signal light Ls is, for example, 60 μW and the output of the spherical reference light Lr is, for example, 1000 μW (1 nW). In reproducing the hologram, the output of the spherical reference light is, for example, about 20 μW.

  It is preferable that the recording medium used in the first hologram recording / reproducing method further includes a light absorption layer between the hologram recording layer and the reflection layer. Specifically, as shown in FIG. 2, a light absorbing layer 15 is laminated on the other surface of the hologram recording layer 11, and a reflective layer 13 is laminated on the other surface of the light absorbing layer 15 via the light transmitting layer 12. Configuration.

The light absorption layer 15 preferably has a light transmittance of 50% or less for light in a wavelength band of, for example, 400 nm to 450 nm (for example, blue laser light).
Such a light absorbing layer 15 can be made of, for example, a plastic material containing a dye that absorbs light in the above-mentioned wavelength band.
The thickness of the light absorbing layer 15 is preferably, for example, 0.1 to 1.5 mm, more preferably 0.5 to 1.0 mm, from the viewpoint of recording / reproducing ability.

In the recording medium 10a, the signal light Ls condensed by the signal light condensing objective lens and irradiated on the recording medium 10a, and the signal light Ls condensed by the reference light condensing objective lens and irradiated on the recording medium 10a. The recording spherical reference light Lr1 interferes with the hologram recording layer 11 of the recording medium 10a to form a hologram. At the time of hologram recording, a part of the signal light Ls and the recording spherical reference light Lr1 transmitted through the hologram recording layer 11 are partially absorbed by the light absorption layer 15, and the signal light Ls reflected by the reflection layer 13 and Most of the light Lr1 ′ reflected by the reflective layer 13 of the recording spherical reference light Lr1 is absorbed by the light absorbing layer 15.
The hologram recorded on the recording medium 10a is irradiated with the reproduction spherical reference light Lr2 having a smaller output than the spherical reference light Lr1 used at the time of recording the hologram, so that the data information recorded on the hologram is obtained. Is played. Lr2 ′ in FIG. 2 is the reflected light of the spherical reference light for reproduction Lr2 by the reflective layer 13.

[Second hologram recording / reproducing method]
The second hologram recording / reproducing method according to the present invention uses a spherical wave (spherical reference light) as reference light, and applies one of an optical mechanism for irradiating signal light and spherical reference light and a reflective recording medium to the other. By moving the hologram recorded on the recording medium while performing the shift multiplexed hologram recording by performing the spherical reference light shift multiplex recording in only one direction on the recording medium by moving the hologram recorded on the recording medium relatively in one direction along the surface of the recording medium. The data information recorded on the hologram is reproduced by irradiating reference light having a different polarization direction from the recording reference light at the time of recording the hologram as reproduction reference light.
In the second hologram recording / reproducing method according to the present invention, the following reflective recording medium is used.

FIG. 3 is an explanatory diagram showing an example of the configuration of a recording medium used in the second hologram recording method according to the present invention.
The recording medium 10b is used for recording a hologram and reproducing a hologram by using a recording spherical reference light Lr1 and a reproduction spherical reference light Lr2 having different deflection directions as reference light, and a signal from one surface side. The hologram recording layer 11 to which the light Ls and the recording spherical reference light Lr1 or the reproduction spherical reference light Lr2 are irradiated via the light transmitting substrate 14, and the other surface of the hologram recording layer 11 via the light transmitting layer 12. And a laminated reflective layer 13a. The reflection layer 13a in the recording medium 10b has a function of transmitting the recording spherical reference light Lr1 and reflecting the reproduction spherical reference light Lr2 (deflection selectivity).

The reflection layer 13a has a light transmittance of the recording spherical reference light (for example, P-polarized light) Lr1 when the incident angle with respect to the reflection layer 13a is 20 degrees in a wavelength band of 400 nm to 410 nm (for example, blue laser light). Preferably, the light reflectance of the spherical reference light for reproduction (for example, S-polarized light) Lr2 is 50% or more.
Such a reflective layer 13a can be made of, for example, polyvinyl alcohol.

In the recording medium 10b, a hologram is formed by the signal light Ls and the recording spherical reference light Lr1 interfering in the hologram recording layer 11 of the recording medium 10b. At the time of hologram recording, the signal light Ls and the recording spherical reference light Lr1 transmitted through the hologram recording layer 11 are transmitted through the reflection layer 13a. Lr1 ″ in FIG. 3 is transmitted light of the recording spherical reference light Lr1.
The hologram recorded on the recording medium 10b is irradiated with reproduction spherical reference light Lr2 having a different deflecting direction from the recording spherical reference light Lr1 used for recording the hologram. The information is reproduced. At the time of hologram reproduction, the reproduction spherical reference light is reflected by the reflection layer 13a. Lr2 ′ in FIG. 3 is the reflected light of the spherical reference light for reproduction Lr2 by the reflective layer 13a.

  In the first and second hologram recording / reproducing methods described above, the shift multiplexed hologram sequence is recorded on the recording medium by performing the spherical reference beam shift multiplexing recording in only one direction, and then performing the shift multiplexed hologram sequence. It is preferable that a new shift multiplexed hologram sequence is multiplex-recorded in the same area as the recording area in which is recorded, for example, through the following multiplex recording step.

  The multiplex recording step includes, when a plane perpendicular to a plane including the optical axis of the signal light and the optical axis of the spherical reference light with respect to the recording medium is set as a reference plane, the spherical surface is arranged in a state where the surface is arranged along the reference plane. In a state where the recording medium on which the first shift multiplexed hologram sequence is recorded and the first shift multiplexed hologram sequence is recorded is rotated (tilted) and tilted, the recording area on which the first shift multiplexed hologram sequence is recorded has a spherical surface. A shift multiplexed hologram row overwriting process of multiplex-recording a second shift multiplexed hologram row by performing reference beam shift multiplexed recording (tilt shift multiplexed recording) is performed at least once.

In tilt-shift multiplex recording, the inclination angle of the surface of the recording medium with respect to a reference plane is determined by irradiating a spherical reference beam onto a recording area in which a plurality of shift-multiplexed hologram arrays are multiplex-recorded. Is preferably an angle at which the reproduced image is reproduced in a separated state on the detector. Specifically, the inclination angle of the surface of the recording medium with respect to the reference plane is preferably 5 ° or more.
In tilt-shift multiplex recording, the direction of inclination of the surface of the recording medium with respect to the reference plane is not particularly limited, and may be any direction.

  Next, a specific example of a hologram recording / reproducing apparatus in which the hologram recording / reproducing method of the present invention is performed will be described with reference to the drawings.

FIG. 4 is an explanatory schematic diagram showing an example of a configuration of a main part of the hologram recording / reproducing apparatus of the present invention together with a recording medium. FIG. 5 is a perspective view schematically showing a configuration example of a recording medium driving mechanism in the hologram recording / reproducing apparatus shown in FIG.
The hologram recording / reproducing apparatus includes an optical mechanism for irradiating the recording medium 10 with the signal light Ls carrying data information and the recording spherical reference light Lr1 or the reproduction spherical reference light Lr2, and a recording medium driving mechanism.

The optical mechanism is, for example, a recording / reproducing light source 21 composed of a blue laser light source, and splitting the laser light from the recording / reproducing light source 21 into light for signal light and light for reference light. Means 22, a signal light irradiating optical system for irradiating the light for signal light from the light separating means 22 to the recording medium 10 as signal light Ls carrying data information (page data), and reference light from the light separating means 22 For irradiating the recording medium 10 with the recording light converted into a spherical wave and irradiating the recording medium 10 with the recording spherical reference light Lr1 or the reproduction spherical reference light Lr2, and for the reproduction light detection for detecting the reproduction light from the hologram. And an optical system.
A shutter 23, a polarizing plate 24, and a beam shaping lens 25 are provided on the optical path of the laser light between the recording / reproducing light source 21 and the light separating means 22.

  The signal light irradiation optical system has an optical path L1 extending from the light separating means 22 to the recording medium 10. On this optical path L1, a beam expander 31 for expanding light for signal light, a polarizing prism beam splitter 32 , A spatial light modulator (SLM) 33, a relay lens 34, a Nyquist filter 35, a phase plate 36 for cutting a DC component of signal light, and a signal light focusing objective lens 38. Here, the polarizing prism beam splitter 32 transmits or reflects according to the polarization direction of light. In the polarizing prism beam splitter 32, the light that has entered first is reflected and made incident on a spatial light modulator (SLM) 33. The light modulated by the spatial light modulator (SLM) 33 is transmitted through the polarization beam splitter 32 this time because the polarization direction is rotated by 90 °.

  The spherical reference light irradiation optical system has an optical path L2 extending from the light separating means 22 to the recording medium 10, and on this optical path L2, a neutral density filter (ND filter) 41 for adjusting the amount of light, a half-wave plate ( λ / 2 wavelength plate) 42 and a reference light converging objective lens 43 that converts the light for reference light into a spherical wave to generate the recording spherical reference light Lr1 or the reproduction spherical reference light Lr2. The half-wave plate 42 is provided, for example, rotatably, and can adjust the deflection direction of the reference light. For example, at the time of hologram reproduction, the deflection direction of the reference light is adjusted so that the recording medium 10 is irradiated with the reproduction spherical reference light Lr2 having a different deflection direction from the recording spherical reference light Lr1 at the time of hologram recording. Reference numerals 46 and 47 are reflection mirrors for changing the traveling direction of the reference light.

The reproducing light detecting optical system includes a polarizing prism 37 provided at a position between the phase plate 36 and the signal light converging objective lens 38 in the optical path L1 in the signal light irradiating optical system, and an image sensor 39 such as a CCD. And
In this hologram recording / reproducing apparatus, the reproduction light from the hologram reflected by the reflection layer 13 of the recording medium 10 reverses the optical path of the signal light emitted from the polarizing prism beam splitter 32 toward the recording medium 10. It will be. Therefore, the image sensor 39 is provided at a position where the reproduction light from the hologram is reflected by the polarizing prism 37 and enters.

  As shown in FIG. 5, for example, the recording medium drive mechanism moves the disk-shaped recording medium 10 to a reference plane whose surface is perpendicular to a plane including the optical axis of the signal light and the optical axis of the reference light with respect to the recording medium 10. Recording medium holding means 51 for holding the recording medium 10 in a position extending along the recording medium, a recording medium rotation mechanism 52 for rotating (rotating) the recording medium 10 in a plane along the surface thereof, and a recording medium rotating mechanism 52 for holding the recording medium 10 along the surface thereof. And a recording medium tilt mechanism 57 that rotates the recording medium 10 to incline the surface of the recording medium 10 with respect to a reference plane.

  The recording medium holding means 51 is provided with a rotating shaft 53 constituting the recording medium rotating mechanism 52 so as to extend in a direction perpendicular to the reference plane. The recording medium 10 is held by fitting and mounting the provided mounting holes. C1 is the rotation center axis of the recording medium 10.

  The recording medium rotating mechanism 52 includes a drive source (not shown) for driving a rotating shaft 53 provided on the recording medium holding means 51. As the driving source, for example, a stepping motor or the like can be used.

  The recording medium moving mechanism 55 includes a uniaxial stage 56 for moving the recording medium 10 in the radial direction. The recording medium holding means 51 is provided on the uniaxial stage 56, and therefore, when the uniaxial stage 56 is driven, the recording medium 10 held by the recording medium holding means 51 is placed in a plane along the surface thereof. Moved within.

  The recording medium tilt mechanism 57 includes a rotation stage 58 that is driven to rotate about a tilt rotation axis C2 extending in a direction perpendicular to a plane including the optical axis of the signal light and the optical axis of the reference light with respect to the recording medium 10. . The tilt rotation axis C2 is located, for example, on the surface of the recording medium 10. On the rotary stage 58, a one-axis stage 56 constituting the recording medium moving mechanism 55 is provided. Therefore, when the rotary stage 58 is driven, the recording medium holding means provided on the one-axis stage 56 is provided. The recording medium 10 held by 51 is rotated about the tilt rotation axis C2, and the surface of the recording medium 10 is inclined with respect to the reference plane. As a driving source of the rotary stage 58, for example, a stepping motor or the like can be used.

  In this hologram recording / reproducing apparatus, a laser beam emitted from a recording / reproducing light source 21 composed of a blue laser light source is split by a light separating means 22 into light for signal light and light for reference light. The light for the reference light is incident on the reference light focusing objective lens 43 via the ND filter 41 and the half-wave plate 42, is converted into a spherical wave by the reference light focusing objective lens 43, and is used as the recording spherical reference light. The recording medium 10 is irradiated as Lr1. On the other hand, the light for the signal light is expanded by the beam expander 31 and then applied to a spatial light modulator (SLM) 33 to be modulated. The light emitted from the spatial light modulator (SLM) 33 is adjusted in the frequency band on the Fourier plane by the Nyquist filter 35, and is further given a random phase to each bit of the two-dimensional bit pattern by the phase plate 36, Unnecessary DC component light on the recording medium surface, that is, the Fourier surface, is cut. Here, unnecessary DC component light on the Fourier surface is cut by the phase plate 36, so that the recording medium 10 does not wastefully consume the photoreactive monomer. The light for signal light transmitted through the phase plate 36 is condensed by the signal light converging objective lens 38 and is irradiated on the recording medium 10 as signal light Ls. Thereby, in the recording medium 10, an interference fringe by the signal light Ls and the recording spherical reference light Lr1 is recorded as a hologram.

Then, the recording medium 10 is moved in the radial direction (indicated by an outline arrow in FIG. 4) by the recording medium moving mechanism 55, and the spherical reference light shift multiplex recording is performed, whereby the shift multiplex hologram sequence is recorded. .
Further, when the shift multiplex recording is overwritten, for example, the recording medium 10 is tilted by, for example, about 5 ° by the recording medium tilt mechanism 57 so that the surface of the recording medium 10 is inclined with respect to the reference plane. By performing the reference beam shift multiplex recording, a new shift multiplex hologram ram sequence is multiplex-recorded in the same region as the recording region where the shift multiplex hologram sequence has already been recorded. At this time, positioning is performed by the recording medium moving mechanism 55 so that the recording medium 10 is positioned at the center position of the recording area of the shift multiplexed hologram row in which the tilt rotation axis C2 has already been recorded.

  At the time of reproducing the data information related to the hologram recorded on the recording medium 10 in this manner, only the reproducing spherical reference light Lr2 whose light quantity is greatly reduced is irradiated on the recording medium 10, so that the reproduction light is obtained from the hologram. Can be The reproduction light from the hologram is reflected by the reflection layer 13 of the recording medium 10 and travels backward in the optical path of the light relating to the signal light emitted from the polarizing prism beam splitter 32 toward the recording medium 10, and is reflected by the polarizing prism 37. Then, the image is detected by the image sensor 39. As a result, the data information recorded on the hologram is reproduced. At the time of this reproduction, since the reproduction light having the same polarization direction as the reproduction spherical reference light Lr2 needs to be reflected by the polarizing prism 37 and incident on the image sensor 39, the polarization direction of the reproduction spherical reference light Lr2 is half. It is rotated 90 ° by the wave plate 42.

FIG. 6 is an explanatory schematic diagram showing another example of the configuration of the main part of the hologram recording / reproducing apparatus of the present invention together with a recording medium.
The hologram recording / reproducing apparatus includes an optical mechanism that irradiates the signal light Ls and the recording spherical reference light Lr1 or the reproduction spherical reference light Lr2 to the recording medium 10, and rotates and rotates the recording medium 10 in a plane along the surface thereof. And a recording medium driving mechanism for performing parallel movement.

The optical mechanism includes a recording / reproducing light source 21 composed of, for example, a blue laser light source, and a light separating unit 22 composed of, for example, a half mirror prism for dividing light from the recording / reproducing light source 21 into light for signal light and light for reference light. A signal light irradiating optical system for irradiating the recording medium 10 with signal light as signal light Ls carrying data information, and converting the reference light to a spherical wave to record spherical reference light Lr1 or reproduction. A spherical reference light irradiating optical system that irradiates the recording medium 10 as the spherical reference light Lr2 for use, and a reproduction light detection optical system that detects reproduction light from the hologram are provided.
A shutter 23, a polarizing plate 24, and a beam shaping lens 25 are provided on the optical path L of the laser light between the recording / reproducing light source 21 and the light separating means 22.

  The signal light irradiating optical system has an optical path L1 from the light separating means 22 to the recording medium 10, and on this optical path L1, a beam expander 44, a phase plate 36, a relay lens 45, a polarizing prism beam splitter 40 , A spatial light modulator (SLM) 33, a Nyquist filter 35, a relay lens 34, and a signal light focusing objective lens 38.

  The spherical reference light irradiation optical system has an optical path L2 extending from the light separating means 22 to the recording medium 10. On this optical path L2, the ND filter 41, the half-wave plate 42, and the light for the reference light are converted into a spherical wave. And a reference light condensing objective lens 43 for generating the recording spherical reference light Lr1 or the reproduction spherical reference light Lr2. The half-wave plate 42 is provided, for example, rotatably, and can adjust the deflection direction of the reference light. For example, at the time of hologram reproduction, the deflection direction of the reference light is adjusted so that the recording medium 10 is irradiated with the reproduction spherical reference light Lr2 having a different deflection direction from the recording spherical reference light Lr1 at the time of hologram recording. Reference numerals 46 and 47 are reflection mirrors for changing the traveling direction of the reference light.

The reproduction light detecting optical system includes an image pickup device 39 composed of, for example, a CCD.
In this hologram recording / reproducing apparatus, the reproduction light from the hologram reflected by the reflection layer 13 of the recording medium 10 reverses the optical path of the light related to the signal light emitted from the polarizing prism beam splitter 40 toward the recording medium 10. Will proceed. Therefore, the imaging element 39 is provided facing the surface of the recording medium 10 at a position where the reproduction light from the hologram is transmitted through the polarizing prism beam splitter 40 and is incident.

  In this hologram recording / reproducing apparatus, a laser beam emitted from a recording / reproducing light source 21 composed of a blue laser light source is split by a light separating means 22 into light for signal light and light for reference light. The light for the reference light is incident on the reference light focusing objective lens 43 via the ND filter 41 and the half-wave plate 42, is converted into a spherical wave by the reference light focusing objective lens 43, and is used as the recording spherical reference light. The recording medium 10 is irradiated as Lr1. On the other hand, the light for signal light is incident on the polarizing prism beam splitter 40 via the beam expander 44, the phase plate 36, and the relay lens 45. The light for the signal light passes through the polarizing prism beam splitter 40 and is applied to a spatial light modulator (SLM) 33. The spatial light modulator (SLM) 33 modulates the signal light into a data pattern whose polarization plane has been changed by 90 °. The light emitted from the spatial light modulator (SLM) 33 is reflected by the polarizing prism beam splitter 40, the traveling direction is changed by 90 °, the spatial frequency band is adjusted by the Nyquist filter 35, and the signal light The light is condensed by the objective lens 38 and is irradiated on the recording medium 10 as signal light Ls. Thereby, in the recording medium 10, an interference fringe by the signal light Ls and the recording spherical reference light Lr1 is recorded as a hologram.

  The recording medium moving mechanism moves the recording medium 10 in the radial direction (indicated by a white arrow in FIG. 6) and performs the shift reference multiplex hologram recording by performing the spherical reference light shift multiplex recording.

  At the time of reproducing the data information related to the hologram recorded on the recording medium 10, only the reproducing spherical reference light Lr <b> 2 whose light quantity is greatly reduced is irradiated on the recording medium 10, so that the hologram emits the reproducing light. The reproduction spherical reference light Lr2 has a deflection direction rotated by 90 ° by the half-wave plate 42, and has a different deflection direction from the recording spherical reference light Lr1. The reproduction light is reflected by the reflection layer 13 and emitted from the surface side of the recording medium 10. The reproduction light travels backward along the optical path of the signal light traveling from the polarizing prism beam splitter 40 toward the recording medium 10 and enters the polarizing prism beam splitter 40. At this time, the reproduction light having the same deflection direction as the reproduction spherical reference light Lr2 is transmitted through the polarizing prism beam splitter 40 and is incident on the image sensor 39. When the reproduction light is detected by the imaging element 39, the data information recorded on the hologram is reproduced.

As described above, in the first hologram recording / reproducing method of the present invention, recording is performed using the spherical reference light on the recording medium 10 in which the reflection layer 13 is laminated on the hologram recording layer 11 via the light transmission layer 12. Therefore, even if the recording medium 10 is of a reflective type, the intensity distribution density becomes extremely low after the signal light Ls is reflected by the reflective layer 13. Further, in the recording medium 10a provided with the light absorbing layer 15 between the hologram recording layer 11 and the light transmitting layer 12, the intensity distribution density of the signal light Ls reflected by the reflecting layer 13 is further reduced. Therefore, at the time of hologram recording, the hologram formed by the reflected signal light and the recording spherical reference light Lr1 is in a range that can be almost ignored.
On the other hand, since the optical axis of the recording spherical reference light Lr1 is incident on the surface of the recording medium 10 at an angle of, for example, about 45 °, the reflected light Lr1 ′ of the recording spherical reference light Lr1 becomes the signal light Ls. There is no interference. Further, since the light is a spherical wave, the intensity of reflected light is extremely small. In the recording medium 10a provided with the light absorbing layer 15 between the hologram recording layer 11 and the light transmitting layer 12, the intensity of the recording spherical reference light Lr1 reflected by the reflection layer 13 of the reflection layer Lr1 'is further reduced. Therefore, the consumption of the photoreactive monomer constituting the hologram recording layer 11 is significantly reduced as compared with the angle multiplex recording using the plane wave reference light.
As described above, in the first hologram recording / reproducing method of the present invention, at the time of hologram recording, the reflected light Lr1 ′ of the signal light Ls by the reflective layer 13 and the reflected light Lr1 ′ of the recording spherical reference light Lr1 by the reflective layer 13 are high. The effect on density multiplex recording is extremely small.
During hologram reproduction, the signal light Ls is cut, and only the reproduction spherical reference light Lr2 is irradiated on the hologram. Specifically, the output (power) of the reproduction spherical reference light Lr2 applied to the recording medium 10 is, for example, about 20 μW. When the hologram is irradiated with the reproduction spherical reference light Lr2, the reproduction light of the hologram is generated in a direction toward the reflection layer 13. After being reflected by the reflection layer 13, the reproduction light travels in a direction opposite to the traveling direction of the signal light Ls during hologram recording. The information recorded on the hologram is reproduced by detecting the reproduction light by the image sensor 39.

  Similarly, in the second hologram recording / reproducing method of the present invention, at the time of hologram recording, the reflected light of the signal light Ls by the reflective layer and the reflected light of the recording spherical reference light Lr1 by the reflective layer are subjected to high-density multiplex recording. The effect is extremely small. That is, in the second hologram recording / reproducing method of the present invention, a spherical reference light is used for the recording medium 10b in which the reflection layer 13a having polarization selectivity is laminated on the hologram recording layer 11 via the light transmission layer 12. Therefore, even if the recording medium 10b is of a reflection type, the signal light Ls and the recording spherical reference light Lr1 transmitted through the hologram recording layer 11 transmit through the reflection layer 13a. Therefore, the influence of the signal light Ls returning to the hologram recording layer 11 and the recording spherical reference light Lr1 is extremely small.

Therefore, according to the hologram recording / reproducing method of the present invention, the hologram is recorded on the reflection type recording medium 10 in which the reflection layer 13 is laminated on the hologram recording layer 11 via the light transmission layer 12 by the spherical reference light shift multiplex recording method. Is performed, the influence of the reflected light of the signal light Ls by the reflective layer 13 and the reflected light Lr1 ′ of the recording spherical reference light Lr1 by the reflective layer 13 on the recording of the hologram can be extremely reduced. In addition, the density of information to be recorded can be increased, and the recorded hologram can be stably reproduced. Further, since the configuration of the hologram recording / reproducing apparatus itself can be simplified, and the unit recording area in the recording medium 10 can be accessed by, for example, moving and rotating the recording medium 10, high-speed access is possible. Become.
Further, in the reflective recording medium 10a provided with a light absorbing layer between the hologram recording layer 11 and the light transmitting layer 12, the above-mentioned effect can be obtained more reliably.

  Furthermore, when reproducing the hologram recorded on the recording medium, reference light having a different polarization direction from the recording spherical reference light Lr1 at the time of recording the hologram is irradiated as the reproducing spherical reference light Lr2. The same effect can be obtained by using the reflective recording medium 10b including the reflective layer 13a that transmits the recording spherical reference light Lr1 and reflects the reproduction spherical reference light Lr2.

  Further, according to the hologram recording / reproducing apparatus of the present invention, the above-mentioned hologram recording / reproducing method is carried out, so that the configuration of the apparatus itself is simplified, but the density of information to be recorded is increased. In addition, the recorded hologram can be stably reproduced, and the information can be easily accessed to increase the speed.

The hologram recording / reproducing method of the present invention is not limited to the above embodiment, and various changes can be made.
For example, a hologram recording / reproducing apparatus other than the hologram recording / reproducing apparatus shown in FIG. 4 and the hologram recording / reproducing apparatus shown in FIG. 6 can be used.
Further, in the present invention, cross-shift multiplex recording is performed in which a plurality of shift multiplex holograms recorded by spherical reference light shift multiplex recording are recorded in a state where a part of the recording area of each shift multiplex hologram array overlaps with each other. Accordingly, the configuration may be such that the density of information recorded on the recording medium is increased.

REFERENCE SIGNS LIST 10 recording medium 10a recording medium 10b recording medium 11 hologram recording layer 12 light transmission layer 13 reflection layer 13a reflection layer 14 light transmission substrate 15 light absorption layer 21 recording / reproduction light source 22 light separation means 23 shutter 24 polarizing plate 25 beam shaping lens Reference Signs List 31 beam expander 32 polarizing prism beam splitter 33 spatial light modulator (SLM)
34 Relay lens 35 Nyquist filter 36 Phase plate 37 Polarizing prism 38 Objective lens for condensing signal light 39 Image sensor 40 Polarizing prism beam splitter 41 Neutral density filter (ND filter)
42 Half-wave plate (λ / 2-wave plate)
43 Objective lens for condensing reference light 44 Beam expander 45 Relay lens 46 Reflecting mirror 47 Reflecting mirror 51 Recording medium holding means 52 Recording medium rotating mechanism 53 Rotating shaft 55 Recording medium moving mechanism 56 Uniaxial stage 57 Recording medium tilting mechanism 58 Rotation stage C1 Rotation center axis of recording medium C2 Tilt rotation axis Lr Spherical reference light Lr1 Spherical reference light for recording Lr1 ′ Reflected light of spherical reference light for recording Lr1 ″ Transmitted light of spherical reference light for recording Lr2 Spherical reference light for reproduction Lr2 ′ Reflected light of reproduction spherical reference light Ls signal light

Claims (4)

A hologram that records an interference fringe between a signal light carrying data information and a reference light as a hologram on a recording medium and irradiates the hologram recorded on the recording medium with the reference light to reproduce data information recorded on the hologram. In the recording / playback method,
As a recording medium, a hologram recording layer irradiated with signal light and reference light from one side, a light absorption layer laminated on the other surface of the hologram recording layer, and a light transmission layer on the other surface of the light absorption layer And a reflective layer that is laminated by using
A spherical wave is used as the reference light,
A hologram recording / reproducing method for performing spherical reference light shift multiplex recording by moving one of a recording medium and a recording medium with a signal light and a reference light relative to the other in one direction. . When a plane perpendicular to a plane including the optical axis of the signal light incident on the recording medium and the optical axis of the reference light incident on the recording medium is set as the reference plane, one plane is formed on the track on the surface of the recording medium along the reference plane. After recording the shift multiplexed hologram array by performing spherical reference light shift multiplexed recording only in the direction, in the same area as the recording area where the shift multiplexed hologram array is recorded, the surface of the recording medium is positioned with respect to the reference plane. 2. The hologram recording / reproducing method according to claim 1 , wherein the spherical reference light shift multiplex recording is performed in a state where the hologram is inclined at a predetermined angle to multiplex record a new shift multiplex recording hologram sequence . The interference fringes between the signal light carrying the data information and the reference light are multiplex-recorded as a hologram on the recording medium, and the hologram recorded on the recording medium is irradiated with the reference light to reproduce the data information recorded on the hologram. In a hologram recording / reproducing device,
As a recording medium, a hologram recording layer irradiated with signal light and reference light from one side, a light absorption layer laminated on the other surface of the hologram recording layer, and a light transmission layer on the other surface of the light absorption layer And a reflective layer that is laminated by using
An optical mechanism that irradiates the recording medium with the signal light and the spherical reference light, and a moving mechanism that moves one of the optical mechanism and the recording medium relative to the other,
One of the optical mechanism and the recording medium is relatively moved in one direction along the surface of the recording medium with respect to the other, and shift multiplex recording is performed on the recording medium, so that a shift multiplex hologram sequence is recorded. A hologram recording / reproducing apparatus characterized by the above-mentioned . When a plane perpendicular to a plane containing the optical axis of the signal light incident on the recording medium and the optical axis of the reference light incident on the recording medium is set as the reference plane, the surface of the recording medium is rotated by rotating the recording medium. Further provided is a recording medium tilt mechanism for inclining with respect to the surface,
In the state where the surface of the recording medium is tilted with respect to the reference plane by the recording medium tilt mechanism, the spherical reference light shift multiplex recording in only one direction is performed, so that a new shift multiplexed hologram sequence is already recorded on the recording medium. 4. The hologram recording / reproducing apparatus according to claim 3, wherein the multiplexed recording is performed in the same area as the recording area of the shifted multiplexed hologram row.

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