JP2015164085A - Optical information recording and reproducing apparatus, phase mask used in optical information recording and reproducing apparatus, and method of recording and reproducing optical information - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize the even consumption of the recording material of an information recording medium, the improvement of shift selectivity, and the extraction of a phase value using the spatial phase shifting method.SOLUTION: An optical information recording and reproducing apparatus comprises: a recording light generation unit 2 generating a signal light component in which two-dimensional phase page data generated by modulating light output from a light source by a spatial light modulator is carried on a light wave, and a reference light component containing no information; an information recording medium 6 recording variations of light and shade of interference fringes formed by the signal light component and the reference light component; and a spatial frequency filtering mechanism 29 filtering the spatial frequency of the signal light component between the spatial light modulator and information recording medium, the recording light generation unit 2 including a phase mask constituted by pixels of four rows by four columns for dividing each pixel of the phase page data of the signal light component into 16 pieces, the phase mask changing the phase of the signal light component, the spatial frequency filtering mechanism 29 dividing the signal light component to outside of a focal point of the signal light component subjected to spatial frequency filtering and radiating the signal light component at a position corresponding to the focal point.

Description

  The present invention relates to an optical information recording / reproducing apparatus, a phase mask used in the optical information recording / reproducing apparatus, and an optical information recording / reproducing method. More specifically, the present invention relates to equalization of consumption of recording material of an information recording medium, improvement of shift selectivity, and The present invention relates to an optical information recording / reproducing apparatus that realizes extraction of a phase value using a spatial phase shift method, a phase mask used in the optical information recording / reproducing apparatus, and an optical information recording / reproducing method using the phase mask.

  A holographic memory using a hologram is one of methods for optically recording information and reproducing the recorded information. 2. Description of the Related Art In recent years, holographic memory has been increasing in the amount of information distributed. Conventionally, CD (Compact Disc), DVD (Digital Versatile Disc), HD-DVD (High-Definition Digital Versatile Disc), BD (Blue-) ray Disc) and the like as an information recording medium replacing the information recording medium.

  The holographic memory records information on the information recording medium as a hologram by causing the signal light having information and the reference light not having information to interfere with each other and irradiating the information recording medium. On the other hand, reproduction light having information is reproduced by irradiating the information recording medium with reference light or signal light. The holographic memory is a system that utilizes the thickness of the information recording medium by recording information three-dimensionally as a three-dimensional refractive index distribution in the information recording medium, and can record a large amount of information. .

  In addition, a polarization holographic memory that uses signal light and reference light that are in a mutually polarized state has been proposed as a method that applies holographic memory (for example, Patent Document 1, Non-Patent Document 1, and Non-Patent Document 2). ).

  The polarization holographic memory records information on an information recording medium by irradiating an information recording medium having polarization sensitivity with signal light and reference light having an arbitrary polarization state. Specifically, optical anisotropy corresponding to the polarization is induced in the information recording medium, and information is recorded as a polarization hologram. That is, this polarization holographic memory records information on an information recording medium as a three-dimensional birefringence distribution by utilizing the property of light as a vector wave. In addition, when reproducing the recorded information, it is performed by irradiating the information recording medium with the reference light or the signal light in the same manner as in the normal holographic recording.

JP 2013-37751 A

Takanori Ochiai et al. , “Angular multiplex recording of data pages by dual-channel polarization holography”, OPTICS LETTERS / Vol. 38, no. 5 / March 1,2033, p748-750 Daisuke Barada et al. , “Dual-channel polarization holography: a technical for recording two complex components of a vector wave”, Optics Letters, Vol. 37, Issue 21, pp. 4528-4530 (2012)

  In the holographic memory, it is desirable that the light intensity of the reference light is larger than the light intensity of the signal light. However, when the signal light is focused and irradiated, the signal light is irradiated in such a manner that the light intensity at one place is large and the light intensity around it is small. For this reason, it is necessary to irradiate the reference light with a light intensity greater than that of the signal light at one location where the light intensity is large.

  On the other hand, photoreactive molecules contained in the recording medium are consumed depending on the light intensity. For this reason, when reference light having a light intensity greater than that of one signal light having a high light intensity is applied to a large area of the recording medium, a large amount of photoreactive molecules are consumed even when the amount of recorded information is small. Is done. As a result, the recording capacity of the information recording medium is reduced.

  In addition, when inline holography or inline polarization holography (retardography) is used in the optical information recording / reproducing apparatus, it is difficult to increase the shift selectivity in shift multiplex recording. In order to improve the transfer rate, it is preferable to extract a phase value using a spatial phase shift method. Therefore, the optical information recording / reproducing apparatus is preferably an apparatus that can extract a phase value using a spatial phase shift method.

  The present invention has been made in order to solve the above-mentioned problems, and its purpose is to suppress consumption of the material of the information recording medium and to consume it uniformly, to improve shift selectivity in shift multiplex recording, And an optical information recording / reproducing apparatus capable of extracting a phase value by a spatial phase shift method, a phase mask used in the optical information recording / reproducing apparatus, and an optical information recording / reproducing method.

  In order to solve the above problems, an optical information recording / reproducing apparatus according to the present invention is a signal light component in which two-dimensional phase page data generated by modulating light output from a light source with a spatial light modulator is placed on a light wave. And a recording light generation unit that generates a reference light component having no information, and information for recording light and darkness of interference fringes formed by the signal light component and the reference light component as an optical anisotropy distribution or a refractive index distribution A recording medium, and a spatial frequency filtering mechanism that filters a spatial frequency of the signal light component between the spatial light modulator and the information recording medium, and the recording light generation unit includes the signal light component. A phase mask composed of pixels of 4 rows and 4 columns that divide each pixel of the phase page data into 16, the phase mask changing the phase of the signal light component, and the spatial frequency filtering device It is at a position corresponding to the focus of the signal light component spatial frequency filtering, and then irradiating said signal light component whose phase is changed by dividing outside the position corresponding to the focal point.

  In addition, a phase mask according to the present invention for solving the above problems includes a signal light component in which two-dimensional phase page data generated by modulating light output from a light source with a spatial light modulator is placed on a light wave, and Used in an optical information recording / reproducing apparatus that forms interference fringes by interfering with a reference light component having no information and records the light and darkness of the interference fringes on an information recording medium as an optical anisotropy distribution or a refractive index distribution. A phase mask, which is a 4-by-4 pixel that divides each pixel of the phase page data of the signal light component into 16, and divides the signal light component by changing the phase of the signal light component. And

  Also, an optical information recording / reproducing method according to the present invention for solving the above-described problem is a signal in which two-dimensional phase page data generated by modulating light output from a light source with a spatial light modulator is placed on a light wave. A recording light generation step for generating a light component and a reference light component having no information, a spatial frequency filtering step for filtering a spatial frequency of the signal light component output from the spatial light modulator, and the signal light component And an information recording step of irradiating the information recording medium with the reference light component and recording the light and darkness of interference fringes formed by the signal light component and the reference light component as an optical anisotropy distribution or a refractive index distribution. And the recording light generation step changes the phase of the signal light component by a phase mask that divides each pixel of the phase page data of the signal light component into pixels of 4 rows and 4 columns, and the space The wave number filtering step divides and irradiates the signal light component whose phase has been changed at a position corresponding to the focal point of the signal light component subjected to spatial frequency filtering, by dividing it outside the position corresponding to the focal point. And

  According to the present invention, since information is recorded on the information recording medium using the phase mask having the above-described configuration, the signal light is distributed and irradiated on the information recording medium, and the light intensity of the signal light is relatively weakened. . In addition, the signal light is dispersed even when the phase mask is not used even at a position close to the focal point. Therefore, the light intensity of the reference light can be relatively weakened. As a result, useless consumption of the recording material of the information recording medium can be suppressed. In the case of inline holography and retarderography, the reference light is localized in the center at a position corresponding to the focal point of the signal light and does not overlap with the signal light on the outside, but interferes at a position close to the focal point. At that time, the larger the distance between the two, the narrower the interval between the interference fringes. Since the signal light is divided and irradiated, the distance between the position where the signal light is irradiated and the position where the reference light is irradiated can be relatively increased. Therefore, the interval between the interference fringes formed by the interference between the signal light and the reference light can be reduced. As a result, shift selectivity in shift multiplex recording can be improved. Further, when reproducing the information recorded on the information recording medium, the phase of the information can be extracted using the spatial phase shift method.

  According to the present invention, the consumption of the material of the information recording medium can be suppressed and evenly consumed, the shift selectivity in the shift multiplex recording can be improved, and the phase value can be extracted by the spatial phase shift method. .

1 is a configuration diagram showing an outline of an optical information recording / reproducing apparatus according to a first embodiment of the present invention. It is the schematic of the signal light production | generation part with which the optical information recording / reproducing apparatus of FIG. 1 is provided. It is a block diagram which shows the outline | summary of the optical information recording / reproducing apparatus using the optical system of off-axis holography. It is the schematic of the signal light generation part of a form different from the signal light generation part shown in FIG. It is explanatory drawing which shows an example of the phase page data which the signal light production | generation part produced | generated. It is a schematic diagram of an imaging part. It is explanatory drawing for demonstrating the state irradiated with the signal light produced | generated by the signal generation part. It is the schematic of the signal light production | generation part with which the optical information recording / reproducing apparatus of 2nd Embodiment which concerns on this invention is provided. It is the schematic of the imaging part with which the optical information recording / reproducing apparatus of 2nd Embodiment which concerns on this invention is provided. It is a block diagram which shows the modification of the optical information recording / reproducing apparatus of 2nd Embodiment which concerns on this invention. It is a matrix that shows the value to be substituted into _{m x} and _{m y} (Formula 1). It is a figure which shows four types of phase masks (polarization dependence phase mask) which concern on this invention, and is explanatory drawing which each showed the phase shifted by each phase mask. It is the schematic of the structure of the phase mask (polarization dependence phase mask) of a 1st form. It is a perspective view which shows the structure outline of the 1st row | line of the wavelength plate array and compensation plate which are used for the phase mask (polarization dependence phase mask) of a 1st form. It is a perspective view which shows the structure outline of the 2nd row of the wavelength plate array and compensation plate which are used for the phase mask (polarization dependence phase mask) of a 1st form. It is a perspective view which shows the structure outline of the 3rd row | line of the wavelength plate array and compensation plate which are used for the phase mask (polarization dependence phase mask) of a 1st form. It is a perspective view which shows the structure outline of the 4th line of the wavelength plate array and compensation plate which are used for the phase mask (polarization dependence phase mask) of a 1st form. It is the schematic of the structure of the phase mask (polarization dependence phase mask) of a 2nd form. (A) is the schematic of the structure of the phase mask (polarization dependence phase mask) of a 3rd form, (B) is a perspective view which shows the structure of the orientation plate currently used. It is the schematic which shows the structure of the spatial light modulator incorporating the phase mask (polarization dependence phase mask). It is the schematic of the structure of a polarization independent phase mask. It is a perspective view which shows the structure outline of the 1st line of the dielectric material plate used for the polarization independent phase mask. It is a perspective view which shows the structure outline of the 2nd row of the dielectric material plate used for the polarization independent phase mask. It is a perspective view which shows the structure outline of the 3rd line of the dielectric material plate used for the polarization independent phase mask. It is a perspective view which shows the structure outline of the 4th line of the dielectric material plate used for the polarization independent phase mask. It is the schematic of the structure of an information reproduction part.

[Basic configuration]
First, the basic configuration of the optical information recording / reproducing apparatus according to the present invention will be described. In this optical information recording / reproducing apparatus, a signal light component in which two-dimensional phase page data generated by modulating light output from a light source with a spatial light modulator is placed on a light wave, and a reference light component having no information are included. A recording light generation unit for generating, an information recording medium for recording light and darkness of interference fringes formed by a signal light component and a reference light component as an optical anisotropy distribution or a refractive index distribution, a spatial light modulator, and an information recording medium And a spatial frequency filtering mechanism for filtering the spatial frequency of the signal light component.

  The recording light generation unit has a phase mask composed of pixels of 4 rows and 4 columns that divide each pixel of the phase page data of the signal light component into 16, and the phase mask changes the phase of the signal light component. Further, the spatial frequency filtering mechanism irradiates the signal light component whose phase is changed at a position corresponding to the focal point of the signal light component subjected to spatial frequency filtering by dividing it outside the position corresponding to the focal point.

  The phase mask can be configured to change the phase of only the signal light component and transmit the phase of the reference light component as it is. Further, the phase mask is configured to change only the phase of the first linearly polarized light component included in the signal light component and to transmit the phase of the second linearly polarized light component orthogonal to the first linearly polarized light component as it is. You can also. further,

The pixels of the phase mask shift the phase of the linearly polarized light component forming the signal light component by ½π from each other between adjacent pixels, and negatively shift the phase of the linearly polarized light component in the positive direction. Rows shifted in the direction may be alternately arranged, and columns that shift the phase of the linearly polarized light component in the positive direction and columns that shift in the negative direction may be alternately arranged. When the phase mask is configured as described above, the spatial light filtering mechanism can irradiate the signal light divided into four regions at a position corresponding to the focal point of the Fourier transform lens constituting the spatial frequency filtering mechanism.

  The phase mask is provided separately from the spatial light modulator, and is disposed between the light source and the spatial light modulator in the optical path of the light output from the light source, or in the spatial light modulator. It can be provided by incorporating.

  Next, the basic configuration of the phase mask according to the present invention will be described. This phase mask interferes with the signal light component in which the two-dimensional phase page data generated by modulating the light output from the light source with the spatial light modulator is placed on the light wave and the reference light component without information The phase mask is used in an optical information recording / reproducing apparatus that forms interference fringes and records the light and darkness of the interference fringes on an information recording medium as an optical anisotropy distribution or a refractive index distribution. This phase mask is a 4-by-4 pixel that divides each pixel of the phase page data of the signal light component into 16, and divides the signal light component by changing the phase of the signal light component.

  The phase mask is configured to change only the phase of the signal light component and transmit the phase of the reference light component as it is, or to change only the phase of the first linearly polarized light component included in the signal light component. The phase of the second linearly polarized light component orthogonal to the first linearly polarized light component can be transmitted as it is.

  The pixels of the phase mask shift the phase of the linearly polarized light component forming the signal light component by ½π from each other between adjacent pixels, and the row and the negative direction shift the phase of the linearly polarized light component in the positive direction. It is also possible to arrange so that the rows shifted in a negative direction are alternately arranged, and the columns that shift the phase of the first linearly polarized light component in the positive direction and the columns that are shifted in the negative direction are alternately arranged. When the phase mask is configured as described above, the spatial light filtering mechanism can irradiate the signal light divided into four regions at a position corresponding to the focal point of the Fourier transform lens constituting the spatial frequency filtering mechanism.

  Next, the basic configuration of the optical information recording / reproducing method according to the present invention will be described. In this optical information recording / reproducing method, two-dimensional phase page data generated by modulating light output from a light source with a spatial light modulator is described. A recording light generation step for generating a signal light component carried on the light wave and a reference light component having no information, and a spatial frequency filtering step for filtering the spatial frequency of the signal light component output from the spatial light modulator, An information recording step of irradiating the information recording medium with the signal light component and the reference light component to record the light and darkness of the interference fringes formed by the signal light component and the reference light component as an optical anisotropy distribution or a refractive index distribution; It has. In the recording light generation step, the phase of the signal light component is changed by a phase mask that divides each pixel of the phase page data of the signal light component into 4 × 4 pixels. The spatial frequency filtering step irradiates the signal light component whose phase has been changed at a position corresponding to the focal point of the signal light component subjected to spatial frequency filtering by dividing it outside the position corresponding to the focal point of the signal light component.

  The recording light generation step can be configured such that the phase mask changes the phase of only the signal light component and transmits the phase of the reference light component as it is. In the recording light generation step, the phase mask changes the phase of only the first linearly polarized light component included in the signal light, and transmits the phase of the second linearly polarized light component orthogonal to the first linearly polarized light component as it is. Can be configured.

  The phase mask shifts the phase of the linearly polarized light component constituting the recording light component by ½π from each other between adjacent pixels, alternately shifts the phase in the positive direction and the negative direction for each row, and The phase can be alternately shifted for each column in the negative direction and the negative direction. When the phase mask is configured as described above, the spatial light filtering mechanism can irradiate the signal light divided into four regions at a position corresponding to the focal point of the Fourier transform lens constituting the spatial frequency filtering mechanism.

  According to this optical information recording / reproducing apparatus, the consumption of the material of the information recording medium is suppressed and evenly consumed, the shift selectivity in the shift multiplex recording is improved, and the phase value is extracted by the spatial phase shift method. can do.

  An optical information recording / reproducing apparatus according to the present invention is a retarderographic apparatus that uses signal light and reference light in a single light wave to travel the same path and uses two polarization components as signal light and reference light. Optical system, in-line holography optical system for causing signal light and reference light to travel in the same path and irradiating the reference light perpendicularly to the hologram surface, and for causing signal light and reference light to travel in different paths Applies to off-axis holography. Holographic optical systems include single channel polarization holography that generates signal light using only one spatial light modulator and dual channel polarization holography that generates signal light using two intermediate light modulators.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The technical scope of the present invention is not limited only to the following description and drawings. In this specification, the signal light component is simply referred to as signal light, and the reference light component is simply referred to as reference light.

[First Embodiment]
The overall configuration of the optical information recording / reproducing apparatus 1A will be described with reference to FIG. 1, taking as an example an apparatus using an in-line holographic optical system, particularly a dual channel apparatus.

  The optical information recording / reproducing apparatus 1A includes a recording light generation unit 2 that generates recording light including signal light and reference light, and an irradiation unit that irradiates the signal light and reference light generated by the recording light generation unit 2. 3 and the information recording medium 6 that records the light and darkness of the interference fringes formed by the signal light and the reference light irradiated by the irradiation unit 3 as an optical anisotropy distribution or a refractive index distribution, and the information recording medium 6 And an imaging unit 7 for imaging the formed interference fringes.

  The recording light generation unit 2 is generated by a laser irradiation unit 10 that outputs recording laser light, a signal light generation unit 20 that generates signal light from the laser light emitted from the laser irradiation unit 10, and the signal generation unit. And a spatial frequency filtering mechanism 29 that filters the spatial frequency of the signal light and the reference light that has passed through the signal generation unit.

  The laser irradiation unit 10 includes a laser light source 11, a half-wave plate 12, two collimator lenses 13 and 15, and a spatial filter 14. The laser light source 11 is a light source that outputs linearly polarized light. The half-wave plate 12 is divided into a polarization component parallel to the optical axis and a polarization component perpendicular to the optical axis by arranging the optical axis in the incident surface of the wave plate, and a phase difference of π is generated by the difference in refractive index. I am letting. As a result, the polarization direction of linearly polarized light can be arbitrarily adjusted. The linearly polarized light adjusted to an arbitrary polarization direction is output with a beam diameter expanded by a beam expander formed by the collimator lens 13, the spatial filter 14, and the collimator lens 15.

  Between the laser irradiation unit 10 and the signal light generation unit 20, two mirrors 17 and 18 and elliptically polarized light formed by being reflected by the two mirrors 17 and 18 are adjusted to linearly polarized light 1 A quarter-wave plate 16 and a half-wave plate 19 for adjusting the polarization direction of linearly polarized light are disposed. The linearly polarized light output from the laser irradiation unit 10 and passed through the half-wave plate 19 is incident on the signal light generation unit 20.

  As shown in FIG. 2, the signal light generation unit 20 includes a polarization beam splitter 21 and two spatial light modulators 23 and 24.

  The polarization beam splitter 21 includes a transmission surface 22 therein, and separates the s-polarized component and the p-polarized component included in the incident polarized light into s-polarized light and p-polarized light. The separated s-polarized light is reflected by the transmission surface 22 and irradiated toward the spatial light modulator 23, and the separated p-polarized light is transmitted through the transmission surface 22 and applied to the spatial light modulator 24.

  The spatial light modulators 23 and 24 have a plurality of pixels arranged in a lattice pattern, and are configured to be able to modulate the phase of emitted light to each pixel. As the spatial light modulators 23 and 24, for example, a combination of a liquid crystal spatial light modulator having a liquid crystal element and a quarter wavelength plate can be used. When liquid crystal molecules having a rod-like molecular structure are aligned in a certain direction, birefringence occurs with an axis parallel to the molecular alignment as a main axis. Due to the birefringence, a phase difference is given to two orthogonal linearly polarized lights. Moreover, since the degree of orientation of the molecular orientation can be electrically modulated, it becomes a variable phase shifter. The spatial light modulator gives a two-dimensional phase distribution by changing the applied voltage for each pixel. When a liquid crystal element is used, it becomes a variable phase shifter for a linearly polarized light base.

  When a quarter-wave plate is disposed in front of the liquid crystal spatial light modulator, one phase of the left and right circularly polarized components of s-polarized light or p-polarized light is modulated. The signal light generation unit 20 uses the first circularly polarized component whose phase is modulated as signal light, and uses the second circularly polarized component orthogonal to the first circularly polarized component as reference light. The two signal lights and the two reference lights generated from the two spatial light modulators 23 and 24 are reflected by the transmission surface 22 to become s-polarized signal light and reference light, and pass through the transmission surface 22. To p-polarized signal light and reference light.

  When recording information on the information recording medium 6, the recording light generating unit 2 having the above configuration irradiates the irradiation unit 3 with signal light and reference light, and reproduces information recorded on the information recording medium 6. When performing, only the reference light is irradiated toward the irradiation unit 3. Specifically, the input polarized light at the time of recording is a polarized light other than the polarized light that is perpendicular or parallel to the polarization direction of the linearly polarized light that is transmitted through the transmission surface 22 of the polarization beam splitter 21, and the output polarized light is Polarized light that is perpendicular to the polarization direction of linearly polarized light that is transmitted through the transmission surface 22 of the polarizing beam splitter 21 and polarized light that is parallel to the polarization direction are superimposed. The input polarization at the time of reproduction is the same as the input polarization at the time of recording, and the output polarization at the time of reproduction is a superposition of the p-polarized reference light and the s-polarized reference light.

  In the case of off-axis dual channel polarization holography in which the reference light shown in FIG. 3 does not pass through the signal light generation unit and travels on an optical path different from that of the signal light, the signal light generation unit is configured as shown in FIG. It can also be configured.

  FIG. 3 shows an outline of an optical information recording / reproducing apparatus 1D using an off-axis dual channel polarization holography optical system. In the optical information recording / reproducing apparatus 1D, the same components as those in the optical information recording / reproducing apparatus 1A shown in FIG. 1 are denoted by the same reference numerals, description thereof is omitted, and only different components are described. The optical information recording / reproducing apparatus 1D is irradiated with the recording light generation unit 2a that generates the signal light, the irradiation unit 3 for irradiating the signal light generated by the recording light generation unit 2a, and the irradiation unit 3. Information recording medium 6 that records the light and darkness of the interference fringes formed by the signal light and the reference light as an optical anisotropy distribution or refractive index distribution, and an imaging unit that images the interference fringes formed on the information recording medium 6 7.

  The recording light generation unit 2a includes a polarization beam splitter 130, and the polarization beam splitter 130 separates the signal light and the reference light. The optical path of the reference light includes a half-wave plate 19, a quarter-wave plate, a galvano mirror 4, a relay lens 5, and a mirror 3a. The reference light output from the polarization beam splitter 130 passes through the half-wave plate 19 and the quarter-wave plate, is reflected by the galvano mirror 4, is then collected by the relay lens 5, and is then reflected by the mirror 3a. Is incident on the irradiation unit 3. The irradiation unit 3 irradiates the information recording medium with signal light and reference light during recording, and irradiates the recording medium with reference light during reproduction.

  As shown in FIG. 4, the signal light generation unit 30 includes a reflection mirror 31 that reflects linearly polarized light and a reference wave, four relay lenses 32, 33, 34, and 35, and two spatial light modulators 36 and 37. It consists of and. The signal light reflected by the reflection mirror 31 is collected by the relay lens 32, and the signal light spread after being collected is converted into parallel light by the relay lens 33 and is incident on the spatial light modulator 36. The spatial light modulator 36 modulates only the first linearly polarized light component having a certain polarization component in the incident parallel light, and carries the two-dimensional phase page data to generate the first signal light component. Further, the signal light output from the spatial light modulator 36 is collected by the relay lens 33, and the signal light spread after being collected is converted into parallel light by the relay lens 34, and the half-wave plate 38 is obtained. , The polarization direction is rotated by 90 degrees, and is incident on the spatial light modulator 37. The spatial light modulator 37 modulates only the second linearly polarized light component having a polarization component perpendicular to the first linearly polarized light component of the incident parallel light, and places the second signal on the two-dimensional phase page data. Generate light components. The signal light output from the spatial light modulator 37 passes through the relay lens 34 and the relay lens 35 and is output from the signal light generation unit 30. If necessary, a quarter wavelength plate 39 may be provided on the output side of the relay lens 35.

  When this signal light generation unit 30 is used, the input polarization and output polarization during recording are in a state other than parallel or perpendicular to the axes of the two spatial light modulators 36 and 37. Further, the input polarization and output polarization during reproduction are in a state in which the first linear polarization component and the second linear polarization component are superimposed. When the quarter wavelength plate 39 is provided, the first linearly polarized component is converted into the first circularly polarized component, and the second linearly polarized component is orthogonally polarized to the first circularly polarized component. Converted into components. The output polarization at the time of recording and reproduction is a superposition of the first circular polarization component and the second circular polarization component.

  The output light output from the signal light generation unit 20 having the above configuration is signal light in which two-dimensional phase page data is placed on a light wave. FIG. 5 shows an example of this signal light, which forms quaternary phase page data. This phase page data represents information in four levels of shading.

  The reference light and the signal light are output from the signal light generation unit 20, and then spatial frequency is filtered by the spatial frequency filtering mechanism 29. The spatial frequency filtering mechanism 29 has a pair of Fourier transform lenses 26 and 28 and a spatial filter 27. The reference light and the signal light are focused on the position of the spatial filter 27 by the Fourier transform lens 26. The reference light and the signal light have a pattern corresponding to the spatial frequency distribution of the reference light and the signal light at the position of the spatial filter 27, and are spatial frequency filtered by passing through the spatial filter 27 and the Fourier transform lens 28. It becomes signal light and reference light.

  The irradiating unit 3 passes the signal light generated by the signal light generating unit 20 and the reference light or the signal light generating unit 30 that has passed through the signal light generating unit 20 to the photosensitive information recording medium 6 when recording information. It functions as an optical system that records information on the information recording medium 6 that records information with an optical anisotropy distribution or refractive index distribution by irradiating the reference light. On the other hand, the irradiating unit 3 functions as an optical system that irradiates the information recording medium 6 having photosensitivity and recording information as an optical anisotropy distribution or a refractive index distribution when information is reproduced.

  The information recording medium 6 has photosensitivity and is disposed between the irradiation unit 3 and the imaging unit 7. Of the information recording medium 6 having photosensitivity, a photopolymerizable polymer material or the like is known as the information recording medium 6 for holographic recording having no polarization sensitivity. On the other hand, among the information recording medium 6 having photosensitivity, the material of the information recording medium 6 for polarization holographic recording having polarization sensitivity includes an azobenzene-based material, an axially selective photoreactive molecule-added polymer, a high photocrosslinking property. Molecular liquid crystals are known.

  In particular, when the information recording medium 6 having polarization sensitivity is irradiated with linearly polarized light or elliptically polarized light, optical anisotropy such as birefringence or dichroism having a principal axis corresponding to the polarization direction of the irradiated polarized light is induced. Has properties. For this reason, if the information recording medium 6 having polarization sensitivity is used, it is possible to record information as a hologram even if signal light and reference light whose polarization states are not identical in principle are superimposed and irradiated. That is, in the case of polarization holographic recording, information can be recorded on the information recording medium 6 as a three-dimensional optical anisotropy distribution such as a three-dimensional birefringence distribution or a three-dimensional dichroism distribution. On the other hand, in the case of holographic recording using the information recording medium 6 having no polarization sensitivity, information is recorded as a three-dimensional refractive index distribution.

  The recorded information is reproduced by irradiating the reproduction signal light on the hologram from the same direction as the reference light at the time of recording. At this time, reproduction signal light is generated from the hologram. Further, in order to extract the phase value, phase extraction reference light having a uniform phase pattern from the same direction as the signal light at the time of recording is simultaneously irradiated. In the case of the inline type as in the configuration example of FIG. 1, the reproduction signal light may be used as phase extraction reference light.

  As shown in FIG. 6, the imaging unit 7 is a system that uses the imaging device 8 to capture an image in a state where the reproduction signal light and the phase extraction reference light are superimposed. The imaging unit 7 is configured to capture an interference fringe between the reproduction signal light having the same phase modulation information as the signal light subjected to phase modulation during recording and the reference light as a two-dimensional image. For example, a CCD or CMOS can be used as the image sensor 8.

  The optical information recording / reproducing apparatus 1A includes a phase mask in addition to the configuration described above. This phase mask has a function of further dividing each pixel constituting page data into pixels of 4 rows and 4 columns. This phase mask separates the signal light on which the page data is placed by the Fourier transform lens 26 included in the spatial frequency filtering mechanism 29 at a certain distance from the focus at the position of the spatial filter 27 that is the focal position of the Fourier transform lens 26. The area around the focal point is divided into four parts. In the optical information recording / reproducing apparatus 1A, the phase mask is incorporated in the spatial light modulators 23 and 24.

  FIG. 7 shows a state in which the spatial frequency is filtered by the spatial frequency filtering mechanism 29 of the signal light output from the signal light generation unit 20 including the spatial light modulators 23 and 24 incorporating the phase mask. FIG. 7 shows only signal light output from one spatial light modulator, for example, the spatial light modulator 23, for ease of explanation. The upper part of FIG. 7 shows an outline of the optical path of the signal light between the Fourier transform lens 26 and the Fourier transform lens 28 of the spatial frequency filtering mechanism 29, and the lower part of FIG. The state of signal light is shown partially.

  As shown in FIG. 7, the signal light is collected by the Fourier transform lens 26 that constitutes the spatial frequency filtering mechanism 29, so that the area gradually decreases from the Fourier transform lens 26 toward the focal point P. Then, at the position of the focal point P, the signal light is divided into four regions that are separated by a certain distance outside the point that originally becomes the focal point P of the signal light. Thus, by dividing the signal light into four, the light intensity at the focal plane of the signal light can be reduced.

  In the holographic memory, it is desirable that the light intensity of the reference light is higher than the light intensity of the signal light. However, when the signal light is collected and irradiated, in the conventional holographic memory, the signal light is irradiated in such a manner that the light intensity at one place is relatively strong and the light intensity around it is weak. For this reason, it is necessary to irradiate the reference light with a light intensity greater than that of the signal light at one location where the light intensity is large.

  On the other hand, when the signal light is divided into four at the position of the focal point P as in the optical information recording / reproducing apparatus 1A of this embodiment, the light intensity becomes relatively weak. For this reason, in the optical information recording / reproducing apparatus 1A of this embodiment, it is possible to use reference light having relatively weak light intensity. As a result, when recording information, consumption of the photoreactive molecules of the information recording medium 6 can be suppressed. Further, since the signal light is dispersed outside the original position of the focal point P, the consumption of photoreactive molecules can be equalized.

  In addition, the optical information recording / reproducing apparatus 1A is formed by interference between the signal light and the reference light by dividing the signal light into four regions that are separated by a certain distance outward from the point where the original focus P becomes. The interval between interference fringes can be made relatively narrow. That is, the reference light is condensed by the Fourier transform lens 26 of the spatial frequency filtering mechanism 29, so that the reference light is focused at the same position as the original focal point P of the signal light and irradiated. However, the signal light is distributed around the focal point P in the focal plane, and the signal light that spreads from a point other than the center and the reference light that spreads from the focal point P forms interference fringes. When the position of the focus P of the reference light and a position other than the focus P of the signal light are close to each other, the interval between the interference fringes formed by the interference between the signal light and the reference light is relatively wide. In order to narrow the interval between the interference fringes, it is necessary that the center of the distribution of the signal light is other than the focal point P, and that the center position and the position of the focal point P of the reference light are separated by a certain distance.

  Since the optical information recording / reproducing apparatus 1A of the present embodiment irradiates the signal light into four regions divided by a certain distance outside the focal point P of the reference light, the positions of the four centers where the signal light is distributed. And the position of the focal point P of the reference light can be separated. As a result, the interval between the interference fringes can be relatively narrowed. Thus, when the interval between the interference fringes is relatively narrow, the shift selectivity in the shift multiplex recording of the information recorded on the information recording medium 6 can be improved. That is, when information is recorded on the information recording medium 6 in a multiplexed manner, the shift amount of the information recording medium 6 can be reduced. As a result, the amount of information that can be recorded on the information recording medium 6 can be increased.

  Details of the phase mask will be described later.

[Second Embodiment]
Next, referring to FIGS. 1, 8, and 9, the signal light and the reference light in the single light wave travel on the same path, and the two polarization components are used as the signal light and the reference light. An outline of the optical information recording / reproducing apparatus 1B using the retarder optical system to be used will be described. Since the basic configuration of the optical information recording / reproducing apparatus 1B is the same as that of the optical information recording / reproducing apparatus 1A shown in FIG. 1, the entire configuration of the optical information recording / reproducing apparatus 1B will be described with reference to FIG. .

  As shown in FIG. 1, the optical information recording / reproducing apparatus 1B includes a recording light generation unit 2 that generates recording light including signal light and reference light, and signal light and reference light generated by the recording light generation unit 2. And an information recording medium 6 for recording the light and darkness of interference fringes formed by the signal light and reference light irradiated by the irradiation unit 3 as an optical anisotropy distribution or a refractive index distribution And an imaging unit 7 that images the interference fringes formed on the information recording medium 6.

  The recording light generation unit 2 includes a laser irradiation unit 10 that outputs recording laser light, a signal light generation unit 20 that generates signal light from the laser light emitted from the laser irradiation unit 10, and the signal light generation unit 20. And a spatial frequency filtering mechanism 29 that filters the generated signal light and the spatial frequency of the reference light that has passed through the signal generation unit.

  The laser irradiation unit 10 includes a laser light source 11, a half-wave plate 12, two collimator lenses 13 and 15, and a spatial filter 14. The laser light source is a light source that outputs linearly polarized light. The configuration and operation of the laser irradiation unit 10 are the same as those of the laser irradiation unit 10 of the optical information recording / reproducing apparatus 1A of the first embodiment.

  Between the laser irradiation unit 10 and the signal light generation unit 20, there are two mirrors 17, 18, a half-wave plate 19 that is reflected by the two mirrors 17, 18 and causes a phase difference in linearly polarized light, and A quarter wavelength plate (not shown) is arranged. The quarter-wave plate is separated into a polarization component parallel to the optical axis and a polarization component perpendicular to the optical axis, and a phase difference of π / 2 is generated due to the difference in refractive index. As a result, by adjusting the direction of the optical axis, the polarization state that has passed through the mirrors 17 and 18 and has become elliptically polarized light can be returned to linearly polarized light. The half-wave plate 19 can further adjust the direction of the linearly polarized light.

  The linearly polarized light output from the laser irradiation unit 10 through the optical path described above is separated into a signal wave linearly polarized light having a polarization component orthogonal to each other and a reference wave, and is incident on the signal light generation unit 20.

  As shown in FIG. 8, the signal light generation unit 20 includes a reflection mirror 41 that reflects linearly polarized light for signal waves and a reference wave, and a relay lens that collects reflected linearly polarized light for signal waves and a reference wave. 42, and a relay lens 43 that converts the linearly polarized wave for the signal wave and the reference wave that are spread after being collected by the relay lens 42 into parallel light. The signal light generation unit 20 receives the converted parallel light, modulates only the linearly polarized light for the signal wave among the incident parallel light, and generates the signal light by placing the two-dimensional phase page data on the light wave. A spatial light modulator 45 is provided. Further, the signal light generation unit 20 includes an output relay lens 44 that converts the reference light and the signal light output from the spatial light modulator 45 and narrowed by the relay lens 43 into parallel light.

  In the recording light generator 2 of the optical information recording / reproducing apparatus 1B, the input polarization during recording is a polarization other than parallel or perpendicular to the axis of the spatial light modulator 45, and the output polarization during recording is signal light. Is a polarized light that is parallel to the axis of the spatial light modulator 45. On the other hand, the input polarization during reproduction is perpendicular to the axis of the spatial light modulator 45, and the output polarization during reproduction is perpendicular to the axis of the spatial light modulator 45. If necessary, a quarter-wave plate 46 may be disposed behind the output relay lens 44 in the optical path. In this case, the output polarization at the time of recording is a superposition of the signal light component of the first circular polarization component and the reference light component of the second circular polarization component orthogonal to the first circular polarization component. Further, the output polarization during reproduction is the same circular polarization as the second circular polarization component described above.

  The reference light and the signal light are output from the signal light generation unit 20, and then spatial frequency is filtered by the spatial frequency filtering mechanism 29. The spatial frequency filtering mechanism 29 includes a pair of Fourier transform lenses 26 and 28 and a spatial filter 27, and focuses the reference light and the signal light on the position of the spatial filter 27 by the Fourier transform lens 26. . At the position of the spatial filter, a pattern corresponding to the spatial frequency distribution of the reference light and the signal light is obtained. By passing through the spatial filter 27 and the Fourier transform lens 28, the reference light and the signal light subjected to spatial frequency filtering are obtained.

  Since the configuration of the irradiation unit 3 and the information recording medium 6 is the same as that of the optical information recording / reproducing apparatus 1A of the first embodiment, the description thereof is omitted.

  As shown in FIG. 9, the imaging unit 7 includes an analyzer 9 disposed immediately before the imaging element 8. When the information recorded on the information recording medium 6 is reproduced and the reproduced information is imaged, the imaging unit 7 uses the transmission axis of the analyzer 9 as reproduction signal light and reproduction illumination light that has become phase detection reference light. By adjusting in a direction in which both of these are partially transmitted, the reproduction signal light and the phase detection reference light are caused to interfere on the image sensor 8. Further, a quarter wavelength plate (not shown) may be disposed immediately before the analyzer 9. When reproducing the information recorded on the information recording medium 6 and imaging the reproduced information, the quarter-wave plate adjusts the intensity ratio between the reproduced signal and the reference light used for reproduction. Can do. However, this quarter-wave plate may be provided as necessary, and is not an essential configuration.

  This optical information recording / reproducing apparatus 1B includes a polarization-dependent phase mask in addition to the configuration described above. The polarization dependent phase mask is incorporated in the spatial light modulator 45. However, the polarization-dependent phase mask is not limited to be provided by being incorporated in the spatial light modulator 45, and the polarization-dependent phase mask is provided as one device separate from the spatial modulator 45, and the polarization-dependent phase mask device is provided. Can also be provided in the optical information recording / reproducing apparatus.

[Modification of Second Embodiment]
FIG. 10 shows an example of an apparatus in which the optical information recording / reproducing apparatus 1C using the retarder optical system has a single polarization-dependent phase mask device. Since the basic configuration of the optical information recording / reproducing apparatus 1C is the same as that of the optical information recording / reproducing apparatus 1B shown in FIG. 1, the same components are denoted by the same reference numerals and the description thereof is omitted. Only different configurations will be described.

  The optical information recording / reproducing apparatus 1C includes a recording light generation unit 50 that generates recording light including signal light and reference light, and an irradiation unit that irradiates the signal light and reference light generated by the recording light generation unit 50. 3 and the information recording medium 6 for recording the light and darkness of the interference fringes formed by the signal light and the reference light irradiated by the irradiation unit 3 as an optical anisotropy distribution or a refractive index distribution, and formed on the information recording medium And an imaging unit 7 for imaging the interference fringes.

  The recording light generation unit 50 of the optical information recording / reproducing apparatus 1C is provided as a single device with the polarization-dependent phase mask 60 independent. The recording light generation unit 50 includes four mirrors 51, 52, 53, and 54 between the laser irradiation unit 10 that outputs linearly polarized light and the polarization-dependent phase mask, and the linearly polarized light output from the laser irradiation unit 10. Are reflected in turn by the four mirrors 51, 52, 53 and 54, and linearly polarized light is incident on the polarization-dependent phase mask 60. Further, the recording light generation unit 50 includes two relay lenses 55 and 56, a mirror 57 positioned between the relay lenses 55 and 56, and a spatial light modulator 58. The polarized light output from the polarization dependent phase mask 60 passes through the relay lens 55 and is reflected by the mirror 57. The reflected polarized light passes through the relay lens 56 and enters the spatial light modulator 58. The polarized light output from the spatial light modulator 58 passes through the relay lens 56 again and travels toward the irradiation unit 3.

  In the recording light generation unit 50 of the optical information recording / reproducing apparatus 1C, the input polarization at the time of recording is a polarization other than parallel or perpendicular to the axis of the spatial light modulator, and the signal light component of the output polarization at the time of recording Is the polarization whose polarization direction is parallel to the axis of the spatial light modulator, and the reference light component is the polarization whose polarization light direction is perpendicular to the axis of the spatial light modulator. On the other hand, the input polarization during reproduction is perpendicular to the axis of the spatial light modulator, and the output polarization during reproduction is perpendicular to the axis of the spatial light modulator.

  Next, details of the polarization independent phase mask provided in the optical information recording / reproducing apparatus 1B and the polarization dependent phase mask 60 provided in the optical information recording / reproducing apparatuses 1A, 1B, 1C will be described.

  Although the polarization-independent phase mask does not appear in the drawings described so far, the polarization-independent phase mask is constituted by pixels of 4 rows and 4 columns. This polarization-independent phase mask is irradiated with only signal light to change the phase of the signal light. On the other hand, the polarization dependent phase mask 60 is composed of pixels of 4 rows and 4 columns. The polarization-dependent phase mask 60 changes the phase of only a certain first linearly polarized light component included in the signal light, and transmits the phase of the second linearly polarized light component orthogonal to the first linearly polarized light component as it is.

  When the polarization-independent phase mask and the polarization-dependent mask have a configuration other than 4 rows and 4 columns, when the phase difference between adjacent positions is a constant value, the signal light is divided into four symmetrically, or It can be divided evenly, resulting in bias. On the other hand, when the polarization-independent phase mask and the polarization-dependent mask are configured in 4 rows and 4 columns, the signal light can be symmetrically divided into four. Therefore, the polarization-independent phase mask and the polarization-dependent mask of this embodiment adopt a configuration of 4 rows and 4 columns.

In this phase-independent phase mask and polarization-dependent phase mask 60, one of s ₁₁ , s ₃₁ , s ₁₃ , and s ₃₃ is −1 in the phase distribution equation expressed by (Equation 1), and the others The three are designed to be 1. At that time, the phase distribution of (Equation 1) of the m _x and m in the _y by substituting the numerical values given by the matrix shown in FIG. 11 polarization-dependent phase mask and polarization dependent phase mask 60 are calculated. Of the values shown in each cell of the matrix shown in FIG. 11, a value which is disposed on the left side value is assigned to m _x, is the value that the value placed on the right side is substituted into m _y .

  The polarization-independent phase mask and the polarization-dependent phase mask 60 designed using the above (Equation 1) can be classified into four types shown in FIGS. 12 (A) to 12 (D). Hereinafter, details of the polarization-dependent phase mask 60 will be described using the polarization-independent phase mask of FIG. 12A as an example. In the following description, the code of the polarization-independent phase mask is described as “60”.

  In each row and each column, pixels in adjacent columns are formed so that the phase of light incident on the polarization-independent phase mask 60 is shifted by 1 / 2π and output. For example, each pixel in the first row located in the uppermost row is shifted in phase by ½π in the positive direction from left to right, and each pixel in the fourth column located on the leftmost side is from top to bottom. The phase is shifted by 1 / 2π in the negative direction. The rows of pixels of the polarization-independent phase mask 60 are rows in which the phase is shifted by 1 / 2π in the positive direction and the phase by 1 / 2π in the negative direction in order from the first row located at the top. And are arranged alternately. On the other hand, the columns of pixels of the polarization-independent phase mask 60 are shifted in sequence from the first column located on the leftmost side by a phase of 1 / 2π in the negative direction and by a phase of 1 / 2π in the positive direction. The columns are arranged alternately.

  Specific structures of the polarization-independent phase mask 60 and the polarization-dependent phase mask 60 shown in FIG. 12A will be described with reference to FIGS. The order of description will be described first for the polarization-dependent phase mask 60 and then for the polarization-independent phase mask 60.

[Polarization-dependent phase mask]
The polarization dependent mask 60 will be described with reference to FIGS. The polarization-dependent mask 60 is a phase mask mainly used for an inline holographic optical system and a retarder optical system.

(Polarization-dependent phase mask of the first form)
As shown in FIG. 13, the polarization-dependent phase mask 61 of the first form includes a substrate 71, a wave plate array 72 laminated on the substrate 71, and a compensation arranged at a certain interval from the wave plate array 72. It is comprised from the board 73. FIG. The board | substrate 71 is comprised by the flat plate-shaped member. The wave plate array 72 and the compensation plate 73 have different shapes depending on each row and each column of the polarization-dependent phase mask 61. Hereinafter, the structure of the wave plate array and the compensation plate in each row will be described with reference to FIGS.

  FIG. 14 shows the structure of the wave plate array 72 and the compensation plate 73 constituting the first row of the polarization dependent phase mask 61 shown in FIG. In the state shown in FIG. 14, the wave plate array 72 is formed such that the bottom surface is flat and the thickness between the bottom surface and the top surface is different for each column. The thickness of the wave plate array 72 is formed so as to gradually decrease from the first column located on the left side of FIG. 14 toward the fourth column located on the right side. This wave plate array 72 gives a phase difference between polarized components along the fast axis and the slow axis. On the other hand, the compensation plate 73 is formed so that the upper surface in the state shown in FIG. 14 is flat and the thickness between the upper surface and the bottom surface is different for each column. The thickness of the compensation plate 73 is formed so as to gradually increase from the first row located on the left side of FIG. 14 toward the fourth row located on the right side. The compensation plate 73 transmits one of the polarization components along the fast axis and the slow axis without changing.

  FIG. 15 shows the structure of the second row of the polarization-dependent phase mask 61 shown in FIG. 12A, and the wave plate array 74 has a thickness that increases from the first column to the fourth column. It is formed to be thicker. On the other hand, the compensation plate 75 is formed so as to become thinner stepwise from the first row to the fourth row.

  FIG. 16 shows the structure of the third row of the polarization dependent phase mask 61 shown in FIG. In the wave plate array 76, the first column located on the leftmost side in FIG. 16 has the second smallest thickness, and the second column has the smallest thickness. Further, the thickness of the third row is the thickest, and the thickness of the fourth row located on the rightmost side in FIG. 16 is the second thickest. On the other hand, the compensation plate 77 is formed such that the thickness of the first row located on the leftmost side in FIG. 16 is the second thickest and the thickness of the second row is the thickest. Further, the thickness of the third row is the thinnest, and the thickness of the fourth row located on the rightmost side in FIG. 16 is the second thinnest.

  FIG. 17 shows the structure of the fourth row of the polarization dependent phase mask 61 shown in FIG. In the wave plate array 78, the first column located on the leftmost side in FIG. 17 has the second largest thickness, and the second column has the largest thickness. Further, the thickness of the third row is the smallest, and the thickness of the fourth row located on the rightmost side in FIG. 17 is the second smallest. On the other hand, in the compensation plate 79, the thickness of the first row located on the leftmost side in FIG. 17 is the second smallest, and the thickness of the second row is the thinnest. Further, the thickness of the third row is the thickest, and the thickness of the fourth row located on the rightmost side in FIG. 17 is the second thickest.

(Polarization-dependent phase mask of the second form)
As shown in FIG. 18, the polarization-dependent phase mask 62 of the second form includes a substrate 81, a reflective film 82 laminated on the substrate 81, a dielectric plate 83 laminated on the reflective film 82, It consists of a dielectric plate 83 and a wire grid polarizer 84 arranged with a gap. The substrate 81 and the reflective film 82 are formed with a constant thickness. On the other hand, the thickness of the dielectric plate 83 differs depending on each row and each column. The wire grid polarizer 84 transmits one linearly polarized light component of two orthogonal linearly polarized light components and reflects the other. The phase of the linearly polarized light component transmitted through the wire grid polarizer 84 is given by the dielectric plate 83.

(Polarization-dependent phase mask of the third form)
The polarization-dependent phase mask 64 of the third form is a liquid crystal phase mask. As shown in FIG. 19A, the polarization-dependent phase mask 64 of the third form is laminated on a substrate 91, a two-layer alignment film 92.94 disposed on the substrate 91, and the alignment film 94. The compensation film 95 is provided. The substrate 91 is formed flat. Of the two alignment films 92 and 94, the first alignment film 92 stacked on the substrate 91 is formed so that the thickness gradually decreases from the first row to the fourth row. Yes. On the other hand, the second alignment film 94 laminated on the first alignment film 92 has a constant thickness. A liquid crystal layer 93 is formed between the first alignment film 92 and the second alignment film 94. The liquid crystal layer 93 is formed so as to increase in thickness from the second column to the fourth column. The compensation film 95 is formed with a constant thickness.

  With reference to FIG. 19B, the structure of the first alignment film 92 will be specifically described. The first alignment film 92 shown in FIG. 19B has a structure that gives the phase distribution of the first row of the polarization-dependent phase mask 61 shown in FIG. In the state shown in FIG. 19B, the first alignment film 92 is formed such that the bottom surface is flat and the thickness between the bottom surface and the top surface is different for each column. The thickness of the first alignment film 92 is formed so as to gradually decrease from the first column located on the left side of FIG. 19B toward the fourth column located on the right side. The structures from the second row to the fourth row are also formed in a structure corresponding to the phase distribution of each row of the polarization-dependent phase mask.

  The polarization-dependent phase mask 64 of the third embodiment having the above configuration gives a phase corresponding to the thickness of the liquid crystal layer to the polarization component parallel to the orientation direction of the liquid crystal molecules. The compensation film 95 compensates so that the phase of the polarization component perpendicular to the paper surface of FIG. 19 does not change.

  Next, an integrated spatial light modulator 100 that is integrally configured by incorporating a polarization-dependent phase mask into the spatial light modulator will be described with reference to FIG.

  The integrated spatial light modulator 100 shown in FIG. 20 is an example in which a polarization dependent phase mask 62 is incorporated in a liquid crystal spatial light modulator 106. The liquid crystal spatial light modulator 106 is configured by laminating a first transparent electrode layer 101, a first alignment film 102, a liquid crystal layer 103, a second alignment film 104, and a second transparent electrode layer 105 in this order from the bottom of FIG. Has been. The polarization dependent phase mask 62 is disposed below the first transparent electrode layer 101 in FIG. The polarization-dependent phase mask 62 has the same structure as the polarization-dependent phase mask 62 of the second form shown in FIG. 18, and a wire grid polarizer 84 is laminated below the first transparent electrode layer 101. Since the configuration and operation of the polarization dependent phase mask 62 are the same as those of the polarization dependent phase mask 62 of the second embodiment, the description thereof is omitted here.

[Polarization-independent phase mask]
Next, the polarization-independent phase mask 60 will be described with reference to FIGS. The polarization independent phase mask 60 is a phase mask mainly used when an off-axis optical system is used.

  As shown in FIG. 21, the polarization-independent phase mask 60 includes a base 121 and a dielectric plate 122 stacked on the substrate 121. The polarization-independent phase mask 60 can be provided with a reflective film 126 as necessary. When the reflective film 126 is provided, the reflective film 126 is laminated between the substrate 121 and the dielectric plate 122. The dielectric plate 122 has a different shape for each row and each column of the polarization-independent phase mask 60. Hereinafter, the structure of the dielectric plates in each row will be described with reference to FIGS.

  FIG. 22 shows the structure of the dielectric plate 122 constituting the first row of the polarization independent phase mask 60 shown in FIG. In the state shown in FIG. 22, the dielectric plate is formed so that the bottom surface is flat and the thickness between the bottom surface and the top surface is different for each column. The thickness of the dielectric plate 122 is formed so as to gradually decrease from the first row located on the left side of FIG. 22 toward the fourth row located on the right side.

  FIG. 23 shows the structure of the second row of the polarization-independent phase mask 60 shown in FIG. 12A, and the thickness of the dielectric plate 123 increases from the first column to the fourth column. It is formed to become thicker in stages.

  FIG. 24 shows the structure of the third row of the polarization-independent phase mask 60 shown in FIG. The dielectric plate 124 is formed such that the first row located on the leftmost side in FIG. 24 has the second smallest thickness and the second row has the smallest thickness. Further, the thickness of the third row is the thickest, and the thickness of the fourth row located on the rightmost side in FIG. 24 is the second thickest.

  FIG. 25 shows the structure of the fourth row of the polarization-independent phase mask 60 shown in FIG. The dielectric plate 125 is formed such that the thickness of the first row located on the leftmost side in FIG. 25 is the second thickest and the thickness of the second row is the thickest. Further, the thickness of the third row is the thinnest, and the thickness of the fourth row located on the rightmost side in FIG. 25 is the second smallest.

  When multi-level phase page data is recorded on an information recording medium using the polarization-independent phase mask 60 or the polarization-dependent phase mask 60 described above, the phase value of the recorded information is calculated using a spatial phase shift method. Can be extracted. In addition, the storage capacity of the information recording medium and the transfer rate can be improved. Furthermore, as described at the beginning, the phase page data can be recorded on the information recording medium even for the off-axis holography method.

  Hereinafter, the principle of extracting the phase value from the information recorded on the information recording medium by the spatial phase shift method will be described.

  The extraction of the phase value is performed by the information reproducing unit 110 shown in FIG. The information reproducing unit 110 is connected to the imaging unit 7, and is reproduced by irradiating the information recording medium 6 with reference light and performing processing based on information captured by the imaging unit 7. The information reproducing unit 6 is configured by a computer, for example, and includes an input device 112, a display device 113, an arithmetic processing unit 11, and the like.

  Hereinafter, a method of extracting phase values will be described in order for a case where information is recorded with a single channel optical system and a case where information is recorded with a dual channel optical system.

[Single channel]
When information is recorded by a single channel optical system, the reproduction signal light Us (m _x , m _y ) when information recorded on the information recording medium 6 is reproduced can be expressed as (Equation 2). . The phase of the reproduction signal light is based on the phase of the reference light for phase extraction.

Further, the phase extraction reference light U _R (m _x , m _y ) used for reproduction can be expressed as the following (Equation 3) when the phase is 0.

The intensity I (m _x , m _y ) due to the reproduction signal light and the phase extraction reference light on the image sensor 8 can be expressed as the following (Equation 4).

Therefore, the phase φ _S can be obtained using the equation for obtaining the declination in (Equation 4). Specifically, the phase φS can be obtained by (Equation 5).

[Dual channel]
When information is recorded by the dual channel optical system, the reproduction signal lights Us ₁ (m _x , m _y ) and Us ₂ (m _x , m _y ) when the information recorded on the information recording medium 6 is reproduced are (Expression 6). The phase of each reproduction signal light is based on the phase of each phase extraction reference light having a polarization state corresponding to each reproduction signal light.

The phase extraction reference beams U _R1 (m _x , m _y ) and U _R2 (m _x , m _y ) used for reproduction are expressed as the following (Expression 7) when the phase is set to 0. be able to.

The intensity I (m _x , m _y ) due to the reproduction signal light and the phase extraction reference light on the image sensor 8 can be expressed as the following (Equation 8).

Therefore, the phase φ _S1 and the phase φ _S2 of the reproduction signal reproduced by each phase extraction reference beam can be obtained using the equations for obtaining the declination in (Equation 8). Specifically, the phase φS can be obtained by (Equation 9).

1A, 1B, 1C Optical information recording / reproducing apparatus 2 Recording light generation unit 3 Irradiation unit 3a Mirror 4 Galvano mirror 5 Relay lens 6 Information recording medium 7 Imaging unit 8 Imaging element 9 Analyzer 10 Laser irradiation unit 11 Laser light source 12 1/2 Wavelength plate 13 Collimator lens 14 Spatial filter 15 Collimator lens 16 1/4 wavelength plate 17, 18 Mirror 19 1/2 wavelength plate 20 Signal light generator 21 Polarizing beam splitter 22 Transmitting surface 23, 24 Spatial light modulator 26, 28 Fourier Conversion lens 27 Spatial filter 29 Spatial frequency filtering mechanism 30 Signal light generation unit 31 Reflection mirror 32, 33, 34, 35 Relay lens 36, 37 Spatial light modulator 38 1/2 wavelength plate 39 1/4 wavelength plate 40 Signal light generation Part 41 Reflection mirror 42, 43, 44 Relay lens 45 Space Modulator 46 1/4 wavelength plate 50 Recording light generator 51, 52, 53, 54 Mirror 55, 56 Relay lens 57 Mirror 58 Spatial light modulator 60, 61, 62, 63, 64 Phase mask 71, 81, 91 Substrate 72, 74, 76, 78 Wavelength plate array 73, 75, 77, 79 Compensation plate 82 Reflective film 83 Dielectric plate 84 Wire grid polarizer 92, 94 Alignment film 93 Liquid crystal layer 95 Compensation film 100 Integrated spatial light modulator 101 , 105 Transparent electrode layer 102, 104 Alignment film 103 Liquid crystal layer 106 Liquid crystal spatial light modulator 110 Information reproduction unit 111 Operation processing unit 112 Input device 113 Display device 121 Substrate 122, 123, 124, 125 Dielectric plate 126 Reflective film 130 Polarization Beam splitter

Claims (14)

A recording light generation unit for generating a signal light component in which two-dimensional phase page data generated by modulating light output from a light source with a spatial light modulator is placed on a light wave, and a reference light component having no information;
An information recording medium for recording light and darkness of interference fringes formed by the signal light component and the reference light component as an optical anisotropy distribution or a refractive index distribution;
A spatial frequency filtering mechanism for filtering a spatial frequency of the signal light component between the spatial light modulator and the information recording medium,
The recording light generation unit has a phase mask composed of pixels of 4 rows and 4 columns that divide each pixel of the phase page data of the signal light component into 16 parts,
The phase mask changes the phase of the signal light component,
The spatial frequency filtering mechanism irradiates the signal light component whose phase has been changed at a position corresponding to the focal point of the signal light component subjected to spatial frequency filtering by dividing it outside the position corresponding to the focal point. An optical information recording / reproducing apparatus.   The information recording / reproducing apparatus according to claim 1, wherein the phase mask changes the phase of only the signal light component and transmits the phase of the reference light component as it is.   The phase mask changes the phase of only the first linearly polarized light component included in the signal light component, and transmits the phase of the second linearly polarized light component orthogonal to the first linearly polarized light component as it is. Or the optical information recording / reproducing apparatus according to 2 above.   The pixels of the phase mask shift the phase of the linearly polarized light component constituting the signal component by ½π from each other between adjacent pixels, and negatively shift the phase of the linearly polarized light component in the positive direction. The optical information according to claim 1, wherein rows shifted in a direction are alternately arranged, and columns that shift the phase of the linearly polarized light component in a positive direction and columns that are shifted in a negative direction are alternately arranged. Recording / playback device. The phase mask is separate from the spatial light modulator;
The optical information recording / reproducing apparatus according to claim 1, wherein the optical information recording / reproducing apparatus is disposed between the light source and the spatial light modulator in an optical path of light output from the light source.   The optical information recording / reproducing apparatus according to claim 1, wherein the phase mask is incorporated in the spatial light modulator. Interference fringes are produced by interfering the signal light component on which the two-dimensional phase page data generated by modulating the light output from the light source with the spatial light modulator is put on the light wave and the reference light component having no information. A phase mask used in an optical information recording / reproducing apparatus that records and records the light and darkness of the interference fringes on an information recording medium as an optical anisotropy distribution or a refractive index distribution,
A phase mask, wherein the signal light component is divided by changing the phase of the signal light component in four rows and four columns of pixels that divide each pixel of the phase page data of the signal light component into 16.   The phase mask according to claim 7, wherein only the phase of the signal light component is changed and the phase of the reference light component is transmitted as it is.   8. The phase mask according to claim 7, wherein the phase of only the first linearly polarized light component included in the signal light component is changed, and the phase of the second linearly polarized light component orthogonal to the first linearly polarized light component is transmitted as it is.   The pixels of the phase mask shift the phase of the linearly polarized light component forming the signal light component by ½π from each other between adjacent pixels, and negatively shift the phase of the linearly polarized light component in the positive direction. The rows shifted in the direction are alternately arranged, and the columns that shift the phase of the first linearly polarized light component in the positive direction and the columns that are shifted in the negative direction are alternately arranged. Phase mask. A recording light generation step for generating a signal light component in which two-dimensional phase page data generated by modulating light output from a light source with a spatial light modulator is placed on a light wave, and a reference light component having no information; ,
A spatial frequency filtering step of filtering a spatial frequency of the signal light component output from the spatial light modulator;
Information for irradiating the information recording medium with the signal light component and the reference light component and recording the light and darkness of interference fringes formed by the signal light component and the reference light component as an optical anisotropy distribution or a refractive index distribution A recording process,
In the recording light generation step, the phase of the signal light component is changed by a phase mask that divides each pixel of the phase page data of the signal light component into pixels of 4 rows and 4 columns,
The spatial frequency filtering step irradiates the signal light component whose phase has been changed at a position corresponding to the focal point of the signal light component subjected to spatial frequency filtering by dividing it outside the position corresponding to the focal point. An optical information recording / reproducing method.   12. The optical information recording / reproducing method according to claim 11, wherein, in the recording light generation step, the phase mask changes the phase of only the signal light component and transmits the phase of the reference light component as it is.   In the recording light generation step, the phase mask changes the phase of only the first linearly polarized light component included in the signal light, and transmits the phase of the second linearly polarized light component orthogonal to the first linearly polarized light component as it is. The optical information recording method according to claim 12.   The phase mask shifts the phase of the linearly polarized light component forming the recording light component by ½π from each other between adjacent pixels, and alternately shifts the phase for each row in the positive direction and the negative direction, and The information recording method according to claim 11, wherein the phase is alternately shifted for each column in a positive direction and a negative direction.