JP2007310933A - Hologram recording/reproducing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hologram recording apparatus and reproducing apparatus having encryption functions. <P>SOLUTION: A recording data reference beam pattern is displayed in a reference beam spatial light modulation part 47 while a recording data signal light pattern is displayed in a signal light spatial light modulation part 46, thereby forming a recording data hologram in the predetermined area of the recording layer 50a of a hologram recording medium 50. An encryption reference beam pattern is displayed in the reference beam spatial light modulation part while an encryption signal light pattern is displayed in the signal light spatial light modulation part, thereby forming an encryption hologram in the same area where the recording data hologram is formed. Thus, the recording data hologram and the encryption hologram are written in a multiplexed manner in the same area of the recording layer 50a of the hologram recording medium 50, and reproduction is inhibited unless a reference beam used for recording is used. Since a signal light phase mask for modulating the phase of a signal light is provided, it is difficult that a recorded hologram is irradiated with the signal light, a recording data reference pattern is detected and encrypted recorded data is reproduced. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a hologram recording / reproducing apparatus.

  In recent years, a hologram memory, which is a recording / reproducing apparatus capable of achieving high recording density and recording / reproducing recorded data at a high transfer rate, has attracted attention. In the hologram memory, the thickness direction of the recording medium is also used, and when recording, the interference fringes between the reference light and the signal light are generated based on the page data corresponding to the recording data with two-dimensional information as one page unit. It is formed as a hologram inside and recorded three-dimensionally at a time. Further, at the time of reproduction, recorded data is reproduced by obtaining diffracted light generated by irradiating the hologram formed in this way with reference light (see Patent Document 1 and Non-Patent Document 2).

In such a hologram memory, a so-called coaxial-type hologram recording / reproducing apparatus has been proposed, and a multiplexing technique has also been proposed (see Non-Patent Document 1). In addition, in order to improve the recording / reproducing characteristics and facilitate the configuration of the hologram memory, as shown in FIG. 10, a spatial light modulator mainly including liquid crystal (FLC) and a high refractive index Ta _{2 are used.} It has been proposed that a phase mask having O ₅ as a main component is formed between silicon and glass so that the spatial light modulator and the phase mask are integrated (see Non-Patent Document 2). .
Japanese Patent Laid-Open No. 2004-226821 Nikkei Electronics January 17, 2005, pages 106-114 Michael J. O'Callaghan et al. `` Spatial light modulators with integrated phase masks for holographic data storage '' Proceeding of ODS 2006 pp 23, MB3

  The volume of recording data that can be stored in such a hologram recording medium is orders of magnitude greater than that of conventional recording media. For this reason, assuming that important recorded data can be easily read by a third party, there is a possibility that confidential matters or personal information may be leaked in a large amount as never before. It has a greater risk of causing serious social problems. Therefore, when reading information from the hologram recording medium, an encryption technology that makes it difficult for a third party to read the recorded data is required, but an encryption technology that takes advantage of the characteristics of hologram recording and reproduction is still available. It has not been.

  Accordingly, an object of the present invention is to provide a hologram recording / reproducing apparatus having an encryption function that takes advantage of the characteristics of hologram recording / reproducing.

  The hologram recording apparatus of the present invention records the hologram on the recording layer of the hologram recording medium by causing the signal light modulated according to the recording data for each page to interfere with the signal light and the reference light having the same light source, A hologram recording / reproducing apparatus that reproduces recording data for each page based on diffracted light obtained by irradiating the hologram recording medium with the reference light, the signal displaying a signal light pattern for generating the signal light An optical spatial light modulator, a reference optical spatial light modulator that displays a reference light pattern for generating the reference light, a signal optical phase mask that performs phase modulation on the signal light, and the signal optical spatial light modulator A control unit that controls each of the modes of the signal light pattern to be displayed on the signal light and the modes of the signal light pattern to be displayed on the reference light spatial light modulation unit, and recording data corresponding to the recording data While displaying the signal light pattern on the signal light spatial light modulator, the recording data reference light pattern corresponding to the recording data signal light pattern is displayed on the reference light spatial light modulator, and the recording data is recorded in a predetermined area of the recording layer. The reference light pattern for encryption corresponding to the signal light pattern for encryption is formed while the hologram is formed and the signal light pattern for encryption for encrypting the recording data hologram is displayed on the signal light spatial light modulator. It is obtained by forming an encryption hologram in the same area as the predetermined area of the recording layer displayed on an optical spatial light modulator, recording the recording data, and irradiating the predetermined area with the recording data reference light pattern. The recorded data is reproduced based on the diffracted light.

  This hologram recording device displays a recording data signal light pattern corresponding to the recording data on the signal light spatial light modulation unit while modulating a recording data reference light pattern specified corresponding to the recording data signal light pattern with a reference light spatial light modulation. The recording data hologram is formed in a predetermined area of the recording layer of the hologram recording medium and the encryption reference light pattern is displayed on the signal light spatial light modulation section while the encryption reference light pattern is displayed on the reference light spatial light modulation. An encryption hologram is formed in the same area as the recording data hologram displayed on the screen. In this way, the recording data hologram and the encryption hologram are multiplexed and written in the same area of the recording layer of the hologram recording medium and cannot be reproduced unless the reference light used for recording is used. Since the signal light phase mask for performing phase modulation on the signal light is provided, it is difficult to reproduce the recorded data by detecting the recorded data reference light pattern by irradiating the recorded hologram with the signal light. It is.

  According to the present invention, a hologram recording / reproducing apparatus having an encryption function can be provided.

  Embodiments of the present invention will be described below. First, as an example of a hologram recording / reproducing apparatus, a coaxial hologram recording / reproducing apparatus having a coaxial optical system will be briefly described, and then the principle of the encryptor and specific examples in the hologram recording / reproducing apparatus will be sequentially described. To do.

(Coaxial hologram recording / reproducing device)
In the coaxial hologram recording apparatus, for each of the signal light and the reference light, which will be described later, by sharing a part of the optical path of the light beam, recording and reproduction can be performed using the same objective lens. The optical system can be simplified. Further, since it is relatively easy to be compatible with conventional optical discs such as CD and DVD, it attracts attention as a future recording / reproducing apparatus.

  FIG. 1 is a schematic diagram of a hologram recording / reproducing apparatus 100 according to an embodiment shown with an optical unit as a main part of the apparatus as a center.

  The hologram recording / reproducing apparatus 100 is provided with a servo optical system 30. Only the main optical components constituting the servo optical system 30 will be described with reference numerals. The laser light source 28 emits a servo light beam. The servo light beam is different from the wavelength of the light beam from the laser light source 20 for recording / reproduction, and as a longer wavelength light beam (for example, a red laser beam), the servo light beam and the recording / reproduction light beam are used. The light beam can be separated.

  The beam splitter 27 is for guiding the return light from the hologram recording medium 50 to the photo detector 29. The photo detector 29 is, for example, an astigma method for focus servo and a push-pull method for radial (tracking) servo. The detector is divided into a plurality of parts so as to correspond to the above. The dichroic mirror 34 is an optical component common to the servo optical system 30 and the recording / reproducing optical system, and is a wavelength separation element that separates the servo light beam and the recording / reproducing light beam. Further, the reflection mirror 56 changes the traveling directions of the servo light beam and the recording / reproducing light beam, guides them to the objective lens 24, and transmits them from the address groove 50c (see FIG. 3) of the hologram recording medium 50 and from the hologram. The traveling direction of each diffracted light is changed and guided to the servo optical system 30 and the recording / reproducing optical system.

  The spindle motor 51 rotates around the geometrical center of the disk shape of the hologram recording medium 50 having the same external shape as an optical disk such as a conventional CD or DVD. Thus, the rotational position of the hologram recording medium 50 is controlled.

  The operation of the hologram recording / reproducing apparatus 100 will be briefly described. First, the operation during recording will be described.

  The light beam from the laser light source 20 enters a spatial light modulator (SLM) 37. The spatial light modulator 37 controls whether the light beam is reflected (changes the direction of the light beam) or not reflected (absorbs the light beam) on a pixel-by-pixel basis. This is a modulator 37. The laser light source 20 has optical components such as a collimator lens (not shown), and the light beam from the laser light source 20 is converted into parallel light.

  FIG. 2 shows a pattern displayed on the spatial light modulator 37. The spatial light modulator 37 has two regions of a signal light spatial light modulation unit 46 and a reference light spatial light modulation unit 47. In order to perform recording on the hologram recording medium 50, the spatial light modulator 37 displays a signal light pattern for generating signal light on the signal light spatial light modulation unit 46 based on the recording data, and a reference light spatial light modulation unit. A reference light pattern for generating reference light is generated in 47. Here, in the hologram recording / reproducing apparatus 100 adopting the coaxial method, the spatial light modulator 37 is configured to include both the signal light spatial light modulation unit 46 and the reference light spatial light modulation unit 47. The regions of the spatial light modulator 37 are divided based on the control signal from the control unit 60, and both are configured on the same plane.

  Each of the signal light and the reference light passes through the relay lens 35, the relay lens 36, the beam splitter 23, the relay lens 38, the relay lens 39, and the dichroic mirror 34, is reflected by the reflection mirror 56, and is recorded and reproduced by the objective lens 24. The recording size is reduced to a beam size suitable for the recording medium 50, and the hologram recording medium 50 is irradiated to the recording layer 50a of the hologram recording medium 50 (see FIG. 3). Is done. Here, in order to move the relay lens 39 in the lateral direction of the paper surface in order to make the image formation point of the image formed by the reference light or the signal light and the reference light modulated by the spatial light modulator 37 appropriate. The relay lens actuator 45 is provided and controlled by a signal from the control unit 60.

  In this case, the focus and radial servo system including the servo optical system 30 is so arranged that the light beam for recording / reproducing is focused on the recording layer of the hologram recording medium 50 and the light beam is arranged at a predetermined position in the radial direction. Is controlled by a spindle servo system that controls the rotation angle of the spindle motor 51 so that the hologram recording medium 50 is located at a predetermined position along a track orthogonal to the radial direction. Such a servo is obtained by processing the electrical signal from the photodetector 29 by the control unit 60. The light beam from the servo optical system 30 is reflected by the dichroic mirror 34 and the reflection mirror 56, passes through the objective lens 24, and is irradiated onto the hologram recording medium 50, while the light beam from the recording / reproducing optical system. Passes through the dichroic mirror 34, is reflected by the reflection mirror 56, passes through the objective lens 24, and is applied to the hologram recording medium 50. In the hologram recording / reproducing apparatus 100 adopting the coaxial method, the signal light, the reference light, and the diffracted light all pass through the objective lens 24.

  Here, the hologram recording medium 50 is provided with an address groove 50c for positioning a recording / reproducing light beam and a servo light beam, and the servo optical system 30 is used in a conventional CD, DVD or the like. The positions of the recording / reproducing light beam and the servo light beam in the hologram recording medium 50 can be detected based on the electrical signal from the photodetector 29. That is, the mutual relationship between the recording / reproducing light beam and the servo light beam is uniquely determined by the relative relationship of the arrangement of the optical components constituting each of the recording / reproducing optical system and the servo servo optical system 30. Mutual relations are defined. Thus, by determining the positional relationship between the servo light beam and the hologram recording medium 50 by the focus, radial servo system, and spindle servo system, the positional relationship of the recording / reproducing light beam can also be controlled. .

  That is, a so-called focus error signal and tracking error signal are detected from the photo detector 29 of the servo optical system 30, and an objective lens actuator composed of a focus actuator and a tracking actuator based on each error signal is provided as a control unit. The objective lens 24 is displaced in the directions indicated by reference numerals F and T in FIG. 1 to be controlled by a focus / tracking servo circuit (not shown) disposed at 60, and the servo light beam and recording / reproducing light are moved. Each light beam of the beam irradiates a target position of the hologram recording medium 50.

  The hologram recording / reproducing apparatus 100 shown in FIG. 1 has been described above as being a hologram recording / reproducing apparatus having both recording and reproduction functions. For example, the hologram recording apparatus of the embodiment may be configured as an apparatus that does not include the image sensor 25 and does not have a reproduction function. In the hologram recording / reproduction apparatus 100, a portion related to the recording function, for example, signal light spatial light modulation The hologram reproducing apparatus of the embodiment may be configured as an apparatus that does not include the unit 46 and has no recording function.

(Structure of hologram recording medium)
FIG. 3 schematically shows the structure cut in the cross-sectional area direction of the hologram recording medium 50 described above, and further includes the signal light 40, the diffracted light 42 (inside the broken line), and the reference light 41 (between the solid line and the broken line). ) And a servo light beam (inside the alternate long and short dash line) how the light enters the objective lens 24. The hologram recording medium 50 includes an antireflection film 50d, a plastic substrate 50g, a recording layer 50a, a gap layer 50e, a dichroic mirror layer 50b that is a recording / reproducing light beam reflecting film, and an address groove 50c. Here, the address groove 50c is formed as a groove having a concavo-convex formed continuously in a spiral shape, and the shape of the groove is deformed so as to be optically readable. The position on the hologram recording medium 50 can be specified by the deformation mode. Note that the deformation of the groove shape may be, for example, such that the grooves are discretely arranged as pits, or may be anything such as meandering of the groove.

  At the time of recording, a hologram is formed on the recording layer 50a according to the shape of the interference fringes generated by the interference between the signal light 40 and the reference light 41, and only the reference light 41 is irradiated to the hologram at the time of reproduction. As a result, the diffracted light 42 corresponding to the hologram is reflected by the reflective film 50 b in the substantially same region as the signal light 40 at the time of recording, and is generated through the objective lens 24. On the other hand, the servo light beam is transmitted through the reflection film 50b having wavelength selection characteristics, reflected by the aluminum reflection film on which the address groove 50c is formed, and servo optically according to the same principle as in CD and DVD. Based on the electrical signal detected from the photodetector 29 of the system 30, the controller 60 uses the error signal for each servo required for the above-described focus servo, radial servo, and spindle motor rotation control processing. Further, an address signal for specifying the position of the recording layer 50a of the hologram recording medium 50 irradiated with the light beam in the hologram recording medium 50 is obtained.

(Explanation of terms used in this specification)
Prior to describing the concept of encryption, terms used in this specification will be described. An uncorrelated term is used below as a term representing a concept about a relationship between one reference light pattern and another reference light pattern different from the one. Uncorrelated means that both the same pixels (pixels at the same position) of one reference light pattern and other reference light patterns displayed on the reference light spatial light modulation unit 47 of the spatial light modulator 37 are white portions. It means that it is not (a pixel that reflects light). The term “uncorrelated” is used not only for the reference light pattern but also for the mutual reference light generated from such a reference light pattern. The term uncorrelated is also used for the relationship between one signal light pattern and another signal light pattern that is different from this, and it is also used for signal light generated from such signal light patterns. It is.

  The term white rate is used in the following. The white rate is a reference light pattern formed by a combination of binary information of a black part (a pixel that absorbs a light beam and prevents reflection of the light beam) and a white part. The ratio of the number of white pixels to the total number of pixels. The white rate of the reference light pattern for encryption when the white rate of the reference light pattern when recording the recording data is 1 is referred to as a standardized white rate. The terms white rate and standardized white rate are also used for signal light patterns.

  Further, M / # (M number) is used as a term representing another concept. M / # is an index of overwriting in the hologram recording medium, and the larger the value of M / #, the larger the number of overwriting in the same area of the recording layer. Further, the terms that M / # consumption is large or M / # consumption is large, and terms that M / # consumption is small or M / # consumption is small are used. “M / # consumption is high (large)” means that the number of times that valid information can be overwritten as a hologram is greatly reduced by recording information on the hologram, and M / # consumption is low (small). Means that the number of times that valid information can be overwritten as a hologram is not relatively reduced by recording information in the hologram.

  Further, the terms of the recording data signal light pattern and the encryption signal light pattern are used. The recording data signal light pattern is a signal light pattern displayed on the signal light spatial light modulator 46 of the spatial light modulator 37 corresponding to the recording data, and the encryption signal light pattern is a spatial light modulator for encryption. 37 is a signal light pattern displayed on the 37 signal light spatial light modulator 46. Further, the terms of the recording data reference light pattern and the encryption reference light pattern are used. The recording data reference light pattern is a reference light pattern displayed on the reference light spatial light modulator 47 of the spatial light modulator 37 together with the recording data signal light pattern, and the encryption signal light pattern is spatial light modulated together with the encryption signal light pattern. This is a reference light pattern displayed on the reference light spatial light modulator 47 of the device 37.

  The terms recording data hologram and encryption hologram are used. The recording data hologram refers to the recording data reference light pattern specified corresponding to the recording data signal light pattern while displaying the recording data signal light pattern, which is a signal light pattern corresponding to the recording data, on the signal light spatial light modulator 46. A hologram displayed on the optical spatial light modulation unit 47 and formed in a predetermined area of the recording layer. The encryption hologram is a signal light pattern for encrypting a recording data hologram. The hologram is formed in a predetermined area of the recording layer by displaying on the reference light spatial light modulation unit 47 the encryption reference light pattern specified in correspondence with the encryption signal light pattern while being displayed on the light modulation unit. The area where each of the recording data hologram and the encryption hologram is formed is the same area or an overlapping area.

  Further, the term “pixel” is used for the spatial light modulator 37 and the image sensor 25. The pixel is the smallest unit that can control the mode of the signal light pattern or the reference light pattern from the control unit to the spatial light modulator, and is the smallest unit that can take the reproduced image of the image sensor 25 into the control unit. It is a unit. Here, it is desirable that one pixel of the image sensor 25 optically corresponds to one pixel of the spatial light modulator 37 from the viewpoint of simplicity of control and ease of processing in the control unit 60. It is not essential for one pixel of the image sensor 25 to optically correspond to one pixel of the modulator 37.

  The terms signal light phase mask and reference light phase mask are used. The signal light phase mask is a phase mask that acts on the signal light, and the reference light phase mask is a phase mask that acts on the reference light.

  One symbol term is used. The term “one symbol” is a unit composed of a plurality of pixels arranged two-dimensionally in the spatial light modulator. For example, one symbol is formed by a set of pixels in four columns and four rows. . In this embodiment, one symbol is encoded as a so-called block code in which digital data corresponding to a predetermined bit length corresponds. Similarly, one symbol is also used as a term indicating a unit constituted by a plurality of pixels arranged two-dimensionally on the image sensor. Several other terms are used, but for terms that are relatively uncommon to those skilled in the art, the meaning of the terms will be briefly explained each time they are cited.

(About the concept of encryption)
The concept of encryption (process of recording on the hologram recording medium) of this embodiment will be described with reference to FIGS. FIG. 4 schematically shows the encryption process, and FIG. 5 schematically shows the decryption process. FIG. 6 schematically shows an image of the diffracted light in the image sensor 25 when the hologram recording medium 50 is irradiated with only signal light. 4 to 6 schematically show a partial range of pixels.

  4A schematically shows four symbols of the signal light pattern 46a and the reference light pattern 47a displayed on the spatial light modulator 37. FIG. Here, one symbol is assumed to be composed of 16 pixels in 4 columns and 4 rows. A part of the signal light pattern 46a is schematically enlarged and shown in the central part of FIG. 4A, and only the position of the reference light pattern 47a is shown in the outer peripheral part of FIG. FIG. 4B schematically shows another signal light pattern 46b and reference light pattern 47b displayed on the spatial light modulator 37, which are different from those shown in FIG. 4A. A part of the signal light pattern 46b is schematically shown at the center of FIG. 4B, and only the position of the reference light pattern 47b is shown at the outer periphery of FIG. Here, the reference light pattern 47a and the reference light pattern 47b are uncorrelated patterns. Here, it is assumed that the signal light pattern 46a is a recording data signal light pattern, the reference light pattern 47a is a recording data reference light pattern, the signal light pattern 46b is an encryption signal light pattern, and the reference light pattern 47b is an encryption reference light pattern. I will explain.

  Using these two sets of signal light patterns and reference light patterns displayed on the spatial light modulator 37, encryption is performed according to the following procedure. First, the signal light pattern 46 a and the reference light pattern 47 a shown in FIG. 4A are displayed on the spatial light modulator 37, and a hologram is formed on the recording layer 50 a of the hologram recording medium 50. Next, the signal light pattern 46b and the reference light pattern 47b shown in FIG. 4B are displayed on the spatial light modulator 37, and a hologram is formed by the signal light pattern 46a and the reference light pattern 47a shown in FIG. A hologram is formed on the same area as the other area. In this way, the encrypted recording of the recording data is completed by overwriting at least twice in the same area.

  Next, decoding (reproduction process from the hologram recording medium) will be described. FIG. 5A shows a reproduced image I25a obtained by the image sensor 25 by irradiating the reference light generated by the reference light pattern 47a onto the hologram (double-written) encrypted as described above. FIG. 5B schematically shows an encrypted hologram with an all-white reference light pattern (a pattern in which the reference light pattern is composed only of a white portion). A part of the reproduced image I25w obtained by irradiating the generated reference light and obtained by the image sensor 25 is schematically shown.

  Comparing FIG. 5 (A) and FIG. 4 (A), the reproduced image I25a shown in FIG. 5 (A) is displayed and recorded on the spatial light modulator 37 shown in FIG. 4 (A). It can be seen that 46a can be completely reproduced. That is, the recording signal can be completely reproduced by processing the electrical signal from the image sensor 25 by the control unit 60. On the other hand, the reproduced image I25w shown in FIG. 5B is a reproduced image in which the signal light pattern 46a and the signal light pattern 46b are mixed, and it is difficult to reproduce the signal light pattern 46a and the recorded data.

  In addition, the hologram formed by encryption as described above is not correlated with the reference light pattern 47a instead of the all-white reference light pattern as a reference light pattern at the time of reproduction, and is a reference. It is not uncorrelated with the light pattern 47b, and for each of both, a signal light pattern (for example, a random pattern in which white portions are randomly distributed in the reference light pattern) in which the number of pixels where white portions overlap is approximately the same number. Even if the signal light pattern 46 is used, the signal pattern in which the signal light pattern 46a and the signal light pattern 46b are mixed is reproduced, and it is difficult to reproduce the signal light pattern 46a and the recorded data.

(Signal light pattern)
From the above description, it can be understood that when encryption is performed using the recording data reference light pattern and the encryption reference light pattern, it is desirable that the two are uncorrelated. This is because, in FIG. 5A, the signal light pattern 46a, that is, the recording data reference light pattern, can be completely reproduced because they are uncorrelated, and there is a correlated portion (of both reference lights). When the recorded data reference light pattern is used for reproduction, the diffracted light from the hologram formed by the encryption signal light pattern becomes noise and the reproduction signal quality deteriorates (reproduction). This is because the characteristics deteriorate.

  Further, it is desirable that the white rate of the reference light pattern for encryption is equal to the white rate of the recording data reference light pattern. Because, for example, when reproducing with an all-white reference light pattern, both information based on the recording data signal light pattern and the encryption signal light pattern is reproduced, and at that time, the reference light intensity (the number of bright pixels) is increased. This is because the power of the diffracted light changes accordingly, and the recording data signal light pattern and the encryption signal light pattern may be separated by this power difference. On the other hand, when the white rate of the reference light pattern for encryption and the recording data reference light pattern is substantially the same, it is difficult to separate both pieces of information, so that it is more difficult to decrypt the encrypted information. .

  The white rate of the reference light is an important factor in relation to M / #. In order to secure the capacity with one hologram recording medium, M / # must be large to some extent. That is, in the encryption of this embodiment, since different holograms are overwritten and formed in the same area, when M / # is small, the number of times of multiplexing in so-called multiplex recording is higher than in the conventional case. In order to be restricted, it is important to reduce the increase in the hologram forming area as much as possible. When the white rate of the reference light is large, M / # is substantially small, and the number of usable multiplexing times is small and M / # is consumed much. On the other hand, when the white rate of the reference light is small, M / # is substantially increased, the number of multiplexing operations that can be used is increased, and M / # is consumed less.

  On the other hand, if the white rate is made too small, the effect of encryption is reduced, so the number of white pixels in the reference light pattern for encryption needs to be increased to some extent so as not to hinder the encryption. Therefore, it is desirable to set the minimum white rate within a range that does not increase the consumption of M / # but produces an encryption effect. Here, the value of the standardized white rate described above is preferably in the range of 1.5 to 0.1, for example. In the above description, the white portion of the reference light pattern in the spatial light modulator 37 defines the desirable range of the value of the standardized white rate assuming that the light beam is completely transmitted. In the spatial light modulator 37, the transmittance of the white portion of the encryption reference light pattern is made smaller than the transmittance of the light beam corresponding to the white portion of the recording data reference light pattern. , M / # may be reduced. For example, the white rate of the reference light pattern for recording data is preferably in the range of 0.01 to 0.5, for example.

(Signal light pattern)
The signal light pattern is obtained by spatially modulating recording data based on a predetermined format. Here, the predetermined format includes an address assignment scheme, an error correction scheme, a recording data spatial modulation scheme, and the like. For example, in this embodiment, the spatial modulation scheme is a block code in units of one symbol that associates 16 pixels with a predetermined length of bits (blocks). Of the 16 pixels, 3 pixels are white portions (portions through which the light beam is transmitted). Such a block code is called a 16: 3 code. A signal light pattern for encryption will be described with reference to FIG. 6 when recording is performed using a 16: 3 code.

  FIG. 6A shows a recording data signal light pattern in the spatial light modulator 37 corresponding to the recording data. The white part (outlined part) represents the part where the light beam is reflected, and the black part (black part). (Portion) represents a portion where the light beam is not reflected. Each of FIGS. 6B to 6E uses diffracted light on the image sensor 25 in the case of using an all-white reference light pattern in which the reference light spatial light modulator 47 is all white as reference light. It is a reproduced image that occurs. Here, when obtaining FIGS. 6B to 6E, encryption signal light patterns (not shown) having white portions at mutually different positions are used.

  When the recording data signal light pattern and the encryption signal light pattern displayed on the spatial light modulator 37 are different at all locations (pixels at the same position), that is, the white portion of the recording data signal light pattern and the encryption signal FIG. 6B shows a reproduction image in the image sensor 25 generated by the diffracted light from the double recording portion of the encryption hologram and the recording data hologram when the white portion of the light pattern does not exist in the common pixel. By the diffracted light from the double recording portion of the encryption hologram and the recording data hologram formed when the white portion of the recording data signal light pattern and the white portion of the encryption signal light pattern are common at one place of the pixel The resulting reproduced image in the image sensor 25 is shown in FIG. 6C, where the white portion of the recording data signal light pattern and the encryption signal light pattern are displayed. FIG. 6D shows a reproduced image in the image sensor 25 generated by the diffracted light from the double recording portion of the encryption hologram and the recording data hologram formed when the white portion of the pixel is common at two locations of the pixel. The reproduced image in the image sensor 25 generated by the diffracted light from the double recording portion of the encryption hologram and the recording data hologram formed when the recording data signal light pattern and the encryption signal light pattern are the same in all locations. Is shown in FIG. In this case, the reference light pattern for encryption at the time of recording is one that is uncorrelated with the recorded data reference light pattern.

  Here, in each of FIGS. 6B to 6E schematically showing a part of the reproduced image of the image sensor 25, the white portion is approximately twice the shaded portion (the shaded portion). The amount of light (light luminance) is schematically represented, and the black portion schematically represents a portion not irradiated with light. When the image generated in the image sensor 25 is associated with the image displayed on the spatial light modulator 37, the shaded portion indicates a portion where the white portion of the recording data signal light pattern and the encryption signal light pattern do not match (spatial light modulation). In the pixel at one position of the device 37, a white portion is shown only when one signal light pattern is displayed, and the white portion matches the recording data signal light pattern and the encryption signal light pattern. (A portion that is a white portion in both signal light patterns in a pixel at one position of the spatial light modulator 37).

  Although not shown, each encryption signal light pattern corresponding to FIG. 6B to FIG. 6E displayed on the spatial light modulator 37 is white as shown in FIG. The hatched portion and the white portion excluding the shaded portion at the position corresponding to the portion are white portions, and the other portions are black portions. For example, the white portion of the signal light pattern for encryption corresponding to FIG. 6B is the first row from the top of the second column from the left side, the second row from the top of the third column from the left side, and 4 from the left side of the drawing. Indicates the first row from the top of the column. The white portion of the encryption signal light pattern corresponding to FIG. 6C is the first row from the top of the second column from the left side, the second row from the top of the third column from the left side, and 4 from the left side of the drawing. Indicates the third row from the top of the column. Also, the white part of the encryption signal light pattern corresponding to FIG. 6D is the second row from the top of the first column from the left side, the first row from the top of the second column from the left side, and 4 from the left side of the drawing. Indicates the third row from the top of the column. Furthermore, the white part of the signal light pattern for encryption corresponding to FIG. 6E is the second row from the top of the first column from the left side, the fourth row from the top of the second column from the left side, and 4 from the left side of the drawing. Indicates the third row from the top of the column.

  As a decoding method for obtaining recording data from the image of the image sensor 25 shown in FIGS. 6B to 6E, 16 data (one symbol) are A / D converted. Generally, there is a method of selecting three in order from the one with the highest level of values taken in by the A / D converter (from the one with the highest luminance), and decoding by obtaining the position where the three exist Is. In such a case, in the case shown in FIG. 6B, six to three positions are substantially specified, and encryption is performed satisfactorily. On the other hand, in the case shown in FIG. 6 (D), four to three positions are substantially specified, and the recording data for one symbol reproduced from these 16 is recorded before encryption. The recorded data signal light pattern can be reproduced with a probability of 1/2, and the effect of encryption is reduced.

  That is, in order to obtain an image as shown in FIG. 6B in the image sensor 25, it is only necessary to make the recording data reference light pattern and the encryption reference light pattern uncorrelated during recording as described above. Further, it is more preferable that the relationship between the recording data signal light pattern and the encryption signal light pattern is also uncorrelated.

  Here, in order to make the recording data signal light pattern and the encryption signal light pattern uncorrelated, an encryption signal light pattern for one page that is uncorrelated for each page may be generated. Since the scheme is performed by a block code, more simply, each time 16 pieces of data corresponding to a recording data signal light pattern are captured, an uncorrelated encryption signal light pattern obtained from the 16 data is obtained. It is possible to easily obtain 16 pieces of data for displaying. In this case, this conversion can be easily performed by writing a correlation table of uncorrelated codes corresponding to 1-symbol recording data composed of all combinations in advance in a ROM (Read Only Memory) provided in the control unit 60. I can do it. In order to make the recording data reference light pattern and the encryption reference light pattern uncorrelated, since the recording data reference light pattern is known in advance, all of the encryption reference light patterns displayed on the spatial light modulator 37 are displayed. The area can be easily stored in the ROM in advance.

  Further, without using a ROM, the control unit 60 can sequentially generate 3 random numbers in a range of 16 numbers, and use a random pattern in which the position indicated by the random number is a white part. Although the effect is impaired as compared with the case of using a ROM, a sufficiently good effect can be obtained. Further, as the number of white portions of the signal light pattern for encryption is reduced as in the case of the reference light, although the effect of encryption is reduced, the M / # consumption can be reduced. Of the 16, the number of 3 or less, which is 2 may be used.

(About decryption of code)
As described above, when encryption is performed, particularly when the recording data signal light pattern and the encryption signal light pattern are uncorrelated, it is difficult to reproduce the recording data unless the recording data reference light pattern is known. It seems that a third party cannot decrypt the code. However, the recording data reference light pattern can be found by the following procedure.

  The relationship between the reference light and the signal light is an exchangeable relationship. That is, the hologram recording medium in which the hologram is formed by the recording data according to the same principle when the recording data corresponding to the signal light pattern is reproduced by irradiating the reference light to the hologram recording medium in which the hologram is formed by the recording data By irradiating with signal light, a signal corresponding to the reference light pattern (hereinafter referred to as reference light data) can be reproduced.

  Therefore, when the recording data is once decoded, only the recording data signal light pattern corresponding to the recording data is displayed on the spatial light modulator 37, and the signal light is applied to the recording area of the hologram where the recording data is recorded. By receiving the diffracted light obtained by irradiation with the image sensor 25, an image of the recording data reference light pattern can be obtained on the light receiving surface of the image sensor 25. In this case, the position of the light receiving surface on which the image of the recording data reference light pattern of the image sensor 25 is projected corresponds to the display position of the recording data reference light pattern of the spatial light modulator 37 at the time of recording. It becomes the outer peripheral part. Here, an example of the recording data signal light pattern corresponding to the recording data is shown in FIG.

  In this way, if even one piece of recording data is known, the recording data reference light pattern is formed as an image on the image sensor 25, and the reference light data is detected from the image sensor 25. The optical data is sent from the control unit 60 to the spatial light modulator 37, whereby the recording data reference light pattern can be displayed on the spatial light modulator 37. In this way, the recorded data reference light pattern is displayed on the spatial light modulator 37, the recorded data is read from the encrypted hologram, and the decryption of the code is performed. The method for detecting the recording data reference light pattern based on one known recording data has been described above. Next, a method for detecting the recording data reference light pattern when the recording data is not known at all. explain.

  Since the hologram is recorded as interference fringes between the reference light and the signal light, a part of the recorded data signal light pattern, that is, the entire recorded data reference light pattern can be known even from one pixel. It is. For example, a recording data reference light pattern can be obtained from one pixel in an arbitrary white portion shown in FIG.

  Specifically, for example, as shown in FIG. 6 (A), within the range shown in FIG. 6 (A), the second row from the top of the first column from the left side or the left side of the drawing. The entire recording data reference light pattern can be known by setting either the third row from the top of the second column or the third row from the top of the third column from the left side as a white portion. At this time, in order to cause the image sensor 25 to generate the entire image of the recording data reference light pattern by the amount of light from one pixel, sufficient S / N is required unless the luminance of the one pixel is very high. And the recording data reference light pattern cannot be detected. For this reason, the intensity of the laser beam of the laser light source 20 of the hologram recording / reproducing apparatus 100 needs to be much higher than that in a normal hologram recording / reproducing apparatus.

  Further, the reproduction of the entire image of the recording data reference light pattern is influenced by what kind of encryption signal light pattern is used for encryption. That is, when the encryption signal light pattern used in forming the region where the hologram is multiplexed and recorded is uncorrelated with the recording data reference light pattern, only one arbitrary pixel of the signal light spatial light modulation unit 46 is used. By making the white portion, only one of the recording data reference light pattern and the encryption reference light pattern can be reproduced. That is, when one arbitrary pixel of the signal light spatial light modulator 46 that is a white portion corresponds to a white portion of the recording data signal light pattern used when forming the hologram, the recording data reference light pattern Is obtained by the image sensor 25, and any one pixel of the signal light spatial light modulation unit 46, which is a white part, corresponds to the white part of the encryption signal light pattern used when forming the hologram In this case, an image of the encryption reference light pattern is obtained by the image sensor 25. Also, an arbitrary one pixel of the signal light spatial light modulation unit 46 that is a white portion is used for encryption used when forming a white portion or hologram of a recording data signal light pattern used when forming a hologram. If none of the white portions of the signal light pattern falls, no image of the reference light pattern can be obtained on the image sensor 25.

  Therefore, a plurality of reference light patterns obtained by setting only one pixel arranged at various positions of the signal light spatial light modulation unit 46 as a white portion a plurality of times are temporarily recorded data reference light patterns. To check whether the recorded data is deciphered. As a result, the recording data reference light pattern corresponds to the reference light pattern from which the found recording data is decoded. In this way, the recording data reference light pattern can be found.

  Next, the case where the encryption signal light pattern in the same hologram formation region is not uncorrelated with the recording data reference light pattern will be described. In this case, when any one pixel of the signal light spatial light modulation unit 46 is not a common white part, as described above, either the recording data reference light pattern or the encryption reference light pattern is used. Or the reference light pattern image cannot be obtained. On the other hand, when any one pixel of the signal light spatial light modulation unit 46 is a common white part, an image in which the image of the recording data reference light pattern and the image of the encryption reference light pattern are mixed is obtained. That is, a pixel corresponding to the white portion of the recording data reference light pattern and corresponding to the white portion of the encryption reference light pattern forms an image on the image sensor 25 with double brightness, and either one of the white portions In this case, an image is formed on the image sensor 25 with 1 × brightness, and any pixel that does not correspond to any white portion is dark.

  The above process is a case where attention is paid to only one pixel of the signal light pattern as described above, and it is arranged as follows for confirmation. 1. If the pixel that becomes the white portion is a white portion only when recording data is recorded, an image corresponding to the recording data reference light pattern is reproduced on the outer peripheral portion of the image sensor 25. 2. If the pixel that becomes the white portion is the white portion only when the encryption is recorded, an image corresponding to the reference light pattern for encryption is reproduced on the outer peripheral portion of the image sensor 25. 3. If the pixel that becomes the white portion is not the white portion when recording the recording data and is not the white portion when recording the encryption, the reproduced image is not reproduced on the outer peripheral portion of the image sensor 25. 4). If the white pixel is a white part when recording data is recorded and a white part when recording a cipher, an image corresponding to the recording data reference light pattern and a reference light pattern for encryption are used. The brightness of the pixel corresponding to the white portion in both patterns (both the recording data reference light pattern and the encryption reference light pattern) is The luminance is doubled compared to the corresponding pixel in the case where only one of the patterns (one of the recording data reference light pattern or the encryption reference light pattern) is a white portion.

  Therefore, first, a diffracted image of the reference light pattern in the image sensor 25 in which pixels having twice the brightness are generated (in this case, an image in which the image of the recording data reference light pattern and the image of the encryption reference light pattern are mixed) Is obtained by the image sensor 25), and the diffraction pattern of the reference light pattern in the image sensor 25 which is an all black pattern (a pattern in which all pixels are black) (in this case, actually diffracted light is generated). Any one pixel of the signal light spatial light modulation unit 46 is sequentially set as a white part until a reference light pattern composed of white and black pixels having uniform luminance is generated. . The diffracted image of the reference light pattern in the image sensor 25 detected in this way is either the recording data reference light pattern image or the encryption reference light pattern image. Therefore, the control unit 60 detects the reference light data from the detected diffraction pattern of the reference light pattern, and the reference light pattern displayed on the spatial light modulator 37 by the control unit 60 based on the reference light data is recorded data reference light. A reference light pattern that can be regarded as a pattern and displayed in order on the reference light spatial light modulation unit 47 to reproduce the recorded data by irradiating the hologram with the light beam can be determined to be the recorded data reference light pattern. Is. The above processing is performed by the control unit 60 having a ROM in which the processing procedure is stored in advance, and the control unit 60 controls each unit according to this procedure.

  That is, in order to perform such decryption of encryption, a hologram reproducing device that satisfies the following conditions may be used. First, regarding the light receiving area of the image sensor 25, in a normal hologram reproducing apparatus not intended for decryption of the code, the light receiving area only needs to receive a central portion corresponding to only the signal light in the diffracted light. However, in order to decrypt the above-described code, in order to receive the diffracted light in the region corresponding to the reference light pattern, the outer peripheral portion of the image sensor 25 is required in addition to the central portion corresponding to only the signal light. That is, it must be configured to receive all of the diffracted light.

  Next, the control unit 60 must be able to perform control so that an arbitrary pixel arranged in the signal light spatial light modulation unit 46 of the spatial light modulator 37 is a white part. That is, it must be possible to control not only in units of symbols but also in units of pixels more finely.

  Further, with respect to the laser light source 20, in a normal hologram reproducing device not intended for decryption, many pixels of the spatial light modulator 37 are set as white portions, and diffracted light generated by the light beam reflected by the white portions is generated. The image sensor 25 receives light. However, in the above-described decoding method, the light beam reflected by only one pixel of the signal light spatial light modulator 46 is irradiated onto the hologram recording medium 50, and diffracted light is emitted from the image sensor. 25 is detected. For this reason, when a normal hologram reproducing apparatus is used, the amount of diffracted light is small. On the other hand, in a hologram reproducing apparatus used for decryption of a code, in order to increase the amount of diffracted light, a laser output much larger than that of a laser light source used in a normal hologram reproducing apparatus must be obtained. I must.

  If each of the above-described light receiving area of the image sensor 25, control processing of the control unit 60, and high output of the laser light source 20 are viewed in relation to the current state of the technology, the enlargement of the light receiving area of the image sensor 25 There is no technical difficulty due to the evolution of processes in etc. In addition, regarding the control by the control unit 60 in units of pixels, the generation of the control signal is based on the adoption of a DSP (Digital Signal Processor) and a device constituting the spatial light modulator 37, for example, liquid crystal and active matrix methods. There is no difficulty by adopting the driver. However, regarding the increase in the output of the laser light source 20, it is currently difficult to obtain the laser light source in terms of the price.

  In view of such a point, a method of decrypting a cipher described below that does not impose a burden on the laser light source 20 different from the above-described one is possible. First, a plurality of pixels of the signal light spatial light modulator 46 are set as white portions. Here, at first, no consideration is given to what each of the white pixels is. However, by using a plurality of pixels as white portions in this way, the amount of diffracted light increases even when a normal output laser light source is employed as the laser light source 20, and the diffracted light forms on the light receiving surface of the image sensor 25. Discrimination of the image to be performed becomes easy.

  Depending on what kind of pixels correspond to the plurality of white portions of the signal light spatial light modulator 46, different phenomena can be obtained when the hologram is irradiated with signal light. When a plurality of pixels are white portions, four cases similar to the case where attention is paid to only one pixel of the signal light pattern described above occur as the integration. That is, among a plurality of pixels that are white portions, there are various cases depending on the size relationship between the number of pixels that were white when recording data and the number of pixels that were white when recording encryption. Will be separated. In this case, even when the intensity of the light beam from the laser light source 20 is small by simultaneously making a plurality of pixels of the signal light spatial light modulator 46 white, it is sufficient to separate into the following three cases: It becomes possible.

  That is: If the number of pixels that were white when recording data was larger than the number of pixels that were white when recording the cipher, an image corresponding to the recording data reference light pattern and the reference light pattern for encryption However, the image corresponding to the recording data reference light pattern is received more clearly (with high brightness). 2. If the number of pixels that were white at the time of recording the recording data is smaller than the number of pixels that were white at the time of recording the cipher, the image corresponding to the recording data reference light pattern and the reference light pattern for encryption However, the image corresponding to the encryption reference light pattern is received more clearly (with high brightness). Furthermore, the luminance of the pixel corresponding to the white portion in both patterns is twice that of the pixel corresponding to the white portion in only one of the patterns. 3. If the number of pixels that are white when recording data is recorded is zero and the number of pixels that are white when recording cipher is also zero, the reproduced image is not detected.

  According to such case classification, the recording data reference light pattern can be detected by the following procedure. 1. When attention is paid to each pixel of the image sensor 25, the luminance becomes four levels. If the number of stages is not clearly four, the combination of a plurality of white parts of the signal light spatial light modulator 46 is changed. 2. Pick out the pixel with the highest brightness. This pixel is a white portion in the recording data reference light pattern (similarly, it is a white portion in the encryption reference light pattern). 3. Pick out the pixel with the lowest brightness. This pixel is a black portion in the recording data reference light pattern (similarly, it is a black portion in the encryption reference light pattern). 4). Pick out the second highest luminance pixel. This pixel is a white part in the recording data reference light pattern or a white part in the encryption reference light pattern, but at this stage, it is unclear (this pixel is added to the reference light pattern with the larger number of white parts). Belongs to). 5. Pick out the third highest luminance pixel. This pixel is a white part in the recording data reference light pattern or a white part in the encryption reference light pattern, but at this stage, this pixel is not included in the reference light pattern with the smaller number of white parts. Belong). 6). A combination of the pixel having the highest luminance and the pixel having the second highest luminance is used to attempt to reproduce the recording data using the reference light pattern having the pixel as a white portion as a recording data reference light pattern. If desired recording data can be reproduced without error, this reference light pattern is the recording data reference light pattern. 7). A combination of the pixel with the highest luminance and the pixel with the third highest luminance is used to attempt to reproduce the recorded data using the reference light pattern with this pixel as a white portion as a recorded data reference light pattern. If desired recording data can be reproduced without error, this reference light pattern is the recording data reference light pattern.

  The above is a method for detecting a recording data reference light pattern when there is one encryption reference light pattern, that is, a cryptanalysis method. Even when there are two or more encryption reference light patterns, the processing described above is performed. The recording data reference light pattern is detected by combining a plurality of processes similar to the above. Then, recording data that can be corrected by using the recording data reference light pattern is obtained, a recording data signal light pattern corresponding to the recording data is displayed, and the recording data is obtained in the hologram forming region. By irradiating the signal light, it is finally possible to detect the recording data reference light pattern. The above processing is performed by the control unit 60 having a ROM in which the processing procedure is stored in advance, and the control unit 60 controls each unit according to this procedure.

(Regarding hologram recording / reproducing apparatus to which a phase mask is added)
In the encryption system of the above-described embodiment, as described above, signal light generated from several signal light patterns is irradiated onto the area where the recording data hologram and the encryption hologram are recorded overlappingly. Finally, the recording data reference light pattern is detected, and the recording data reference light pattern is used to decrypt the code. The cipher can be decrypted through the above-described procedure. There is a problem that there is. Hereinafter, an encryption method that is more difficult to decipher will be described.

  FIG. 7 shows a hologram recording / reproducing apparatus 200 according to an embodiment that enables encryption with improved improvement. The hologram recording / reproducing apparatus 200 shown in FIG. 7 is different from the hologram recording / reproducing apparatus 100 shown in FIG. Here, of the light beam that has undergone spatial modulation by the spatial light modulator 37, only the signal light component of the real image portion projected by the relay lens 35 and the relay lens 36 passes through the phase mask 44 (FIG. 9). That is, the phase mask 44 is configured as a signal light phase mask. FIG. 9 is a diagram showing the arrangement of the phase mask 44. The phase mask 44 is disposed only in the signal light passing region within the broken line, and the phase mask 44 is not disposed in the reference light passing region between the broken line and the solid line. As described above, the influence of the phase mask 44 only on the signal light makes the encryption decryption method as described above ineffective.

  On the other hand, in a plurality of hologram recording / reproducing devices, each hologram recording / reproducing device has a different signal light phase mask, or a hologram recording / reproducing device that does not include a phase mask. The compatibility of the hologram recording medium 50 is maintained between the hologram recording / reproducing apparatuses. That is, when recording data is encrypted and recorded by any one hologram recording / reproducing apparatus of hologram recording / reproducing apparatuses having different signal light phase masks, the recording data reference light pattern and the reproduction at the time of recording are reproduced. As long as the recording data reference light pattern at the time is the same, what is necessary to reproduce the recording data from the hologram recording medium 50 by the hologram recording / reproducing apparatus having the signal light phase mask of another arbitrary mode different from this? There is no difficulty.

  Here, the difference in the mode of the phase mask is not only the difference in the phase pattern formed on the phase mask, but also the mask pattern of the phase mask is formed corresponding to the pixels of the spatial light modulator, for example. Whether or not to give a phase pattern gently regardless of the pixel pattern, whether to use a diffuser like ground glass, and whether to have a phase mask It is.

  The operation of the hologram recording / reproducing apparatus 200 is substantially the same as that of the hologram recording / reproducing apparatus 100 for many parts. The operation will be described below. The light beam from the laser light source 20 enters the spatial light modulator 37. The spatial light modulator 37 generates a recording pattern and a reference light pattern for performing hologram recording. The relay lens 35, the relay lens 36, the phase mask 44, the beam splitter 23, the second set of relay lens 38, the relay lens 39, The light passes through the dichroic mirror 34, is reflected by the reflection mirror 56, forms an image, and the image is narrowed down to an optimum beam size by the objective lens 24 and irradiated onto the hologram recording medium 50. Light and recording light overlap to form a hologram.

  The servo optical system 30 is used so that the light beam for recording / reproducing can be irradiated to a predetermined position of the hologram recording medium 50. The servo optical system 30 includes, for example, a red laser light source 28, a photodetector 29, a beam splitter 27, and the like. The light beam from the servo optical system 30 is reflected by the dichroic mirror 34 and the reflection mirror 56, passes through the objective lens 24, and is irradiated onto the hologram recording medium 50. The hologram recording medium 50 is provided with an address groove for positioning, and the servo optical system 30 is composed of an optical system similar to a conventional CD, DVD, etc., and the position on the hologram recording medium 50 is determined from the photodetector 29. It can be detected by the reproduction signal.

  Further, a focus servo error signal and a tracking error signal from the hologram recording medium 50 are detected from the photo detector 29 of the servo optical system 30, and the focus actuator and the tracking actuator are controlled by the servo circuit based on the error signal, and the target position is always set. It is kept in. The image formation point 65 of the recording pattern image formed by the spatial light modulator 37 is determined by the arrangement position and focal length of the relay lens 39 controlled by the relay lens actuator 45, and the positional relationship with the objective lens 24 is also optimal. It is considered as a position.

  At the time of recording, recording is performed with the reference light pattern and the signal light from the spatial light modulator 37, and encryption recording is performed by the rotation of the hologram recording medium 50 in the same manner as in the hologram recording / reproducing apparatus 100.

(About the effect of encryption that adds a phase mask)
As described above, in the hologram recording / reproducing apparatus 200 having the phase mask, even when the signal light is variously changed, if the phase mask used at the time of recording is different from the phase mask used at the time of reproduction, different references are made. As a result, an optical pattern is obtained, and it is impossible to apply the encryption decryption method when the above-described phase mask is not provided. Therefore, the encryption effect is extremely large.

(Modification of hologram recording / reproducing apparatus to which a phase mask is added)
Examples of modifications of the hologram recording / reproducing apparatus to which the phase mask is added include the following.

  A hologram recording / reproducing apparatus 300 shown in FIG. 8 includes a spatial light modulator 67 with a phase mask. As a background art, the phase mask can be integrated with the spatial light modulator as shown in FIG. FIG. 8 shows a spatial light modulator 67 with a phase mask in which a phase mask and a spatial light modulator are integrated as shown in FIG. Need not be adjusted in units of μm (micrometer). Further, the phase mask may be applied not only to the signal light spatial light modulator in the spatial light modulator 67 with a phase mask but also to the reference light spatial light modulator. That is, the spatial light modulator 67 with a phase mask is not only configured as a spatial light modulator with a signal light phase mask to which a signal light phase mask is added, but also a signal light phase mask to which a signal light phase mask and a reference light phase mask are added. And a spatial light modulator with a reference light phase mask. In this case, the reference light phase mask at the time of recording and the reference light phase mask at the time of reproduction must be in the same mode, but the efficiency of interference between the reference light and the signal light is improved and good. The hologram having the recording / reproducing characteristics can be formed.

  Each of the above-described embodiments is merely an embodiment of the present invention, and the present invention is not limited to the above-described embodiment. For example, in the above description, the coaxial method in which the signal light and the reference light are arranged coaxially has been described. However, in the two-beam method in which the signal light and the reference light are incident on the hologram recording medium through different optical components. Implementation is possible based on the same technical idea. Also, for example, the spatial light modulator can be implemented using either a transmission type or a reflection type.

1 is a schematic diagram of a hologram recording / reproducing apparatus according to an embodiment with an optical unit as a center. An example of the signal light pattern and the reference light pattern displayed on the spatial light modulator is shown. 1 schematically shows a structure cut in a cross-sectional area direction of a hologram recording medium. 2 schematically shows a signal light pattern and a reference light pattern displayed on a spatial light modulator. It is a figure which shows the process of decoding typically. It is a figure for demonstrating the signal light pattern for encryption. It is a schematic diagram of the hologram recording / reproducing apparatus of an embodiment provided with a phase mask. It is a schematic diagram of the hologram recording / reproducing apparatus of an embodiment provided with a spatial light modulator with a phase mask. It is a figure which shows arrangement | positioning of a phase mask. This shows a technique in which a phase mask and a spatial light modulator of the background art are integrated.

Explanation of symbols

20, 28 Laser light source, 23 Beam splitter, 24 Objective lens, 25 Image sensor, 27 Beam splitter, 29 Photo detector, 30 Optical system for servo, 34 Dichroic mirror, 35, 36, 38, 39 Relay lens, 37 Spatial light modulator , 40 Signal light, 41 Reference light, 42 Diffracted light, 44 Phase mask, 45 Relay lens actuator, 46 Signal light spatial light modulator, 46a, 46b, Signal light pattern, 47 Reference light spatial light modulator, 47a, 47b Optical pattern, 50 hologram recording medium, 50a recording layer, 50b dichroic mirror layer, 50c address groove, 50d antireflection film, 50e gap layer, 50g plastic substrate, 51 spindle motor, 56 reflection mirror, 60 control unit, 65 connection Point, 67 with a phase mask spatial light modulator, 100,200,300 hologram recording and reproducing apparatus

Claims (5)

A hologram is recorded on the recording layer of the hologram recording medium by causing the signal light modulated according to the recording data for each page to interfere with the signal light and the reference light having the same light source, and the reference light is recorded on the hologram recording medium. A hologram recording / reproducing apparatus for reproducing the recording data for each page based on the diffracted light obtained by irradiating
A signal light spatial light modulator that displays a signal light pattern for generating the signal light;
A reference light spatial light modulator for displaying a reference light pattern for generating the reference light;
A signal light phase mask for performing phase modulation on the signal light;
A control unit that controls each of the aspects of the signal light pattern to be displayed on the signal light spatial light modulator or the aspects of the signal light pattern to be displayed on the reference light spatial light modulator;
With
Displaying a recording data reference light pattern corresponding to the recording data signal light pattern on the reference light spatial light modulator while displaying a recording data signal light pattern corresponding to the recording data on the signal light spatial light modulator. While forming a recording data hologram in a predetermined area of the recording layer,
An encryption reference light pattern corresponding to the encryption signal light pattern is displayed on the reference light spatial light modulation unit while an encryption signal light pattern for encrypting the recording data hologram is displayed on the signal light spatial light modulation unit. Displaying and recording the recording data by forming an encryption hologram in the same area as the predetermined area of the recording layer,
A hologram recording / reproducing apparatus, wherein the recording data is reproduced based on diffracted light obtained by irradiating the predetermined area with the recording data reference light pattern.   2. The hologram recording / reproducing apparatus according to claim 1, wherein the signal light spatial light modulator and the reference light spatial light modulator are arranged on the same plane.   2. The hologram recording / reproducing apparatus according to claim 1, wherein the signal light spatial light modulator and the signal light phase mask are integrally formed.   5. The hologram recording / reproducing according to claim 4, further comprising a reference light phase mask for performing phase modulation on the reference light, wherein the reference light spatial light modulator and the reference light phase mask are integrally formed. apparatus. A relay lens that passes the signal light from the signal light spatial light modulator;
The hologram recording / reproducing apparatus according to claim 1, wherein the signal light phase mask is provided on a real image forming surface of the signal light that has passed through the relay lens.

Images