JP2005241773A - Phase mask and hologram recording and reproducing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a configuration of a phase mask with which the condensing spot size of reference light can be easily optimized with respect to the condensing spot size of the signal light at a hologram recording medium. <P>SOLUTION: The phase mask 11 is manufactured by arraying a plurality of projecting parts to a transparent glass substrate 110 and by photolithography and the like and such phase mask 11 is used as a phase mask for making reference light into a speckle form. In such a case, the phase mask 11 can be created by arbitrarily designing the ways of arraying of the projecting parts and their sizes. Consequently, the sizes of the projecting parts can be made smaller as much as needed with respect to the sizes of the pixels of a space phase modulator for intensity modulation of signal light and therefore the condensing spot size of the reference light can be easily optimized with respect to the condensing spot size of the signal light at the hologram recording medium. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an in-line hologram recording / reproducing apparatus, and more particularly, to a phase mask for making reproduction light into a speckle shape.

  In recent years, holographic technology has been rapidly developed for the practical application of holographic memory, which is attracting attention as a candidate for powerful storage that competes with next-generation and next-generation optical discs. Thus, a hologram recording / reproducing system for recording / reproducing a large amount of data has been proposed (see, for example, Non-Patent Document 1).

  In such a hologram recording / reproducing apparatus, interference fringes generated by causing interference between the signal light intensity-modulated with the recording data and the reference light are recorded on the hologram recording medium. There are two-beam type holograms that are irradiated to the hologram and in-line holograms in which signal light and reference light are irradiated to the hologram recording medium from the same direction. In this in-line hologram, when the hologram is multiplexed by the shift multiplexing method, the shift selectivity is poor due to the Bragg selectivity compared to the two-beam hologram. Therefore, in order to improve the shift selectivity, a phase mask is incorporated in the reference light. A technique for making the reference beam speckle on the recording medium (Fourier plane) is essential.

  As an inline hologram recording apparatus, for example, there is a configuration performed by the US national project HDSS as shown in FIG. 6, and a phase mask 2 is arranged around a spatial light modulator (liquid crystal panel) 1 to divide the pupil. There is a method to do. That is, a laser beam 50 emitted from a laser light source (not shown) and collimated by a beam expander or the like is incident on the spatial light modulator 1 and the phase mask 2 disposed above and below the spatial light modulator 1. .

  The spatial light modulator 1 modulates the intensity of incident laser light with a displayed data page pattern to form signal light 100, and this signal light 100 is recorded on a hologram recording medium (such as a photopolymer) 4 by a Fourier transform lens 3. The light is focused on a spot 10 (here, a spot indicates a three-dimensional range). At the same time, the laser beam 50 is input to the phase mask 2 to become a speckle-shaped reference beam 200, and this reference beam 200 is condensed on the spot 20 of the hologram recording medium 4 by the Fourier transform lens 3.

Thereby, the interference fringes generated by the interference between the signal light 100 and the reference light 200 are recorded on the recording spot 10 of the hologram recording medium 4. At this time, the reference light 200 irradiating the spot 20 has a speckle shape and its wavefront. Therefore, even if it is slightly shifted, a wavefront mismatch occurs between the original reference light and the moved reference light, and the shift selectivity can be sharpened. The density can be improved.
IBM J.RES DEVELOP VOL 44 NO.3 MAY 2000 `` Holographic data storage ''

  In the configuration as described above, diffraction at a diffraction angle determined by the grain size as shown in 36 of FIG. 7 forming the phase mask 2 occurs in the portion serving as the reference light 200, and the signal passing through the spatial light modulator 1 In the light 100, diffraction occurs due to the pitch of the liquid crystal panel, and the spot size on each Fourier plane is determined by these diffraction angles. At this time, when the pitch of the phase mask 2 is not optimized, the condensing spot 20 of the reference light 200 cannot cover the condensing spot 10 of the signal light 100, and the hologram image is deteriorated or the reference light 200 Since the size of the focused spot 20 is too large with respect to the size of the focused spot 10 of the signal light 100 and wasteful exposure that does not contribute to reproduction by the reference light 200 is performed, the photopolymer is wasted, There is a problem that the recording density is lowered. However, with the conventional phase mask 2, it is difficult to control the grain size described above, and it is difficult to optimize the size of the focused spot 20 of the reference light 200 and the focused spot 10 of the signal light 100.

  The present invention has been devised in view of the above circumstances, and an object of the present invention is to optimize the condensing spot size of the reference light with respect to the condensing spot size of the signal light on the hologram recording medium (Fourier plane). And a hologram recording / reproducing apparatus using the phase mask.

  In order to achieve the above object, the present invention provides a phase mask that speckles the reference light when recording interference fringes between signal light and reference light on a hologram recording medium, and includes a transparent substrate, It is characterized by comprising a plurality of transparent convex portions or concave portions arranged on one surface.

  The present invention also provides a hologram recording apparatus for irradiating a hologram recording medium with signal light and reference light to record interference fringes generated by the signal light and the reference light on the hologram recording medium, wherein the reference light is speckled. The phase mask includes a transparent substrate and a plurality of transparent protrusions or recesses arranged on one surface of the transparent substrate.

  The present invention is also a hologram reproducing apparatus for reproducing recorded data by irradiating a hologram recording medium with illumination reference light, comprising a phase mask for making the illumination reference light speckled, wherein the phase mask is transparent It is characterized by comprising a substrate and a plurality of transparent convex portions or concave portions arranged on one surface of the transparent substrate.

  As described above, in the present invention, a configuration in which a plurality of transparent convex portions or concave portions are arranged on one surface of the transparent substrate is used as a phase mask that makes the reference light speckle. Such a phase mask can be easily produced by photolithography, and the size of the convex portion or the concave portion can be easily controlled at that time. Therefore, the size of the convex portion or concave portion of the phase mask can be set to be substantially equal to or as small as necessary with respect to the pixel size of the spatial light modulator for intensity-modulating the signal light. Therefore, it is possible to easily create a phase mask that covers the spot size of the signal light and minimizes the portion where the hologram recording medium is unnecessarily exposed.

  According to the present invention, a phase mask formed by arranging a plurality of transparent convex portions or concave portions on one surface of a transparent substrate is prepared by, for example, photolithography, and the phase mask is used as a speckle-shaped phase mask. By using it, the condensing spot size of the reference light can be optimized with respect to the condensing spot size of the signal light on the hologram recording medium, and therefore the recording density of the hologram recording medium is not impaired and there is no deterioration. Playback data can be obtained.

  For the purpose of optimizing the converging spot size of the reference light with respect to the converging spot size of the signal light on the hologram recording medium, a phase mask comprising a plurality of transparent convex portions or concave portions arranged on one surface of the transparent substrate is provided. It was realized by making the reference beam into a speckle shape.

  1A and 1B are diagrams showing a configuration of a phase mask according to an embodiment of the present invention, in which FIG. 1A is a top view and FIG. 1B is a side view. The phase mask 11 has a structure in which a plurality of cubic convex projections 111 are arranged in a matrix on one surface of a transparent substrate 110 made of, for example, a rectangular glass material, and the convex portions 111 are omitted in some places. Yes.

  FIG. 2 is a perspective view showing a configuration when the above-described phase mask 11 is mounted on an in-line hologram type hologram recording / reproducing apparatus. A phase mask 11 having a rectangular outer shape is disposed around the spatial light modulator 12. The structure of this phase mask 11 is the same as that shown in FIG. 1, and a plurality of cubic convex projections 111 are arranged in a matrix on one surface of a transparent substrate 110 made of glass.

  Here, when the reference light 200 is made into a speckle shape using the phase mask 11, diffraction of a diffraction angle determined by the size of the convex portion 111 occurs, and the spot size of the reference light 200 on the Fourier plane is determined by this diffraction angle. Determined. Therefore, it is assumed that the size of the convex portion 111 of the phase mask 11 is set to be approximately equal to or smaller than the pixel size of the spatial light modulator 12 that modulates the intensity of the signal light 100.

  In FIG. 2, a data page to be recorded is displayed on the spatial light modulator 12 during recording. Thereafter, the laser light 50 emitted from a laser light source (not shown) and converted into parallel light by a beam expander or the like passes through both the spatial light modulator 12 and the phase mask 11 at the same time. The reference light 200 is generated, and the signal light 100 that is intensity-modulated according to the data page pattern displayed on the spatial light modulator 12 is generated.

  The signal light 100 and the reference light 200 are condensed on the hologram recording medium 14 by the Fourier transform lens 13. In this case, since the size of the convex portion 111 of the phase mask 11 is substantially equal to or smaller than the pixel size of the spatial light modulator 12, the condensing spot size of the signal light 100 on the hologram recording medium 14 (Fourier plane). As compared with the above, the condensing spot size of the reference light 200 is the same or larger, and the condensing spot of the reference light 200 covers the condensing spot of the signal light 100. Therefore, all the signal light 100 on the Fourier plane interferes with the reference light 200, and the interference fringes are recorded on the hologram recording medium 14.

  At the time of reproduction, since the reference beam 200 is irradiated so as to cover the signal recording spot of the hologram recording medium 14, diffracted light including all information recorded in the signal recording spot is generated. The image is imaged on the image sensor 15 through the inverse Fourier lens, and data without deterioration is reproduced.

  According to the present embodiment, the phase mask 11 has a structure in which a plurality of cubic convex protrusions 111 are arranged in a matrix on one surface of a glass material, and this is manufactured by photolithography or the like, The size of the convex portion 111 can be easily controlled. Therefore, when the reference light 200 is speckled using the phase mask 11, the size of the convex portion 111 can be made as small as necessary with respect to the pixel size of the spatial light modulator 12. Therefore, if the reference light 200 is speckled using the phase mask 11, the condensing spot size of the reference light 200 on the hologram recording medium 14 covers the condensing spot size of the signal light 100 and is useless. In addition, it is possible to easily achieve an optimum size that minimizes a portion where the hologram recording medium 14 is exposed. Thereby, hologram reproduction data without deterioration can be obtained without impairing the recording density of the hologram recording medium 14.

  Further, since the phase mask 11 of the present embodiment can be designed and manufactured arbitrarily such as the shape and size of the convex portion 111 and a pattern for removing the convex portion 111, the same phase mask can be easily reproduced with good reproducibility. Therefore, compatibility between reproducing apparatuses equipped with these phase masks 11 can be easily achieved.

  The material of the phase mask 11 is not limited to glass as long as it is a transparent material having no birefringence. The reason is that if the material has birefringence, the polarization plane changes when the reference light passes through the phase mask, and the interference efficiency with the signal light deteriorates.

  In addition, this invention is not limited to the said embodiment, In the range which does not deviate from the summary, it can implement also with another various form in a concrete structure, a function, an effect | action, and an effect. For example, as long as the shape of the convex part 111 of the phase mask 11 of the said embodiment is not restricted to a rectangle and can be created with sufficient reproducibility, as shown in the side view of FIG. 3, the tip is rounded. However, it may be conical, although not shown.

  Further, as shown in the top view of FIG. 4, in addition to the matrix shape, the protrusions 111 may be arranged in a hexagonal shape in a honeycomb shape, or in a rhombus shape. However, the same effect can be obtained, and there are various shapes of the convex portions 111 and their arrangement forms, so long as the size of the convex portions 111 can be controlled, it is not limited to the above example. .

  Further, in the example shown in FIG. 2, the configuration is such that the phase mask for making the intensity distribution of the signal light 100 uniform is not used at the condensing spot of the signal light 100 on the hologram recording medium 14. When the phase mask for use is arranged close to the spatial light modulator 12, the phase mask for signal light and the phase mask for making the above-mentioned reference light speckled can be shared. In that case, the height L of the convex portion 111 is expressed by the following equation in order to obtain a modulation of 0, π. When the wavelength of the light source to be used is λ, n is the refractive index of the phase mask 11, and m is an integer, L = 532 ÷ 2 (n−1) × (2m−1) (nm).

  In the example shown in FIG. 2, the phase mask 11 having the structure shown in FIG. 1 is used in an in-line hologram type hologram recording / reproducing apparatus. It can also be used in a hologram recording / reproducing apparatus that performs the same, and the same effect can be obtained.

  Further, in the above-described embodiment, the example in which the phase mask is formed by arranging the plurality of convex portions 111 on the transparent substrate 110 has been described. However, it is also possible to form the phase mask by arranging a plurality of concave portions on the transparent substrate. There is.

It is the figure which showed the structure of the phase mask which concerns on one embodiment of this invention. It is the perspective view which showed the structure of the hologram recording / reproducing apparatus of an in-line system equipped with the phase mask shown in FIG. It is the side view which showed other embodiment of the phase mask of this invention. It is the top view which showed other embodiment of the phase mask of this invention. It is the top view which showed other embodiment of the phase mask of this invention. It is sectional drawing which showed the structure of the conventional hologram recording apparatus of an in-line system. It is the figure which showed the grain size of the phase mask shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Phase mask, 12 ... Spatial light modulator, 13 ... Fourier-transform lens, 14 ... Hologram recording medium, 110 ... Transparent substrate, 111 ... Convex part.

Claims (11)

A phase mask that speckles the reference light when recording interference fringes of signal light and reference light on a hologram recording medium,
A transparent substrate;
A plurality of transparent convex portions or concave portions arranged on one surface of the transparent substrate;
A phase mask characterized by comprising:   The phase mask according to claim 1, wherein the transparent substrate and the convex portion or the concave portion are integrally formed.   2. The phase mask according to claim 1, wherein an upper surface shape of the plurality of convex portions or concave portions is a quadrangular shape and is arranged in a matrix on the transparent substrate surface, and there are portions where the convex portions or concave portions are not arranged in some places.   2. The phase mask according to claim 1, wherein an upper surface shape of the plurality of convex portions or concave portions is hexagonal and is arranged in a honeycomb shape on the transparent substrate surface, and there are portions where the convex portions or concave portions are not arranged in some places.   2. The phase mask according to claim 1, wherein an upper surface shape of the plurality of convex portions or concave portions is a rhombus and is arranged in a rhombus shape on the transparent substrate surface, and there are portions where the convex portions or the concave portions are not arranged in some places.   The phase mask according to claim 1, wherein the transparent substrate and the convex portion or the concave portion are made of a transparent glass material. A hologram recording apparatus for irradiating a hologram recording medium with signal light and reference light and recording interference fringes generated by the signal light and the reference light on the hologram recording medium,
Comprising a phase mask that makes the reference beam speckled;
2. The hologram recording apparatus according to claim 1, wherein the phase mask includes a transparent substrate and a plurality of transparent convex portions or concave portions arranged on one surface of the transparent substrate.   8. The hologram recording apparatus according to claim 7, wherein the size of the convex portion or the concave portion of the phase mask is substantially equal to or smaller than a pixel size of a spatial light modulator that modulates the intensity of the signal light.   The hologram recording apparatus according to claim 7, wherein the signal light and the reference light are applied to the hologram recording medium from one direction.   The signal light and the reference light are applied to the hologram recording medium from one direction, and the phase mask is shared with a phase mask that makes the intensity distribution of the signal light uniform in a Fourier plane. 7. The hologram recording device according to 7. A hologram reproduction apparatus for reproducing recorded data by irradiating a hologram recording medium with illumination reference light,
Comprising a phase mask that makes the illumination reference light speckled;
2. The hologram reproducing apparatus according to claim 1, wherein the phase mask includes a transparent substrate and a plurality of transparent convex portions or concave portions arranged on one surface of the transparent substrate.

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