JP2006017898A - Hologram recording device, and reference light beam diameter control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To keep the irradiation range of a hologram recording medium by a reference light always almost constant even when the incident angle of the reference light is changed at the time of recording a hologram by an angle multiple recording system. <P>SOLUTION: At the time of recording, laser light emitted from a laser light source 1 is split into signal light 100 and reference light 200 by a beam splitter 2, and the reference light 200 is almost made into parallel light by a zoom type beam expander 13. At this time, a controller 15 changes the magnification of the zoom type beam expander 13 in accordance with the rotation angle of a variable type rotary mirror 4, so as to change the diameter of the reference light beam. Thus, without depending on the incident angle of the reference light 200 on a recording medium 20, the irradiation range of the reference light 200 onto the recording medium 20 is kept almost constant. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a hologram recording apparatus that multiplex-records a hologram on a hologram recording medium by an angle multiplexing method, and more particularly to a reference light beam diameter adjusting method that makes an irradiation range of a reference light on a recording medium substantially constant.

  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 system, a method called multiple recording is used to improve the recording density. This is to record a large number of independent data pages in the same recording area of the hologram recording medium. Typical multiplex recording methods include angle multiplex recording, shift multiplex recording, phase modulation multiplex recording, speckle multiplex, etc. It has been known.

  FIG. 7 is a block diagram showing a configuration of an optical system of a hologram recording / reproducing apparatus using an angle multiplex recording method. At the time of recording, the coherent laser beam emitted from the laser light source 1 is branched into the signal beam 100 and the reference beam 200 by the beam splitter 2. The reference light 200 is expanded by the beam expander 3 so that the beam (light flux) becomes substantially parallel light, and is incident on the mirror 4 having a variable angle. The reference beam 200 whose optical path is changed according to the angle of the mirror 4 is incident on a hologram recording medium (hereinafter simply referred to as a recording medium) 20. On the other hand, the signal light 100 is changed in its optical path by the mirror 5 having a fixed angle, and then becomes parallel light by the beam expander 6 and is incident on the spatial light modulator 7. The signal light 100 spatially modulated by the spatial light modulator 7 enters the Fourier transform lens 8. The signal light 100 is condensed on the recording medium 20 by the Fourier transform lens 8 and interferes with the reference light 200 here, and the interference fringes are recorded on the recording medium 20. At this time, the data page to be displayed on the spatial light modulator 7 is changed and the angle of the variable angle mirror 4 is changed to change the incident angle of the reference light with respect to the recording medium 20 so that the data is recorded in one recording area. Multiple pages can be recorded.

During reproduction, illumination reference light (same as reference light 200) 200 whose incident angle is changed by the variable angle mirror 4 is irradiated onto the recording medium 20, and the reproduction light generated thereby becomes parallel light by the Fourier transform lens 9. The data pages incident on the image sensor 10 and recorded in a multiplexed manner are sequentially reproduced as the incident angle of the illumination reference light 200 changes.
IBM J.RES DEVELOP VOL 44 NO.3 MAY 2000 `` Holographic data storage ''

  By the way, in the angle multiplexing method as described above, as shown in FIG. 8, when the reference beam 200 is incident on the recording medium 20, the change on the incident angles (1) and (2) is caused on the recording medium 20. The beam diameters D1 and D2 also change. That is, when the angle is 0 degree with respect to the normal line of the recording medium 20, the beam diameter is D1, and when the incident angle is increased, the beam diameter is D2, and D1 <D2.

  Therefore, in the angle multiplexing method, as shown in FIG. 9, the signal light 100 is also obtained when the reference beam diameter that changes with the change in the incident angle of the reference beam 200 is minimized (incidence angle 0). Therefore, when the beam diameter is increased from the minimum value, an unnecessary portion (unnecessary photosensitive region 30) of the recording medium 20 is exposed to the reference light 200 during recording when the beam diameter is increased from the minimum value. I will let you. If unnecessary portions are exposed in this way, the dynamic range of the recording medium 20 is consumed, and it becomes difficult to improve the multiplicity (that is, the recording density) in angle multiplex recording.

  The present invention has been devised in view of the above circumstances, and an object of the present invention is to provide a hologram recording medium in which the reference light is used even when the incident angle of the reference light changes during hologram recording by the angle multiplex recording method. It is an object of the present invention to provide a hologram recording apparatus and a reference light beam diameter adjusting method capable of always making the irradiation range substantially constant.

  In order to achieve the above object, the present invention is a hologram recording apparatus that records interference fringes generated by interference between signal light and reference light whose incident angle changes to the hologram recording medium on the hologram recording medium by an angle multiplexing method. Zoom means for enlarging / reducing the beam diameter of the reference light provided in an optical element that makes the reference light substantially parallel light, and control means for changing the optical magnification of the zoom means in accordance with the incident angle of the reference light It is characterized by comprising.

  Further, the present invention provides a beam diameter of the reference light when the interference fringes generated by causing the signal light and the reference light whose incident angle to the hologram recording medium change to interfere with each other are recorded on the hologram recording medium by an angle multiplexing method. A reference light beam diameter adjusting method for adjusting, wherein the reference light beam is always constant so that a range in which the reference light illuminates the hologram recording medium surface is always constant regardless of a change in an incident angle of the reference light. The diameter is adjusted.

  As described above, according to the present invention, the optical magnification of the zoom means, for example, a zoom beam expander, provided in the optical element that makes the reference light substantially parallel light is changed according to the incident angle of the reference light to the hologram recording medium. Thus, the irradiation range of the reference light on the recording medium 20 can be made substantially constant regardless of the incident angle of the reference light.

According to the present invention, by changing the optical magnification of a zoom means, for example, a zoom beam expander, provided in an optical element that makes the reference light substantially parallel light according to the incident angle of the reference light to the hologram recording medium. When recording holograms using the angle multiplex recording method, even if the incident angle of the reference light changes, the range in which the reference light irradiates the hologram recording medium can be kept substantially constant, thereby eliminating the need for the hologram recording medium. The recording density can be improved by minimizing the photosensitive area.
In particular, as a means of changing the optical magnification of the reference light, a beam expander, which is an optical element that makes the reference light substantially parallel, is realized by zooming, so that the number of optical components is not increased, and the optical system is complicated The above-mentioned effect can be obtained very easily and without doing so.

  When a hologram is recorded by the angle multiplex recording method, the reference beam incident angle on the hologram recording medium is set so as to keep the reference light irradiating the hologram recording medium substantially constant even if the incident angle of the reference light changes. This is achieved by changing the optical magnification of the zoom means, for example, a zoom beam expander.

  FIG. 1 is a schematic diagram showing a configuration of an optical system of a hologram recording apparatus according to an embodiment of the present invention. However, the same parts as those in the conventional example will be described with the same reference numerals. The hologram recording apparatus includes a laser light source 1, a shutter 11, a beam splitter 2, a zoom beam expander 13, a variable rotation mirror 4, a shutter 12, a fixed mirror 5, a beam expander 6, a spatial light modulator (SLM) 7, and a Fourier transform. The lens 8, the hologram recording medium 20, the Fourier transform lens 9, and the image sensor 10 are configured. In the figure, the playback function is also shown.

  Next, the operation of the present embodiment will be described. Since the basic operation of the present embodiment is the same as that of the conventional example, different points will be described below. At the time of recording, the beam of the reference beam 200 is expanded into parallel light by a zoom beam expander 13 with variable optical magnification (hereinafter simply referred to as magnification), and the optical path is changed by the variable rotating mirror 4 to change the recording medium. 20 is incident. On the other hand, the signal light 100 is converted into parallel light by a beam expander 6 having a fixed magnification, spatial light modulated by a spatial light modulator 7 on a data page, and condensed on a recording medium 20 by a Fourier transform lens 8. The interference fringes of the reference beam 200 are recorded on the recording medium 20. At that time, in order to multiplex-record the data page by the angle multiplexing method, the angle of the variable rotating mirror 4 is changed along with the change of the data page displayed on the spatial light modulator 7, and the reference light 200 is recorded on the recording medium 20. The incident angle is changed, and a plurality of data pages are recorded in the same recording area of the recording medium 20.

  At that time, as shown in FIG. 2, the magnification K of the zoom beam expander 13 is changed as shown in FIG. By changing the beam to the beam diameters d1 to d2, the major axis D of the range in which the reference light 200 irradiates the recording medium 20 is always substantially constant so that the irradiation range does not change due to the change in the incident angle of the reference light 200. Yes.

  FIG. 4 is a block diagram showing a control system of the hologram recording apparatus shown in FIG. The control system of the hologram recording apparatus is configured by connecting a variable rotating mirror 4, a spatial light modulator 7, shutters 11 and 12, a zoom beam expander 13, and an image sensor 10 to a control device 15 such as a personal computer.

  Next, the operation of the present embodiment will be described. During recording, the control device 15 opens the shutters 11 and 12, displays a data page on the spatial light modulator 7, sets the angle θ of the variable rotating mirror 4 to a predetermined value, and the reference light 200 corresponding to the predetermined value. The magnification K of the zoom type beam expander 13 is set so that the beam diameter can be obtained.

  Here, when the control device 15 sets the angle θ of the variable rotating mirror 4 to θ1, the magnification K of the zoom beam expander 13 is set to K1, and the reference beam 200 incident on the zoom beam expander 13 is set. Assuming that the beam diameter is φ0, as shown in FIG. 5A, the beam diameter becomes φ1 by the zoom beam expander 13, and there is a relationship of φ1 = K1φ0. When the reference beam 200 of the beam of φ1 is incident on the recording medium surface at an incident angle θ1 as shown in FIG. 6A, the major axis φ1 ′ of the irradiation range is represented by φ1 ′ = φ1 / COSθ1.

  Further, as shown in FIG. 5B, when the incident angle of the reference light 200 is θ2, and the magnification of the zoom beam expander 13 at that time is K2, as shown in FIG. The major axis of the irradiation range is represented by φ2 ′ as φ2 ′ = φ2 / COSθ2.

  In this case, it is necessary to determine K1 and K2 so that the major axis of the irradiation range is substantially constant regardless of the incident angle of the reference beam 200, that is, φ1 ′ = φ2 ′. Therefore, if the magnification of the zoom beam expander 13 is determined so that there is a functional relationship with the incident angle θ such that K1 = αCOSθ1 and K2 = αCOSθ2, φ1 ′ = φ2 ′ = αφ0 and the reference beam 200 is obtained. The magnification of the zoom type beam expander 13 can be set so that the major axis of the irradiation range can be made substantially constant regardless of the incident angle of. Where α is a constant.

  That is, when the above is generalized, when the incident angle of the reference beam 200 is θ, the magnification K of the zoom beam expander 13 is set to a value that satisfies K = αCOSθ. It can be seen that the major axis of the irradiation range can be set to a constant value αφ0 irrespective of the incident angle. Therefore, when the angle of the variable rotating mirror 4 is set to θ, the control device 15 calculates and sets the magnification K of the zoom beam expander 13 by K = αCOSθ. Thus, the major axis of the irradiation range is always controlled to a constant value of αφ0 regardless of the incident angle of the reference beam 200. Note that by changing the value of α, the size of the irradiation range that is always constant can be adjusted to an optimum size.

  At the time of reproduction, reproduction light 300 is generated by irradiating the recording medium 20 with the reference light 200. This reproduction light 300 is input to the image sensor 10 by the Fourier transform lens 9 and subjected to photoelectric conversion. The data page is reproduced by being input to the control device 15 and processed. Also in this case, by changing the magnification of the zoom beam expander 13 according to the angle of the variable rotating mirror 4 by the control device 15, the irradiation range on the recording medium 20 can be set regardless of the incident angle of the reference light 200. Control is performed so as to be substantially constant.

  According to the present embodiment, by changing the magnification of the zoom beam expander 13 according to the angle of the variable rotating mirror 4, the irradiation range on the recording medium 20 can be set regardless of the incident angle of the reference light 200. By performing the control to be substantially constant, reference light is not irradiated to unnecessary portions of the recording medium 20 particularly during recording, so that the dynamic range of the recording medium 20 is not impaired, and the recording density of the multiple recording by the angle multiplexing method Can be improved.

  Since the recording medium 20 has already been exposed at the time of reproduction, it is not necessary to make the range in which the reference light 200 irradiates the recording medium 20 constant when the incident angle of the reference light 200 changes.

  In addition, the present invention is not limited to the above-described embodiment, and can be implemented in various other forms in specific configurations, functions, operations, and effects without departing from the scope of the invention. In the above embodiment, the reference light beam is converted into parallel light by the beam expander. However, the reference light beam can also be converted into parallel light by a spatial filter and a collimating lens. In this case, the magnification of the reference light beam can be changed. The same effect can be obtained.

It is the schematic which showed the structure of the optical system of the hologram recording device which concerns on one embodiment of this invention. It is a figure explaining the relationship between the incident angle of reference light, and an illumination range. It is a figure explaining operation | movement of the zoom type beam expander shown in FIG. It is the block diagram which showed the control system of the hologram recording apparatus shown in FIG. It is a figure explaining the relationship between the magnification of a zoom type beam expander, and the beam diameter of reference light. It is the figure which showed the relationship between the incident angle to the recording medium of reference light, and its irradiation range. It is the block diagram which showed the structure of the optical system of the hologram recording / reproducing apparatus by the conventional angle multiplexing system. It is the figure which showed the relationship between the incident angle to the recording medium of the reference beam in the conventional structure, and its irradiation range. It is a figure explaining the unnecessary photosensitive area | region of the recording medium in a conventional structure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Laser light source, 2 ... Beam splitter, 4 ... Variable rotation mirror, 5 ... Fixed mirror, 6 ... Beam expander, 7 ... Spatial light modulator (SLM), 8, 9 ... Fourier transform Lens 10, imaging device 11, 12 shutter 12, zoom expander 15 control device 20 hologram recording medium

Claims (5)

A hologram recording apparatus for recording interference fringes generated by causing signal light and reference light whose incident angle to the hologram recording medium changes to interfere with the hologram recording medium by an angle multiplexing method,
Zoom means provided in an optical element that makes the reference light substantially parallel light, and that enlarges or reduces the beam diameter of the reference light;
Control means for changing the optical magnification of the zoom means according to the incident angle of the reference light;
A holographic recording apparatus comprising:   2. The hologram recording apparatus according to claim 1, wherein the optical element is a beam expander, and a zoom beam expander provided with a zoom function for changing an optical magnification is used for the beam expander.   The control means changes the optical magnification of the zoom means so that a range in which the reference light illuminates the hologram recording medium surface is always substantially constant regardless of an incident angle of the reference light. Item 2. A hologram recording apparatus according to Item 1.   The control means changes the optical magnification K such that K = αCOSθ, where θ is an incident angle of the reference light, K is an optical magnification of the zoom means, and α is a constant. The hologram recording apparatus according to claim 3. Reference light beam diameter for adjusting the beam diameter of the reference light when an interference fringe generated by interfering the signal light with the reference light whose incident angle changes to the hologram recording medium is recorded on the hologram recording medium by the angle multiplexing method An adjustment method,
Regardless of the change in the incident angle of the reference light, the reference light beam is adjusted so that the range in which the reference light irradiates the surface of the hologram recording medium is always substantially constant. Diameter adjustment method.

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