JP2007041436A - Hologram recording device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hologram recording apparatus capable of further improving optical characteristics.
SOLUTION: A signal light objective lens 7 for converging a signal light S to a predetermined irradiation site, a signal light lens holder 70 for holding the objective lens 7 in the vicinity of a hologram recording medium B, and a reference light R Objective light lenses 10A and 10B for converging to a predetermined irradiation site while traveling obliquely with respect to the signal light S, and for the reference light holding the objective lenses 10A and 10B in the vicinity of the hologram recording medium B And at least one of the signal light and reference light lens holders 70 and 10 does not block light traveling from the other lens holder toward the predetermined irradiation site. Thus, it has the missing part 70a partially missing.
[Selection] Figure 2

Description

  The present invention relates to a hologram recording apparatus for recording a hologram on a hologram recording medium.

  An example of a conventional hologram recording apparatus is disclosed in Patent Document 1. This type of hologram recording apparatus basically has the following configuration. In other words, the hologram recording device separates the laser light emitted from the laser light source into signal light and reference light, modulates one signal light with a spatial light modulator and irradiates the hologram recording medium, while the other reference light Is irradiated so as to overlap the signal light at a predetermined irradiation site on the hologram recording medium. In a predetermined irradiation site, as a result of interference between the signal light and the reference light, a hologram as an interference fringe is recorded.

In order to improve the optical characteristics in such a hologram recording apparatus, an objective lens for signal light and reference light is arranged in the vicinity of the hologram recording medium, and the angle between the signal light and the reference light is made as small as possible. In addition, a lens having a numerical aperture as large as possible may be adopted as the objective lens for signal light. Therefore, for example, as a signal light objective lens, a compound lens that can have a large numerical aperture by combining a plurality of lenses is generally used.
JP 2002-216359 A

  However, in the conventional hologram recording apparatus, since the objective lens for signal light and the reference light are each held by a cylindrical lens holder, the smaller the angle between the signal light and the reference light is, the smaller the angle is. These lens holders interfere with each other, and may block light traveling toward the hologram recording medium. That is, in the conventional hologram recording apparatus, there is a difficulty that the two types of objective lenses have to be arranged to some extent apart from each other, and the optical characteristics cannot be improved so much due to such structural problems, and the recording density is reduced. There is room for improving the optical characteristics in order to improve the optical characteristics.

  The present invention has been conceived under the circumstances described above, and an object thereof is to provide a hologram recording apparatus capable of further improving optical characteristics.

  In order to solve the above problems, the present invention takes the following technical means.

  The hologram recording apparatus provided by the present invention separates coherent light emitted from a light source into signal light and reference light, modulates one signal light with a spatial light modulator and irradiates the hologram recording medium, while the other The hologram recording apparatus records a hologram on the predetermined irradiation site by irradiating the reference beam of the reference beam on the hologram recording medium so as to overlap the signal light, and is emitted from the spatial light modulator. A signal light objective lens that converges the signal light to the predetermined irradiation site, a signal light lens holder that holds the signal light objective lens in the vicinity of the hologram recording medium, and the reference light as described above. An objective lens for reference light that converges on the predetermined irradiation site while traveling obliquely with respect to the signal light, and an objective lens for reference light that is the hologram A reference light lens holder held in the vicinity of the recording medium, and at least one of the signal light and reference light lens holders from the other lens holder to the predetermined irradiation site. It is characterized by having a missing part partially missing at a part along the optical path of the light traveling toward.

  As a preferred embodiment, the signal light objective lens is composed of a compound lens in which a plurality of lenses are combined, and the signal light lens holder has the missing portion formed therein.

  In another preferred embodiment, a part of the signal light objective lens is exposed in the missing portion.

  In another preferred embodiment, the signal light and reference light lens holders are integrated in the vicinity of the missing portion.

  According to such a configuration, for example, when a missing portion is formed in the lens holder for signal light, the optical path of the reference light can be made as close as possible to the missing portion, and the angle formed by the signal light and the reference light is a small acute angle. As described above, the lens holders for signal light and reference light can be arranged close to each other. That is, by reducing the angle formed by the signal light and the reference light as much as possible, the optical characteristics can be further improved, and consequently the recording density can be increased.

  Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the accompanying drawings.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. 1 to 3 show an embodiment of a hologram recording apparatus according to the present invention.

  As shown in FIG. 1, the hologram recording apparatus A according to the present embodiment includes a light source 1, a collimator lens 2, a first beam splitter 3, beam expanders 4A and 4B, a spatial light modulator 5, and a second light modulator 1. Beam splitter 6, signal light objective lens 7, fixed mirrors 8A, 8B, and 8C, recording galvano mirror 9, reference light objective lenses 10A and 10B at the time of recording, reproduction galvano mirror 11, and at the time of reproduction Reference light objective lenses 12 </ b> A and 12 </ b> B and a photodetector 13 are provided. The signal light objective lens 7 is held in the signal light lens holder 70, and the reference light objective lenses 10A and 10B (12A and 12B) are also held in the reference light lens holder 10 (12). Has been. Other components not shown include a rotation mechanism for rotating the hologram recording medium B as a rotating disk, and an optical system such as the objective lens 7, 10A, 10B, 12A, 12B in the radial direction of the hologram recording medium B. A tracking servo mechanism is provided.

  The hologram recording medium B used in the hologram recording apparatus A has a recording layer 91 between two light-transmitting protective layers 90A and 90B, and irradiates a predetermined irradiation site of the recording layer 91 from both sides. It is configured to be able to. In the predetermined irradiation site, the signal light S and the reference light R interfere with each other while intersecting at a predetermined angle, whereby an interference fringe pattern hologram corresponding to the angle is recorded. As the angle between the signal light S and the reference light R becomes sharper and smaller, the coherence between the signal light S and the reference light R increases, and the recording amount by the hologram per unit volume increases. At the time of reproduction, as indicated by a one-dot chain line, the hologram recording medium B is irradiated with the reference light R from the side opposite to the recording time, and the light emitted from the hologram recording medium B in response to the reference light R is used as the reproduction light P. Proceed to the objective lens 7.

  The light source 1 is made of, for example, a semiconductor laser element, and emits laser light as coherent light having a relatively narrow band and high coherence during recording and reproduction. The collimator lens 2 converts the laser light emitted from the light source 1 into parallel light. The parallel light emitted from the collimator lens 2 is guided to the first beam splitter 3, and the first beam splitter 3 is connected to the signal light S directed to the spatial light modulator 5 by the incident parallel light. The light is separated into the reference light R that goes to the galvanometer mirrors 9 and 11 for recording and reproduction via another optical path. The beam expanders 4 </ b> A and 4 </ b> B are composed of combination lenses, and guide the signal light S to the spatial light modulator 5 while expanding the diameter of the signal light S.

  The spatial light modulator 5 is composed of, for example, a liquid crystal display device, and modulates and emits light incident upon recording into light (signal light S) representing a two-dimensional pixel pattern. The signal light S emitted from the spatial light modulator 5 passes through the second beam splitter 6, is guided to the signal light objective lens 7, and is finally irradiated onto the hologram recording medium B.

  As shown in FIG. 2 and FIG. 3 as an example, the signal light objective lens 7 is composed of a compound lens in which three lenses 7A to 7C are combined, and is generally a telecentric system in which the entrance pupil is located at infinity. It is a lens configuration. According to the objective lens 7 having such a lens configuration, it is possible to set a large numerical aperture, and to obtain optically excellent lens characteristics in terms of aberration correction and the like. The signal light objective lens 7 is held by the signal light lens holder 70 so that the signal light S is applied to the hologram recording medium B at a substantially right angle (incident angle 0).

  The lens holder 70 for signal light has a cylindrical shape as a whole and is disposed in the vicinity of the hologram recording medium B. The lens holder 70 is formed with a notched portion 70 a that is obliquely cut out on the optical path side of the reference light R traveling to the hologram recording medium B. Part of the objective lens 7 for signal light (in the example shown in FIGS. 2 and 3, part of the lenses 7B and 7C) is exposed in the missing part 70a. Such an exposed portion of the objective lens 7 does not contact the inner wall of the lens holder 70, but most of the edge surface other than the exposed portion is joined to the inner wall of the lens holder 70, so The lens 7 is securely held. According to the lens holder 70 having such a missing portion 70a, the optical path of the reference light R can be as close as possible to the missing portion 70a.

  In the case of recording, the reference light R emitted from the first beam splitter 3 is guided to the recording galvanometer mirror 9 via the fixed mirrors 8A and 8B. The recording galvanometer mirror 9 can change the incident angle and the reflection angle of the reference light R during recording, and is arranged so that the reference light R travels toward the hologram recording medium B. The reference light objective lenses 10A and 10B are held by the reference light lens holder 10 so that the reference light R is irradiated obliquely at a certain angle to the hologram recording medium B. The reference light lens holder 10 has a simple cylindrical shape, and is close to the hologram recording medium B in a state where the exit port side (objective lens 10B side) is as close as possible to the missing portion 70a of the signal light lens holder 70. Is arranged. That is, the reference light R emitted from the recording galvanometer mirror 9 is irradiated so as to overlap the signal light S at a predetermined irradiation site on the hologram recording medium B through the reference lenses 10A and 10B. At that time, the angle of the reference light R with respect to the signal light S (corresponding to the incident angle of the reference light R with respect to the hologram recording medium B) is changed to a plurality of different angles according to the operation of the recording galvanometer mirror 9. As a result, holograms having different patterns corresponding to the incident angle of the reference light R are multiplexed and recorded on a predetermined irradiation site where the signal light S and the reference light R overlap.

  In the case of reproduction, the reference light R is guided to the reproduction galvanometer mirror 11 through the fixed mirror 8C. The reproduction galvanometer mirror 11 is configured to change the incident angle and the reflection angle of the reference light R during reproduction, and advances the reference light R toward the hologram recording medium B from the opposite side to the recording time. Are arranged as follows. The objective lenses 12A and 12B for reference light at the time of reproduction are also held by the lens holder 12 so that the reference light R is irradiated obliquely at a certain angle to the hologram recording medium B. The reference light R emitted from the reproducing galvanometer mirror 11 is applied to the hologram recording medium B through the objective lenses 12A and 12B. At the time of reproduction, the reference light R is irradiated so as to interfere with the recorded hologram in the recording layer 91 of the hologram recording medium B. In the present embodiment, the reproduction galvanometer mirror is adapted so that the incident angle of the reference light R matches the incident angle at the time of recording while irradiating the reference light R at the time of reproduction as conjugate light having the opposite direction to that at the time of recording. 11 is operating. As a result, the reproduction light P including the same pixel pattern as the signal light S is emitted from the hologram recording medium B.

  The photodetector 13 includes a CCD area sensor or a CMOS area sensor, and receives the reproduction light P from the hologram recording medium B that has returned to the second beam splitter 6 through the signal light objective lens 7 during reproduction. According to such a photodetector 13, a light reception signal corresponding to the pixel pattern of the reproduction light P is obtained, and information corresponding to the pixel pattern at the time of recording is reproduced based on this light reception signal.

  In particular, when focusing on the signal light lens holder 70 and the reference light lens holder 10, the exit of the reference light lens holder 10 is as close as possible to the missing portion 70 a of the signal light lens holder 70. Therefore, the incident angle of the reference light R can be made as small as possible while preventing the so-called scuffing of the reference light R traveling from the reference light lens holder 10 to the hologram recording medium B.

  That is, the angle formed by the signal light S and the reference light R can be made smaller than when a simple cylindrical lens holder is used for the signal light. Thus, the smaller the angle formed by the signal light S and the reference light R, the larger the overlapping portion of the signal light S and the reference light R at a predetermined irradiation site, improving the optical characteristics and improving the recording density. This is advantageous.

  Therefore, according to the hologram recording apparatus A of the present embodiment, the optical path of the reference light R from the reference light objective lens 10B to the hologram recording medium B is made as close as possible to the missing portion 70a of the signal light lens holder 70, Since the signal light and reference light lens holders 70 and 10 can be arranged close to each other with a small acute angle formed between the signal light and the reference light, optical properties such as the coherence between the signal light S and the reference light R, etc. Recording characteristics can be improved, and consequently the recording density can be increased.

  FIG. 4 shows another embodiment of the hologram recording apparatus according to the present invention. In addition, the same code | symbol is attached | subjected about the component which is the same as that of the embodiment mentioned above, or similar, and the description is abbreviate | omitted.

  In the configuration shown in FIG. 4, the exit side of the reference light lens holder 10 is joined to the appropriate portion 70 b in the vicinity of the missing portion 70 a of the signal light lens holder 70. According to such a configuration, the signal light optical system (the objective lens 7 and its lens holder 70) and the reference light optical system (the objective lenses 10A and 10B and its lens holder 10) are integrated into one unit. It can be handled as an optical part, and the trouble of handling these separately can be eliminated.

  The present invention is not limited to the above embodiments.

  In each of the above embodiments, the missing portion 70a is formed in the lens holder 70 for signal light. Of course, the missing portion may be formed in the lens holder for reference light.

1 is an overall configuration diagram showing an embodiment of a hologram recording apparatus according to the present invention. It is principal part sectional drawing of the hologram recording apparatus shown in FIG. It is a principal part perspective view of the hologram recording apparatus shown in FIG. It is principal part sectional drawing which shows other embodiment of the hologram recording apparatus which concerns on this invention.

Explanation of symbols

A hologram recording device B hologram recording medium S signal light R reference light 1 light source 5 spatial light modulator 7 signal light objective lens 70 signal light lens holder 70a missing portion 10A, 10B reference light objective lens 10 reference light Lens holder

Claims (4)

The coherent light emitted from the light source is separated into signal light and reference light, one of the signal light is modulated by the spatial light modulator and irradiated to the hologram recording medium, and the other reference light is applied to the predetermined hologram recording medium. A hologram recording apparatus for recording a hologram on the predetermined irradiation portion by irradiating the irradiation portion so as to overlap with the signal light,
An objective lens for signal light that converges the signal light emitted from the spatial light modulator to the predetermined irradiation site;
A lens holder for signal light that holds the objective lens for signal light in the vicinity of the hologram recording medium;
An objective lens for reference light that converges on the predetermined irradiation site while traveling the reference light obliquely with respect to the signal light;
A reference light lens holder for holding the reference light objective lens in the vicinity of the hologram recording medium;
And
At least one of the signal light and reference light lens holders has a partially missing portion at a position along the optical path of light traveling from the other lens holder toward the predetermined irradiation position. A hologram recording apparatus characterized by comprising:   The hologram recording apparatus according to claim 1, wherein the signal light objective lens is formed of a compound lens in which a plurality of lenses are combined, and the missing portion is formed in the signal light lens holder.   The hologram recording apparatus according to claim 2, wherein a part of the signal light objective lens is exposed in the missing portion.   4. The hologram recording apparatus according to claim 2, wherein the signal light and reference light lens holders are integrated in the vicinity of the missing portion.

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