Holographic multiplex recording method, and holographic recording apparatus and holographic recording medium employing the method

Abstract

A holographic multiplex recording method which can keep a recording data rate constant and equalize nonuniformity in recording due to vibrations or the like, and a holographic recording apparatus and a holographic recording medium, which employ the method are provided. In a process of multiplex-recording information, the time of exposure to a laser beam per data page is kept constant, and the laser output power of the laser beam is increased in accordance with a decrease in recording sensitivity of the holographic recording medium.

Description

TECHNICAL FIELD [0001] The present invention relates to a holographic multiplex recording method, and a holographic recording apparatus and a holographic recording medium which employ the method. BACKGROUND ART [0002] As shown in FIG. 4, conventionally suggested as one of holographic recording methods is a holographic multiplex recording method based on angle multiplexing, in which the incident angle of a reference beam 6 is modulated while the incident angle of an object beam 4 is kept constant with respect to a recording layer 2A in a holographic recording medium 2 (e.g., see Japanese Patent Laid-Open Publication No. 2003-178460). [0003] Note that since such angle multiplex recording allows a number of multiplexed holograms to be provided in the same area of a recording material, the amount of exposure for recording needs to be increased step by step as the multiplex recording proceeds. Thus, “scheduling of recording” is carried out to control the amount of exposure for recording ...

AI Technical Summary

Benefits of technology

[0008] The present invention has been made to solve the abovementioned problems. It is therefore an object of the invention to provide a holographic multiplex recording method which can provide a constant recording data rate and equalize nonuniformity in recording due to vibrations or the like, and a holographic recording apparatus and a holographic recording medium which employ the method.

[0009] The present inventors have conducted intensive studies and consequently found that a holographic multiplex recording method which can provide a constant recording data rate and equalize nonuniformity in recording due to vibrations or the like, and a holographic recording apparatus and a holographic recording medium which employ the method.

[0012] (2) A holographic multiplex recording method for multiplex-recording information as a hologram on a holographic recording medium using interference fringes of an object beam and a reference beam, into which a laser beam is split, wherein in a process of multiplex-recording the information, a time of exposure to the laser beam per data page and a laser output power are kept constant, and a spatial light modulator having a plurality of pixels for intensity modulating of the object beam is used to increase the number of pixels of the spatial light modulator to be allocated to one bit of the information in accordance with a decrease in recording sensitivity of the holographic recording medium.

Problems solved by technology

However, since a photosensitive component in the photosensitive material decreases as the multiplex recording proceeds causing degradation in photosensitivity (recording sensitivity) to a laser beam, the refractive index modulation degree and the exposure time t exhibit a nonlinear relationship.

Accordingly, this causes control to be readily complicated and the time required for recording to vary for each data page, resulting in inconsistency in recording data rate.

Furthermore, there is a problem with the holographic recording that microscopic vibrations or scintillations during recording cause blurring (nonuniformity in recording) to occur in interference fringes.

In addition, there is a problem that different exposure times t for each data page cause such blurring to have inconsistent effects thereby impeding proper data readout.

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