Hologram recording medium, hologram recording-reproducing method, and horogram recording-reproducing apparatus

A hologram recording and reproducing apparatus for forming a plurality of areas of a refractive index grating corresponding to one portion of a three-dimensional light interference pattern of a coherent signal light beam and coherent reference light of a first wavelength modulated in accordance with information data within a recording medium made of a photo refractive crystal of a uniaxial crystal having a shape of parallel flat plates,

• said hologram recording and reproducing apparatus comprising:
• a supporting part for detachably holding the recording medium made of the photo refractive crystal having the shape of parallel flat plates;
• a reference light part for making a coherent recording reference light beam of the first wavelength approximately perpendicularly incident to a main face of said recording medium;
• a signal light part for making the coherent signal light beam of the first wavelength modulated in accordance with the information data of one screen incident to said recording medium, and making the coherent signal light beam cross said recording reference light beam within the recording medium, and generating a light interference pattern of said signal light beam and the recording reference light beam;
• a gate light part for making a gate light beam of a second wavelength for revealing recording sensitivity of said recording medium approximately perpendicularly incident to the main face of said recording medium together with said recording reference light beam, and forming the refractive index grating of one portion of said light interference pattern which passes through a portion of said recording medium for crossing said signal light beam and the recording reference light beam and demarcates a volume smaller than that of this crossing portion;
• a switching part for irradiating said signal light beam to said gate light beam in a portion of said recording medium from a different direction such that lattice vectors of said refractive index grating in adjacent areas of said refractive index grating exist in directions different from each other for each area of said refractive index grating;
• a phase conjugate wave generating part for generating a phase conjugate wave with respect to said signal light beam by irradiating a reproducing reference light beam coaxial with respect to said recording reference light beam and propagated in an opposite direction to said refractive index grating of said recording medium;
• a separating part for separating said phase conjugate wave from an optical path of said signal light beam;
• and
• a detecting part for detecting the information data formed as an image by said phase conjugate wave.