Patent ID: 7477588

Claim:
An apparatus for recording and reproducing holograms, comprising: a recording system configured to record a light interference intensity as a refractive index change when a plurality of light beams emitted from one light source are caused to interfere with each other in a recording medium; a reproducing system configured to read information recorded in said recording medium by detecting, with a light detector, a reproduced beam that is generated when a reference beam as a portion of divided light beams is applied to the recording medium; and a medium control system configured to move said recording medium for recording and reproducing a plurality of interference patterns when information is recorded on and reproduced from the recording medium, wherein the reference beam applied to said recording medium has an angular spectrum providing an RMS error which is 0.18 or more times the wavelength when the phase of the reference beam is fitted by a polynomial of degree four; and a number M of a plurality of multiplexed recording mediums to be recorded in a projected area S on the surface of said recording medium satisfies the following condition (1): M ≦ S · L · NA R 3 ⁢ NA S 0.3 ⁢ Z 2 ⁢ nλ 3 ⁢ N ( 1 ) where n represents the refractive index of said recording medium, λ the wavelength in vacuum of light used to record and reproduce the information, L the thickness of said recording medium, ±NA R the range of an angular spectrum in air of the reference beam, ±NA S the range of an angular spectrum in air of the reproduced beam applied to the light detector, S the projected area of a recording region to be recorded in one recording cycle onto the surface of the recording medium, N the number of bits to be recorded in one recording cycle, and Z the signal vs. signal noise ratio as a target ratio.