1. Field of the Invention
The present invention relates to a hologram memory apparatus for recording and reconstructing spatial pattern information. More precisely, the present invention relates to an improvement of such an apparatus of which the structure is greatly simplified by using the one-dimensional hologram recording.
2. Description of the Prior Art
As a conventional method and apparatus for recording information in a one-dimensional hologram, it is known to use a computer-generated hologram, in which an input information is Fourier transformed by means of a computer to produce an electric holographic signal and an electron beam or a laser beam is modulated by the electric signal and is used for recording. For instance, Adam Kozma et al had submitted a report in the 1971 IEEE/OSA Conference on Laser Engineering and Applications (Session No. 152). This suggested system has an advantage in that a spatial modulator is not required; however, it contains a disadvantage in that the writing speed cannot be made high enough owing to a long computation time.
There are various disclosures with respect to the two-dimensional page-oriented hologram memory. This kind of apparatus, however, had encountered a number of technical difficulties mainly due to the complicated construction of the structural devices since it requires various elements such as a two-dimensional spatial modulator, i.e. page composer or a two-dimensional photo detector matrix, etc.
Furthermore, there had been an attempt to realize a simplified hologram memory system considering applications as wideband recorders. For instance, Andrew Bardos disclosed such a system in Applied Optics, Vol. 13, No. 4, April 1974, pp. 832-840. In this system, a time series of a given electrical pulse information is rearranged into multi-channel information and by using such multi-channel information the respective channel of a multi-channel acousto-optic light deflector is controlled as a spatial modulator and thus the input signal light beam is formed. The input signal light beam is subjected with a doppler shift. Accordingly, in the recording of the hologram in order to stabilize the interference fringe, the reference light should also be subjected with such a doppler shift to the same extent with the signal light by using another acousto-optic light deflector, names an acoustic beam splitter, to give diffractive deflection for the laser beam. Accordingly, the optical path for the reference light beam is separated from that of the signal light path at the acoustic beam splitter and thus the strip-shaped hologram recording is made through a writing lens after readjustment of the signal light beam and the reference light beam to be parallel with each other. There exist two problems in this step. One is the stability of the system due to use of a separate optical path. Another is the demand for large aperture lens systems, which make them costly and difficult to produce.