<title>Electro-Optical Systems And Photosensitive Materials For Information Storage</title>

Abstract

Advantages of using optical wavelengths for informationstorage and processing has been widely discussed in the last few years and extensive research work has been done on optical memory sys terns and storage medium because powerful coherent sources are now available and allow theoritically a diffraction limited storage density. Several laboratories have already demonstrated potential capabilities of optical systems coinpared to magnetic technology but it now appears clearly that, optical memories sys tern will only find a place in the hierarchy of storage systems used to day if they will courpete in capacity, acess speed, and very inportant in cost per bit of stored information. Considering these requirements, the "Optical Videodisc" is a pood example of a cheap read only optical storage sys tern providing 10 bits capacity, nearly diffraction limited-storage density and video recording and readout bandwidth. Two main principles of optical storage techniques have been considered up to now : bit oriented memories provinding sequential acces to the storage medium ; page organized holographic memories provinding parallel writing and readout and microsecond random access speed by laser beam deflection. Each of these principles were applied to permanent storage media such as photographic plates or photopolymers materials but many attemps are actually made in the field of read-write optical memories which need erasable photosensitive materials ; Thermomagnetic ; Thermoplastic ; Photoretractive materials are the most attractive candidates for read-write systems which are actually mainly limited by the storage material performances