Abstract: A binary bit pattern is reconstructed from a block of analog signals corresponding to the number of known bit positions of the pattern being reconstructed. The analog signals, which may take the form of light intensity signals, vary in signal level with the binary level represented as well as with a characteristic which causes the signal levels of the analog signals to vary in a known manner as a function of bit position. In reconstructing the bit pattern, an output signal is developed having a value dependent upon that of at least one of the analog signals which has a known bit level reconstruction. This signal is used for providing a variable threshold having a value which varies in dependence upon the outut signal as modified by a modifying factor which varies in the known manner as a function of bit position. Bit decision circuitry includes a comparator for sequentially comparing the analog signals with the variable threshold to provide bit decision indications.

Abstract: The present invention relates to a holographic optical storage device utilizing a material in which the transfer of photo-induced charges is orientated along the cristallographic axis C of the material. On the faces of the material perpendicular to said axis, two transparent electrodes connected together are arranged so that the field developed between said two faces is zero whatever the uniform illumination superimposed upon the modulation. The selective erasing of a first induced spatial variation in refractive index is achieved by recording a second spatial variation which is the complement of the first, the number of successive record-erase cycles being unlimited.

Abstract: A wideband holographic information storage system records Fourier holograms on film in rapid succession, each hologram storing 128 bits of data. The hologram fringe pattern is held stationary by varying the reference beam frequency to track the variations of frequency of the signal beam that are caused by acoustic-optic modulation of the signal beam. Holograms are successively recorded in adjacent positions by scanning a light beam across a photosensitive film with a rotating polygonal mirror, the recording light beam being wide enough to cover two facets of the mirror so as to achieve nearly 100% scanning duty cycle. During readout, a readout light beam is steered to compensate for prismatic deflection effects caused by variations in thickness of the film.