Abstract: A method for encoding and decoding digital data for storage in a holographic medium (12). Digital data, consisting of binary data (B.sub.i) or grey scale data (A.sub.i), is encoded in bit groups or digit groups (B.sub.k, A.sub.k) containing at least k=1 bits or digits, respectively, by assigning to each bit group (B.sub.k) one reference bit (B.sub.r) and to each digit group (A.sub.k) two reference digits (A.sub.r1, A.sub.r2), assigning the bits of group (B.sub.k) to information bits (B.sub.j), assigning the digits of group (A.sub.k) to information digits (A.sub.j), assigning the reference bit (B.sub.r) and information digits (B.sub.j) to a reference pixel (P.sub.r) and information pixels (P.sub.j) chosen from pixels (24) of a holographic signal modulator (18), and assigning the reference digits (A.sub.r1, A.sub.r2) and information digits (A.sub.j) to reference pixels (P.sub.r1, P.sub.r2) and information pixels (P.sub.j) chosen from pixels (24) of the holographic signal modulator (18).

Abstract: A method for promoting enhanced nondestructive reconstruction of holograms recorded in photorefractive media involves control of the polarization states of the reconstruction beam and the recording beams, control of the cummulative recording energy, and use of a relatively high external field applied across the media during recording which is subsequently reduced during reconstruction. The resulting reconstruction history characteristics are selectively tailored by adjusting the polarization and intensity of the reconstruction beam, the recording geometry, and the applied voltage during reconstruction and recording, and various other parameters. In general, the reconstruction efficiency starts at a relatively high level, initially reduces, and then subsequently grows above the starting value, and can be made substantially nondestructive over a typical reconstruction cycle, with erasure times exceeding forty-five minutes.

Abstract: A photorefractive crystallyte array for image recording and signal processing is disclosed. The photorefractive crystallytes are configured as a two-dimensional array of selected position and spacing designed, for example, to coincide with the spatial frequency components of an associated optical image, such as a Fourier transform image, and to permit optical signal processing.

Abstract: An optical system for selectively enhancing and/or suppressing the spectral intensity of components in an object beam, is disclosed. In one exemplary application, the optical system includes means for performing a forward transform operation on an input beam, a non-linear optical medium such as, for example, Bi.sub.12 SiO.sub.20 or Bi.sub.12 GeO.sub.20 and means for performing an inverse transform operation. In operation, the forward transform is performed on an input beam that contains a complex function characteristic of an object or subject, the resulting transform of the object beam is applied to the non-linear optical medium to form a hologram, then the hologram is read-out and the inverse transform operation is performed to provide an output optical beam that contains, for example, selectively enhanced intensity components and/or selectively suppressed intensity components.

Abstract: Index of refraction measurements are made by means of an optical device in which a coherent light beam is divided into an object beam and a reference beam, each of which is directed through a separate path in a common light transmitting medium. The object beam is also transmitted en route through a test volume that accommodates a substance to be tested. It is subsequently recombined with the reference beam to form a single output beam. The output beam is received by a photo detector and its intensity is measured. The intensity of the detected output beam is related to any phase shift between the object and reference beams. The phase shift in turn is a measure of the index of refraction of the test substance. Information relating to density, temperature and pressure of the test substance can be derived from measured index of refraction values by using conventional conversion formulas.