Double grating formation in anisotropic photorefractive crystals

Double gratings form in anisotropic photorefractive crystals when two plane waves intersecting inside the crystal have both extraordinary and ordinary wave components. The effect can be observed by reading out the two gratings with extraordinary or ordinary light. Experiments confirm the theoretical predictions. The relevance of these results in using photorefractive crystals for holographic storage is discussed

Alignment sensitivity of holographic three-dimensional disks

We describe the rotational alignment sensitivity of three-dimensional holographic disks. It is shown that the reconstructed image always rotates by the angle by which the disk rotates; however, the center and the radius of rotation change as the recording geometry changes. A comparison among image plane, Fourier plane, and Fresnel holograms is given, and an optimum configuration (in terms of alignment sensitivity) in which the radius of rotation is zero is derived. We present experimental results and also discuss how the rotation alignment sensitivity affects the storage density and the readout–recording speed of the three-dimensional disk. A brief summary of other sources of misalignment is given

Three-dimensional holographic disks

We describe optical disks that store data holographically in three dimensions by using either angle multiplexing or wavelength multiplexing. Data are stored and retrieved in parallel blocks or pages, and each page consists of approximately 106 bits. The storage capacity of such disks is derived as a function of disk thickness, pixel size, page size, and scanning parameters. The optimum storage density is approximately 120 bits/µm^2

Nonvolatile storage in photorefractive crystals

We propose and demonstrate a nonvolatile holographic recording system for storing two-dimensional images. The readout light in this system is not absorbed by the holographic medium, and the data are preformatted or postformatted so that lines from different holograms are interleaved to satisfy the Bragg-matching condition

Optical network for real-time face recognition

An optical network is described that is capable of recognizing at standard video rates the identity of faces for which it has been trained. The faces are presented under a wide variety of conditions to the system and the classification performance is measured. The system is trained by gradually adapting photorefractive holograms

Volume storage in photorefractive disks

We describe a photorefractive 3-D optical disk for data storage. The information is stored at several recording locations on the disk as angle-multiplexed holograms. Design parameters that affect alignment sensitivity and diffraction efficiency are considered

Dynamics of grating formation in photovoltaic media

The Kukhtarev equations are solved taking into account the photovoltaic effect and different boundary conditions. In the case of open circuit, the voltage across the crystal is found to vary with a time scale similar to the photorefractive time constant. This effect explains the dynamic behavior observed experimentally

Improved real-time imaging spectrometer

An improved AOTF-based imaging spectrometer that offers several advantages over prior art AOTF imaging spectrometers is presented. The ability to electronically set the bandpass wavelength provides observational flexibility. Various improvements in optical architecture provide simplified magnification variability, improved image resolution and light throughput efficiency and reduced sensitivity to ambient light. Two embodiments of the invention are: (1) operation in the visible/near-infrared domain of wavelength range 0.48 to 0.76 microns; and (2) infrared configuration which operates in the wavelength range of 1.2 to 2.5 microns