Associative memories based on message-bearing optical modes in phase-conjugate resonators

We describe in generic terms a class of associative memory that is based on (1) an oscillating message-bearing optical mode in a resonator containing a multimessage hologram, (2) image-selective (discriminatory) amplification of the desired picture in a photorefractive crystal, and (3) phase-conjugate reflection

Theory of laser oscillation in resonators with photorefractive gain

A theory for oscillation in an optical resonator with photorefractive gain was formulated. The threshold conditions for the oscillation were also obtained. The result, applicable to a whole class of new devices, is a prediction for an oscillation frequency different from that of the pump beam

Optical tracking filter using transient energy coupling

Transient energy coupling between two coherent beams occurs in dynamic holographic media with local and noninstantaneous responses. The physical origin of the effect is described, and an optical tracking filter based on the effect is demonstrated in a photorefractive Bi12SiO20 crystal

Real time image subtraction and "exclusive or" operation using a self-pumped phase conjugate mirror

Real time "exclusive or" operation with an interferometer using a self-pumped phase conjugate mirror is reported. Also, results of image subtraction and intensity inversion are shown

Theory and Applications of Wave-Mixings in Photorefractive Crystals

This thesis is an experimental and theoretical investigation of wave-mixing in photorefractive crystals and applications thereof. In the first part, the physics of the photorefractive effect is described. The figures of merit useful in characterizing various photorefractive crystals are also discussed. In the second part, the coupled wave theory of two interacting optical waves in photorefractive crystals is reviewed. Both the energy coupling and the phase delay of the two beams are analyzed. In the third part, the coupled wave formalism is extended to four wave mixing in photorefractive crystals. Aspects of real-time holography and phase conjugation are discussed. The coupled wave equations are solved in two special cases: (1) single grating and undepleted pump approximation; and (2) single grating and negligible absorption. The theory is then compared with the experimental results. The solutions of the phase of phase conjugation are presented. The recent developments in self-pumped phase conjugate mirrors are also discussed. In the fourth part, new types of oscillators ultilizing the photorefractive gain are described and demonstrated. Two approaches to derive the conditions for unidirectional ring oscillation are presented and compared. The theory and experimental demonstration of a double phase conjugate resonator are described. Two applications, the optical path length to frequency conversion interferometer and the one-way real time wave front converters, are also described. In the last part, some applications of the previous studies are described. Two novel bistable devices using the self-pumped phase conjugate mirror are demonstrated. Mathematical operations on images, such as real time 'exclusive or' operation, image subtraction, differentiation, and intensity inversion are demonstrated using an interferometer with a self-pumped phase conjugate mirror. Finally, the theory and the experimental demonstration of an all-optical associative holographic memory are discussed . Methods of extending the number of stored messages are also discussed.</p

Conversion of optical path length to frequency by an interferometer using photorefractive oscillation

Frequency detuning effects in photorefractive oscillators are used in a new type of (passive) interferometry which converts optical path length changes to frequency shifts. Such an interferometer is potentially more accurate than conventional interferometers which convert optical path length changes to phase or intensity changes

Experimental studies of phase conjugation with depleted pumps in photorefractive media

We describe the experimental measurement of phase-conjugate reflectivity versus various ratios of input-beam intensities in photorefractive barium titanate and strontium barium niobate crystals. The experimental results are compared with the theoretical prediction from the coupled-wave theory. Three different methods to measure the nonlinear coupling constant of the crystal are also presented and compared

Polarization and spatial information recovery by modal dispersal and phase conjugation: properties and applications

We describe recent theoretical and experimental studies of polarization and spatial information recovery by modal dispersal and phase conjugation. We discuss the fidelity of this phase-conjugation process as a function of input-beam launching conditions. We also describe several new applications of the scheme which involve correction of nonreciprocal polarization distortions, correction of lossy amplitude distortions, phase-conjugate multimode fiber-optic interferometers and gyros, temporal data channeling between beams, and all-optical beam thresholding