Sze-Keung Kwong

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.

Narrow linewidth, single frequency semiconductor laser with a phase conjugate external cavity mirror

We measure the spectral characteristics of an external cavity semiconductor laser which uses a phase conjugate mirror for its external reflection. This device has significant advantages over the conventional external cavity system owing to the self-aligning nature of the phase conjugate mirror. The fiber delay line self-heterodyne technique is used to measure the fundamental linewidth for single mode operation of this device. It shows the linewidth to be at least as narrow as the instrumental resolution of 100 kHz.

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.

Demonstration of an all‐optical associative holographic memory

We describe a new type of associative holographic memory and some related results. The memory can retrieve overlapping images which are stored in a volume hologram. The storage and retrieval of more than one image is demonstrated for the first time. The important role of thresholding in assuring ‘‘clean’’ retrieval is demonstrated.

Oscillation with photorefractive gain

We review theories and experimental demonstrations of oscillation with photorefractive gain. The unidirectional ring resonator; the linear passive phase conjugate mirror, a phase conjugate resonator (the semilinear passive phase conjugate mirror), and the double phase conjugate resonator are treated, the applications in path-length-to-frequency converting interferometers and one-way wavefront converters are described.

Optical bistability and hysteresis with a photorefractive self‐pumped phase conjugate mirror

Bistability and hysteresis have been observed in a photorefractive passive phase conjugate mirror. A threshold basis for the effect is presented and the results of an experimental demonstration of the device are given.

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.

Polarization recovery in phase conjugation by modal dispersal

We demonstrate scalar phase conjugation, i.e., one in which both transverse components of the incident beam are phase conjugated, which is achieved by tandem combination of a mode scrambling fiber and a photorefractive passive phase conjugate mirror.

Bistable oscillations with a self-pumped phase-conjugate mirror

Optical bistable oscillation beams with a self-pumped phase-conjugate mirror are reported. The results of an experimental demonstration are given, and an explanation based on the threshold of oscillation is presented.

Phase of phase conjugation and its effect in the double phase-conjugate resonator

Expressions for the phase of reflection from a photorefractive phase-conjugate mirror are obtained as a function of the intensity and phase of the pump and the probe beams. The phase is independent of these parameters in common photorefractive conditions in which the index grating is spatially shifted 90 degrees with respect to the light-interference pattern. Multiple solutions exist for the phase and intensity of the reflection at large coupling strength. Oscillation conditions involving frequency detuning are obtained for the double phase-conjugate resonator (resonator formed with two phase-conjugate mirrors).