Daniel N. Rogovin

Fractal (self-VQ) encoding of video sequences

We present results of a scheme to encode video sequences of digital image data based on a quadtree still-image fractal method. The scheme encodes each frame using image pieces, or vectors, from its predecessor; hence it can be thought of as a VQ scheme in which the code book is derived from the previous image. We present results showing: near real-time (5 - 12 frames/sec) software-only decoding; resolution independence; high compression ratios (25 - 244:1); and low compression times (2.4 - 66 sec/frame) as compared with standard fixed image fractal schemes.

Comparison of fractal methods with discrete cosine transform (DCT) and wavelets

The paper contains a brief description of fractal image compression methods with sample compression results. We also present comparative results between two fractal schemes, discrete cosine transform and a wavelet method. We show that, with the PSNR as a measure of image quality, some fractal schemes perform best over the range of compressions of most interest.

Microwave phase conjugation via degenerate four-wave mixing in an artificial Kerr medium

Collinear microwave phase conjugation was observed in an artificial Kerr medium consisting of short graphite fibers suspended in a binary liquid mixture. Using an 18 GHz pump beam with up to 20 W continuous power, characterization of the changes in the 94 GHz refractive index were made by interferometry. A nonperturbative method for describing the response of the medium was used to analyze the phase-shift measurements for the static berefringence and the time response as functions of microwave intensity.

Four-Wave Mixing In Liquid Suspensions Of Microparticles

Saturation characteristics and response times are examined for a liquid suspension of Brownian microparticles subjected to electromagnetic fields in a four-wave mixing configuration. Calculations are presented for the evolution of particle density in the field of two degenerate plane waves of arbitrary intensity and angle of incidence. The analysis is then extended to include the additional presence of weak probe and conjugate-wave fields. Nonlinear field particle interactions are shown to give rise to the formation of higher order particle gratings and to novel pump grating modulation effects which greatly enhance the phase-conjugate characteristics of the microparticle suspension.

Nonlinear optical effects in polyacetylene films

Polyacetylene is one of the most studied nonlinear organic materials. Its nearly one- dimensional nature and the conjugate electrons along the carbon-backbone are responsible for its unusual physical, chemical, and optical properties. Polyacetylene has attracted the attention of physicists, chemists, and optical engineers. In particular, the highly nonlinear optical properties of polyacetylene can imply efficient optoelectronic applications.

Nondegenerate two-wave mixing in shaped microparticle suspensions

Polarization-resolved coherent beam combination via nondegenerate two-wave mixing have been observed in water-glycerol suspensions of shaped polytetrafluoroethylene microparticles. Experiments detect coherent energy transfer arising from two different types of moving index gratings: translational and orientational. Additionally, the dependence of the two-wave mixing gain coefficient on the frequency-difference of the beams, pump intensity, and microparticle volume fraction was measured and found to be in accord with theory. Finally, beam combination was also achieved using degenerate laser beams and moving the suspension relative to the laser interference pattern.

Noise in nonlinear optics

This paper examines thermal (light-scattering) fluctuations as a dominant noise source in nonlinear optical processes. Fundamental limits to conjugate wave fidelity and signal power requirement are obtained through the statistical thermodynamic treatment of light-scattering noise in four-wave mixing based on the fluctuation-dissipation theorem. Several types of nonlinear media are examined including artificial Kerr suspensions, isotropic Kerr media, and fluids near a critical point. Where measurements are available, excellent quantitative agreement is obtained between theory and experiment.

Acoustically pumped optical phase conjugation

Several years ago, Shiren, Arnold and Kazaka achieved an acousto-optical analog of optical phase conjugation via degenerate four-wave mixing in glasses. These experiments, which were conducted at 9 GHz, involved the generation of a time-reversed acoustic pulse from a pulsed acoustic probe wave utilizing microwave beams as the pump waves. Here, we examine the reverse situation; i.e., acoustic beams serve as the pump waves and the probe is electromagnetic in nature. It is shown that the medium generates a phase conjugate electromagnetic wave and the physics of this effect is examined.

Degenerate transient beam combination

Recently, energy transfer has been observed between two pulsed, degenerate laser beams copropagating almost collinearly into isotropic Kerr media with temporal relaxation. Theoretical calculations have been made which agree with the experimental data. This paper will briefly describe the experiment, and develop the theory which simulates the lab situation. The physical mechanism regulating this beam combination will also be discussed. Comparisons between the numerical simulations and the experimental data will also be presented.

Nonlinear optical processes at long wavelengths utilizing magnetostatic waves

Optical phase conjugation at microwave and millimeter wavelengths offers numerous applications for communications, radar and navigation. Recently, we have examined the feasability of achieving phase conjugation at typical radar wavelengths ulitizing magnetic thin films as the active medium. Our calculations indicate that magnetic materials are unusally promising for generating phase conjugate radiation at microwave frequencies.