Engineering topics

Gheen, Gregory

Publications and source records attributed to Gheen, Gregory.

8 records

NASA NTRS1989

Optical Matrix.Matrix Multiplier

Proposed apparatus for optical multiplication of two matrices based on Stanford optical vector.matrix multiplier. Does not require redundant representation of one of matrices. Because apparatus performs multiplication in fully parallel manner, incorporated as subsystem into large optical-processing system. Optical matrix.matrix multiplier processes inputs in fully parallel fashion, without redundant matrix images or ancillary intermediate electronic processing.

Gheen, Gregory↗

NASA NTRS1989

Optical Processing With Photorefractive Semiconductors

Experimental phase-conjugate four-wave-mixing apparatus used to demonstrate capabilities of GaAs (and potentially of other photorefractive semiconductors like InP and CdTe) for optical processing of information. With modifications, performs any of three basic image-processing functions: transfer to different light beam, enhancement of edges, and autocorrelation. Includes crystal of GaAs of 5 by 9 by 9 mm with cubic crystalline axes. Advantages include high speed and compatibilty with other semiconductor devices.

Cheng, Li-Jen↗

NASA NTRS1989

Spatial Modulation Of Light In GaAs

Spatial modulation of light in gallium arsenide demonstrated by transferring image from one of two coherent, crossing beams of light to other one. Technique relies on cross-polarization beam coupling, product of photorefractive effect in GaAs crystal.

Cheng, Li-Jen↗

NASA NTRS1988

Matrix-vector multiplication in thin photorefractive GaAs crystals

Optical matrix-vector multiplication using four-wave mixing in a thin photorefractive GaAs crystal is demonstrated. Using a thin wafer of GaAs offers the potential to integrate the encoding spatial light modulators directly on the wave-mixing medium.

Cheng, Li-Jen↗

NASA NTRS1988

Optical correlators with fast updating speed using photorefractive semiconductor materials

The performance of an updatable optical correlator which uses a photorefractive semiconductor to generate real-time matched filters is discussed. The application of compound semiconductors makes possible high-speed operation and low optical input intensities. The Bragg diffraction is considered, along with the speed and power characteristics of these materials. Experimental results on photorefractive GaAs are presented.

Gheen, Gregory↗

NASA NTRS1987

Image processing by four-wave mixing in photorefractive GaAs

Three image processing experiments were performed by degenerate four-wave mixing in photorefractive GaAs. The experiments were imaging by phase conjugation, edge enhancement, and autocorrelation. The results show that undoped, semiinsulating, liquid-encapsulated Czochralski-grown GaAs crystals can be used as effective optical processing media despite their small electrooptic coefficient.

Gheen, Gregory↗

NASA NTRS1987

Image transfer in photorefractive GaAs

Image transfer from one beam to the other using counterpropagation beam coupling in GaAs was demonstrated. Good image quality was achieved. The results also reveal that local birefringence due to the residual stress/strain field in the crystal can degrade the image quality.

Cheng, Li-Jen↗

NASA NTRS1987

Spatial light modulation by beam coupling in GaAs crystals

The first demonstration of spatial light modulation in GaAs using the photorefractive effect is reported. A special configuration was employed in which polarization rotation created by beam coupling was utilized. The ability to obtain these results despite a small coupling gain coefficient demonstrates the usefulness of the polarization technique presented here for optical processing with GaAs crystals.

Cheng, Li-Jen↗