Gilmore J. Dunning

Associative holographic memory with feedback using phase-conjugate mirrors.

We describe an all-optical associative memory system that uses a holographic data base. Phase-conjugate mirrors are used to provide optical feedback, thresholding, and gain. Analysis and preliminary experiments are discussed.

Holographic associative memory with nonlinearities in the correlation domain.

We describe a shift-invariant all-optical holographic associative memory implemented using phase conjugate mirrors and Fourier transform holograms. A key feature of our system is the large storage capacity obtained through the use of nonlinearities in the correlation domain. The use of angularly multiplexed plane wave reference beams allows access to the correlation domain where nonlinearities in the phase conjugate mirrors can be used to reduce greatly crosstalk and correlation noise.

Demonstration of image transmission through fibers by optical phase conjugation.

We have demonstrated image transmission through a multimode fiber by using optical phase conjugation. By using the wave-front reversal properties of degenerate four-wave mixing, we have compensated for the degradation of the image that is due to modal dispersion in a fiber.

Imaging threshold detector using a phase-conjugate resonator in BaTiO 3

We have demonstrated an imaging threshold detector using a phase-conjugate resonator to provide high spatial resolution and signal regeneration near threshold. The device is based on spatially resolved grating erasure in photorefractive BaTiO(3) and has the capability of high resolution and low cross talk.

Observation of optical chaos in a phase-conjugate resonator

The outcoupled power of a phase-conjugate resonator that uses four-wave mixing in BaTiO(3) is observed to undergo transitions from steady to periodic and from periodic to chaotic behavior as a function of time. Period doubling, period-three cycles, and period-five cycles are observed. Control parameters for the transitions are the diameter of an intracavity pinhole aperture, the length of the resonator, and the radius of curvature of the outcoupling mirror.

All-optical associative memory with shift invariance and multiple-image recall.

We present experimental results from an all-optical associative memory that combines holography and phase conjugation. The device has the capability to recall a complete image when merely a portion of the stored image is input to the system. Multiple superimposed two-dimensional images with gray scale can be stored and recalled. In addition, we have demonstrated the systems invariance to translation of the input images.

Self-organized coherence in fiber laser arrays

Self-organized coherence between fiber lasers has been reported both via all-fiber 2x2 directional coupler trees and in spatially multi-core fibers. We have taken this a major step forward, coupling together a number of independent fiber lasers to obtain a spatially and spectrally coherent far field, with no active length, polarization, or amplitude control. The near field output comes from a spatial array rather than from a single fiber, making this approach scalable to extremely high power.

Hybrid optoelectronic neural networks using a mutually pumped phase-conjugate mirror.

We discuss an optical interconnection method for neural networks based on mutually pumped phase conjugation in a photorefractive crystal. Cross talk due to Bragg degeneracies is reduced by storing each connection weight in a continuum of angularly and spatially multiplexed volume gratings.

Spatial and temporal properties of a continuous-wave phase-conjugateresonator based on the photorefractive crystal BaTiO 3

We report measurements on spatial and temporal properties of a cw phase-conjugate resonator (PCR) based on the photorefractive crystal BaTiO(3) and pumped with millwatt power levels from a He-Ne or a Kr(+)-ion laser. In the absence of an intracavity aperture, the output beam is observed to be elongated in the direction of the crystal c axis by means of preferential self-defocusing of the beam by the highly anisotropic photorefractive effect in BaTiO(3). When the coherence length of the pump laser is much smaller than the round-trip distance in the PCR, the time constants for buildup and decay of the PCR power are found to be much larger than those of the photorefractive response.

Enhanced responsivity of non-steady-state photoinduced electromotive force sensors using asymmetric interdigitated contacts.

The responsivity at a constant detection area of non-steady-state photoinduced electromotive force (photo-emf) detectors is improved by a factor equal to the number of contact pairs contained in asymmetric interdigitated surface contacts. The polar nature of photo-emf current generation requires contact asymmetry in which one increases the total signal by blocking the illumination between alternate contact pairs, in distinct contrast to the behavior of conventional interdigitated contacts fabricated upon isotropic photoconductors.