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.

Ultralong dark decay measurements in BaTiO(3).

We have observed dark decay rates in BaTiO(3) crystals at elevated temperatures that correspond to dark decay times as long as 2200 years at room temperature. Our investigations have shown that cerium is a desirable dopant in BaTiO(3) for enhancing the dark storage time.

Bistable operation of a phase-conjugate resonator containing an intracavity saturable absorber.

We have demonstrated bistability in a phase-conjugate resonator containing an intracavity saturable absorber. The saturable absorber was a film of fluorescein-doped boric acid glass. The state of the resonator is determined by an external control beam incident upon the saturable absorber. When the resonator is switched to the on state by means of the control beam, it remains in that state even with the control beam turned off.

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.

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 system's invariance to translation of the input images.

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.

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.

Spatial and temporal properties of a continuous-wave phaseconjugate resonator 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.

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.

Scattering from high efficiency diffraction gratings.

This paper has characterized and measured scatter from high efficiency and reflective diffraction gratings. Three major types of scatter are identified: (1) random, which occurs over 27pi sr; (2) band or ghost scatter, which occurs in the plane of incidence; and (3) structured scatter, which is a symmetrical pattern repeated about each order. Measurements were taken at 10.6 Am on gratings made by ruling, ion etching, holography, or a combination of these techniques. We found that the characteristic scatter from these high efficiency gratings depends strongly on the way the gratings are fabricated.