Organic photorefractive materials

About: Organic photorefractive materials is a research topic. Over the lifetime, 697 publications have been published within this topic receiving 13041 citations.

Photorefractive wave mixing in semi-insulating InGaAs/GaAs multiple quantum wells

Abstract: Summary form only given. Photorefractive multiple quantum wells (MQWs) have become important for the realization of fast and two-dimensional optical image processing devices. Wang et al. have reported the photorefractive effect in InGaAs-GaAs MQWs around 0.9 /spl mu/m. But the details of two-wave mixing (TWM) have not been mentioned. Here we report the photorefractive effect including the TWM properties in InGaAs-GaAs MQWs around a wavelength of 0.93 /spl mu/m.

Polymeric composite photorefractive materials for nonlinear optical applications

Abstract: Polymeric composite materials constitute a new and very promising class of photorefractive materials. In the design of polymeric photorefractive materials we use multicomponent composites in which necessary functionalities can be independently optimized. The investigated composites consisted of charge transporting polymeric matrix, and optically second-order active molecules. Two different photosensitizers were used to vary the wavelength response. Photorefractive properties of these materials were investigated using erasable volume holography in a non-degenerate four-wave mixing geometry and two-beam coupling techniques. A previously developed model of space-charge field grating formation in photoconductive polymers was used to explain the field dependence of four-wave mixing diffraction efficiency. The model takes into account the field dependence of charge photogeneration quantum yield, carrier field mobility, and electro-optic coefficient. Necessary information about these parameters was obtained from the results of photoconductivity and electro-optic modulation experiments. Special attention was focused on the kinetics of photorefractive response in the composite for optical signal processing and optical storage. It was found that a very effective switching of diffraction efficiency induced by dc electric field occurs in this system. Also, the results of kinetic studies of the index grating writing and its subsequent light-induced erasure, as well as a demonstration of the holographic image recording and retrieval, are reported.

A new class of strongly photorefractive materials

Abstract: Certain doped compound semiconductors exhibit persistent photoconductivity (PPC) at low temperatures as a result of the optical ionization of electrons from deep, spatially localized, donor levels known as DX centers We calculate that this release of carriers also produces a refractive index shift (through the plasma effect) which is 30 times larger than that of conventional photorefractive materials, We report the results of diffraction measurements on samples of AlGaAs which support this prediction The induced index changes can be erased by heating above an annealing temperature determined by the material composition >

Research on optical A/D conversion using interference modulators

Abstract: During the high speed processing, the intensity of the light beam must be detected and converted into some digital signals without electronic device for system controlling. The A/D converting should be in full optics way. The interferometer may make some fringes correspond the input light, while the fringe intensity contains some important information. When a photorefractive material was put into the interference field, another reading-laser beam would be diffracted. The order of the diffraction can be controlled because the nonlinear reactivity of photorefractive materials. Then, the reading laser beam goes into an encoder to demodulate signals. Through the demodulating processing in light speed, the group-codes may be output as the input signals of other control system. The speed of the modulating should be tied from the photorefractive materials. The important step is how to change the time domain information into space domain information. If the responding speed of the photorefractive material is suitable to react on the input signal light, the conversion is successful. In that process, organic photorefractive materials or crystal photorefractive materials have different application features.

Holographic storage dynamics, phase conjugation, and nonlinear optics in photorefractive materials

Abstract: This thesis explores the application of photorefractive materials in two distinct areas: the holographic data storage and the dynamic nonlinear optical interactions. First, we have established that partial ferroelectric domain reversal in certain ferroelectric materials can be used to permanently fix the dynamic holographic gratings, and analyzed the interaction between the fixed and the dynamic components of a hologram. A comprehensive analysis of the storage temporal dynamics in photorefractive materials is further developed for the case of thermal ionic fixing. An experimental study of holographic storage dynamics in photorefractive lithium niobate revealed new features related to the ionic conductivity in this and similar materials. We established and developed techniques for long-lifetime and high-efficiency hologram fixing in the holographic data storage applications. We further analyze theoretically the impact of the recording response properties of different storage media (including photorefractive materials and photopolymers) and optical detection noise on the ultimate storage capacity of holographic memories. Second, the transverse properties of the photorefractive double phase conjugate mirror (DPCM) have been studied. We have established that the DPCM exhibits a sharp conjugation fidelity gain threshold which increases with image resolution, while the reflectivity is a smoothly varying function of nonlinear gain. The conjugation fidelity was found to degrade dramatically for unequal intensities ratio. The DPCM exhibits critical slowing down in the vicinity of the oscillation threshold. A two-dimensional coupled-modes perturbation analysis of the DPCM is introduced and its basic predictions are in a good qualitative agreement with the results of the experimental study. Finally, we analyze the nonlinear optical second harmonic generation in materials with strong photorefractivity. In the presence of strong self-phase modulation the phase matching conditions are modified and we found that in some cases this leads to a unique effect, namely, the nonlinear self-phase matching of optical nonlinear interaction. Strong photorefractive response manifests itself in two characteristic and very apparent manners; a large change in the conversion efficiency and self-defocusing of the generated second harmonic beam. We introduced a two-dimensional model of photorefractive effect and found its predictions to be in a good qualitative agreement with the observed transverse dynamics.