Showing papers on "Organic photorefractive materials published in 1989"
Journal Article•
TL;DR: In this article, the authors reviewed recent developments involving the nonlinear interactions of light in photorefractive crystals, including the mutual light-crystal interactions which govern their operation, and all-optical applications based on these oscillators.
Abstract: Recent developments, both theoretical and experimental, involving the nonlinear interactions of light in photorefractive crystals are reviewed. When pumped by light beams in various configurations, certain crystals, such as barium titanate (BaTiO/sub 3/), respond with the self-build up of gratings in the crystal and formation of new light beams. The emphasis here is on these devices, known as photorefractive oscillators, the mutual light-crystal interactions which govern their operation, and all-optical applications which are based on these oscillators. >
60 citations
33 citations
Book•
01 Jan 1989
TL;DR: In this paper, the photorefractive effects in waveguides and wave propagation in photore-fractive media have been investigated in the context of spatial light modulators.
Abstract: Amplification, oscillation, and light-induced scattering in photorefractive crystals.- Photorefractive effects in waveguides.- Wave propagation in photorefractive media.- Phase-conjugate mirrors and resonators with photorefractive materials.- Optical processing using wave mixing in photorefractive crystals.- The photorefractive incoherent-to-coherent optical converter.- Photorefractive crystals in PRIZ spatial light modulators.
30 citations
TL;DR: In this paper, the frequency dependence of the photorefractive effect is considered and the analysis results in a second-order model with an explicit dependence on both the grating spacing and the temporal grating frequency.
Abstract: The frequency dependence of the photorefractive effect is considered. The frequencies can be applied by introducing a temporal phase shift in one of the beams in a two-wave mixing configuration. The analysis of the Kukhtarev equations is based on the small modulation approximation, but in contrast to earlier papers, no a priori approximations are made. The analysis results in a second-order model with an explicit dependence on both the grating spacing and the temporal grating frequency. Curves for the modulus and the imaginary part of the space-charge field are obtained, and it is concluded that, for small fringe spacings, the second-order model presented provides important information on the photorefractive effect. >
25 citations
Patent•
21 Dec 1989
TL;DR: The photorefractive effect results in a change in the refractive index of bulk chalcogenide glass when it is exposed to certain wavelengths of light, in particular, sub-band-gap light as mentioned in this paper.
Abstract: The photorefractive effect results in a change in the refractive index of bulk chalcogenide glass when it is exposed to certain wavelengths of light, in particular, sub-band-gap light. The effect results in a variety of device structures including a fiber optic faceplate; an optical waveguide; a fiber tap; a lens and a Bragg grating. Methods for fabricating the various devices are described.
20 citations
TL;DR: In this article, the photorefractive effects of pure and iron doped KNbO3 crystals with concentrations between 150 ppm and 300 ppm were investigated and the experimental results were discussed in terms of a two carrier model.
Abstract: Photorefractive effects of pure and iron doped KNbO3 crystals with concentrations between 150 ppm and 300 ppm have been investigated. In order to optimize the photorefractive recording times and the amplitude of the refractive index changes the crystals were thermally treated with simultaneous photorefractive testing. The photoconductivity data and the photorefractive beam coupling gain dependent on the grating spacing show that the relative influence of electron and hole contribution is altered depending on the reduction treatment. The experimental results are discussed in terms of a two carrier model.
13 citations
TL;DR: In this paper, the photorefractive properties of KNbO3 were improved by electrochemical reduction, such as photoconductivity, beam coupling gain and response time, and anisotropic self-diffraction was used to obtain a resolution of up to 10 linepairs per mm.
Abstract: With the electro-chemical reduction method developed recently we are able to improve the photorefractive properties of KNbO3 such as photoconductivity, beam coupling gain and response time. The preparation of large monodomain crystals with good optical and photorefractive homogeneity for photorefractive incoherent optical conversion (PICOC) is described. The image conversion was achieved by the anisotropic self-diffraction technique. The optimal crystal configuration for this application was verified experimentally. A resolution of up to 10 linepairs per mm was achieved for modulating a laser beam by a white light image.
7 citations
TL;DR: In this paper, the photorefractive effect of Ti-diffused LiNbO3 optical waveguides is quantified using the time constant of the relaxation process.
Abstract: We report on a new novel method of quantifying the photorefractive effect (optically induced index change) of Ti-diffused LiNbO3 optical waveguides. The evolution and decay behavior of the photorefractive effect was investigated. The resistivity of Ti-diffused LiNbO3 estimated from the time constant of the relaxation process is about the same as the resistivity of bulk LiNbO3.
6 citations
TL;DR: In this article, photorefractive effects in LEC-grown, semi-insulating, undoped GaAs crystals were investigated and the existence of both neutral and ionized states of the EL-2 center makes this material photore-fractive.
Abstract: Photorefractive effects in LEC-grown, semi-insulating, undoped GaAs crystals were investigated. The existence of both neutral and ionized states of the EL-2 center makes this material photorefractive. However, the presence of other defects and impurities can drastically deteriorate photorefractive properties.
3 citations
14 Dec 1989
TL;DR: In this paper, the photorefractive properties of LiNb03:Fe bulk crystals with different proton concentrations and of proton-exchanged planar waveguides fabricated with LiNi-Fe substrates are investigated.
Abstract: The photorefractive properties of LiNb03:Fe bulk crystals with different proton concentrations and of proton-exchanged planar waveguides fabricated with LiNb03:Fe substrates are investigated. The saturation values of refractive index change, the photoconductivity, the photorefractive sensitivity and the photovoltaic current density of bulk LiNb03:Fe crystals are only determined by the Fe impurities and do not depend on proton concentration. But the dark conductivity is increased by protons. In Li1-xHxNb03 waveguides we find after fabrication a strong decrease of the saturation value of light-induced refractive index change due to an increase of dark conductivity and a decrease of the electrooptic coefficients. Absorption measurements indicate that mainly Fe3+ ions are present in the waveguide region. After annealing photorefractive index changes increase and the dark conductivity decreases again.
1 citations
01 Apr 1989
TL;DR: In this article, the photorefractive properties of BaTiO3 have been investigated in the context of phase conjugation using degenerate four-wave mixing, and it has been shown that iron (in the forms Fe2+ and Fe3+) is the dominant photore-fractive species.
Abstract: : Photorefractive materials offer great promise for applications in optical data processing and phase conjugation using degenerate four-wave mixing. BaTiO3 is a particularly promising material, primarily because the very large value of the electro-optic tensor component r42 yields correspondingly large values of grating efficiency, beam coupling gain, and four-wave mixing reflectivity. Unfortunately, the commercial availability of BaTiO3 crystals is limited, and samples which are available are relatively small and impure and have not been characterized or optimized for photorefractive applications. In the program reviewed here, we have addressed two of the most important problems in the development and use of photorefractive BaTiO3: stabilization of the cubic phase in order to permit more rapid crystal growth than is now possible, and determination and characterization of the photorefractive species in commercial BaTiO3. The second major effort of this program was the identification and characterization of the photorefractive species in BaTiO3. Using the results of a number of experiments, we have concluded that iron (in the forms Fe2+ and Fe3+) is the dominant photorefractive species in commercial BaTiO3. We have been able to measure the densities of Fe2+ and Fe3+, along with the sign of the photocarriers, the effective electro-optic coefficient, and a lumped parameter taking into account the transport properties of holes and electrons.
31 Jan 1989
TL;DR: In this paper, the photorefractive properties (photoconductivity, beam coupling gain, response time) of KNbO3 were improved by changing the valencies of iron-impurities.
Abstract: Strongly nonlinear optical and fast responding materials are required for real-time optical information processing. KNbO3 has been shown to have very fast photorefractive response times and good photosensitivity. With the electro-chemical reduction method developed recently we were able to improve the photorefractive properties (photoconductivity, beam coupling gain, response time) of KNbO3 by changing the valencies of iron-impurities. The preparation of large monodomain crystals with good optical and photorefractive homogeneity for photorefractive incoherent to coherent optical conversion (PICOC) is described. The image conversion was achieved by the anisotropic self-diffraction technique. The optimal crystal configuration for this application has been experimentally verified. A resolution of up to 10 linepairs per mm has been achieved for converting a white light image onto a laser beam.
TL;DR: In this article, the photorefractive donor and acceptor densities of BaTiO3, crysta1s are derived from a thermodynamic point defect model, and the beam coupling gain and response time are calculated using the electron-hole model.
Abstract: We present a model which can be used to predict the effects of doping and oxidation-reduction treatment on the photorefractive behavior of BaTiO3, crysta1s.1 The densities of photorefractive centers are calculated from a thermodynamic point defect model. These centers may exist in multiple charge states; the occupation of each the temperature and oxygen partial pressure of processing and dopant concentration. The beam coupling gain and response time are calculated using the electron-hole model, where the photorefractive donor and acceptor densities are derived from the defect model.