The authors demonstrate a technique to optically imprint through linear beam propagation an index pattern in the bulk of a photorefractive crystal capable of beam reshaping and waveguiding. The procedure is based on the separation into two distinct phases of the photosensitive and refractive response, so that light is in all cases undergoing only linear propagation. When saturation in the response becomes dominant, the scheme is able to achieve both one-dimensional and two-dimensional waveguiding. The result allows the straightforward writing of multiwaveguide circuits, where traditional schemes based on spatial solitons are in practice burdened by nonlinearity. [ABSTRACT FROM AUTHOR]Copyright of Applied Physics Letters is the property of American Institute of Physics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Slab waveguides were constructed in [K.sub.1-x]-[Li.sub.x][Ta.sub.1-y] [Nb.sub.y][O.sub.3] crystals by the implantation of [sup.12][C.sup.+4] ions at 30 MeV and [sup.16][O.sup.+5] ions at 30 and 40 MeV. The waveguides were characterized by a prism coupler setup. A refractive index drop of 10.9% was observed in a layer formed by the implantation of [sup.16][O.sup.+5] ions at 30 MeV. The carbon-implanted waveguides were found to be thermally stable after annealing at 450 [degrees]C. A semiempirical formula for predicting the change in the refractive index given the parameters of the implantation process was developed. It is argued that the combination of the basic implantation process with the semiempirical formula can be developed to become a generic method for constructing complex electro-optic circuits with a wave-guided architecture. OCIS codes: 160.2260, 230.7400, 220.4000, 130.3120, 350.4600.

Volume phase gratings have been fabricated by controlled generation of periodic striations during the growth of copper doped potassium lithium tantalate niobate crystals. Gratings with periods ranging from below 1 to 5 μm were fabricated. It is shown that the fabricated composition grating induces a refractive index grating which is a superposition of a fixed grating and an electrically controlled (electrooptic) grating. The electrooptic grating is produced due to the generation of a spatial modulation of the Curie temperature which is manifested as a correlated modulation of the static dielectric constant. It was also observed that when operated at the immediate vicinity of the phase transition temperature the diffraction efficiency from these gratings was bi-stable at a specific electric field due to an induced shift of the Curie temperature.

The percolative nature of the ferroelectric phase transition in a potassium tantalate niobate (KTN) crystal is studied using time domain dielectric spectroscopy. A relaxation process linked to the off-center niobium ions is observed. The dynamic nature of this relaxation shows well defined temperature regimes in which it progresses from independent (Arrhenius) to cooperative (Vogel-Fulcher-Tammann) behavior. A recursive fractal model was applied in order to interpret the data obtained from the dielectric measurements. The structural parameters, nu and mu, derived from the correlation functions, enable the investigation of the onset of the phase transition in terms of the fractal dimensions of the polarization excitation. (c) 2007 Elsevier B.V. All rights reserved.

Electrically controlled Bragg gratings implemented by periodic striations that were produced during the crystal growth are demonstrated in potassium lithium tantalate niobate crystals. The striations were generated by blowing air with periodic flow at the flux surface. The gratings were investigated by measurements of the diffraction efficiency versus the applied electric field. It was found that the composition grating induced correlated gratings of the refractive index and the low frequency dielectric constant. The latter, under the application of a uniform electric field, produced an electrically controlled birefringence grating through the quadratic electro-optic effect. [ABSTRACT FROM AUTHOR]Copyright of Applied Physics Letters is the property of American Institute of Physics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)