We investigate experimentally the energy exchange patterns and consequent propagation dynamics of an extended hybrid-dimensional interaction between a one-dimensional and a two-dimensional spatial soliton in a biased photorefractive crystal. Results show that conditions can be found in which the coupling manifests propagation invariant features. The mechanism hinges on mutual distortion through spatially nonlocal components of response, as opposed to standard wave overlap, which would lead to a diffusion of the needle into the slab mode. These nonlocal-nonlinearity-driven ridge modes represent the instrument for writing fiber-slab couplers, the key to attaining soliton-based wavelength selectivity with electroactivated features. [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.)
A slab waveguide was fabricated in a potassium lithium tantalate niobate crystal by the implantation of He2+ ions at 2.26 MeV. The waveguide profile and loss were evaluated by measuring the dark mode TE spectrum using the prism coupling method at λ=1.3 μm. The implantation generated amorphous cladding layer 5 μm below the surface of the crystal with a refractive index lower by 3.9% then that of the substrate. The propagation loss of the waveguided modes was found to be 0.1–0.2 dB/cm. Thermal stability of the waveguide was obtained by isothermal annealing at 351 and 446 °C. Following the annealing the waveguide index profile remained unchanged when subjected to annealing at 150 °C for one week. [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.)
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We present a broadband dielectric spectroscopy study of potassium tantalate niobate (KTN) crystals, doped with varying amounts of Cu ions. The dielectric landscape in frequency and temperature is rich, with multiple processes in different temperature phases of the crystals. Of particular interest are the processes resulting from Cu and Nb ions in the paraelectric phase of the crystal and from Cu ions in the ferroelectric phase. The linear dependence of the ferroelectric transition temperature in KTN crystals (KTa0.62Nb0.38O3Cu) on the concentration of Nb, as well as the dielectric behavior of the ferroelectric phase transition in these crystals, are well known. We concentrate of the dielectric relaxation resulting from the Cu ions in the crystal lattice. Cu dopants in very small concentrations have been added in the past to enhance the photoreftractive properties of KTN crystals. However the small ionic radius of such dopants, relative to their lattice site, results in virtual dipoles exhibiting dielectric relaxation. The random nature of their distribution throughout the ordered KTN lattice leads to relaxation behavior reminiscent of glass formers. In particular Vogel Fulcher Tammann relaxation of these ions is evident in the paraelectric phase of the crystal. This cooperativity is broken at a critical temperature (T = 354 K) and the relaxation becomes Arrhenius in nature. An explanation in terms of Adam-Gibbs theory is presented where the cooperative cluster is realized by polarized Nb ions linking the widely space Cu ions. At the phase transition (T-c = 295.6 K) this relaxation is 'frozen' by large internal fields caused by the structural shift of the Nb ion in the unit cell. As the temperature drops the Cu ions undergo a reorganization about the multiwell potential leading to a saddle-like process characteristic of liquids in confined systems. An explanation for this behavior is proposed based on free volume concepts, where the relatively small ionic radius of the Cu ions provides the free volume for the relaxing species. The role of the oxygen octahedra as the relaxing species is discussed. (c) 2005 Published by Elsevier BV.
