Theory of beam coupling in a hybrid photorefractive-liquid crystal cell
ABSTRACT A theory of beam coupling in a hybrid photorefractive liquid crystal cell is developed. The hybrid cell consists of layers of undoped nematic liquid crystal contained within wafers of photorefractive crystal or photoconductors. Reorientation of the liquid crystal is induced by the evanescent component of the space charge field propagating from the photorefractive layers, leading to a modulation of the liquid crystal refractive index. Using coupled wave theory, an analytic solution is obtained for the small signal gain in good agreement with previously published experimental work.
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ABSTRACT: A photorefractive system composed of liquid crystal droplets dispersed in a photoconducting polymer is characterized by means of two-beam coupling. The amplitudes and phases of the spatial variations of the refractive index and the absorption coefficient are measured using the moving grating technique. Dynamic measurements indicate that the phase of the refractive index modulation is nearly constant while the amplitude increases gradually. The maximum value of the internal space charge field can be estimated from the amplitude of the phase grating and is found to be of the order of one-hundredth of the external bias field.Journal of Applied Physics 01/2006; 100. · 2.19 Impact Factor
Conference Paper: Gain dynamics in liquid crystal photorefractive hybrids[Show abstract] [Hide abstract]
ABSTRACT: Photorefractive (PR) hybrid liquid crystal (LC) cells have combined the space-charge field generated in either a polymer (using e.g. PVK;C60) with the large birefringence from a LC layer to generate PR grating for beam coupling applications. The efficiency of PR beam coupling in hybrid devices is dependent on the amplitude of the space-charge field, as well as the ability of the LC molecules to align with the corresponding field. In this paper the time dynamics of the formation of the PR gratings are measured in LC hybrid systems and are used to explain the large variation of gain coefficients found in the literature.SPIE Optical Engineering + Applications; 09/2014
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ABSTRACT: This work is a theoretical study of energy exchange between two coupled TE-wave modes on director diffraction grating in a planar waveguide containing a layer of nematic liquid crystal. The diffraction grating is produced by an external electric field in the nematic layer with spatial periodic anchoring energy between director and waveguide surface. The intensity of a signal mode at the output of the nematic layer has been calculated in dependence of anchoring energy amplitude and modulation period, the size of nematic layer and electrical field value. The cases of co-propagating and oppositely propagating modes have been analysed. The analytical expressions that describe the maximum values of signal mode intensity have been derived. The maximum intensity value output from the nematic has been shown to depend monotonously on the anchoring energy parameters in the case of oppositely propagating wave modes and non-monotonously in the case of co-propagating wave modes. In both cases, the maximum value of signal mode intensity grows with the increase in electric field.Liquid Crystals 10/2013; 40(10). · 2.35 Impact Factor