![]() ![]() ![]() On the other hand, it has to be underlined that liquid crystal devices can also switch and route signals due to the modulation of external electric fields and the interplay between the light and molecules, especially when the nonlinearity of NLC plays a crucial role. Such NLC-waveguide architectures, as reported by the Fraunhofer IPMS, are based on a pure electro-optic approach. Such a configuration uses NLC in their isotropic phase for electro-optical-induced waveguides and supports polarization-independent light propagation. The presented waveguides consisted of an NLC infiltrated core made in PDMS channels. In addition to electro-optic and nonlinear effects that can be utilized for controlling the light propagation in photonic channels, the optical switching between waveguides can be realized using ferroelectric or smectic liquid crystals. The concept of NLC waveguide channels for polarization-independent light propagation was presented, and, for the first time, the concept and performance of a liquid-crystal-based electro-optical router was discussed. In the last decades, another geometry in which the light beam propagates in the NLC layer along the glass substrates has also attracted considerable attention. Spatially structured NLC cells are also used to transform linearly polarized light beams into beams with radial or azimuthal polarization. Different possibilities are associated with the light beams reflected from the spatially modulated NLC structures. The simplest example is the pixelated microdisplay (i.e., a spatial light modulator) for free-space beam shaping and steering. Several optical types of NLC devices were demonstrated, using the linear properties of the material and electrical switching. The transmission of light beams directed perpendicular to the substrates of the cell can be electrically controlled. Light beams are directed perpendicular to the substrates. The electric field oscillations are perpendicular and parallel to the direction of molecular orientation, and then an ordinary and extraordinary wave can be excited, respectively.Ī standard configuration of the planar NLC cell that comprises two glass substrates and a liquid crystal layer is used. ![]() ![]() Most nematics are optically uniaxial and positive birefringent materials (with an extraordinary refractive index greater than the ordinary one, n e > n o) with an optical axis corresponding to the long axis of the molecules. The averaged alignment direction defines a dimensionless unit vector n called the director. In a specific temperature range, called the nematic phase, long axes of molecules are approximately parallel to each other in. Due to anisotropy in molecular structures, they exhibit electrical anisotropy. The fluid nature of NLCs and their compatibility with most optoelectronic materials, polymers, and organic materials allow them to be easily incorporated with other elements in various configurations, forms, and geometries, thereby increasing the potential applications in novel photonic networks. Due to the very high birefringence, combined with the possibility of changing it under the effect of external stimuli in thin-film NLC elements, the latter offers an excellent opportunity to develop novel methods and devices for the control of light beams. Commonly used materials for electro-optic waveguides are LiNbO 3, LiTaO 3, BaTiO 3, electro-optic polymers, and nematic liquid crystals (NLCs). The classic electro-optic (EO) effect is related to the refractive index alteration due to the modification of the index ellipsoid (or optical indicatrix) by applying an external electric field. In most optical waveguide designs with external modulators, the optical switching is commonly realized through electro-optic, magneto-optic, all-optical, and thermo-optical effects. ![]()
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