A liquid crystal (LC) device, called a "q-plate" (QP), which is based on axially symmetric photo-alignment was investigated. The electrically tunable LC QP device could be modulated to control the shape and polarization of a linearly polarized Gaussian laser beam that propagated through it. The intensity profile and polarization distribution were simulated by MATLAB and 1D-DIMOS. The results of the simulation were consistent with experimental findings. In the fabricated electrically tunable LC QP device, switching between different beam-profile configurations can be realized by applying a voltage. Moreover, the fabrication of an LC QP is relatively simple, and the device has potential for such practical applications as beam shape modulators and spatial polarization converters use in diffractive optics and imaging systems.
This study demonstrates all optical switches between the four diffractive light levels of a body-centered tetragonal photonic crystal. The sample is based on holographic polymer-dispersed liquid crystals that are fabricated using a two-beam interference with multiple exposures. The switching mechanism bases on the effective index modulation of the PC that contains a liquid crystal/azo-dye mixture could be controlled by two pumping laser beams. The switching time between the blue-laser-pumped and the blue-and-green-laser-pumped levels is fast. The study also discusses the switching time of the various levels.
A continuous multiple exposure diffraction grating (CMEDG) is fabricated holographically on polymer dispersed liquid crystal (PDLC) films using two-beam interference with multiple exposures. The grating is fabricated by exposing a PDLC film to 18 repeated exposure/non-exposure cycles with an angular step of ~10°/10° while it revolves a circle on a rotation stage. The structure of the sample thus formed is analyzed using a scanning electron microscope (SEM) and shows arc-ripples around the center. From the diffraction patterns of the formed grating obtained using a normally incident laser beam, some or all of the 18 recorded arc beams can be reconstructed, as determined by the probing location. Thus, it can be applied for use as a beam-vibration sensor for a laser.
This study demonstrates an optical switch of the diffractive light from a body-centered tetragonal photonic crystal based on holographic polymer-dispersed liquid crystals that are fabricated using two-beam interference with multiple exposures. The liquid crystal-rich regions form the lattice points of the PC, which contains a liquid crystal/azo-dye mixture. The concentration of the cis isomer changes under laser light exposure; this change, in turn, modulates the effective index of the LCs, and then switches diffractive light.
This study describes an electrically tunable two-dimensional (2D) liquid crystal holographic polarization grating. It is a twisted nematic grating array, which is obtained by orthogonally overlaying two crossed one-dimensional (1D) polarization holograms. A 1D polarization hologram has a rotating linear polarization pattern, generated by the interference of two orthogonal circularly polarized beams on a substrate that is coated with an azo-dye-doped polyvinyl alcohol layer. The images under a polarized optical microscope and the diffraction patterns from the 2D grating are simulated using the Jones matrix and a Fourier transformation. The experimental results agree with the simulated results. This work represents a substantial advance toward the realization of highly functionalized passive optical devices in which both the beam propagation direction and the polarization state can be controlled in two dimensions.
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