Multiple-Color Reflectors Using Bichiral Liquid Crystal Polymer Films and Their Applications in Liquid Crystal Displays.

Multiple-color reflectors using bichiral liquid crystal polymer films (BLCPFs) are investigated. The BLCPFs consist of alternate layers of two different single-pitch cholesteric liquid crystal (CLC) layers, named CLC#A and CLC#B. The thickness of each CLC layer equals its single pitch length. The optical properties in terms of reflections, reflection-wavelength ranges, and distributions of reflection spectra of the BLCPFs that result from the fixed pitch length of CLC#A along with the decrease of the pitch length of CLC#B are qualitatively simulated and investigated. The results indicate that the above optical properties of the BLCPFs depend on the LC birefringence and pitch lengths of CLC#A and CLC#B layers. The concept of fabrication method of the BLCPFs by using polymerizable CLCs and thin films of poly(vinylalcohol) or photoalignment materials is discussed. They have potential practical applications in functional color filters, asymmetrical transmission systems, etc., owing to the multiple reflection bands of BLCPFs. Moreover, the BLCPFs, which can enhance the color gamut and light-utilization efficiency of light sources/LC displays, are reported herein.

Polarization converters based on axially symmetric twisted nematic liquid crystal.

An axially symmetric twisted nematic liquid crystal (ASTNLC) device, based on axially symmetric photoalignment, was demonstrated. Such an ASTNLC device can convert axial (azimuthal) to azimuthal (axial) polarization. The optical properties of the ASTNLC device are analyzed and found to agree with simulation results. The ASTNLC device with a specific device can be adopted as an arbitrary axial symmetric polarization converter or waveplate for axially, azimuthally or vertically polarized light. A design for converting linear polarized light to axially symmetric circular polarized light is also demonstrated.

Axially symmetric liquid crystal devices based on double-side photo-alignment.

This investigation demonstrates the feasibility of the radial and azimuthal axially symmetric LC structure using double-side photoalignment in a dye-doped liquid crystal (DDLC) cell. A linear and linearly polarized beam is applied to a rotated DDLC cell to produce an axially symmetric LC alignment. Notably, double-sided photoalignment is performed at a temperature that is maintained just above the clear point. Conformation of the axially symmetric LC devices can be controlled by varying the polarization direction of the pumping light, and the simulation results correlate well with OR closely correspond to the experimental results.

Axially symmetric polarization converters based on photo-aligned liquid crystal films.

This work demonstrates axially symmetric polarization converters based on photo-alignment in dye-doped liquid crystal (DDLC) films. A linear-shape and linearly polarized beam is applied onto a rotated homogeneous DDLC cell to achieve three axially symmetric polarizations - radial, azimuthal and vortical. Additionally, the spiral degree of the axially symmetric vortical polarization can be controlled by varying the polarization of the pumping light and the simulation results agree well with the experiment.

Electrically switchable and optically rewritable reflective Fresnel zone plate in dye-doped cholesteric liquid crystals.

This work demonstrates a reflective Fresnel zone plate based on dye-doped cholesteric liquid crystals (DDCLC) using the photo-induced realignment technique. Illumination of a DDCLC film with a laser beam through a Fresnel-zone-plate mask yields a reflective lens with binary-amplitude structures - planar and focal conic textures, which reflect and scatter probed light, respectively. The formed lens persists without any external disturbance, and its focusing efficiency, analyzed using circularly polarized light, is ~ 23.7%, which almost equals the measured diffraction efficiency of the used Fresnel-zone-plate mask (~ 25.6%). The lens is thermally erasable, rewritable and switchable between focusing and defocusing states, upon application of a voltage.

Optical simulation of cholesteric liquid crystal displays using the finite-difference time-domain method.

The finite-difference time-domain (FDTD) method is a powerful numerical algorithm used to directly solve Maxwell's equations. We introduce the idea of the FDTD method and the techniques required for optical simulation of cholesteric liquid crystal (Ch-LC) devices. Bragg reflection characteristics of Ch-LC cells are investigated using the FDTD method. Three approaches to broadening the bandwidth of Bragg reflection are demonstrated: (1) using a higher birefringence LC, (2) using a cell with a gradient pitch length, and (3) using a cell with a new multidimensional structure of a Ch-LC.