Chi-Lun Ting

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.

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.

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.

Optical Simulation of Axially Symmetrical Vertically Aligned Liquid Crystal Displays With Circularly Symmetric Iso-Contrast

This investigation reports the optical simulation of axially symmetric vertically aligned liquid crystal displays (ASVA LCDs). The circularly symmetric iso-light leakage and iso-transmittance contours of one subpixel result in the circularly symmetric iso-contrast contours. The contrast ratio of the area close to x- and y-axes at a polar angle of around 30° exceeds 10. The LCs near some azimuthal angles are not perfectly aligned in circularly symmetric manner because of the square subpixel. Such a reason causes major reduction of the light utilization efficiency. Additionally, the circularly symmetric iso-contrast has potential for fabricating private mobile products.

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 Maxwells 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.

Fresnel lenses based on dye-doped liquid crystals

We demonstrated transmissive- and reflective-type Fresnel lenses based on dye-doped liquid crystal using photoalignment technique. The former is a polarization-independent and electrically tunable. The maximum diffraction efficiency reaches 37%, which approaches the theoretical limit ~ 41 %. Such a lens functions as a half-wave plate, and this feature could be well preserved under the applied voltage. The reflective-type Fresnel lens is based on dye-doped cholesteric liquid crystals (DDCLC). 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, and rewritable. Notably, both of the transmissive- and reflective-type Fresnel lenses are switchable between focusing and defocusing states, upon application of a voltage. In addition, these devices are simple to fabricate, and have fast switching responses between focusing and defocusing state.

Polymer microlens array with tunable focal intensity by the polarization control of the incident light

This paper proposes an optically tunable focal intensity microlens array (MLA) by using a focusing unit with birefringent liquid crystalline polymer (LCP) and a tuning unit with photoalignment for controlling the polarization state of the incident light. Due to the different refractive indices of LCP, it acts as a positive or negative microlens with respect to the polarization state. The resultant tunable focal intensity MLA shows the fast optical switching time without voltage and the multi-stable characteristics.

P-181: Axially Symmetric Liquid-Crystal Polarization Converter

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.

P-128: Multi-dimensional Cholesteric Liquid Crystal Displays for Broadband Reflection and Wide Viewing Angle

The finite-difference time-domain (FDTD) method is applied to investigate the Bragg reflection of cholesteric liquid crystal (CLC) devices, and a multi-dimensional structure of CLC for achieving broadband Bragg reflection and wide viewing angle is introduced.