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.

This work demonstrates the feasibility of a polarizer-free, electrically switchable and optically rewritable display based on dye-doped polymer-dispersed liquid crystals (DD-PDLCs). Experimental results indicate that the doped dyes are homeotropically adsorbed onto the polymer film when an appropriate AC voltage is applied during patterning. The adsorbed dyes in the illuminated region then align the liquid crystals homeotropically, and produce a transparent pattern in the scattering background without any polarizer. Notably, the adsorbed dyes can be erased and readsorbed using thermal and optical treatments, respectively. The switching time of the fabricated display is of the order of milliseconds, and the contrast ratio is approximately 30.

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This letter demonstrates the feasibility of producing variable liquid crystal ͑LC͒ pretilt angles using light-induced ripple structures ͑LIRSs͒ in homeotropically aligned azo dye-doped liquid crystals ͑ADDLCs͒. Illuminating homeotropically aligned ADDLCs with a linearly polarized light for a suitable period yields the LIRSs which provide LCs an anisotropic homogeneous anchoring force. Experimentally, the effective alignment force produced by the homeotropic alignment layer and the LIRSs determines the LC pretilt angle ͑24°to 63.5°͒, defined from the normal to the substrate. A no-bias pi cell for liquid crystal displays is demonstrated using this approach.

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The direct optical switching of bistable cholesteric textures (i.e., planar and focal conic textures) in chiral azobenzene-doped liquid crystals (LCs) is demonstrated. Chiral azobenzene is a chiral dopant with optically tuned helical twisting power that results from the photo-isomerization between trans- and cis- isomers via exposure to UV or visible light. The pitch length of the material can be optically and repeatedly elongated and shortened. With regard to free energy, LCs tend to be stable at planar (focal conic) textures when pitch length is elongated (shortened) by exposure to UV (visible) light. Thus, direct optical switchable LC displays are investigated.

We show that the Helfrich deformation can be used for fast response time, low driving voltage reflective displays by using cholesteric liquid crystals under short voltage pulses (∼10 ms). Rather than turning planar domains into focal conic domains through a nucleation process, as used in bistable modes, the fast voltage pulse only deforms the cholesteric planar layers to form wrinkled layers. Since the deformed state is formed through a homogeneous process, quick response times and low operating voltage can be achieved. We studied the effects of alignment layer and dispersed polymer on the stability of the Helfrich deformed cholesteric layers, and found that homogeneous alignment layer and polymer network can inhibit the nucleation process responsible for breaking the layers.

Negative dielectric nematic liquid crystals (LCs) doped with two azobenzene materials provide electrically switchable and permanently stable scattering mode light modulators based on dynamic fingerprint chiral textures (DFCT) with inhomogeneously helical axes. These light modulators can be switched between transparent (stable large domains of DFCT) states and scattering (stable small domains of DFCT) states by applying electric fields with different frequencies. The generation of DFCT results from the long flexible side chains of the doped chiral dopant. That is, if the DFCT can be obtained, then the large domains of DFCT reflect an intrinsically stable state. Moreover, the stabilization of the small domains of DFCT are caused by the terminal rigid restricted side chains of the other doped chiral dopant. Experimentally, the required amplitude to switch the light modulator from a scattering (transparent) state to a transparent (scattering) state decreases as the frequency of the applied electric field increases (decreases) within the set limits. This study is the first report on the advantages of the light scattering mode of DFCT, including low operating voltage, permanently stable transmission, wide viewing angle, high contrast, and polarization-independent scattering and transparency.