Electrically switchable cholesteric gratings based on slit electrodes.

An electrically switchable diffraction grating (ESDG) based on cholesteric liquid crystal (CLC) filled into the cell with slit electrodes is demonstrated in this study. On one hand, with low voltage, the ESDG has high second order diffraction efficiency because of the alternating planar and fingerprint textures. With high voltage, on the other hand, the ESDG has high first order diffraction efficiency because of the alternating planar and homeotropic textures. The first and second order diffraction efficiencies of ESDG are electrically swapped. The maximum diffraction efficiency of the ESDG is approximately 32% at each grating mode.

Rotatable diffractive gratings based on hybrid-aligned cholesteric liquid crystals.

This work proposes a thermally rotatable grating that is based on hybrid-aligned cholesteric liquid crystals (HBA-cholesteric LCs). Experiments reveal that the HBA-cholesteric texture has a uniformly striped domain, which forms a grating, when the ratio of the cell gap to the helical pitch (d/p) is in the range of 2≤d/p≤3. The stripe direction of the HBA-cholesteric grating is predicted by the proposed vertically aligned LC layer model. The stripe direction of the HBA-cholesteric grating rotates continuously under thermal and electrical effects. Furthermore, the HBA-cholesteric grating has a larger rotational angle under the thermal effect (~101°) than under the electrical effect (~48°). Potential applications of the proposed thermally rotatable cholesteric grating for beam steering devices are emphasized.

Extraordinarily wide-view and wide spectral bandwidth transflective liquid-crystal displays.

This work presents a simple compensation method for widening the viewing angle of transflective liquid-crystal displays (TR-LCDs). For an off-axis light, the slow axis of a biaxial film shifts linearly as the Nz factor is varied. By using this optical characteristic of a biaxial film, the broadband condition of broadband circular polarizers exactly holds over a full 80 degrees viewing cone, thus eliminating the off-axis light leakage to widen the viewing angle of TR-LCDs. Based on the proposed compensation method, the TR-LCDs theoretically have a wide spectral bandwidth and a viewing angle of 80 degrees for contrast-ratio (CR) >100:1 and >30:1 in transmissive and reflective modes, respectively. Experiments also show that the proposed TR-LCD has a viewing angle of over the entire 80 degrees and 65 degrees viewing cone in T-mode and R-mode, respectively, for CR>10:1. The proposed TR-LCD is highly promising for mobile display applications.