Hui-Yu Chen

Relation between physical parameters and thermal stability of liquid-crystal blue phase

Correlations between the stability of blue phases and the physical parameters of liquid-crystal hosts are reported in this study. Experimental results show that liquid-crystal blue phases are more thermostabilized when the dielectric anisotropy is reduced or the elastic constants increased. These correlations can be explained by Defect theory and Landau theory for blue phases. Moreover, the results give us the clues to develop more suitable blue-phase materials for fundamental researches or fast photonic devices.

Reversible and fast shift in reflection band of a cubic blue phase in a vertical electric field

Two electro-optical phenomena of liquid-crystal blue phase with cubic lattice structure—(1) a fast and reversible shift in reflection band and (2) a phase transition from blue phase to chiral nematic phase—are observed in this study. By increasing the magnitude of a vertical electric field, the reflected wavelength of the blue phase can be shifted to a longer wavelength in a range of 80 nm within a few ms. This reflection band shift is induced by the reorientation of liquid-crystal molecules constructing double twist cylinders, which induces lattice distortion of the blue phase.

Full-field optical coherence tomography using nematic liquid-crystal phase shifter.

We present a polarization Linnik interference microscope with a nematic liquid-crystal (NLC) phase shifter for full-field optical coherence tomography of high-quality images. The rotating half-wave plate in conventional achromatic phase shifters was replaced by three liquid-crystal (LC) half-wave plates for implementing three-step phase-shifting interferometry. Thus, the NLC device generates phase shifts quickly and has no vibrations. In addition, the phase shift can be set to an arbitrary value between 0 and 2π by altering the azimuth angles of the LC cells. A tomographic image is retrieved from three sequential phase-shifted interferograms by using a three-step algorithm. The experimental results confirm the feasibility of the proposed technology.

Fast tunable reflection in amorphous blue phase III liquid crystal

The dynamic reflection spectra of amorphous blue phase III were investigated. When an electric field is applied to a blue phase III cell, the reflected wavelength does not shift obviously, but the intensity of reflection increases or decreases in a few ms. This fast intensity-tunable phenomenon in blue phase III relates to the dielectric anisotropies and chiralities of the liquid crystal and can be explained by the double twist model consisting of randomly orientated double-twisted cylinders. This study shows that blue phase III can act as a fast intensity-tunable reflector for a specific wavelength.

Bistable SmA liquid-crystal display driven by a two-direction electric field

Abstract— A new operation mode of a bistable smectic A (SmA) display using two sets of electrodes, one without specific features to induce homeotropic orientation of the director and the other with an in-plane pattern to induce planar orientation of the director, has been demonstrated. Both statements of the director orientation are the stable states of SmA liquid crystals. Compared with the electrical addressing mode of a conventional SmA display, the SmA display mode presented in this study exhibits a high contrast ratio, excellent bistability, and reasonably fast switching under the employment of two crossed polarizers. Moreover, gray level can be achieved by regulating the frequency, owing to the formation of the focal-conic defect. This operation mode of a bistable SmA device demonstrated great potential for the further application in flexible displays.

A multistable smectic-A liquid-crystal device with low threshold field

— A multistable liquid-crystal device has been realized in this study; its smectic-A LC is oriented by in-plane and out-of-plane electric fields with various amplitudes. This paper introduces improvements made to electrode structure and hybrid surface treatments that have enhanced SmA LC device performance. The driving voltage of the hybrid-aligned cell has been reduced to 20% of the vertical-aligned one, and light leakage has been suppressed by out-of-plane electric-field-strength modulation. The many advantages of this multi-stabilized LC device could be applied to memory devices and to flexible displays.

Unusual electro-optical behavior in a wide-temperature BPIII cell

A low driving voltage and fast response blue phase III (BPIII) liquid-crystal device with very low dielectric anisotropy is demonstrated. To stabilize BPIII in a wide temperature range (> 15°C), a chiral molecule with good solubility was chosen. By studying field-dependent polarization state of the transmitting light, it was found that the field-induced birefringence becomes saturated in the high field. However, the transmitting intensity exhibits a tendency to increase as the electric field increases. This indicates that the electro-optical behavior in BPIII device may be from the flexoelectric effect, which induces tilted optical axis and then induces birefringence. Because the phase transition from BPIII to chiral nematic phase does not happen, the device shows no hysteresis effect and no residual birefringence, exhibits fast response, and can be a candidate for fast photonic application.

P‐127: Multistabilized SmA LC Device Controlled by a Fringe‐Field Switching Mode

Main approach to obtain a multistabilized SmA LC device is to drive the orientations of the SmA LC through applying an in-plane or an out-plane electric field. To get better electric-optical performances of the SmA LC device, an idea of the improvements on the electrode structure and the surface treatment of the cell is introduced here The experimental observations on the modification SmA LC device exhibit not only a high contrast ratio but also a low driving voltage.