Jiamin Yuan

Electro-optic response of polymer-stabilized blue phase liquid crystals

The dynamic response of a polymer-stabilized blue phase liquid crystal (BPLC) is comprised of two distinct processes: Kerr effect-induced local reorientation and electrostriction-induced lattice distortion. A double exponential rise/decay model is proposed to analyze the underlying physical mechanisms. If the electric field is below a critical field (Ec), Kerr effect dominates and the response time is fast. However, when E > Ec electrostriction effect manifests, leading to an increased response time and a noticeable hysteresis. A higher polymer concentration helps suppress electrostriction, but the tradeoff is increased operation voltage. These results provide useful guidelines for future BPLC material and device optimizations.

Image sticking in liquid crystal displays with lateral electric fields

We propose a kinetic model to account for the nonuniform adsorption and desorption processes in fringe field switching (FFS) and in-plane-switching liquid crystal displays. An equation is proposed to describe the generation mechanism of residual DC voltage and good agreements with experiment are obtained. Based on this model, the mechanisms underlying the formation and relaxation processes of residual DC voltage as well as their dependences on offset DC voltage and temperature are investigated. Moreover, the residual DC voltages of FFS cells employing positive and negative dielectric anisotropy LCs are compared and the physics responsible for the observed difference is explained.

Blue phase liquid crystals stabilized by linear photo-polymerization

Stabilizing a photopolymer-embedded blue phase liquid crystal precursor with linearly polarized UV light is investigated experimentally. When the UV polarization axis is perpendicular to the stripe electrodes of an in-plane-switching cell, anisotropic polymer networks are formed through the linear photo-polymerization process and the electrostriction effect is suppressed. As a result, the measured hysteresis is dramatically reduced from 6.95% to 0.36% and the response time shortened by ∼2× compared to unpolarized UV exposure. To induce larger anisotropy in polymer networks for mitigating the electrostriction effect, high-intensity linearly polarized UV exposure is preferred.

Low temperature and high frequency effects on polymer-stabilized blue phase liquid crystals with large dielectric anisotropy

We report the low temperature and high frequency effects on polymer-stabilized blue phase liquid crystals (BPLCs) comprising of a large dielectric anisotropy nematic host. Debye dielectric relaxation sets a practical limit even when the device operation temperature is still within the blue phase range. To explain these phenomena, we propose a model to describe the temperature and frequency dependent Kerr constant and obtain excellent agreement with experiment. Doping a diluter compound to the BPLC host helps to reduce viscosity, which in turn boosts the dielectric relaxation frequency and extends the low temperature operation range.

Controllable Multiwave Mixing Talbot Effect

We theoretically study the Talbot effects resulted from the four-wave mixing and six-wave mixing signals, which are periodically modulated due to the coherence control effect. Corresponding to different dressing states, the enhancement and suppression conditions that will affect the properties of the multiwave mixing signals are also discussed in detail. Such proposal can be useful in all-optical-controlled pattern formation and propagation of light.

Functional reflective polarizer for augmented reality and color vision deficiency

We report a functional reflective polarizer that can be incorporated into a compact augmented reality system. The design principle of the functional reflective polarizer is explained and two design examples are illustrated. In the first example, with the specially designed functional reflective polarizer, the transmittance of the augment reality system is relatively high as compared to a polarizing beam splitter or a conventional reflective polarizer. Such a functional reflective polarizer can also be used for vehicular displays. For the second example, the functional reflective polarizer is specially tailored to help those people with color vision deficiency.

Low-voltage and fast-response polymer-stabilized hyper-twisted nematic liquid crystal

We report a low-voltage and submillisecond-response polymer-stabilized hyper-twisted-nematic (HTN) liquid crystal cell with a large dielectric anisotropy host mixture. To correct the measured voltage-dependent transmittance, we have to take the voltage shielding effect of the alignment layers into consideration. Both Kerr effect and flexoelectro-optic effect contribute to the observed induced birefringence. To evaluate the dynamic responses of these two effects, we fit the decay time data with a double relaxation model. A good agreement between the experiment and simulation is obtained. Such a HTN cell still exhibits fast response time (<2ms) even at low temperature (0°C). Potential applications for display and photonic devices are foreseeable.

Observation of angle-modulated switch between enhancement and suppression of nonlinear optical processes

We simultaneously investigate the four-wave mixing and the fluorescence signals via two cascade electromagnetically induced transparency (EIT) systems in atomic rubidium vapor. By manipulating the deflection angle between the probe beam and certain coupling beams, the dark state can extraordinarily switch to bright state, induced by the angle-modulation on the dressing effect. Besides, in the fluorescence signal, the peak of two-photon fluorescence due to classical emission and the dip of single-photon fluorescence due to dressing effect are distinguished, both in separate spectral curves and in the global profile of spectrum. Meanwhile, we observe and analyze the similarities and discrepancies between the two ground-state hyperfine levels F = 2 and F = 3 of Rb 85 for the first time.

Stabilizing blue phase liquid crystals with linearly polarized UV light

Polymer-stabilized blue-phase liquid crystal (PS-BPLC) has become an increasingly important technology trend for information display and photonic applications. BPLC exhibits several attractive features, such as reasonably wide temperature range, submillisecond gray-to-gray response time, no need for alignment layer, optically isotropic voltageoff state, and large cell gap tolerance when an in-plane switching (IPS) cell is employed. However, some bottlenecks such as high operation voltage, relatively low transmittance, and noticeable hysteresis and prolonged response time at high field region for IPS mode, still remain to be overcome before widespread application of BPLC can be realized. To reduce operation voltage, both new BPLC materials and new device structures have been investigated. In this paper, we demonstrate the stabilization a photopolymer-embedded blue phase liquid crystal precursor using a linearly polarized UV light for first time. When the UV polarization axis is perpendicular to the stripe electrodes of an IPS cell, anisotropic polymer networks are formed through the linear photo-polymerization process and the electrostriction effect is suppressed. As a result, the measured hysteresis is dramatically reduced from 6.95% to 0.36% and the response time shortened by ~2X compared to unpolarized UV exposure. To induce larger anisotropy in polymer networks for mitigating the electrostriction effect, high-intensity linearly polarized UV exposure is preferred. It is foreseeable this method will guide future BPLC device and material development as well as manufacturing process. The dawn of BPLCD is near.