Yuge Huang

Optimized blue-phase liquid crystal for field-sequential-color displays

We report an optimized blue phase liquid crystal (BPLC) mixture JC-BP08 for field-sequential-color (FSC) display applications. JC-BP08 exhibits several attractive features: 1) its fast average gray-to-gray response time enables FSC display, which in turn triples the resolution density and optical efficiency. 2) Its voltage holding ratio is >99.4% at 25°C and >93.2% at 60°C. 3) Its average dielectric constant e’≈87 is still manageable by the bootstrapping driving to enable 240 Hz operation. 4) Using a triangular protrusion electrode structure, the transmittance can reach 74% at 15V, which enables single-TFT driving. 5) With two-domain structure, it offers indistinguishable gamma shift and wide viewing angle. We proposed a voltage charging model and found a linear relationship between the required charging time and e’, which is validated by our experimental results.

High performance liquid crystals for vehicle displays

We report three liquid crystal (LC) mixtures with a wide nematic range (−40°C to ~100°C), small visco-elastic coefficient and low activation energy for vehicular displays. Physical properties at different temperatures were characterized. These LCs greatly improve the performance of different display devices in a car: 1) for head-up projection using liquid-crystal-on-silicon with an average gray-to-gray (GTG) response time less than 1 ms at an elevated temperature. 2) The average GTG response time is maintained at ~10 ms for fringing field switching LCD at T = 0°C and also ~10 ms for twisted nematic LCD at T = −20°C.

A Low Voltage Liquid Crystal Phase Grating with Switchable Diffraction Angles

We demonstrate a simple yet high performance phase grating with switchable diffraction angles using a fringe field switching (FFS) liquid crystal (LC) cell. The LC rubbing angle is parallel to the FFS electrodes (i.e. α = 0°), leading to symmetric LC director distribution in a voltage-on state. Such a grating exhibits three unique features: 1) Two grating periods can be formed by controlling the applied voltage, resulting in switchable diffraction angles. In our design, the 1st diffraction order occurs at 4.3°, while the 2nd order appears at 8.6°. 2) The required voltage to achieve peak diffraction efficiency (η~32%) for the 1st order is only 4.4 V at λ = 633 nm as compared to 70 V for a conventional FFS-based phase grating in which α ≈ 7°, while the 2nd order (η~27%) is 15 V. 3). The measured rise and decay time for the 1st order is 7.62 ms and 6.75 ms, and for the 2nd order is 0.75 ms and 3.87 ms, respectively. To understand the physical mechanisms, we also perform device simulations. Good agreement between experiment and simulation is obtained.

Fast-response liquid crystal phase modulators for augmented reality displays

We report three new liquid crystal mixtures optimized for the phase modulator of an augmented reality display. The mixtures exhibit a relatively high birefringence (Δn) yet low viscosity, modest dielectric anisotropy (Δe), and acceptable resistivity and UV stability. High Δn enables a thin cell gap (d≈1.7 μm) for achieving 2π phase change with a reflective Liquid-Crystal-on-Silicon (LCoS) device and ~2 ms average phase-to-phase response time at 40°C. The modest Δe helps lower the operation voltage to 5V. To improve the response time of a full-color LCoS, we propose a new driving method by shifting the operation voltage away from the threshold. We also applied such a high Δn LC mixture to LCoS based amplitude modulators and achieved submillisecond response time. Widespread applications of these materials for the emerging augmented reality displays are foreseeable.

Dielectric broadband meta-vector-polarizers based on nematic liquid crystal

Polarizer, as an indispensable optical element, has been widely used in various optical systems, which splits a beam into two beams of orthogonal linear polarizations. Due to the appearance of the vector optical field (VOF) and its unique properties, the vector polarizer also meets the requirement in a wide variety of applications. Here we present and demonstrate the realization of dielectric broadband vector polarizer, being in fact a liquid-crystal-based space-variant uniaxial crystal (LC-SV-UAC), which is made by a wedged thin cell adhered with space-variant photo-aligned dichroic dye films and filled with the nematic liquid crystal with a thickness of tens of microns. The vector polarizer works based on the birefringent mechanism to spatially separate the orthogonally polarized ordinary and extraordinary beams. The vector polarizers via a LC-SV-UAC have the advantages of mass-production and easy fabrication of large-size and complex structures. In particular, the high-performance broadband vector pola...

High-frame-rate liquid crystal phase modulator for augmented reality displays

ABSTRACT We optimise a new liquid crystal mixture with wide nematic range, high birefringence (Δn), high resistivity, moderate dielectric anisotropy (∆ε) and relatively low rotational viscosity for augmented reality display applications. High Δn and large Δε allow a thin cell gap (d ≈ 1.5 μm) to be employed in a reflective liquid-crystal-on-silicon (LCoS) device to achieve 2π phase change at 5 V and 2.87 ms average phase-to-phase response time at 40°C without complicated overdrive circuitry. Such a fast response time enables an LCoS panel to achieve 240 Hz frame rate for field sequential colour operation to avoid image flickering. Graphical Abstract