Daming Xu

A low voltage and submillisecond-response polymer-stabilized blue phase liquid crystal

We report a polymer-stabilized blue phase liquid crystal (BPLC) whose Kerr constant is about 2.2× larger than previous record. When filled in a 3.2-μm-thick vertical field switching cell, the on-state voltage is merely 8.4 V (at λ = 514 nm) while keeping submillisecond response time and negligible hysteresis (<1%) at the room temperature. These results imply that the dawn of BPLC era for high speed display and photonic devices has finally arrived.

Polarization-independent actively tunable colour generation on imprinted plasmonic surfaces.

Structural colour arising from nanostructured metallic surfaces offers many benefits compared to conventional pigmentation based display technologies, such as increased resolution and scalability of their optical response with structure dimensions. However, once these structures are fabricated their optical characteristics remain static, limiting their potential application. Here, by using a specially designed nanostructured plasmonic surface in conjunction with high birefringence liquid crystals, we demonstrate a tunable polarization-independent reflective surface where the colour of the surface is changed as a function of applied voltage. A large range of colour tunability is achieved over previous reports by utilizing an engineered surface which allows full liquid crystal reorientation while maximizing the overlap between plasmonic fields and liquid crystal. In combination with imprinted structures of varying periods, a full range of colours spanning the entire visible spectrum is achieved, paving the way towards dynamic pixels for reflective displays.

Emerging Quantum-Dots-Enhanced LCDs

Quantum dots (QDs)-based backlight greatly enhances the color performance for liquid crystal displays (LCDs). In this review paper, we start with a brief introduction of QD backlight, and then present a systematic photometric approach to reveal the remarkable advantages of QD backlight over white LED, such as much wider color gamut, higher optical efficiency, enhanced ambient contrast ratio, and smaller color shift. Some popular LC modes are investigated, including twisted nematic, fringing field switching (FFS) for touch panels, multi-domain vertical alignment (MVA) for TVs, and blue phase liquid crystal (BPLC) for next-generation displays. Especially, QD-enhanced BPLC combines the major advantages of FFS and submillisecond response time. It has potential to become a unified display solution.

High performance liquid crystal displays with a low dielectric constant material

We report high performance liquid crystal displays (LCDs), including fringe field switching (p-FFS) and in-plane switching (p-IPS), with a small average dielectric constant (e) but positive dielectric anisotropy material. Our low e based p-FFS and p-IPS LCDs offer several attractive properties, such as high transmittance, low operation voltage, fast response time (even at −20°C), which is particularly desirable for outdoor applications of mobile or wearable display devices, and suppressed flexoelectric effect. Combining these advantages with the inherent outstanding features, such as wide viewing angle, no grayscale inversion, negligible color shift, and pressure resistance, the low e LC based p-FFS and p-IPS are strong contenders for next-generation mobile displays, and high resolution and high frame rate TVs.

Refraction effect in an in-plane-switching blue phase liquid crystal cell.

We develop a refraction model to analyze the electro-optic effects of an in-plane-switching blue phase liquid crystal (IPS-BPLC) cell. Good agreement with experiment is obtained. Based on this model, we optimize the parameters affecting the electro-optics of IPS-BPLC, such as electrode dimension, saturated induced birefringence, saturation electric field, and cell gap. An IPS-BPLC with low operation voltage (<10V(rms)) and high transmittance (~80%) with single gamma curve can be achieved by optimizing the BPLC material and device structure.

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.

Nematic Liquid Crystal Display With Submillisecond Grayscale Response Time

A nematic display with three electrodes and double fringing fields is proposed. Both top and bottom substrates have pixel and common electrodes to generate complementary fringing fields for achieving high transmittance. This mode exhibits submillisecond gray-to-gray response time and high contrast ratio. The effect of pixel misalignment on transmittance is discussed.

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.

Optical rotatory power of polymer-stabilized blue phase liquid crystals

Macroscopically, a polymer-stabilized blue phase liquid crystal (BPLC) is assumed to be an optically isotropic medium. Our experiment challenges this assumption. Our results indicate that the optical rotatory power (ORP) of some nano-scale double-twist cylinders in a BPLC composite causes the polarization axis of the transmitted light to rotate a small angle, which in turn leaks through the crossed polarizers. Rotating the analyzer in azimuthal direction to correct this ORP can greatly improve the contrast ratio. A modified De Vries equation based on a thin twisted-nematic layer is proposed to explain the observed phenomena.

A hysteresis-free polymer-stabilised blue-phase liquid crystal

We report a polymer-stabilised blue-phase liquid crystal (BPLC) in an in-plane-switching (IPS) cell with negligible hysteresis and good stability. Long ultraviolet (UV) wavelength and top-side (no IPS electrode) exposure create uniform polymer network, which in turn helps to suppress hysteresis. The effect of photoinitiator is also investigated. Although a BPLC precursor without photoinitiator requires a higher UV dosage to stabilise the polymer network, it is favourable for keeping high resistivity and reducing image sticking.