Meizi Jiao

Electro-optics of polymer-stabilized blue phase liquid crystal displays

Electro-optics of polymer-stabilized blue phase liquid crystal displays (BP LCDs) is analyzed and validated experimentally. A numerical model for characterizing and optimizing the electro-optical and display properties of BP LCDs in in-plane switching and fringe field switching cells is developed. The simulated voltage-dependent transmittance curves agree well with the measured results. To lower the operating voltage while keeping a high transmittance, both electrode width and gap, and large Kerr constant make important contributions. A wide-view BP LCD using a single biaxial compensation film is simulated.

Extended Kerr effect of polymer-stabilized blue-phase liquid crystals

Electric-field-induced birefringence of a polymer-stabilized blue-phase liquid crystal (BPLC) is investigated. In the low field region, conventional Kerr effect holds. As the electric field increases, the induced birefringence gradually saturates and deviates from Kerr effect. An exponential convergence model, called extended Kerr effect, is proposed to fit the experimental data. Good agreement between experiment and model is obtained. This extended Kerr effect will make a significant impact to the optimization of emerging BPLC display devices.

Low voltage and high transmittance blue-phase liquid crystal displays with corrugated electrodes

A low voltage (<10 V) and high transmittance (∼85.6%) polymer-stabilized blue-phase liquid crystal (BPLC) display is proposed. The periodic corrugated electrodes generate a strong horizontal field component to induce isotropic-to-anisotropic transition in the BPLC medium through Kerr effect. Moreover, this field is uniformly distributed across the entire LC layer so that the accumulated phase retardation along the beam path is large, resulting in low voltage and high transmittance. This approach enables BPLC to be addressed by amorphous-silicon thin film transistors, which would accelerate its emergence as next-wave display technology.

Polymer-stabilized optically isotropic liquid crystals for next-generation display and photonics applications

Polymer-stabilized optically isotropic liquid crystals, including blue phases, are emerging as a strong contender for next-generation display technology because they exhibit some revolutionary features such as no need for surface alignment, submillisecond response time, isotropic dark state, and cell gap insensitivity. The basic material properties, including electric field-induced birefringence, dispersion relation of Kerr constant, and temperature dependent Kerr constant, are reviewed. Recent progress on blue phase liquid crystal material development and device structures for lowering the operating voltage are introduced. Promising applications and remaining technical challenges are also discussed.

Alignment layer effects on thin liquid crystal cells

Factors affecting the thin cell performance of a liquid crystal cell are analyzed. Examples based on vertically aligned thin cells are given to illustrate these effects. When the cell gap is below ∼2μm, the liquid crystal alignment material, layer thickness, and anchoring energy all play important roles. The first two factors affect the threshold and on-state voltage, while the last one affects the operating voltage and response time. Three reflective liquid crystal cells are studied experimentally. Good agreement between experiment and theory is obtained.

Direct measurement of electric-field-induced birefringence in a polymer-stabilized blue-phase liquid crystal composite

We demonstrate a method to directly measure the electric-field-induced birefringence of a polymer-stabilized blue-phase liquid crystal (PS-BPLC) composite. The induced birefringence follows the extended Kerr effect well and is approximately 3X the ordinary refractive index change. The measured data are validated by comparing the simulated and measured voltage-dependent transmittance with an in-plane switching cell. The impact of these results to the material optimization of emerging BPLC displays is discussed.

Wide-View and Broadband Circular Polarizers for Transflective Liquid Crystal Displays

A simple wide-view and broadband circular polarizer comprising of a linear polarizer and two uniaxial films is proposed to enhance the viewing angle of transflective liquid crystal displays (LCDs). For the transmissive mode, over the entire 90deg viewing cone, the normalized light leakage from two stacked circular polarizers is suppressed to below 1.5times10-2, and contrast ratio over 10:1 is obtained using a normally black vertically aligned transflective LCD. At the same time, this configuration warrants a broadband operation and reasonably good viewing angle (10:1 contrast ratio is over 40 at all directions) for the reflective mode. The physical mechanisms for achieving broadband operation and wide viewing angle are discussed.

Transflective display using a polymer-stabilized blue-phase liquid crystal

A wide view, submillisecond response, and single-cell-gap transflective display using a blue-phase liquid crystal (BPLC) is proposed. To balance the optical phase retardation between transmissive (T) and reflective (R) regions, in-plane protrusion electrodes are formed with different gaps in the two regions. This display exhibits reasonably high optical efficiency and well matched voltage dependent transmittance and reflectance curves. Using biaxial films and broadband wide-view circular polarizers, the viewing angle with 100:1 contrast ratio is obtained over the entire viewing cone in the T region, and 10:1 over 50 degrees in the R region. The potential application is emphasized.

Fast‐response liquid‐crystal displays using crossed fringe fields

— A fast-response and wide-view liquid-crystal display (LCD) using the crossed fringe-field-switching (CFFS) mode is proposed, where the fringe-field electrodes exist on both the top and bottom substrates. The bottom fringe field is used to turn on the LC directors and the top fringe field is used to assist in the LC decay process. The decay time is reduced by ∼2× compared to that of the conventional FFS mode between the full bright and dark states, and more than a 2× improvement is obtained for other gray-scale transitions. This CFFS mode also preserves the wide-view characteristics as the conventional FFS mode. Its applications to LCD TVs and monitors for reducing image blur are addressed.

Submillisecond response nematic liquid crystal modulators using dual fringe field switching in a vertically aligned cell

A fast response nematic liquid crystal (LC) modulator using dual fringe field switching (DFFS) mode is demonstrated. Both top and bottom substrates have pixel and common electrodes to generate complementary fringing fields. The cell consists of a vertically aligned LC layer whose dielectric anisotropy is positive. In a voltage-on state, self-imposed thin LC walls near the center of the slits and electrodes are formed and the surrounding LC molecules exert a strong restoring force. As a result, submillisecond gray-to-gray response time is achieved. Two DFFS cells are used as examples to illustrate the design principles for display and photonic applications.