Xiangyi Nie

Anchoring energy and cell gap effects on liquid crystal response time

The anchoring energy and cell gap effects on liquid crystal response time (τ0) is analyzed theoretically and validated experimentally. Analytical expressions are derived using two different approaches: effective cell gap and surface dynamic equation methods. Consistent results are deduced from these two approaches. A simplified equation τ0∼dx also fits the experimental data well, where d is the liquid crystal cell gap and x is the exponent. Under two extreme (strong and weak) anchoring limits, the exponent x approaches 2 and 1, respectively. This information is helpful for optimizing liquid crystal devices for display applications.

Pretilt Angle Effects on Liquid Crystal Response Time

Pretilt angle effect on liquid crystal dynamics is analyzed theoretically. Analytical expressions are derived to describe liquid crystal response time under nonzero pretilt angle conditions. The theoretical analysis is confirmed experimentally using vertically aligned liquid crystal cells. This finding quantitatively correlates pretilt angles with liquid crystal response time. This study improves the understanding of the liquid crystal dynamic process which is helpful for optimizing liquid crystal response time.

Polar anchoring energy measurement of vertically aligned liquid-crystal cells

An electric-field method is developed for measuring the polar anchoring energy of vertically aligned nematic liquid-crystal cells. Both theoretical analyses and confirming experimental results are presented. Vertically aligned liquid-crystal cells with buffed polyimide alignment layers are used to investigate the measurement techniques. Based on the voltage-dependent transmittance of the liquid-crystal cells, a linear fitting can be obtained, leading to a precise determination of the anchoring energy. If some specific liquid-crystal material parameters are known, measuring of the cell capacitance is not necessary.

Axially-symmetric sheared polymer network liquid crystals

An axially-symmetric sheared polymer network liquid crystal (SPNLC) device is demonstrated and its performances characterized. Through analyzing the structure of this axially-symmetric SPNLC, we constructed a 3-D model to explain the observed phenomena. The simulation results agree well with the experiment. Two potential applications of such an axially-symmetric SPNLC, namely tunable-focus negative lens and spatial polarization converter, are discussed.

Dual-Frequency Addressed Infrared Liquid Crystal Phase Modulators with Submillisecond Response Time

Dynamic response of a dual-frequency liquid crystal (DFLC) based near infrared phase modulator is investigated through numerical simulations and experiments. The relationships between the optical response times and various voltage driving conditions are studied. An optical phase retarder operating at 1.55 μm wavelength is demonstrated by using our homemade high figure-of-merit DFLC mixture. To improve the response time, both dual- frequency addressing and high voltage overdrive methods are employed. The obtained optical rising and decay times are reduced to less than 0.5 ms for a 2π phase change. The optical transition curves simulated with finite element method show good agreement with our experimental results.

Cell Gap Effect on the Dynamics of Liquid Crystal Phase Modulators

This paper provides a complete physical picture of optical response time as a function of cell gap (d) in a wide voltage regime. Normally both rise and decay times are known to be proportional to d 2 in the small angle approximation ( ), and in the high voltage regime where V π < V < V i the optical decay time is independent of d. In this paper, we found that between these two extremes there is a region where the response time is linearly proportional to d. Our analytical derivation is confirmed by experimental results.

Second and Fourth Harmonic Frequencies in Electric Field-Induced Liquid Crystal Reorientations

The second and fourth harmonics of low frequency electric field-induced liquid crystal reorientations are analyzed theoretically and confirming results observed experimentally. These transient dynamic optical responses manifest when the phase of a homogeneous cell is nearby Nπ or , where N is an integer. These ripples would influence the grayscales of liquid crystal devices if the driving electric field frequency is comparable to the liquid crystal response rate.

Dopant-Enhanced Vertical Alignment of Negative Liquid Crystals

A simple method for achieving high-contrast vertical alignment of high birefringence (Δn ∼ 0.28) negative dielectric anisotropic liquid crystal mixture using buffed polyimide substrates is demonstrated. By doping a positive, or non-polar dielectric anisotropic compound or mixture to the laterally difluorinated tolane liquid crystal host, an excellent vertical alignment was obtained. This alignment is stable throughout the entire nematic range. Its application for large screen liquid crystal televisions is considered.

Color performance of an MVA-LCD using an LED backlight

Ruibo Lu (SID Member) Xiangyi Nie Shin-Tson Wu (SID Fellow) Abstract — The color performance, including color gamut, color shift, and gamma curve, of a multidomain vertical-alignment (MVA) liquid-crystal display (LCD) using an LED backlight are calculated quantitatively. Simulation results indicate that an LED backlight exhibits better angular color uniformity and smaller color shifts than a CCFL backlight. Color gamut can be further widened and color shift reduced when using a color-sequential RGB-LED backlight without color filters, while the angular-dependent gamma curves are less influenced using different backlights. The obtained quantitative results are useful for optimizing the color performance and color management of high-end LCD monitors and LCD TVs.

Molecular Alignment of Axially-Symmetric Sheared Polymer Network Liquid Crystals

An axially-symmetric sheared polymer network liquid crystal (AS-SPNLC) device is demonstrated and its performances characterized. The formation mechanism of the AS-SPNLC is investigated by observing the dynamic pattern change of the structure during the fabrication process. We also analyze the structure from the electro-optic properties and then construct a simulation model to explain the observed phenomena. Several potential applications, such as tunable-focus negative lens and spatial polarization converter, are discussed.