Feihong Yu

Reflective twisted nematic liquid crystal displays. I. Retardation compensation

Reflective twisted nematic displays where the output polarizer is eliminated are analyzed and demonstrated. The absence of the rear output polarizer has many advantages, including much higher brightness and higher resolution. In this article, we examine the solution space for the design of such reflective displays. Both the cases of a simple reflective display and the use of a retardation film within the display to compensate for color dispersion are explored. It is shown that excellent black and white displays can be obtained using film compensation. Experimentally, over 90% reflectance from a compensated reflective display has been obtained with low color dispersion. The optical response of this reflective display was also found to be quite fast and suitable for video rate applications.

Comparison of extended Jones matrices for twisted nematic liquid-crystal displays at oblique angles of incidence

Detailed formulas were derived by using Yeh’s formulation of the extended 2×2 Jones matrix and applied to twisted nematic liquid-crystal displays at oblique angles of incidence. Numerical comparisons of this extended Jones matrix method with the exact 4×4 Berreman matrix and with the extended Jones matrix of Lien are presented. The various extended Jones matrix formulations differ in their approach to boundary-condition matching between the model birefringent layers. We show that Yeh’s version is a more accurate approximation to the full 4×4 matrix. This extended Jones matrix method is fast, direct, and simple. It is also physically more intuitive.

Free-form reflector optimization for general lighting

A slope angle-based reflector profile optimization method is introduced at the first time. Compared to the traditional profile-based optimization method, better optimization results are obtained with this method. Design examples of reflectors for general lighting applications are given to compare both types of optimization methods. Disadvantages, such as range definition, range overlapping, and parameter-dependent problems, which existed in the traditional profile-based optimization method can be totally overcome with the proposed method.

Reflective twisted nematic liquid crystal displays. II. Elimination of retardation film and rear polarizer

Reflective twisted nematic liquid crystal displays consisting of just one input polarizer, a liquid crystal cell, and a rear reflector are discussed. We first show that all such display modes reported in the literature can be depicted systematically in a series of parameter space diagrams. Then by making use of such diagrams as a guide, we show that other new high quality reflective display modes can be obtained. The three parameters that are varied are the input polarizer angle α, the liquid crystal twist angle φ, and the cell gap–liquid crystal birefringence product dΔn. A full numerical simulation which takes into account of the liquid crystal director deformation under the application of an electric field was used to optimize such displays. Experimental results agree well with the theoretical predictions.

Particle swarm optimization-based approach for optical finite impulse response filter design.

This study presents what is to our knowledge a new and efficient method for the design of an optical finite impulse response (FIR) filter by employing a particle swarm optimization technique. With the method proposed, the design of an optical FIR filter, which is able to provide an arbitrary spectrum output based on crystal birefringence, could be implemented with good performance and high efficiency. The design procedure is discussed. A typical example of a green/magenta filter used in a liquid crystal on silicon projection display is included to demonstrate the feasibility and efficiency of this method in this design process as compared with simulated annealing.

Iterative finite-difference method for calculating the distribution of a liquid-crystal director

Iterative finite-difference method for calculating the distribution of a liquid-crystal director

Reflective Supertwisted Nematic Liquid Crystal Displays

Supertwisted nematic (STN) liquid crystal displays are widely used commercially. However, there is still room for improvement. In this paper, we discuss reflective STN displays in which the rear polarizer has been removed and no retardation film is used for dispersion compensation. This new design can potentially yield higher brightness than conventional STN displays. They can also have better chromaticity. Numerical calculations and experimental data on such reflective STN liquid crystal displays with twist angles of 190–240° are presented in this paper. These new displays have reasonably steep reflectance-voltage characteristics and can be multiplex-driven like ordinary transflective STN displays. An additional advantage of this new display is the absence of a viewing parallax if the reflector is placed inside the liquid crystal cell.

Design of an elliptic spot illumination system in LED-based color filter-liquid-crystal-on-silicon pico projectors for mobile embedded projection.

We present an elliptic spot illumination system for a color filter-liquid-crystal-on-silicon (CF-LCoS) pico projector employing a specifically designed free-form lens and a cylindrical lens to improve on previous designs in terms of optical efficiency while yielding an ultracompact and low-cost optical architecture. The detailed design description of the optical system is thoroughly investigated. Simulation results coincide well with the theoretical calculation. The single 1  mm×1  mm LED chip-powered optical engine, which employs a CF-LCoS panel with a diagonal of 0.28 in and an aspect ratio of 4:3, has an estimated output efficiency over 9.8% (11.8 lm@1 W) and an ANSI 9-point uniformity over 88.5%, with the ultrasmall volume 24  mm×19  mm×7  mm. Compared to the circular spot-illuminated projection system, a total increment of about 23% of system efficiency is available with this improved optical engine. It is believed that there would be a huge market potential to commercialize our design.

Optical modified signed-digit addition module based on Boolean polarization-encoded logic algebra

The modified signed-digit (MSD) number system satisfies the requirements of totally parallel addition using identical units and enables the addition of any two numbers in three sucessive steps. We show a simple and compact design of the parallel optical addition module based on MSD number representation using Boolean polarization-encoded logic algebra (BPLA). The four transforms of MSD addition are ex- pressed mathematically and the realization of the transform module us- ing liquid crystal devices (LCDs) are also given.

Generalized mixed-mode reflective LCDs with large cell gaps and high contrast ratios

Abstract— A generalized mixed twisted-nematic/birefringent-effect mode reflective LCD is presented. This new mode encompasses all previously published reflective nematic LCD modes and is clearly shown on the parameter space diagrams. We also discuss how to obtain operating conditions of this generalized mixed-mode display with large cell gaps, low color dispersion, and high contrast at low voltages. This operating mode is particularly suitable for reflective crystalline-silicon-backplane active-matrix LCDs.