James E. Anderson

Modeling and Design of an Optimized Liquid-Crystal Optical Phased Array

In this paper, the physics that determines the performance limits of a diffractive optical element based on a liquid-crystal (LC) optical phased array (OPA) is investigated by numerical modeling. The influence of the fringing electric fields, the LC material properties, and the voltage optimization process is discussed. General design issues related to the LC OPA configuration, the diffraction angle, and the diffraction efficiency are discussed. A design for a wide-angle LC OPA is proposed for high-efficiency laser beam steering. This work provides fundamental understanding for a light beam deflected by a diffractive liquid-crystal device.

Methods and Concerns of Compensating In-Plane Switching Liquid Crystal Displays

It is well known that uncompensated in-plane switching (IPS) liquid crystal displays (LCDs) have much better viewing angle than conventional twisted-nematic (TN) LCDs. However, to achieve optimal viewing angle performance in these devices, they must be compensated by one or more films. In this paper, we will study the optimization of such compensation. We will show the benefit of using polarizers which do not have a birefringent substrate. We will also show the effect of which side of the LCD the compensation films are placed. Finally, we will investigate the surprising effect of the pretilt angle on the viewing angle of the compensated IPS LCD.

Performance evaluation of a liquid-crystal-on-silicon spatial light modulator

D optical phased array antennas formed by a liquid crystal on silicon (LCOS) spatial light modulator are described for free-space laser communication and high-resolution wavefront control. The device consists of an 2-D array of 10243768 phase modulator elements, each with controlled voltage, and can induce a phase shift from 0 to 2p for wavelengths up to the near IR. When the device is used as a wavefront corrector, 18.7 waves peak-valley (at 632.8 nm) of aberration in the op- tical system is corrected to a residual of 1/9 wave peak-valley, or 1/30 wave rms. The Strehl ratio improved from 0.006 to 0.83 after correction. An additional linear phase ramp was added to the correction phase ramp to simultaneously correct and steer the laser beam. Continuous steering over 64 mrad in the X-Y plane with a steering accuracy higher than 10 mrad has been obtained. The 1-D beam-steering efficiency is 80% at the maximum steering angle of 4 mrad. These results suggest that an LCOS device can be used to achieve very high-resolution wavefront control at very high efficiency.

Finite-difference time-domain simulation of a liquid-crystal optical phased array

Accurate modeling of a high-resolution, liquid-crystal-based, optical phased array (OPA) is demonstrated. The modeling method is extendable to cases where the array element size is close to the wavelength of light. This is accomplished through calculating an equilibrium liquid-crystal (LC) director field that takes into account the fringing electric fields in LC OPAs with small array elements and by calculating the light transmission with a finite-difference time-domain method that has been extended for use in birefringent materials. The diffraction efficiency for a test device is calculated and compared with the simulation.

Fast Q-Tensor Method for Modeling Liquid Crystal Director Configurations with Defects

A fast Q-tensor method, which can model the configuration of the liquid crystal director fields containing defects, is proposed. Conceptually based on the Oseen–Frank approach, we have added temperature energy density terms in addition to the strain energy term. We have also derived an improved normalization method for fast calculations. The method is used to model the conversion of a reverse tilt wall to a pair of disclination lines.

Improved liquid crystals for vertical alignment applications

Liquid crystals with a large negative dielectric anisotropy are difficult to align vertically on silicon oxide surfaces and sometimes even on polyimides. An interesting method has been found to generate high quality vertical alignment by doping the host liquid crystal with materials that have a cyanogroup along their long molecular axis. The effect is explained by considering both long range and short range interactions between liquid crystal and the alignment layer. Using this method we propose a way to design new liquid crystal mixtures with large negative dielectric anisotropy that have improved aligning ability for applications requiring vertical alignment. The method also allows for increased birefringence.

Modeling and performance limits of a large aperture high-resolution wavefront control system based on a liquid crystal spatial light modulator

The aberration introduced by the primary optical element of a lightweight large aperture telescope can be corrected with a diffractive optical element called the liquid crystal spatial light modulator. Such aberration is usually very large, which makes the design and modeling of such a system difficult. A method to analyze the system is introduced, and the performance limitation of the system is studied through extensive modeling. An experimental system is demonstrated to validate the analysis. The connection between the modeling data and the experimental data is given.

Comparisons of the vector method and tensor method for simulating liquid crystal devices

In calculating the director configuration in a liquid crystal device, two methods are commonly employed: a vector model and a tensor model. In this paper, we compare and contrast these methods for liquid crystal devices consisting of a layer of liquid crystal sandwiched between two plates. We compare the reliability and accuracy of the results, the speed of computation and the complexity of implementations of each method.

Long Term Bistable Twisted Nematic Liquid Crystal Display and Its Computer Simulations

The multidimensional alignment (MDA) technique realized by the polymer wall has been previously proposed as a means to stabilize the liquid crystal configurations for twist angles of 0 and 2π so that very low power and real bistable twisted nematic (BTN) liquid crystal display (LCD) can be obtained. In this study, a two-dimensional liquid crystal director simulation software was employed to explore the stability of BTN devices. The simulation results showed that the homeotropic aligned polymer wall will stabilize the BTN device when the ratio of d/p is close to the switching d/p ratio, but when the d/p ratio is higher than 0.9, the director field will convert the configuration from a high-energy 0 twist state to low-energy 2π twist state automatically, therefore the BTN bistability will be destroyed.

35.4: Significant Speed and Stability Increases in Multi‐Dimensional Director Simulations

Multi-dimensional director calculations have typically taken an inordinate amount of time on all but the fastest computers. In this paper we will show methods for increasing the speed and stability of multi-dimensional calculations such that they can be run on desktop PCs. We will also present an “open-source” algorithm in which these methods are implemented. Details of the algorithms design, accuracy and operation are discussed.