High-definition vertically aligned liquid crystal microdisplays using a circularly polarized light

A high-definition vertically aligned liquid crystal (LC) microdisplay exhibits a excellent contrast ratio, but its fringing field effect splits the bright state unevenly and leads to a very slow response time. By utilizing a circularly polarized light instead of conventional linearly polarized light, we have overcome the long-standing problems of poor sharpness, low brightness, and slow response time. Confirming computer simulations agree with the experimental results well. This approach can be applied to both reflective and transmissive LC microdisplays

An Optical Method for Pretilt and Profile Determination in LCOS VAN displays

Pretilt angle and cell thickness are two extremely important parameters in predicting the behavior of vertically aligned negative nematic liquid crystal (LC) displays. The accurate estimation of pretilt angle and cell thickness is not a trivial task when these devices work in reflective mode, as in liquid crystal on silicon (LCOS) vertically aligned nematic (VAN) displays. Usual experimental setups are based on the proportionality between the retardation of the polarization components of the incident light and the product effective birefringence times thickness. However, any attempt to separate the two product variables is cancelled out by symmetry from reflection. This work shows a relatively simple method capable of separating both variables, allowing accurate, independent measurements of pretilt and thickness, as well as other configurations details, such as residual twist. A simulation model based on the properties of actual reflective displays has been developed. An experimental setup specifically designed for measuring LCOS VAN cells has been prepared. Initial comparisons between experimental measurements of intensity and theoretical results showed some discrepancies that could be explained assuming that the LC profile contains a residual twist from the manufacturing process. Including that twist in the model, an excellent agreement between theory and experiment has been achieved. Matching simulations and experimental results yield separate determinations of pretilt angle and thickness, and give good estimates for the residual twist angle

Fringe-field-induced out-of-plane reorientation in vertically aligned nematic spatial light modulators and its effect on light diffraction

Liquid crystal (LC)-based spatial light modulators (SLMs) have the ability to shape the wavefront of a light beam and are widely used in applications where phase or amplitude modulation is required. In this work we study the LC director configuration in vertically aligned nematic (VAN) SLMs, with a focus on 1D binary gratings with different driving voltages. By comparing experimental microscopy measurements with simulations, we demonstrate that the director can rotate out of the plane determined by the pretilt of the SLM. By twisting out of the pretilt plane, the formation of a reverse tilt zone in the LC director configuration is avoided. The twist effect is asymmetric and only occurs at the edges where the fringe-field of the high voltage pixel is inclined in the same direction as the pretilt. Due to the out-of-plane reorientation of the director at one side of the pixel, binary gratings show strongly asymmetric diffraction in the pretilt plane. The out-of-plane reorientation also induces changes in the polarisation state of the light beam and the competition between two different out-of-plane reorientation directions may lead to slow switching. It is therefore of utmost importance to consider this effect when using VAN SLMs in applications

Fundamentals of phase-only liquid crystal on silicon (LCOS) devices

This paper describes the fundamentals of phase-only liquid crystal on silicon (LCOS) technology, which have not been previously discussed in detail. This technology is widely utilized in high efficiency applications for real-time holography and diffractive optics. The paper begins with a brief introduction on the developmental trajectory of phase-only LCOS technology, followed by the correct selection of liquid crystal (LC) materials and corresponding electro-optic effects in such devices. Attention is focused on the essential requirements of the physical aspects of the LC layer as well as the indispensable parameters for the response time of the device. Furthermore, the basic functionalities embedded in the complementary metal oxide semiconductor (CMOS) silicon backplane for phase-only LCOS devices are illustrated, including two typical addressing schemes. Finally, the application of phase-only LCOS devices in real-time holography will be introduced in association with the use of cutting-edge computer-generated holograms.This is the final version. It has been published by NPG in Light: Science & Applications here: http://www.nature.com/lsa/journal/v3/n10/full/lsa201494a.html