Liquid Crystal On Silicon Microdisplay Research Articles

Polarimetric analysis of cross-talk phenomena induced by the pixelation in PA-LCoS devices

Liquid crystal on silicon (LCoS) microdisplays are an element commonly found in advanced photonic applications. Phase-only modulation and spatial light modulators (SLMs) use parallel-aligned LCoS (PA-LCoS) microdisplays due to their large resolution and small pixel size. However, the crosstalk between neighbouring pixels induces several phenomena, i.e. the smoothing of the electric field in the interpixel region known as fringing fields, out-of-plane reorientation of the liquid crystal director, and diffraction effects due to the finite pixel grid pattern. These effects degrade the performance in SLM applications. Therefore, a rigorous numerical analysis is carried out based on a full 3D model that estimates the LC director distribution of the PA-LCoS microdisplay through uniform applied voltages. Once the LC director distribution is known, a numerical finite-difference scheme simulates light propagation across the structure. Here, the impact of crosstalk is analysed from the polarimetric point of view for different pixel and interpixel sizes. It has been found that the finite-patterned pixel scheme induces the phenomena previously addressed, degrading the responses of the Stokes vector components S0, and S1 and also the degree of polarization (DOP). Furthermore, the impact over these parameters is generally inversely proportional to the fill factor. To isolate the influence of diffraction, out-of-plane, and fringing fields effects is challenging since all phenomena are mixed in both time and space, however we have found some useful trends.

Design of Diffraction Limited Head Mounted Display Optical System Based on High Efficiency Diffractive Elements

A diffraction limited optical system for head mounted displays (HMDs) was designed. This optical system consists of four modules, including 1:5 mm and 5:30 mm beam expanders, polarization grating-polarization conversion system (PG-PCS) and refractive/diffractive projection optical module. The PG-PCS module transforms the unpolarized Gaussian beam to a linearly polarized beam and it simultaneously homogenizes the spatial intensity profile. The optical projector module has a 30° field of view, a 22 mm eye relief, and a 10 mm exit pupil diameter with a compact structure. Common acrylic materials were utilized in the optical design process; therefore, the final optical system was lightweight. The whole optical system is suitable for a 0.7 inch liquid crystal on silicon microdisplay (LCOS) with HDTV resolution (1920×1080) and 8.0 μm pixel pitch.

LCoS SLM Study and Its Application in Wavelength Selective Switch

The Liquid-Crystal on Silicon (LCoS) spatial light modulator (SLM) has been used in wavelength selective switch (WSS) systems since the 1990s. However, most of the LCoS devices used for WSS systems have a pixel size larger than 6 µm. Although there are some negative physical effects related to smaller pixel sizes, the benefits of more available ports, larger spatial bandwidth, improved resolution, and the compactness of the whole system make the latest generation LCoS microdisplays highly appealing as the core component in WSS systems. In this review work, three specifications of the WSS system including response time, crosstalk and insertion loss, and optimization directions are discussed. With respect to response time, the achievements of liquid crystal material are briefly surveyed. For the study of crosstalk and insertion loss, related physical effects and their relation to the crosstalk or insertion loss are discussed in detail, preliminary experimental study for these physical effects based on a small pixel LCoS SLM device (GAEA device, provided by Holoeye, 3.74 µm pixel pitch, 10 megapixel resolution, telecom) is first performed, which helps with predicting and optimizing the performance of a WSS system with a small pixel size SLM. In the last part, the trend of LCoS devices for future WSS modules is discussed based on the performance of the GAEA device. Tradeoffs between multiple factors are illustrated. In this work, we present the first study, to our knowledge, of the possible application of a small pixel sized SLM as a switching component in a WSS system.

Microdisplay‐based industrial 3‐D and microstructure measurement systems

Abstract— Microdisplays, whether they are of the liquid‐crystal‐on‐silicon (LCOS) or organic light‐emitting diode (OLED) type, have been, up until now, mainly used in multimedia applications or head‐mounted displays. Due to their interesting possibilities, these displays open more and more alternative applications; for example, in optical metrology. Projection lenses for this application area need to be specially designed because the requirements on these systems differ completely from those for multimedia applications. The lenses must have very low geometrical image distortion and they have to be adapted to small objects and/or image distances. On the other hand, they often work with light sources with small spectral bandwidths; consequently, they do not need to be corrected for chromatic aberrations. In addition, the numerical aperture has to be large enough to collect and transfer as much light as possible, but also the size of the projection lens has to be as small as possible to ensure compact measurement systems. All these requirements lead to a compromise in optical lens design. Three optical system designs and realizations — one with an OLED microdisplay and two with an LCOS microdisplay — are presented.

Invited Paper: The evolution of projection displays: From mechanical scanners to microdisplays

Abstract— The development of electronic projection systems from its earliest days in the 1930s to the present will be reviewed. Early projection systems were dominated by cathode‐ray tubes (CRTs) and mechanical scanners (Scophony). Until the invention of the Eidophor oil‐film light‐valve (LV) projector in the 1940s, there was no all‐electronic alternative to CRTs. Oil‐film LVs and CRTs dominated projection until the introduction of the first liquid‐crystal‐device (LCD) light‐amplifier system by Hughes. Today, the oil‐film LV has vanished and the CRT is vanishing. The light amplifier has morphed into several variations of liquid crystal‐on‐silicon (LCoS). Mechanical scanners are starting to be re‐introduced for laser display systems. However, transmissive LCDs, the digital micromirror device (DMD), and LCoS microdisplays dominate the projection‐display market today. In addition to discussing the projection systems themselves, certain key component technologies that have made modern projection systems possible will be discussed.

Fast-switching liquid-crystal-on-silicon microdisplay with framebuffer pixels and surface-mode optically compensated birefringence

A 64×32 liquid-crystal-on-silicon (LCOS) backplane with a novel framebuffer pixel array has been designed and fabricated using the AMI Semiconductor 0.5-µm double-poly triple-metal CMOS process. The pixel circuit described herein increases the brightness significantly without sacrificing image contrast ratio. Characteristics of various liquid-crystal modes applicable to field sequential color displays have been investigated. The LCOS microdisplay, employing an optimized optically compensated birefringence mode, demonstrates fast response times (OFF=0.3 ms, ON=1.2 ms) enabling a frame rate of 720 Hz, with a potentially high contrast ratio of up to 1600:1.

39.4: Fast Switching VA Mode LCOS for Single Panel Application

Reflective LCOS (liquid crystal on silicon) microdisplays are widely used in various projection and near-eye application. For single panel projection system, liquid crystal response time is an important variable. The panel must switch fast enough to support field color sequential display with high field rates. In order to have fast response and good contrast, a vertical alignment (VA) cell was used in this study. In this study, we report cell design results of single panel VA mode LCOS. By simulation, with suitable selection on LC parameters like temperature, viscosity, elastic constant and birefringence, it is possible to get response time of around 2ms from a 2.0 um-thick vertical alignment cell. The experimental result also indicated good consistency with simulation from room temperature to 45 degree C.

P‐102: High‐Resolution Microencapsulated Electrophoretic Display on Silicon

AbstractThe first high‐resolution microencapsulated electrophoretic display on silicon has been demonstrated using a 400ppi LSI (large‐scale integration) silicon backplane designed for LCoS (liquid crystal on silicon) micro‐displays. A micrograph analysis method was developed to quantify the optical performance at the ink capsule level and calculate contrast ratio and contrast modulation as a function of effective resolution.

High-contrast, fast-switching liquid-crystal-on-silicon microdisplay with a frame buffer pixel array

A 64 x 32 liquid-crystal-on-silicon (LCOS) microdisplay with a frame buffer pixel architecture is described. The advantage of frame buffer pixel circuits is an increase in brightness and image contrast ratio. The increase in brightness is attributed to maximizing the overall image viewing time, allowing an image to be displayed at full contrast while the next image is loaded onto the pixels. The LCOS microdisplay employs a fast-switching optically compensated birefringence mode that operates at a 720-Hz frame frequency with a potentially high contrast ratio.

Novel Frame Buffer Pixel Circuits for Liquid-Crystal-on-Silicon Microdisplays

A 32 /spl times/ 16 liquid-crystal-on-silicon (LCOS) backplane with novel frame buffer pixels is designed and fabricated using the AMI Semiconductor's 0.5-/spl mu/m double-poly triple-metal CMOS process. The three novel pixel circuits described herein increase the brightness of an XGA LCOS microdisplay by at least 36% without sacrificing image contrast ratio. The increase of brightness is attributed to maximizing overall image view time, allowing an image to be displayed at full contrast while the next image is buffered onto the backplane. The new circuits achieve this by removing charge sharing and charge inducement problems shown in previously proposed frame buffer pixel circuits. Voltages on the pixel electrodes measured through rail-to-rail operational amplifiers with negative feedback vary from 0 to 4.25 V (6-V power source). All data voltage levels remain constant over a frame time with less than 1% drop, thus ensuring maximum contrast ratio. Modeling and experimental measurement on the fabricated chip show that these pixel circuits outperform all others to date based on storage time, data storage level, and potential for highest contrast ratio with maximum brightness.

Methods for measuring performance of LCoS microdisplays

Abstract— Liquid‐crystal‐on‐silicon (LCoS) microdisplays have unique measurement requirements not shared by direct‐view flat‐panel displays. We developed a series of measurement techniques for measuring reflectance, contrast ratio, and uniformity of LCoS microdisplays. Reflectance is determined by comparing light reflected off of the microdisplay in its “white” state with that reflected off of a calibrated mirror. Several corrections are applied to take into account polarization differences between the reference measurement and display measurement. Contrast ratio is determined by measuring display reflectance in the “white” and “black” states. Reflectance and contrast data can be reduced to scalar values once the spectral content of the intended illumination source is defined. There are several methods for measuring uniformity of contrast and reflectance. An approach that we have developed closely follows the sampled uniformity measurements outlined by VESA for direct‐view displays (Ref. 1).