Phase masks are used to eliminate the Fourier-plane hotspot that otherwise degrades holographic data storage
performance. In order to eliminate the cost, bulk, and precision alignment difficulties of inserting a discrete phase mask
into an optical system we have designed phase masks integrated directly into the structure of a spatial light modulator
used as the storage system's write head. A micron-thick ferroelectric liquid crystal film is confined between the surface
of a VLSI integrated circuit and a window containing planarized relief structures on its inward-facing surface. This
arrangement avoids depth-of-field problems encountered by designs that place the phase mask on the outer surface of the
window. Any of a variety of phase mask designs can be implemented in this fashion. An alternative architecture in
which pixel surfaces of the CMOS VLSI backplane are etched to differing heights is also investigated.
We report design and test of a high brightness laboratory-breadboard LED/LCOS HMD system employing a 0.78-inchdiagonal
1280× 768 ferroelectric liquid-crystal-on-silicon microdisplay and a red-green-blue LED. With an 8× viewing
optic giving a 35°-diagonal field of view, the system yielded brightnesses greater 40,000 cd/m<sup>2</sup> (12,000 fL) in colorsequential
mode and greater than 100,000 cd/m<sup>2</sup> (30,000 fL) in monochrome mode, at LED power consumptions of
1.1 W and 3.3 W, respectively. The illumination optics employed a rectangular light pipe and tailored diffuser to efficiently
fill the microdisplay panel aperture and exit pupil. The high efficiency of such image generators facilitates
display readability in see-through HMDs operating in high-ambient-light environments, as well as enabling ultra-low
power HMDs (less than 100 mW total) for dismounted users of battery-powered systems.
The stressed liquid-crystal (SLC) electro-optic effect promises fast electro-optic response times even for design wavelengths
in the infrared (IR). Here we report characteristics of SLC devices appropriate for use as liquid-crystal-onsilicon
(LCOS) spatial light modulators (SLMs) in the near ( λ = 1.8-2.5 μm), mid (3-5.5 μm) and far (8-14 μm) IR
bands. For these three bands we fabricated SLC devices with 5, 10, and 20 μm thicknesses; at drive voltages of 25, 50,
and 125 V respectively these devices gave half-wave modulation with response speeds in the 1.3-1.6 ms range. Visiblelight
measurements on a 20-μm-thick SLC device between crossed polarizers gave a contrast ratio of 360:1 which
improved to nearly 18,000:1 with a Babinet-Soleil compensator offsetting residual SLC retardance. Widely available
high-voltage options in standard CMOS processes offer sufficient drive for near- and mid-IR SLCOS devices; with
modest increase of SLC material birefringence Δn and dielectric anisotropy Δε far-IR devices would be feasible, too.
Pixel drivers utilizing these options have pitches less than 24 μm, making 1000 ×1000 SLMs feasible.
The road from a new technology's proof-of-principle prototype to commercially successful products always seems to be more challenging, more expensive, and longer than its inventors had imagined. Displaytech built its first experimental FLC-VLSI SLMs in 1989, began ramping up its efforts to commercialize FLC-VLSI displays around 1995, and now is building more than 100,000 displays per month with its manufacturing partner Miyota. Here we review the motivation for using FLC-VLSI technology and trace the developments that were necessary for its commercialization. We discuss problems that had to be overcome in FLC materials, device design, manufacturing, applications, product definition, and systems support in order to develop the technology and to lower barriers to its adoption by customers. The principal focus here is on technical challenges encountered in manufacturing and in FLC materials development that had to be met to go from hand-built prototypes to mass production. We also review future potential markets other than displays and describe some of our work on experimental FLC-VLSI devices that addresses those opportunities. Examples include holographic optical data storage, 3D projection, optical image processing, smart-pixel SLMs, and high-speed computer interfaces needed to support high frame rate SLMs.
we demonstrate that with a single manufacturing process and custom FLC materials, individual reflective FLC SLMs can be optimized for a wide range of chosen wavelength regions. One lot of 256 X 256 SLM cells were prepared from a single silicon wafer. These cells were filed wit five different FLC materials having birefringence spanning a range from 0.129 to 0.218. The resulting retardance variation allowed SLM characteristics to be tailored to give optimized performance in any wavelength region from 400nm to 1000nm.
We present a binary reflective spatial light modulator (SLM) constructed using a patented ferroelectric liquid crystal (FLC) technique. The device is built atop a planarized 0.6 micrometer CMOS SRAM backplane with 15 micrometer pixel pitch and 88% fill factor. The device achieves better than 25% optical throughput when used with collimated laser light and better than 100:1 contrast when oriented for amplitude modulation. When oriented for phase modulation, the device achieves 180 degrees of phase shift between its 2 states. The device can be operated as fast as 5 kHz with complete switching of the liquid crystal. Applications in the fields of optical computing and optical information processing are suggested.
We report prototype active-matrix liquid crystal spatial light modulators using ordinary silicon integrated-circuit backplanes and incorporating a fast-switching ferroelectric liquid crystal light modulating layer at the backplane's surface. Backplanes reported here utilize a fully- planarized three-metal CMOS process for improved optical throughput, contrast, and light tolerance. We report a 256 X 256 device with 15 micrometers SRAM pixels having 87% fill- factor, optical throughput of 36 - 45%, contrast ratio of 80:1, and electrical rise/fall times of 85 microsecond(s) . We also report DRAM arrays with pixel pitches of 7.5 micrometers and 5.7 micrometers , with fill factors of 75% and 69%, respectively.
Single-crystal ultra-thin (< 100 nm) silicon on sapphire (UTSOS) has been fabricated using solid-phase epitaxy and regrowth techniques to produce a high quality semiconductor material on a transparent substrate ideal for active-matrix liquid crystal display (AMLCD) applications. MOS devices fabricated in this material have lower leakages, small thresholds, and higher transconductances than those fabricated in conventional unimproved SOS.
We have made 128 X 128 and 256 X 256 spatial light modulators using active backplanes fabricated through a commodity silicon foundry and incorporating a thin ferroelectric liquid crystal light modulating layer at the backplane's surface by means of postprocessing of individual foundry die. These electrically addressed devices exhibit optical rise and fall times as short as 105 microsecond(s) , with contrast ratios in images as high as 100:1, and in zero-order diffracted light as high as 200:1. Total optical throughput to the zero-order diffracted beam exceeds 10% for the 256 X 256 devices and 17% for the 128 X 128 devices. Frame update times shorter than 100 microsecond(s) , corresponding to image information throughput of greater than 80 MBytes/s, were realized by employing pipelining techniques in conjunction with a wide digital input word.
We report here on analog modulation effects in ferroelectric liquid crystal (FLC) materials and electrical drive schemes that are appropriate to FLC/VLSI spatial light modulations (SLMs). The deformable-helix ferroelectric (DHF) effect paired with fixed-charge drive can give sub- millisecond grey-scale response with VLSI-compatible drive voltages. New DHF materials with long-pitch nematic phases give superior alignment quality and contrast ratio. We present analog FLC driver circuits suitable for VLSI implementation, and show that providing adequate read/write isolation in optically addressed FLC/VLSI SLMs requires special care.
The fabrication of ferroelectric-liquid-crystal (FLC) light modulators directly atop silicon integrated-circuit (IC) active backplanes makes possible a new family of spatial light modulators (SLMs). Both FLC and IC characteristics play a role in determining the hybrid SLM''s performance capabilities. Total element number is limited to about 1000 x 1000 by current VLSI resolution and die-size constraints. SLM frame times are limited to about 100 microns by FLC response times for element numbers below about 256 x 256 and by IC power dissipation and electronic interconnect bandwidth above that size. Corrugations on the IC surface produced by the VLSI processing can cause severe intrapixel optical wavefront nonuniformity, but elements on the prototypes whose reflectors are restricted to circuitry-free regions have peak-to-valley roughness of less than 0.1 micron across a single pixel. Standard silicon foundry IC dies yielded SLMs flat to about a quarter-wave at 546 nm across a 5-mm aperture.
A parametric analysis is conducted for device and system design issues associated with the miniaturization of a hybrid optical correlator that incorporates an electronically addressed liquid-crystal spatial light modulator (SLM). Attention is given to the requirements of drive and readout electronics, as well as the associated optics. The parametrics resolve around the SLM, which is the correlator size-limiting element; emphasis is accordingly placed on the importance of small pixel pitch and minimization of ''dead space'' in order to maximize the miniaturized correlator''s performance.