High-Density Optical Storage
Principal Investigator - Peter Palffy-Muhoray
Laser-written image (2cm x 2cm) of Telly Savalas, written in a twisted nematic cell.
(Photo from Nature, copyright 1978, Sid Avery).
Liquid crystals are widely used for flat-screen optical displays, but not yet for optical data storage media. Until recently, such applications were limited by the difficulties of encoding gray-scale images and the complexity of writing and rewriting. ALCOM researchers, in cooperation with Hercules, Inc., have been able to solve these problems, demonstrating the formation of continuous gray-scale images using polarized-light alignment of liquid crystals. Continuous variation of the liquid crystal orientation yields striking high-resolution gray-scale images, with data-storage densities of above 3 gigabits per square inch now possible.
FEATURES
Projection Light Valves
Principal Investigator - Philip J. Bos
The key to bright projection systems for television and electronic movie projectors is an efficient light valve. While liquid crystals are often considered for these applications, LCDs using polarizers have undesirable light loss. A projection system that does not have this loss is preferable, and is being developed by ALCOM researchers.
This system, called the Optically Active Diffractive (OAD) device, makes use of the phenomenon of diffraction and a Schlieren optical system. Initial experiments on the usefulness of this device have been encouraging. Researchers at Florida Atlantic University, working with ALCOM researchers, have measured 94% light throughput and contrast ratios of over 900:1.
FEATURES
Four-Domain Pixel
Principal Investigator - Philip J. Bos
The four-domain twisted nematic (TN) pixel is a theo-retical solution for improving the viewing angle of gray scale Active Matrix Liquid Crystal Display (AMLCD) devices. ALCOM Center researchers invented and are perfecting three techniques for producing a display with four-domain pixels.
Liquid crystal structure of
a four-domain pixel.
This work, combined with other ALCOM activities, will provide U.S. companies with the best methods for improving the wide-angle view of AMLCD technologies.
Display Modeling Software
Principal Investigator - Jack R. Kelly
Two modeling software programs have
resulted from ALCOM research. Twist Cell Optics, introduced in 1994, calculates director configurations and optical performance of user-specified display configurations and parameters.
The newest program, LC2D, has all the capabilities of Twist Cell Optics with added dimensionality. It can be used to study defects at pixel edges or to model optics of inherently two-dimensional display modes such as in-plane switching or homeotropic EOC mode. It has both static and dynamic optical performance. The program provides a realistic description of optical performance including most layers usually found in a liquid crystal display such as polarizers, retarders, substrates, alignment layers, ITO, and liquid crystal.
Optical Diode
Principal Investigator - Oleg D. Lavrentovich
Researchers at the Liquid Crystal Institute invented a nematic cell that responds only to one polarity of the applied electric field.
The cell is transparent for polarized light if the positive voltage is applied (fig. 1) but blocks the light when the opposite negative voltage is applied (fig. 2). The physical mechanism that governs the behavior of this optical diode is the orientation of molecular dipoles.
Figures 1 & 2
Switchable Window
Principal Investigators - J.W. Doane and John L. West
Photos courtesy of Marvin
Windows & Doors
Polymer dispersed liquid crystals were invented at Kent State University in 1983. A major application of these materials is in switchable windows.
The windows change from opaque to clear with the flip of a switch. Popular uses are glass walls in offices, conference rooms, lobbies, and store fronts. Privacy glass also provides unique opportunities for use by homeowners in bathrooms, entryways, family rooms, bedrooms, and skylights. The windows use the same voltage as standard household appliances. Multiple windows can be controlled from one switch and can be connected to a timer.
In the scattering (opaque) state, the glass diffuses direct sunlight and eliminates 99% of the UV rays that fade carpet and furniture.
How it works:
PDLCs operate on the principle of electrically controlled light scattering. They consist of liquid crystal droplets durrounded by a polymer mixture sandwiched between two pieces of conducting glass. When no electricity is applied the liquid crystal droplets are randomly oriented, creating an opaque state. When electricity is applied the liquid crystals align parallel to the electric field and light passes through, creating a transparent state
FEATURES
Allows total privacy or
unobstructed viewing
Diffuses annoying sunglare
Reduces solar heating
Limitless designpossibilities
Low power
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