Donald B. Taber

Thin-film birefringent devices based on form birefringence

The twisted nematic liquid crystal display (TN-LCD) is the leading technology for high performance flat panel displays. However, the region of high contrast for TN-LCDs is limited. Birefringent elements, of compensators, may be used to provide improved contrast at high viewing angles. The phenomenon of form birefringence has been used to design a compensator that can be fabricated by physical vapor deposition of silica and titania, two common coating materials. Improved viewing angle characteristics, particularly in the horizontal direction, have been demonstrated using the compensator. The 20:1 isocontrast region has been extended to +/- 50 degree(s) in displays incorporating the compensator, an improvement of 10 degree(s) or more relative to uncompensated displays. The compensator design includes integrated antireflection coatings to reduce glare. In this way, display legibility is maximized in the presence of both high and low ambient illumination.

Properties of mixed composition Si/ZnSe and ZnSe/LaF 3 infrared optical thin films

The behavior of codeposited thin films of ZnSe/LaF(3) and Si/ZnSe has been investigated. Mixed ZnSe/LaF(3) films are polycrystalline with intermediate compositions with moderately high compressive stress (1500-2000 kg/cm(2)). Mixed Si/ZnSe films are amorphous with intermediate compositions with low compressive stress (<1000kg/cm(2)). Optical properties of the ZnSe/LaFcm(3) system vary monotonically with composition, but those of the Si/ZnSe system do not, which is explained by the possible chemical reaction of the two species.

Liquid Crystal Tunable Polarization Filter for Target Detection Applications

Many natural materials produce polarization signatures, but man-made objects, typically having more planar or smoother surfaces, tend to produce relatively strong polarization signatures. These signatures, when used in combination with other means, can significantly aid in the detection of man-made objects. To explore the utility of polarization signatures for target detection applications we have developed a new type of polarimetric imaging sensor based on tunable liquid crystal components. Current state-of-the-art polarimetric sensors employ numerous types of imaging polarimeters, the most common of which are aperture division, micropolarizer, and rotating polarizer/analyzer. Our design uses an electronically tunable device that rotates the polarization of incoming light followed by a single fixed oriented linear polarizer. Its unique features include: 1) sub-millisecond response time switching speed, 2) ~75% transmission throughput, 3) no loss of sensor resolution, 4) zero mechanical moving parts, 5) broadband (~75% of center wavelength), 6) ~100:1 contrast ratio, 7) wide acceptance angle (±10°), and 8) compact and monolithic architecture (~10 inch3). This paper summarizes our tunable liquid crystal polarimetric imaging sensor architecture, benefits of our design, analysis of laboratory and field data, and the applicability of polarization signatures in target detection applications.

Ellipsometric measurements applied to liquid crystal display technology

Variable angle transmission ellipsometry has been used to characterize the various elements of the liquid crystal display (LCD) architecture. Ellipsometric data, which are in the form of polarization ellipses as a function of incident angle, are analyzed using the 2 X 2 extended Jones matrix formalism. Information which can be deduced from the ellipsometric data includes the birefringence, cell gap, twist angle, and pretilt angle of the liquid crystal cell, polarization efficiency of the polarizers, as well as the retardation values of birefringent compensators. The ellipsometric method is capable of complete characterization of the polarization state of the transmitted light.

Liquid Crystal Tunable Polarization Filters for Polarization Imaging

We report a new familiy of polarimetric imaging cameras based on tunable liquid crystal components. Our camera designs use a dual frequency liquid crystal tunable filter that rotates the polarization of incoming light, in front of a single linear polarizer. The unique features of this approach include fast switching speed, high transmission throughput, no mechanical moving parts, broad bandwidth, high contrast ratio, wide viewing angle, and compact/monolithic architecture. This paper discusses these tunable liquid crystal polarimetric imaging camera architectures (time division, amplitude division), the benefits of our design, the analysis of laboratory and field data, and the applicability of polarization signatures in imaging.