Hiroyuki Yoshimi

Achromatic Normally Black Twisted Nematic Device with Wide Viewing Angle Using Negative-in-plane Compensation Films

We have approximated the uniformly twisted structure of an ideal compensator for the dark state of a normally black twisted nematic (NBTN) device by stacking several layers of a polymer film having in-plane negative birefringence. It was found from modeling that 4 layers are enough to achieve high contrast and reasonable achromaticity. The computer simulation was supported by measurements of optical performance of compensated single and dual domain TN devices. Head-on contrast of greater than 200:1 is achieved with contrast greater than 20:1 in nearly all viewing directions out to polar angles of 60° for o-mode operation, accompanied by grayscale improvement.

Improvement of optical films for high-performance LCDs

Optical performance of the LCD is strongly affected by optical films such as polarizers and retardation films. The characteristics of polarizers, which determine the contrast ratio and the hue balance of the LCD, need to be improved, in particular, to meet the current requirements on high-performance LCDs. Most polarizers for LCDs are made from polyvinyl-alcohol (PVA) films and iodine compounds by the wet dyeing method. Polarizers with high polarization efficiency and transmittance can be obtained by optimizing the dyeing and stretching conditions. In transmissive LCDs, blue decolorization in black images need to be improved by controlling the chemical species of PVA-iodine complexes. The authors analyzed the dichroic ratios of chemical species by separating each absorption peak, and presented a guide for the neutralization of the hue balance of polarizers. The characteristics of reflective LCDs, on the other hand, are largely dependent on the optical design of circular polarizers and quarter-wave plates, which constitute the circular polarizers. The important design elements of reflective LCDs include wavelength dispersion and viewing angle characteristics. The authors have contributed to the improvement of the performance of reflective LCDs by enhancing the characteristics of polymer films using stretching and optical lamination technologies

26.1: Optical Films for Reflective LCDs to Achieve High Image Quality

Characteristics of reflective LCDs, which have gained a lot of notice in recent years, rely largely on optical design of circular polarizers and the quarter-wave plates, as a component. Important design includes wavelength dispersion, viewing angle, uniformity of display and matching of refractive index. Our work has contributed to improving performance of reflective LCDs by enhancing the characteristics of polymer film using stretching and optical lamination technologies. To design that offers higher contrast and wider viewing angle, we have discovered that it is necessary to control viewing angle variation of the polarizing axis in order to compensate for the viewing angle of the polarizing film as well as the optical anisotropic properties of liquid crystal. Applying this technology to circular polarizers used for reflective LCDs enables design of wide viewing angle circular polarizers. In order to realize higher contrast for reflective LCDs, it is also necessary to design other optical materials including polarizing films. For design of hybrid optical film, it is particularly necessary to reduce surface reflection and interface reflection. This paper also reports our findings concerning this topic.

High-performance optical films for LCDs

Optical performance of the LCD is strongly affected by optical films such as polarizers and retardation films. The characteristics of polarizers, which determine the contrast ratio and the hue balance of the LCD, need to be improved, in particular, to meet the current requirements on high-performance LCDs. Most polarizers for LCDs are made from polyvinyl-alcohol (PVA) films and iodine compounds by the wet dyeing method. Polarizers with high polarization efficiency and transmittance can be obtained by optimizing the dyeing and stretching conditions. In transmissive LCDs, blue decolorization in black images need to be improved by controlling the chemical species of PVA-iodine complexes. The authors analyzed the dichroic ratios of chemical species by separating each absorption peak, and presented a guide for the neutralization of the hue balance of polarizers. The characteristics of reflective LCDs, on the other hand, are largely dependent on the optical design of circular polarizers and quarter-wave plates, which constitute the circular polarizers. The important design elements of reflective LCDs include wavelength dispersion and viewing angle characteristics. The authors have contributed to the improvement of the performance of reflective LCDs by enhancing the characteristics of polymer films using stretching and optical lamination technologies.