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 compe nsator for the dark state of a normally black twisted nematic (NBTN) d evice by stacking several layers of a polymer film having in-plane neg ative birefringence. It was found from modeling that 4 layers are enou gh to achieve high contrast and reasonable achromaticity. The computer simulation was supported by measurements of optical performance of co mpensated single and dual domain TN devices. Head-on contrast of great er than 200:1 is achieved with contrast greater than 20:1 in nearly al l viewing directions out to polar angles of 60 degrees for o-mode oper ation, accompanied by grayscale improvement.