HKUST Generalized Mixed-Mode Reflective LCDs for Three Panel Color Projection Applications (+Improved Projector Optics) J Chen, P W Cheng, H C Huang and H S Kwok C enter for D isplay R esearch Hong Kong University of Science & Technology S K Kwok, C S Li and Steve Yeung V aritronix L td, Hong Kong

HKUST Silicon Microdisplays High aperture ratio at high resolution Twisted nematic modes or ECB mode More difficult reflective optics: e.g. PBS - small acceptance angle

HKUST Observation At any voltageT = T(  d  n) For a single polarizer reflective display R = R(  d  n) Therefore, T or R can be plotted as a function of 2 variables by fixing the third or fourth variable - parameter space

HKUST For reflective display with one polarizer Reflective displays

HKUST Parameter Space Diagrams for Reflective Displays

HKUST Parameter Space Diagrams for Reflective Displays - effect of change in polarizer angle ECB

HKUST Both NW and NB modes are possible (//-// polarizers) NB NW Better nomenclature: In-well and out-well modes

HKUST In-well and out-well modes Note: No retardation film

HKUST Electro-optic properties of in-well and out-well modes

HKUST Relationship between various MTB modes (Mixed TN-Birefringence modes)

HKUST Can optimize these MTB modes using various objectives: e.g. least dispersion (for B/W displays) or highest contrast (low voltage operation). Least dispersion criteria: Define Y =  R/R within nm for the bright state. Search in parameter space to find (  d  n) with smallest Y. Highest contrast criteria: Define

HKUST Least Dispersive Modes Needed for B/W displays Also for color displays with one type of panel

HKUST High Contrast Modes - Contrast Parameter Space PS is obtained for V=0 Take V ns = 0 and use appropriate V s from RVC and calculate new PS Calculate R ns and R n and take the ratio to get the Contrast PS (CPS) Contrast is given by R s /R ns for NB mode or R ns /R s for NW mode

HKUST Example of CPS for reflective LCD SCTN mode has highest contrast for the same voltage, but dispersion is large

HKUST Viewing Angle of Light Valves Not an issue with present PBS designs (10 o acceptance angle) Will be an important issue with new improved optical elements Strongly dependent on operating voltages and LCD modes

HKUST Viewing angle of MTB mode - importance of operating voltage V3V 4V4V ±10 o for CR = 250± 4 o for CR = 125

HKUST Normally Black Modes with PBS (Out-well modes)

HKUST Compact Projection System MH lamp PBS B-LCD G-LCD R-LCD Trichroic prism A A B c

HKUST S-P polarization split of color filters The reflectance spectrum of a color filter coating depends on the polarization of the incident light The polarization of light is modified by the reflective LCOS light valve -> The color separator and recombiner operate at reverse polarizations -> Have to reduce s-p polarization split

HKUST  = 45 o This is actually the principle of PBS! Needs smaller incidence angles ps Reflectance Polarization split is strongly dependent on incident angle  

HKUST  has to be at least 24 o for conventional TPA   Blue Red + Green coating

HKUST The PBS does not have to be cubic! blue green Both coatings have  = 16 o *patent pending red

HKUST Comparison of 24 o and 16 o TPA Measured with prisms made at Zhejiang University

HKUST Summary Have shown that PS is a good tool for the optimization of MTB modes for reflective displays For 3 panel color projector, contrast is more important than dispersion Viewing angle will be an important issue for wide acceptance angle PBS Have demonstrated a new trichroic prism assembly which is compact and can perform color separation and recombination satisfactorily