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J Chen, P W Cheng, H C Huang and H S Kwok

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

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J Chen, P W Cheng, H C Huang and H S Kwok

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  1. 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 Center for Display ResearchHong Kong University of Science & Technology S K Kwok, C S Li and Steve Yeung Varitronix Ltd, Hong Kong

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

  3. Observation At any voltage T = T(a, g, f, dDn) For a single polarizer reflective display R = R(a, f, dDn) Therefore, T or R can be plotted as a function of 2 variables by fixing the third or fourth variable - parameter space

  4. Reflective displays For reflective display with one polarizer

  5. Parameter Space Diagrams for Reflective Displays

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

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

  8. In-well and out-well modes Note: No retardation film

  9. Electro-optic properties of in-well and out-well modes

  10. Relationship between various MTB modes (Mixed TN-Birefringence modes)

  11. 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 = DR/R within 450-700nm for the bright state. Search in parameter space to find (a, f, dDn) with smallest Y. Highest contrast criteria: Define

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

  13. High Contrast Modes - Contrast Parameter Space • PS is obtained for V=0 • Take Vns = 0 and use appropriate Vs from RVC and calculate new PS • Calculate Rns and Rn and take the ratio to get the Contrast PS (CPS) • Contrast is given by Rs/Rns for NB mode or Rns/Rs for NW mode

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

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

  16. Viewing angle of MTB mode - importance of operating voltage 250 125 3V 4V ± 4o for CR = 125 ±10o for CR = 250

  17. Normally Black Modes with PBS (Out-well modes)

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

  19. 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

  20. Polarization split is strongly dependent on incident angle p s Reflectance q = 45o q = 16o This is actually the principle of PBS! Needs smaller incidence angles

  21. q has to be at least 24o for conventional TPA q coating Red + Green q Blue

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

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

  24. 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

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