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Optical compensation design of vertically aligned LC cell using wide view circular polarizer Je-Wook Moon, Byung-June Mun, Dong-Eon Lim and Gi-Dong Lee Department of Electronics Engineering, Dong-A University, Busan 604-714, Korea Dong-A University 1 Display Device Lab Outline ▷ What are required for LCD applications ? ▷ Light leakage of the conventional circular polarizer in oblique direction ▷ Optical Design on the Poincaré sphere ▷ Calculation results ▷ Conclusion Dong-A University 2 Display Device Lab Ⅰ. What are required for LCD applications ? High Brightness Wide Viewing Angle High Contrast Ratio Highly ‘interesting’ Color Gamut Fast Response Time Thin, Lightweight Low Power Consumption Cost Competitiveness Dong-A University 3 Display Device Lab 450 nm 550 nm 630 nm Ⅱ. Light leakage in the oblique direction ▣ Polarization of the conventional circular polarizer on the Poincaré sphere Fig.(b) Polarization states in the oblique direction Fig.(a) Basic circular polarizer configuration Off-axis light leakage in the dark state occurs in the conventional circular polarizer for the transmissive mode Dong-A University 4 Display Device Lab Ⅱ. Light leakage in the oblique direction ▣ Optical transmittance of the conventional circular polarier We improve the optical performance of the circular polarizer at the diagonal direction (θ=70°, Φ=45° ). Dong-A University 5 Display Device Lab Ⅱ. Light leakage in the oblique direction ▣ Requirements for operating on the Poincaré sphere 1). Numerical analysis of the uni-axial retardation film (1) Deviation angle for any A-plate (Polarizer) o c sin 2c sin 2 (o / 2) sin( o) 1 (sin c sino )2 : azimuth angle of the optical axis ne : extraordinary refractive index of retardation film no : ordinary refractive index of retardation film d : thickness of the film (2) Phase-retardation for C-plate and VA LC 2 sin 2 sin 2 C no d 1 1 2 2 n n e o : polar angle of the incident light in the LC layer : polar angle of the incident light in free space : azimuth angle of the incident light : wavelength of the incident light (3) Phase-retardation for A-plate 12 12 2 sin 2 sin 2 sin 2 cos2 sin 2 no 1 d n 1 2 e ne2 no2 n o Reference: Optics of Liquid Crystal Displays, Pochi Yeh and Claire Gu, Ch. 8. X. Zhu, Z. Ge, and S.-T. Wu, J. Display Technology, Vol. 2, pp. 2-20 (2006). Dong-A University 6 Display Device Lab Ⅱ. Light leakage in the oblique direction ▣ Requirements for operating on the Poincaré sphere 2). Numerical analysis of the bi-axial retardation film 1. Interface coordinate system x kt Region 2 Region 1 -. principal dielectric axes, laboratory coordinate system -. Euler angles (Φ, ρ and ψ) in the x convention -. permittivity tensor z Dt 2. Phase-matching at the interface θt -. refractive indices for the incident wave -. transmitted, reflected wave-vectors (kz1, kz2) -. phase-velocity index of refraction vt Dr kr Start θr vr 3. Characteristic angle for each wave -. angles of transmission and reflection (vt, vr) -. electric field direction, unit displacement vector (E, D) -. polarization angle (θ ), walk-off angle (η) vi θi Di y 4. Calculate the phase-retardation of the biaxial film ki biaxial film Coordinate system for a single planar interface between two general dielectric media 2 (kt1 kt 2 )d END Reference: Gary D. Landry and Theresa A. Maldonado, J. Opt. Soc. Am. A, Vol.12, No. 9, pp. 2048-2063 (1995) Dong-A University 7 Display Device Lab Ⅲ. Optical design on the Poincaré sphere ▣ Compensated optical configurations Optical configuration Fig. Compensated optical configuration of the circular polarizer Dong-A University 8 Display Device Lab Ⅲ. Optical design on the Poincaré sphere 1. Compensated optical configuration 1) Polarization path on the Poincaré sphere in the oblique direction Polarization of the light passing through the configuration optical configuration Blocking of the light leakage in the dark state in the diagonal direction Dong-A University 9 Display Device Lab Ⅲ. Optical design on the Poincaré sphere 2. Calculation results 1) Optical transmittance graph of each mode Optical transmittance of each mode at Φ=45 ° in the dark state shows the decrease in the off-axis light leakage by the optically compensated configurations Dong-A University 10 Display Device Lab Ⅲ. Optical design on the Poincaré sphere 2. Calculation results 2) Normalized iso-luminance contours of each mode (a) Basic configuration Dong-A University (b) Proposed configuration 11 Display Device Lab Ⅳ. Conclusion We presented an optical configuration for the circular polarizers that can provide wide viewing angle characteristics of the VA mode. We could effectively get an achromatic dark state through the compensation method on the Poincaré sphere. The introduced circular polarizers for transmissive mode can be one of the excellent solutions for mobile device applications with wide viewing angle. Dong-A University 12 Display Device Lab Thank you for your attention !!! Dong-A University 13 Display Device Lab