1 Display Device Lab Dong-A University Dong-A University 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 , Korea

2 Display Device Lab Dong-A University Dong-A University ▷ 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 Outline

3 Display Device Lab Dong-A University Dong-A University Ⅰ. What are required for LCD applications ?  High Brightness  Wide Viewing Angle  High Contrast Ratio  Color Gamut  Fast Response Time  Thin, Lightweight  Low Power Consumption  Cost Competitiveness Highly ‘interesting’

4 Display Device Lab Dong-A University Dong-A University 450 nm 550 nm 630 nm Ⅱ. Light leakage in the oblique direction  Off-axis light leakage in the dark state occurs in the conventional circular polarizer for the transmissive mode ▣ Polarization of the conventional circular polarizer on the Poincaré sphere Fig.(a) Basic circular polarizer configuration Fig.(b) Polarization states in the oblique direction

5 Display Device Lab Dong-A University Dong-A University ▣ Optical transmittance of the conventional circular polarier  We improve the optical performance of the circular polarizer at the diagonal direction (θ=70°, Φ=45° ). Ⅱ. Light leakage in the oblique direction

6 Display Device Lab Dong-A University Dong-A University (1) Deviation angle for any A-plate (Polarizer) : polar angle of the incident light in the LC layer : azimuth angle of the optical axis (2) Phase-retardation for C-plate and VA LC ▣ Requirements for operating on the Poincaré sphere : polar angle of the incident light in free space : azimuth angle of the incident light : extraordinary refractive index of retardation film : ordinary refractive index of retardation film : thickness of the film : wavelength of the incident light 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 (2006). X. Zhu, Z. Ge, and S.-T. Wu, J. Display Technology, Vol. 2, pp (2006). (3) Phase-retardation for A-plate Ⅱ. Light leakage in the oblique direction 1). Numerical analysis of the uni-axial retardation film

7 Display Device Lab Dong-A University Dong-A University θtθt θiθi x y z Region 2 Region 1 vtvt vivi kiki ktkt krkr vrvr DiDi DrDr DtDt θrθr Coordinate system for a single planar interface between two general dielectric media Start 1. Interface coordinate system 2. Phase-matching at the interface 3. Characteristic angle for each wave 4. Calculate the phase-retardation of the biaxial film END -. principal dielectric axes, laboratory coordinate system -. Euler angles (Φ, ρ and ψ) in the x convention -. permittivity tensor -. refractive indices for the incident wave -. transmitted, reflected wave-vectors (k z1, k z2 ) -. phase-velocity index of refraction -. angles of transmission and reflection (v t, v r ) -. electric field direction, unit displacement vector (E, D) -. polarization angle (θ ), walk-off angle (η) Reference: Gary D. Landry and Theresa A. Maldonado, J. Opt. Soc. Am. A, Vol.12, No. 9, pp (1995) ▣ Requirements for operating on the Poincaré sphere 2). Numerical analysis of the bi-axial retardation film Ⅱ. Light leakage in the oblique direction

8 Display Device Lab Dong-A University Dong-A University Ⅲ. Optical design on the Poincaré sphere ▣ Compensated optical configurations Optical configuration Fig. Compensated optical configuration of the circular polarizer

9 Display Device Lab Dong-A University Dong-A University Ⅲ. Optical design on the Poincaré sphere 1. Compensated optical configuration 1) Polarization path on the Poincaré sphere in the oblique direction  Blocking of the light leakage in the dark state in the diagonal direction optical configuration Polarization of the light passing through the configuration

10 Display Device Lab Dong-A University Dong-A University 1) Optical transmittance graph of each mode 2. Calculation results Ⅲ. Optical design on the Poincaré sphere shows the decrease in the off-axis light leakage by the optically compensated configurations Optical transmittance of each mode at Φ=45 ° in the dark state

11 Display Device Lab Dong-A University Dong-A University 2. Calculation results Ⅲ. Optical design on the Poincaré sphere 2) Normalized iso-luminance contours of each mode (a) Basic configuration(b) Proposed configuration

12 Display Device Lab Dong-A University Dong-A University 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.

13 Display Device Lab Dong-A University Dong-A University Thank you for your attention !!!