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Optical compensation design of Optical compensation design of

vertically aligned LC cell using wide view vertically aligned LC cell using wide view

circular polarizercircular 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

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▷ 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 DDisplay isplay DDevice evice LLabab Dong-A UniversityDong-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’

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450 nm550 nm630 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

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▣ 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

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(1) Deviation angle for any A-plate (Polarizer)

o : polar angle of the incident light in the LC layer

c : azimuth angle of the optical axis

2

2

sin2 sin ( /2)sin( )1 (sin sin )

c o

c o

o

2 2

2 2

2 sin sin1 1C o

e o

n dn n

(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

en : extraordinary refractive index of retardation film

on : ordinary refractive index of retardation film

d : thickness of the film

: wavelength of the incident light

Reference: Optics of Liquid Crystal Displays, Pochi Yeh and Claire Gu, Ch. 8.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).X. Zhu, Z. Ge, and S.-T. Wu, J. Display Technology, Vol. 2, pp. 2-20 (2006).

(3) Phase-retardation for A-plate

1 2 1 22 2 2 2 2

2 2 2

sin sin sin cos2 sin1 1e oe o o

d n nn n n

Ⅱ. Light leakage in the oblique direction

1). Numerical analysis of the uni-axial retardation film

7 DDisplay isplay DDevice evice LLabab Dong-A UniversityDong-A University

θt

θi

x

y

zRegion 2

Region 1

vt

vi

ki

kt

krvr

Di

Dr

Dt

θr

Coordinate system for a single planar interfacebetween 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 (kz1, kz2)-. phase-velocity index of refraction

-. angles of transmission and reflection (vt, vr)-. electric field direction, unit displacement vector (E, D)-. polarization angle (θ ), walk-off angle (η)

1 22 ( )t tbiaxial film

k k d

Reference: Gary D. Landry and Theresa A. Maldonado, J. Opt. Soc. Am. A, Vol.12, No. 9, pp. 2048-2063 (1995)Reference: Gary D. Landry and Theresa A. Maldonado, J. Opt. Soc. Am. A, Vol.12, No. 9, pp. 2048-2063 (1995)

▣ Requirements for operating on the Poincaré sphere

2). Numerical analysis of the bi-axial retardation film

Ⅱ. Light leakage in the oblique direction

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Ⅲ. Optical design on the Poincaré sphere

▣ Compensated optical configurations

Optical configuration

Fig. Compensated optical configuration of the circular polarizer

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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

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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 leakageby the optically compensated configurations

Optical transmittance of each mode at Φ=45 ° in the dark state

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2. Calculation results

Ⅲ. Optical design on the Poincaré sphere

2) Normalized iso-luminance contours of each mode

(a) Basic configuration (b) Proposed configuration

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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.

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Thank you for your attention !!!