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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
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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
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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
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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
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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° ).
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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 2c sin 2 (o / 2)
sin(   o)  
1 (sin c sino )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).
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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)
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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
Polarization of the light
passing through the configuration
optical configuration
 Blocking of the light leakage in the dark state in the diagonal direction
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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
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Ⅲ. Optical design on the Poincaré sphere
2. Calculation results
2) Normalized iso-luminance contours of each mode
(a) Basic configuration
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(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 !!!
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