Retardation Compensation Element for Liquid Crystal Displays
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Solution Overview
Problem
VA mode liquid crystal display devices suffer from viewing angle dependency issues due to optical retardation, leading to light leakage and poor contrast ratio, even when liquid crystal molecules are not completely vertically aligned.
Innovation Solution
A retardation compensation element comprising multiple thin optical anisotropic layers with specific refractive index differences and orientations, including a negative C-plate and positive O-plates, is used to compensate for optical retardation, ensuring wide viewing angles and optimal contrast ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single C-plate optical element is used to compensate retardation, then oblique angle viewing is improved, but the best contrast ratio shifts away from the normal direction
Solution Approach 1:
The patent divides the single optical compensation element into multiple layers: a C-plate layer and one or more O-plate layers. Each layer has specific optical axis orientations and retardation values that work together to compensate retardation while keeping the best contrast ratio at the normal viewing angle. The C-plate layer addresses oblique angle issues while the O-plate layers correct the peak position shift.
Solution Approach 2:
Different regions of the optical compensation element have different optical properties. The C-plate layer has its optical axis parallel to the substrate normal, while the O-plate layers have optical axes in the substrate plane. Each layer is positioned and configured to address specific viewing angle conditions, creating locally optimized compensation for different light paths.
2Ease of manufacture
If liquid crystal molecules are not completely vertically aligned, then ease of manufacture is improved, but optical retardation causes light leakage and poor contrast
Solution Approach 1:
The optical compensation element is designed to preemptively counteract the retardation effects caused by non-vertical liquid crystal alignment. By incorporating the C-plate and O-plate layers with specific retardation values and orientations, the system pre-compensates for the optical path differences that would otherwise cause light leakage, allowing manufacturing with relaxed alignment tolerances.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively prevents light leakage across a wide viewing angle, maintaining high contrast ratios and image quality by aligning the best contrast ratio with the normal of the substrate, even when liquid crystal molecules are not completely vertical.
Implementation Method 1
A retardation compensation element is proposed which has a negative C-plate layer whose optical axis extends along normal of the element substrate, and one or more positive O-plate layers whose optical axis(axes) is inclined at 45 degrees from the normal of the element substrate
Implementation Method 2
Disposed outside the glass substrates is a pair of polarizing plates in crossed nicols arrangement. When no voltage is applied, linearly polarized light that passed through the polarizing plate on a light incoming side (polarizer) goes through the liquid crystal layer with its polarization plane substantially unchanged. This light is subsequently blocked by the polarizing plate on a light outgoing side (analyzer)
Data Source
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Figure 3~4
AI summary
A retardation compensation element (32, 32a) has a first optical anisotropic layer (42) that functions as a negative C-plate, and a second and a third optical anisotropic layers (43, 44) that function as positive O-plates. VA mode liquid crystal molecules (37) tilt at an azimuth angle of 45 degrees and a polar angle of 5 degrees when no voltage is applied thereto. The second and third optical anisotropic layers have optical axes respectively at an angle of -105 degrees and +105 degrees from the tilt direction of the liquid crystal molecule. The first optical anisotropic layer (42) compensates the retardation of light that enters a liquid crystal layer (38) at an oblique angle while the second and third optical anisotropic layers (43, 44) compensate the retardation of light that enters the liquid crystal layer at a right angle.