Optical Film With Diffraction Gratings For Wide Viewing Angle LCDs
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Solution Overview
Problem
Liquid crystal displays suffer from color washout and light leakage at wide viewing angles due to asymmetry of liquid crystal molecules, leading to varying contrast ratios and color accuracy, affecting visual experience.
Innovation Solution
An optical film with a light directing structure layer, first and second diffraction gratings, and filling layers with specific refractive index differences, designed to collimate and redirect light, reducing light leakage and enhancing image uniformity by incorporating micro structures and diffraction gratings with varying dimensions and orientations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a common liquid crystal display is used, then the image quality at center viewing angle is maintained, but the image quality at wide viewing angle deteriorates with color washout and light leakage
Solution Approach 1:
The optical film is divided into multiple functional layers including a light directing structure layer with micro-prisms, a first diffraction grating layer, and a second diffraction grating layer. Each layer performs a specific function: the light directing structure redirects light from the backlight unit, while the diffraction grating layers further control light distribution. This segmentation allows independent optimization of each layer to achieve uniform light distribution across wide viewing angles without color washout
Solution Approach 2:
The light directing micro structures have specific geometric parameters (height between 10-50 μm, width between 5-15 μm, apex angle between 60-120 degrees) that are optimized for redirecting light at specific angles. The diffraction grating periods (first grating period between 1-5 μm, second grating period between 1-5 μm) are carefully selected to control the diffraction angles for different wavelengths, ensuring uniform color performance across the viewing angle range
2Illumination intensity
If the backlight unit cannot be turned off, then the display can maintain brightness, but light leakage occurs in dark state at wide viewing angles
Solution Approach 1:
The patent converts the harmful light leakage phenomenon into a beneficial effect by using diffraction grating structures that intentionally redirect light. The first and second diffraction grating layers work together to direct light from the always-on backlight unit toward the viewer's direction, transforming the unwanted light leakage at wide viewing angles into controlled light distribution that maintains image uniformity across the entire viewing angle range
3Ease of operation
If liquid crystal molecules are arranged asymmetrically, then the display can function, but color accuracy varies with viewing angle
Solution Approach 1:
The optical film employs a composite structure combining transparent resin materials with different refractive indices. The light directing structure layer uses resin with refractive index between 1.4-1.7, while the diffraction grating layers use resins with refractive indices between 1.4-1.8. This composite material approach allows precise control of light propagation and diffraction, compensating for the asymmetric liquid crystal molecule arrangement and maintaining color accuracy across wide viewing angles
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 optical film effectively reduces light leakage and improves image quality by maintaining uniform dark-state images and color accuracy across different viewing angles, as demonstrated by reduced maximum brightness in the dark state and improved Gamma Distortion Index and P-value measurements.
Implementation Method 1
a light directing structure layer comprising a plurality of light directing micro structures... the ratios of height to width of the light directing micro structures are in the range of 1.5 to 6
Implementation Method 2
a plurality of first diffraction gratings along with first direction formed on the first filling layer... a plurality of second diffraction gratings along with second direction formed on the second filling layer
Data Source
AI summary
The invention provides an optical film for improving image quality of a liquid crystal display comprising: a light directing structure layer, a first filling layer, a plurality of first diffraction gratings and a second filling layer. The light directing structure layer comprises a plurality of light directing micro structures, wherein the ratio of height to width of each light directing micro structure is in the range of 1.5 to 6. The first filling layer is disposed on the light directing structure layer, and the refractive index of the first filling layer and the light directing structure layer are different. The first diffraction gratings along with a first direction are formed on the first filling layer. The second filling layer is disposed on the first diffraction gratings and the refractive index of the second filling layer and the first diffraction gratings are different.