Optically-Anisotropic Layer for Uniform AR Light-Guide Brightness
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Solution Overview
Problem
In augmented reality (AR) glasses, the brightness of light emitted from a light guide plate is non-uniform due to uniform diffraction efficiency of the liquid crystal diffraction element, leading to uneven viewing zones.
Innovation Solution
An optically-anisotropic layer formed of a composition containing a liquid crystal compound with varying birefringence indices in the thickness direction, featuring regions with different birefringence indices and alignment patterns that gradually change across the plane, ensuring uniform brightness of emitted light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a liquid crystal diffraction element with uniform diffraction efficiency is used, then the diffraction function is achieved, but the brightness of emitted light becomes non-uniform
Solution Approach 1:
The patent applies local quality by creating regions with different birefringence indices within the liquid crystal layer. Specifically, it forms a first liquid crystal layer with a first birefringence index and a second liquid crystal layer with a second birefringence index different from the first. This spatial variation in optical properties allows different regions to contribute differently to the overall diffraction, achieving uniform brightness across the emitted light while maintaining the diffraction function.
Solution Approach 2:
The patent uses composite materials by combining multiple liquid crystal layers with different birefringence characteristics. The first and second liquid crystal layers are stacked to form a composite structure where each layer has distinct optical properties. This composite approach enables the system to achieve both uniform brightness and effective diffraction by leveraging the complementary characteristics of different liquid crystal materials.
2Device complexity
If the birefringence index is uniform throughout the layer, then the structure is simple, but the viewing zone uniformity deteriorates
Solution Approach 1:
The patent implements local quality by introducing spatial variation in birefringence index through stacked liquid crystal layers. Instead of maintaining uniform simplicity, it deliberately creates localized differences in optical properties to achieve uniform viewing zones. The first and second liquid crystal layers are configured with specific birefringence indices that vary across the structure, ensuring consistent performance across the entire viewing area.
3Illumination intensity
If multiple regions with different birefringence indices are introduced, then brightness uniformity is improved, but the manufacturing complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the liquid crystal structure into multiple discrete layers, each with controlled birefringence properties. The first and second liquid crystal layers are formed as separate entities that can be independently characterized and assembled. This segmentation approach manages manufacturing complexity by breaking down the complex optical requirement into manageable layer-by-layer construction, where each layer's properties can be controlled separately to achieve the desired overall brightness uniformity.
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 achieves uniform brightness of light emitted from the light guide plate, enhancing the viewing experience by maintaining consistent illumination across the expanded viewing zone.
Implementation Method 1
a birefringence index Δn of the optically-anisotropic layer in a thickness direction varies in at least a part of a plane
Implementation Method 2
light (projection light) projected from the display is diffracted (refracted) using a diffraction element
Implementation Method 3
the light is introduced into the light guide plate with an angle and propagates up to the other end part of the light guide plate while being reflected from an interface
Data Source
AI summary
Provided are an optically-anisotropic layer which can make brightness of light emitted from a light guide plate uniform, a light guide element, and an AR display device. The optically-anisotropic layer is an optically-anisotropic layer formed of a composition containing a liquid crystal compound, in which a birefringence index Δn of the optically-anisotropic layer in a thickness direction varies in at least a part of a plane, and the optically-anisotropic layer has a birefringence index change region where an average value Δna of the birefringence indices in the thickness direction varies in the plane of the optically-anisotropic layer.