Cholesteric Polarization Diffraction for Uniform AR Glasses Brightness
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Solution Overview
Problem
Existing image display apparatuses, such as AR glasses, suffer from brightness unevenness in the observed image due to differences in light amount across the display plane.
Innovation Solution
Incorporating a reflective polarization diffraction element with a cholesteric liquid crystal layer that has a liquid crystal alignment pattern with continuously rotating optical axes and varying helical structure pitches, reducing brightness unevenness by adjusting the length of the single period and pitch of the helical structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a conventional reflective polarization diffraction element is used, then the image can be displayed, but brightness unevenness occurs across the display plane
Solution Approach 1:
The patent applies local quality by making the diffraction structure period position-dependent. Specifically, the period of the diffraction grating is designed to vary continuously across the display plane, with shorter periods in regions receiving higher incident light intensity and longer periods in regions receiving lower intensity. This local adaptation of the diffraction period compensates for the non-uniform light distribution, ensuring uniform reflected brightness across the entire display area.
Solution Approach 2:
The patent implements parameter changes by systematically varying the diffraction structure period as a function of position on the display plane. The period parameter is not kept constant but is instead modulated spatially to match the light intensity distribution profile. This continuous parameter adjustment allows the diffraction element to adapt its optical response to local conditions, resolving the brightness unevenness problem while maintaining manufacturing feasibility through controlled gradient structures.
2Use of energy by moving object
If the diffraction structure period is decreased in a predetermined direction, then light reflection is improved, but brightness unevenness increases
Solution Approach 1:
The patent resolves this contradiction by applying local quality principles: the diffraction period is optimized locally for each region based on its specific light reception characteristics. Regions with higher incident light intensity use shorter periods to reflect more light, while regions with lower intensity use longer periods to maintain brightness. This localized optimization ensures that each area operates at peak reflection efficiency for its specific conditions, achieving overall uniformity without sacrificing local performance.
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 reduces brightness unevenness in the observed image, providing a more uniform and consistent display experience.
Implementation Method 1
the polarization diffraction element includes a cholesteric liquid crystal layer obtained by immobilizing a cholesteric liquid crystalline phase
Implementation Method 2
a reflective polarization diffraction element that reflects an image projected by the image projection element
Implementation Method 3
the cholesteric liquid crystal layer has regions where a pitch of a helical structure in the cholesteric liquid crystal layer varies in a plane
Data Source
AI summary
An image display apparatus with reduced brightness unevenness and AR glasses including the apparatus are provided. The apparatus comprises an image projection element and a reflective polarization diffraction element that reflects the projected image. The polarization diffraction element includes a cholesteric liquid crystal layer formed by immobilizing a cholesteric liquid crystalline phase. The layer has an alignment pattern in which an optical axis orientation continuously rotates in at least one in-plane direction. When a 180° rotation length in the alignment pattern is set as a single period, the layer includes a region where the period length decreases away from the projection element, and regions where the helical structure pitch varies in-plane.