Optical Waveguide Grating Layout for AR Color Uniformity
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Solution Overview
Problem
Existing optical waveguide structures in AR display devices face challenges in simultaneously balancing color uniformity and diffraction efficiency, with current solutions either suffering from inefficient diffraction or color deviation due to inconsistent wavelength propagation.
Innovation Solution
An optical waveguide structure with a waveguide substrate featuring multiple diffraction grating areas on both sides, including a coupling-in area, diffraction grating areas, and a coupling-out area, designed to perform multiple pupil expansions and reduce total reflection steps, ensuring equal periods and grating vector directions to enhance diffraction efficiency and color uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If surface relief or volume holography is used for diffraction, then diffraction efficiency is improved, but color uniformity deteriorates due to wavelength dispersion
Solution Approach 1:
The waveguide substrate is divided into multiple diffraction grating areas with different grating vectors, where each area handles specific wavelength ranges. This segmentation allows different regions to optimize for different colors, preventing the wavelength dispersion that causes color uniformity issues in conventional single-grating designs.
Solution Approach 2:
Different diffraction grating areas are assigned different local properties (grating vectors, periods, or orientations) tailored to specific wavelength ranges. This local optimization ensures that each region of the waveguide is specifically designed to handle particular colors efficiently, thereby maintaining both high diffraction efficiency and color uniformity across the entire display.
2Manufacturing precision
If array waveguide with geometric ray reflection is used, then color uniformity is improved, but diffraction efficiency deteriorates
Solution Approach 1:
The patent merges the advantages of geometric optics (color uniformity through controlled reflection paths) with diffractive optics (high efficiency through constructive interference). Multiple diffraction grating areas are strategically positioned and oriented to create controlled reflection paths while maintaining high diffraction efficiency through proper grating design.
Solution Approach 2:
The patent introduces additional spatial dimensions by arranging diffraction grating areas on multiple faces of the waveguide substrate and using three-dimensional light propagation paths. This multi-dimensional arrangement allows light to undergo multiple pupil expansions while maintaining color uniformity through controlled geometric paths.
3Area of stationary object
If multiple pupil expansions are performed, then field of view is improved, but light loss increases due to multiple reflections
Solution Approach 1:
The patent converts the harmful effect of multiple reflections (which cause light loss) into a beneficial mechanism for pupil expansion. By strategically designing diffraction grating areas with specific grating vectors and orientations, the multiple reflections are transformed into constructive interference patterns that expand the pupil while maintaining high light efficiency.
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 proposed structure improves diffraction efficiency and color uniformity by reducing light-pupil separation and light loss, achieving high efficiency and uniform illumination through geometrically planned diffraction grating arrangements.
Implementation Method 1
a plurality of diffraction grating areas are provided, two side surfaces of the waveguide substrate are provided with the diffraction grating area, and a number of the diffraction grating areas on at least one side surface of the waveguide substrate is greater than or equal to 2, periods of the plurality of diffraction grating areas are equal, and the plurality of diffraction grating areas are configured to perform multiple pupil expansion transmissions on a light
Implementation Method 2
The array waveguide is based on a principle of a geometric ray, and mainly uses a light transmission process including reflection, total reflection or partial reflection, and partial transmission without dispersion
Data Source
AI summary
The disclosure provides an optical waveguide structure and an AR display device. The optical waveguide structure includes: a waveguide substrate; a coupling-in area, the coupling-in area is arranged on the waveguide substrate; a plurality of diffraction grating areas, two side surfaces of the waveguide substrate are provided with the diffraction grating areas, a number of the diffraction grating areas on at least one side surface of the waveguide substrate is greater than or equal to 2, periods of the diffraction grating areas are equal, and the diffraction grating areas are configured to perform multiple pupil expansions on a light; and a coupling-out area, the coupling-out area is arranged on the waveguide substrate, the diffraction grating areas are all located between the coupling-in area and the coupling-out area, and the coupling-out area is configured to perform pupil expansion transmission on a light in the waveguide substrate and emit the light.