Photonic Crystal Waveguide for Uniform AR/VR Display Brightness
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Solution Overview
Problem
Existing waveguides in augmented reality displays exhibit a brightness gradient in the output image, which is undesirable for users.
Innovation Solution
The diffraction efficiency of the photonic crystal is controlled by varying the cross-sectional areas of optical structures along the first and second axes, and in discrete groups, to achieve uniformity of luminosity in the output light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the diffraction efficiency of the photonic crystal is controlled by varying the cross-sectional areas of optical structures, then the uniformity of luminosity in the output image is improved, but the device complexity increases
Solution Approach 1:
The patent applies local quality by varying the cross-sectional areas of optical structures at different positions within the photonic crystal array. Specifically, the cross-sectional area is modified along the first axis (propagation direction) and/or second axis (lateral direction) to create position-dependent diffraction efficiencies. This allows different regions of the photonic crystal to have different optical properties, compensating for brightness gradients and achieving uniform luminosity output while managing the added structural complexity through systematic variation rather than complete redesign.
2Illumination intensity
If the cross-sectional areas of optical structures are varied along the first and second axes, then the brightness gradient in the output image is mitigated, but the manufacturing precision requirements increase
Solution Approach 1:
The patent implements parameter changes by systematically varying the cross-sectional area parameter of optical structures along the first axis (propagation direction) and/or second axis (lateral direction). This parameter variation creates a gradient in diffraction efficiency that compensates for brightness gradients in the output image. The changes are designed to be gradual and systematic, which helps manage manufacturing precision requirements compared to abrupt or random variations, while still achieving the desired brightness uniformity improvement.
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
This approach improves the uniformity of luminosity in the output image, mitigating the brightness gradient and enhancing the display quality.
Implementation Method 1
The diffraction efficiency of the photonic crystal can be controlled at different points in the array to achieve particular effects. By varying the diffraction efficiencies of the optical structures along the first axis, the uniformity of luminosity of the output light can be improved.
Implementation Method 2
Light from the projector is coupled into the waveguide by a diffraction grating. The projected light is totally internally reflected within the waveguide.
Data Source
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AI summary
A waveguide (60) for use in an augmented reality or virtual reality display is provided and comprises a plurality of optical structures in or on a photonic crystal (30; 50; 70; 80), wherein the plurality of optical structures are arranged in an array to provide two diffractive optical elements (H1, H2) overlaid on one another in the waveguide (60), wherein each of the two diffractive optical elements (H1, H2) is configured to receive light from an input direction and couple it towards the other diffractive optical element which can then act as an output diffractive optical element (20), providing outcoupled orders towards a viewer; wherein the plurality of optical structures have different respective cross sectional shapes, for a cross section parallel to the plane of the waveguide (60), at different positions in the array in order to provide different diffraction efficiencies at different positions in the array, wherein at least one characteristic of the cross sectional shape of the plurality of optical structures is variable, in the direction of a first axis which is parallel to the input direction; wherein the at least one characteristic is related to the cross sectional area of the optical structures, for a cross section parallel to the plane of the waveguide.