Square Waveguide Layout for AR Display Cross-Talk Reduction
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Solution Overview
Problem
Existing waveguide designs for augmented reality devices suffer from image quality degradation due to cross-talk between different colors, particularly when holograms for various colors are optically coupled together, leading to reduced diffraction efficiency and unwanted beam angles.
Innovation Solution
The proposed square-shape waveguide layout separates red, green, and blue holograms laterally, with each color following distinct beam paths to minimize cross-talk, allowing all three colors to reside in one waveguide without degrading image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If holograms for different colors (RGB) are overlaid on top of each other with the same orientation in a waveguide, then the device complexity is reduced, but cross-talk between colors occurs which degrades image quality
Solution Approach 1:
The patent segments the holographic elements by laterally separating them in the waveguide plane. Instead of stacking all holograms at the same location, the input holograms, redirection holograms, and output holograms for different colors are positioned at different lateral locations. This spatial segmentation prevents cross-talk between colors while maintaining a single integrated waveguide structure, thus resolving the contradiction between device complexity and image quality.
Solution Approach 2:
The patent transitions from a vertical stacking arrangement (single layer) to a two-dimensional lateral arrangement of holographic elements within the waveguide. By distributing holograms across different lateral positions rather than stacking them vertically at the same location, the patent eliminates cross-talk while keeping the waveguide thickness manageable. This dimensional change from 1D stacking to 2D lateral distribution resolves the contradiction between structural simplicity and optical performance.
2Manufacturing precision
If separate waveguides are used for different colors to reduce cross-talk, then image quality is improved, but the device thickness and complexity increase
Solution Approach 1:
The patent merges all color channels (RGB) into a single waveguide structure by laterally positioning their respective holographic elements within the same waveguide plane. This consolidation eliminates the need for multiple separate waveguides, thereby reducing overall device thickness while preventing cross-talk through proper lateral separation. The merging principle resolves the contradiction by achieving color isolation without requiring physically separate waveguide layers.
Solution Approach 2:
Instead of using multiple waveguide layers stacked vertically (increasing thickness), the patent distributes color-specific holographic elements laterally across the waveguide plane. This lateral distribution in the horizontal dimension replaces the vertical stacking approach, thereby maintaining thin waveguide structure while achieving the same cross-talk reduction effect. This dimensional transition resolves the contradiction between image quality and waveguide thickness.
3Volume of moving object
If diffractive elements are used for input, pupil expansion, and output, then compactness is achieved, but cross-talk between neighboring colors (blue and green) increases due to small spectral separation
Solution Approach 1:
The patent segments the diffractive elements by their function and color specificity, positioning input holograms, redirection holograms, and output holograms at distinct lateral locations. This segmentation ensures that blue light primarily interacts with blue-optimized holograms and green light with green-optimized holograms, minimizing cross-talk despite the small spectral separation. The spatial segmentation maintains compact device volume while improving diffraction efficiency for each color channel.
Solution Approach 2:
The patent resolves the cross-talk issue by transitioning from vertical stacking of diffractive elements to lateral distribution within the waveguide plane. This lateral arrangement in the horizontal dimension allows sufficient spatial separation between blue and green holographic elements, reducing their optical interaction and cross-talk. Meanwhile, the overall device remains compact because all elements are integrated within a single thin waveguide layer, thus resolving the contradiction between compactness and diffraction 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
This design significantly reduces cross-talk between colors, minimizing the number of unwanted beams and improving image quality by ensuring each color's light is diffracted only by its intended hologram, thus enhancing the overall performance of augmented reality displays.
Implementation Method 1
Image projection through a waveguide via total internal reflectance (TIR) is an especially elegant way to build augmented reality (AR) devices
Implementation Method 2
using diffractive elements such as surface relief gratings (SRG) or volume holograms (Bragg grating) offers advantages such as compactness and lower cost of production
Data Source
AI summary
The present invention features new waveguide layouts for input, redirection (expansion), and output holograms that minimize cross talk between colors and allow all three colors to reside in a single waveguide. The use of multiple incoupling holograms that diffract different colors of light in different directions, or along different paths, through a waveguide substrate advantageously provides for a reduction of cross-talk between the colors of a holographic image. In a square-shaped design, red, green, and blue input and output holograms approximately overlay on top of each other. The green redirection hologram is laterally separated from the red and blue redirection holograms. Using this square-shape design, the light beams for the three colors are separated into two paths propagating from input to output holograms.