Diffractive Waveguide Zoning for AR/VR Rainbow Artefact Reduction
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Solution Overview
Problem
Existing diffractive waveguide combiners for augmented and virtual reality displays suffer from issues such as rainbow artefacts due to external light scattering, limited eyebox expansion, and manufacturing constraints, which affect image uniformity and user experience.
Innovation Solution
A waveguide with an output region comprising multiple zones of varying diffraction efficiencies, including a second zone with optimized diffraction efficiencies for external light reduction and improved image uniformity, using interleaved rectangular gratings to minimize rainbow artefacts and enhance eyebox expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a diffractive waveguide combiner is used to expand eyebox and relay projected image, then pupil replication and eyebox expansion are achieved, but rainbow artefacts appear due to external light scattering
Solution Approach 1:
The output region is segmented into multiple zones with different diffraction efficiencies. Each zone is optimized to handle specific light propagation directions, with zones having reduced diffraction efficiency for external light directions to minimize rainbow artefacts while maintaining high efficiency for image-bearing light paths.
Solution Approach 2:
Different regions of the output region are assigned different optical properties (diffraction efficiencies) based on their function. Zones are selectively optimized for either image-bearing light outcoupling or external light suppression, creating spatially varying local qualities that resolve the contradiction between eyebox expansion and artefact reduction.
2Ease of manufacture
If uniform diffraction efficiency is used across the output region, then manufacturing is simplified, but image uniformity deteriorates due to varying light propagation directions
Solution Approach 1:
The diffraction efficiency is made dynamically adaptive to the propagation direction of incident light. By configuring zones with different efficiencies, the system automatically optimizes performance for each light path without requiring complex real-time adjustments, achieving image uniformity through static spatial variation.
3Volume of moving object
If the waveguide size is reduced for compact form factor, then portability is improved, but eyebox expansion capability is limited
Solution Approach 1:
The patent utilizes the third dimension (depth/propagation direction) to achieve two-dimensional eyebox expansion. By creating multiple zones at different positions and orientations within the waveguide, light is outcoupled in multiple directions, effectively expanding the eyebox area without increasing the waveguide's planar footprint.
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 rainbow artefacts and enhances image uniformity while maintaining a compact form factor by optimizing diffraction efficiencies and eyebox expansion, improving user experience in augmented and virtual reality devices.
Implementation Method 1
an input region configured to couple light into the waveguide so that it propagates under total internal reflection (TIR) within the waveguide
Implementation Method 2
an output region comprising optical structures configured to receive image bearing light from the input region in a direction along a first axis, the output region providing diffractive interactions for light that propagates under TIR within the waveguide
Data Source
AI summary
A waveguide for use in a virtual reality, VR, or augmented reality, AR, device, is disclosed. The waveguide comprising an input region configured to couple light into the waveguide so that it propagates under total internal reflection (TIR) within the waveguide, and an output region comprising optical structures configured to receive image bearing light from the input region. The output region comprises a plurality of zones having different diffraction to each other, the plurality of zones comprising diffraction efficiencies so as to reduce rainbow artefacts.