Gradient Refractive Index Grating for Waveguide Leakage Reduction
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Solution Overview
Problem
Optical see-through waveguide displays in augmented and mixed reality systems suffer from display light leakage, where a fraction of the display light is coupled out of the waveguide and into the ambient environment, causing aesthetic, privacy, and security issues.
Innovation Solution
The implementation of a waveguide display with grating couplers featuring multiple layers with different refractive indices and thickness profiles, including a gradient refractive index modulation, to reduce the coupling of display light into the ambient environment, utilizing surface-relief gratings with slanted grooves and an overcoat layer to minimize light leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single-layer grating coupler is used to couple display light out of the waveguide, then the device complexity is low, but display light leakage into the ambient environment occurs
Solution Approach 1:
The grating coupler is divided into multiple layers (first grating layer, second grating layer, third grating layer) with different refractive indices and thickness profiles. Each layer is configured with specific parameters to collectively reduce display light leakage while maintaining coupling efficiency to the eyebox.
Solution Approach 2:
Different regions of the grating coupler have different local properties - the first grating layer has a first refractive index and thickness profile, the second grating layer has a second refractive index and thickness profile, and the third grating layer has a third refractive index and thickness profile. These localized variations in refractive index and thickness are optimized to reduce light leakage in specific directions while maintaining coupling efficiency.
2Object-generated harmful factors
If multiple grating layers with different refractive indices are implemented to reduce light leakage, then display light leakage is reduced, but the device complexity increases
Solution Approach 1:
The grating coupler uses composite material structure with multiple layers having different refractive indices (first refractive index, second refractive index, third refractive index). This composite structure enables reduced display light leakage by creating interference patterns that suppress light coupling in unwanted directions while maintaining coupling efficiency to the eyebox.
Solution Approach 2:
The solution moves from a single-layer two-dimensional grating structure to a multi-layer three-dimensional structure. By adding the vertical dimension with multiple layers at different heights above the waveguide, the system achieves better control over light leakage while maintaining a compact form factor.
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
Significantly reduces display light leakage, ensuring that less than 1% of the display light is coupled out of the waveguide into the ambient environment, thereby enhancing user privacy and reducing unwanted visibility of the displayed content.
Implementation Method 1
grating couplers that may diffractively couple display light into or out of a waveguide
Implementation Method 2
Each of the grating couplers may include two or more grating layers having different respective refractive indices and/or thickness profiles to reduce the coupling of display light out of the waveguide display towards the ambient environment
Data Source
AI summary
A waveguide display includes a waveguide, an input coupler configured to couple display light into the waveguide, and a surface-relief grating on the waveguide and configured to couple the display light out of the waveguide towards an eyebox of the waveguide display on a first side of the waveguide. The surface-relief grating is formed in a plurality of grating layers having uniform or non-uniform thickness profiles. The plurality of grating layers is characterized by a refractive index modulation that increases and then decreases as the distance of the grating layer from the waveguide increases.