Phase Structure on Volume Bragg Grating Waveguide Display
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Solution Overview
Problem
Grating-based waveguide displays for near-eye augmented reality systems face limitations in coupling efficiency due to polarization dependence, angular dependence, and leakage, leading to suboptimal image quality and reduced field of view.
Innovation Solution
Incorporating a phase structure with birefringent materials or subwavelength structures on the waveguide substrate to change the polarization state of light, optimizing the location and orientation of the phase structure relative to the grating couplers to enhance diffraction efficiency and reduce leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If grating-based waveguide displays are used for near-eye augmented reality systems, then light coupling into the waveguide is achieved, but polarization dependence and angular dependence cause reduced coupling efficiency and limited field of view
Solution Approach 1:
A phase structure is introduced as an intermediary element between the grating coupler and the waveguide core. This phase structure modifies the polarization state of light before it enters the waveguide, acting as a mediator that resolves the polarization dependence issue of the grating coupler while maintaining efficient light coupling into the waveguide.
Solution Approach 2:
The phase structure changes the polarization parameter of the light by converting linearly polarized light to circularly polarized light or vice versa. This parameter transformation allows the light to satisfy the coupling requirements of the grating structure more effectively, improving coupling efficiency across different angles and polarizations.
2Device complexity
If conventional grating couplers are used without phase structures, then device simplicity is maintained, but polarization-dependent diffraction efficiency causes light leakage and reduced image quality
Solution Approach 1:
The waveguide structure is enhanced by incorporating a phase structure made of birefringent material or subwavelength structures onto the waveguide substrate. This composite structure combines the light-coupling function of the grating with the polarization-modifying function of the phase structure, improving image quality while maintaining reasonable device complexity.
3Productivity
If the phase structure is optimized for maximum diffraction efficiency, then coupling efficiency improves, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The phase structure is implemented using thin-film deposition techniques that create relatively simple, planar structures that can be manufactured using standard semiconductor fabrication processes. This approach prioritizes manufacturing ease over achieving maximum theoretical diffraction efficiency, accepting a practical level of performance that is sufficient for commercial applications.
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
Improves the overall coupling efficiency of waveguide displays by preferentially directing light to desired diffraction orders, expanding the eyebox and enhancing image quality across the field of view.
Implementation Method 1
a phase structure with birefringent materials or subwavelength structures on the waveguide substrate to change the polarization state of light
Implementation Method 2
a first surface-relief grating on the substrate and configured to couple display light into or out of the substrate
Implementation Method 3
The first surface-relief grating is characterized by a polarization-dependent diffraction efficiency
Implementation Method 4
at least one volume Bragg grating between the display light source and the phase structure
Data Source
AI summary
A waveguide display includes a substrate transparent to visible light, a first grating on the substrate and configured to couple display light into or out of the substrate, and a phase structure on the substrate and configured to change a polarization state of the display light after or before the display light reaches the first grating. The first grating is characterized by a polarization-dependent diffraction efficiency. The first grating includes, for example, a surface-relief grating or a volume Bragg grating.