Waveguide Display Grating Staircase Structure
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Solution Overview
Problem
Grating-based waveguide displays face limitations in coupling efficiency due to less than 100% diffraction efficiency, leakage, polarization dependence, angular dependence, and wavelength dependence, leading to reduced image quality and field of view in near-eye display systems.
Innovation Solution
The implementation of a staircase structure with a holographic material layer and separate grating layers for input and output couplers, optimized for thickness and shape to avoid field of view clipping, along with the use of phase structures to change polarization, enhances diffraction efficiency and reduces leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single grating layer is used for both input and output couplers, then device complexity is reduced, but coupling efficiency deteriorates due to polarization dependence and angular dependence
Solution Approach 1:
The patent divides the grating function into separate input and output grating layers. The input grating layer is optimized for coupling light into the waveguide with specific polarization and angular characteristics, while the output grating layer is optimized for diffracting light out of the waveguide. This segmentation allows each grating layer to be independently optimized for its specific function, resolving the contradiction between device simplicity and coupling efficiency.
Solution Approach 2:
The patent applies different grating characteristics to different locations within the waveguide. The input grating has specific parameters (pitch, depth, orientation) optimized for light coupling, while the output grating has different parameters optimized for light extraction. This local optimization of grating quality at different positions enables high coupling efficiency without requiring a completely different grating structure throughout.
2Reliability
If grating thickness is increased to improve diffraction efficiency, then coupling efficiency improves, but field of view is clipped due to increased optical path length
Solution Approach 1:
The patent transitions from a single-plane grating to a multi-layer three-dimensional grating structure. By distributing the grating function across multiple layers at different depths and positions, the system achieves high diffraction efficiency through cumulative grating effect while maintaining a compact overall thickness that does not clip the field of view. The staircase structure enables light to interact with multiple grating elements without increasing the apparent optical path length in the viewing direction.
Solution Approach 2:
The patent embeds multiple grating layers within the waveguide thickness, creating a nested structure where input and output gratings are positioned at different depths. This nesting allows the grating elements to be stacked vertically rather than requiring lateral expansion, achieving high diffraction efficiency without increasing the field of view footprint.
3Reliability
If multiple holographic material layers are added to improve diffraction efficiency, then coupling efficiency improves, but manufacturing complexity increases
Solution Approach 1:
The patent segments the holographic material into separate input and output grating layers, each recorded with specific holographic patterns optimized for their respective functions. This segmentation allows independent optimization of each layer's diffraction characteristics while maintaining a modular structure that can be manufactured using sequential holographic recording processes, balancing manufacturing feasibility with performance requirements.
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 significantly improves the coupling efficiency of waveguide displays, enhancing image quality and expanding the field of view by minimizing unwanted light diffraction and optimizing the alignment of gratings within the waveguide.
Implementation Method 1
The first grating is configured to redirect the display light coupled into the waveguide by the input grating towards the second grating
Implementation Method 2
The phase structure may be configured to change a polarization state of the display light incident on the phase structure before or after the display light is redirected by the first grating
Implementation Method 3
Light of projected images may be coupled into a waveguide (e.g., a transparent substrate), propagate within the waveguide, and be coupled out of the waveguide at different locations
Data Source
AI summary
A waveguide display includes a waveguide, three input gratings configured to couple display light in different respective colors into the waveguide, one or more first middle gratings configured to receive and redirect the display light from the three input gratings, a second middle grating configured to diffract, at two or more regions of the second middle grating, the display light from the one or more first middle gratings, and an output grating configured to couple the display light from each of the two or more regions of the second middle grating out of the waveguide at two or more regions of the output grating.