Staircase In-Coupling for Waveguide Display Efficiency
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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, and angular dependence, leading to reduced image quality and field of view in near-eye display systems.
Innovation Solution
The implementation of a waveguide display system with a staircase structure that includes a holographic material layer with a first grating and a second grating, where the staircase structure is designed to avoid field of view clipping and enhance coupling efficiency by optimizing thickness and shape, and the use of phase structures to change the polarization state of light for improved diffraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If grating-based waveguide displays are used to couple light into the waveguide, then the display can be compact and lightweight, but the coupling efficiency is reduced due to less than 100% diffraction efficiency
Solution Approach 1:
The waveguide is divided into multiple functional sections: input grating region, staircase structure region with intermediate gratings, and output grating region. Each section performs a specific function in the light coupling and guiding process, allowing optimization of each segment independently to improve overall coupling efficiency while managing complexity through functional decomposition.
Solution Approach 2:
The staircase structure with intermediate gratings acts as an intermediary between the input grating and the waveguide core. This intermediate structure redirects light progressively through multiple stages, improving coupling efficiency by capturing and redirecting light that would otherwise be lost, while maintaining a manageable device complexity through modular design.
2Reliability
If conventional grating structures are used, then the manufacturing process is simpler, but leakage and polarization dependence reduce image quality
Solution Approach 1:
Different regions of the waveguide are assigned different grating structures optimized for their specific functions. The input region uses gratings optimized for light coupling, the staircase structure uses intermediate gratings optimized for rediriction with specific polarization characteristics, and the output region uses gratings optimized for light extraction. This local optimization improves image quality by reducing leakage and polarization dependence while maintaining ease of manufacture through region-specific fabrication approaches.
3Loss of energy
If the waveguide thickness is increased to improve light coupling, then coupling efficiency improves, but field of view is clipped by the waveguide structure
Solution Approach 1:
The staircase structure introduces a vertical dimension to the light redirection process. Instead of relying solely on horizontal waveguide thickness, the staircase structure uses vertical steps with intermediate gratings to redirect light progressively. This dimensional approach allows improved coupling efficiency without increasing the horizontal footprint that would clip the field of view, as the redirection occurs through vertical stacking rather than horizontal expansion.
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 display light into the waveguide, enhancing image quality and expanding the field of view by reducing leakage and polarization-dependent issues, resulting in a more immersive and efficient near-eye display experience.
Implementation Method 1
the light of the projected images may be coupled into or out of the waveguide using diffractive optical elements, such as volume holographic gratings and/or surface-relief gratings
Implementation Method 2
The first grating and the second grating may include transmissive volume Bragg gratings or reflective volume Bragg gratings
Implementation Method 3
The phase structure may include a waveplate, a layer of a birefringent material, or a subwavelength structure and an overcoat layer
Implementation Method 4
The phase structure may include a waveplate, a layer of a birefringent material
Implementation Method 5
propagate within the waveguide
Data Source
AI summary
A waveguide display includes a waveguide and a staircase structure coupled to the waveguide. The waveguide includes a first substrate, a second substrate, and a holographic material layer between the first substrate and the second substrate. The holographic material layer includes a first grating and a second grating. The staircase structure is positioned on top of at least a portion of the first grating but not on top of the second grating. The staircase structure includes an input grating that is on top of the first grating and is configured to couple display light into the waveguide. The first grating is configured to redirect the display light coupled into the waveguide by the input grating towards the second grating.