Waveguide Phase Distortion Mitigation via DOE Height Offsets
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Solution Overview
Problem
Waveguide-based display systems suffer from phase distortions caused by diffractive optical elements, leading to image quality issues such as beam spreading and loss of sharpness, which conventional methods like apodization only partially address while compromising efficiency.
Innovation Solution
Introducing suitable height offsets for diffractive optical elements relative to each other and the blank surface of the waveguide, ensuring that the total phase retardance for rays reflected from the offset gratings matches that of rays undergoing total internal reflection, thereby mitigating phase distortions without reducing grating efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If diffractive optical elements are used in waveguide-based display systems, then beam expansion and image visibility over wider area are achieved, but phase distortions occur leading to beam spreading and loss of sharpness
Solution Approach 1:
The patent applies local quality by introducing height offsets specifically at the edges of diffractive optical elements (DOEs) rather than uniformly across the entire waveguide. The offset amount varies locally - larger at DOE edges where phase distortions are most severe, and zero or minimal in the center regions. This localized approach compensates for edge-induced phase errors while preserving the beam expansion function across the entire eye box area.
Solution Approach 2:
The patent changes the physical parameter of the waveguide surface by introducing vertical height offsets to the diffractive optical elements. By modifying the optical path length through controlled surface height variations, the phase distortions caused by diffractive elements are compensated. The offset height is calculated based on the phase error magnitude at different locations, transforming the wavefront to achieve proper collimation while maintaining the expanded beam area.
2Manufacturing precision
If conventional apodization methods are used to address phase distortions, then some image quality issues are mitigated, but grating efficiency is reduced
Solution Approach 1:
The patent segments the waveguide surface into distinct regions: areas with height offsets and areas without offsets. By applying height offsets only in specific locations (primarily at DOE edges) rather than uniformly across the entire grating structure, the solution addresses phase distortions locally while leaving the majority of the grating surface unchanged. This segmentation preserves grating efficiency in the non-offset regions while correcting image quality issues in the offset regions.
3Manufacturing precision
If height offsets are introduced for diffractive optical elements, then phase distortions are reduced and image sharpness is improved, but device complexity increases
Solution Approach 1:
The patent merges the height offset feature with the existing diffractive optical element fabrication process. The offset regions are integrated into the same manufacturing workflow as the DOE patterns, using similar lithography and etching techniques. This combining approach allows the height offsets to be added during the normal manufacturing process without requiring completely separate fabrication steps, thereby limiting the increase in device complexity while achieving the desired phase correction and image sharpness improvement.
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 reduces phase distortions and maintains grating efficiency across the entire surface area, including the edges, resulting in improved image quality with sharper images and better beam collimation.
Implementation Method 1
The light is guided through the waveguide by reflection at the front and rear surfaces
Implementation Method 2
Such systems can incorporate diffraction gratings, which cause effective beam expansion so as to output expanded versions of the beams provided by the light engine
Data Source
AI summary
A waveguide has a front and a rear surface, the waveguide for a display system and arranged to guide light from a light engine onto an eye of a user to make an image visible to the user, the light guided through the waveguide by reflection at the front and rear surfaces. A first portion of the front or rear surface has a structure which causes light to change phase upon reflection from the first portion by a first amount. A second portion of the same surface has a different structure which causes light to change phase upon reflection from the second portion by a second amount different from the first amount. The first portion is offset from the second portion by a distance which substantially matches the difference between the second amount and the first amount.