Zoned Diffractive Optic for HMD Waveguide Uniformity
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Solution Overview
Problem
Conventional image light guides for Head-Mounted Displays (HMDs) face challenges in achieving improved diffraction efficiency, image-bearing light output intensity, and uniformity across the entire output aperture, leading to suboptimal virtual image presentation, especially in compact devices.
Innovation Solution
The implementation of an image light guide with a zoned out-coupling diffractive optic, featuring multiple zones with distinct diffractive features and a two-dimensional periodic lattice, which directs image-bearing light beams at specific angles to enhance diffraction efficiency and uniformity, ensuring consistent virtual image presentation across the eyebox.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional single-zone out-coupling diffractive optic is used, then the device structure is simple, but the diffraction efficiency and light output uniformity are insufficient
Solution Approach 1:
The out-coupling diffractive optic is divided into multiple zones (first zone, second zone, third zone) with different diffractive feature configurations. Each zone is responsible for directing light from specific pixel regions, enabling differentiated control of diffraction efficiency and light output uniformity across the entire aperture while maintaining a relatively simple overall structure.
Solution Approach 2:
Different regions of the out-coupling diffractive optic are assigned different diffractive feature characteristics. The first zone has features for directing light from a first pixel region, the second zone for a second pixel region, and the third zone for a third pixel region. This local differentiation optimizes diffraction efficiency and light uniformity for each region without requiring complete redesign of the entire optic.
2Reliability
If diffractive features are designed to direct light at specific angles for each pixel region, then light output uniformity improves, but the complexity of the diffractive optic increases
Solution Approach 1:
The complex diffractive optic is segmented into multiple zones, each handling a specific pixel region. This segmentation allows the complexity to be distributed and managed locally rather than requiring a completely complex design across the entire optic, making the system more manageable while achieving uniform light output.
Solution Approach 2:
The diffractive features in different zones are designed with asymmetric characteristics tailored to their specific regions. The first, second, and third zones have different diffractive feature configurations optimized for their respective pixel regions, allowing specific angle directionality for uniform light output while maintaining an overall manageable structure through asymmetric design.
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 solution significantly improves diffraction efficiency and light output uniformity, providing a more robust and consistent virtual image presentation, reducing visual hotspots and enhancing the viewing experience in HMDs and similar imaging apparatus.
Implementation Method 1
an out-coupling diffractive optic operable to direct the image-bearing light beams from the waveguide toward an eyebox. The out-coupling diffractive optic including two or more zones each comprising a set of diffractive features, wherein successive zones along one dimension of the out-coupling diffractive optic have different respective sets of diffractive features, wherein the diffractive features are operable to direct a portion of image-bearing light beams of a first pixel incident upon the diffractive features at a first angle
Data Source
AI summary
An image light guide for conveying a virtual image, including a waveguide, an in-coupling diffractive optic operable to direct image-bearing light beams into the waveguide, and an out-coupling diffractive optic operable to direct the image-bearing light beams from the waveguide toward an eyebox. The out-coupling diffractive optic having two or more zones each including a set of diffractive features, wherein successive zones along one dimension of the out-coupling diffractive optic have different respective sets of diffractive features, wherein the diffractive features are operable to direct image-bearing light beams of a first pixel incident upon the diffractive features at a first angle whereby the directed image-bearing light beams of the first pixel further propagate within the waveguide, and wherein the diffractive features are operable to out-couple a portion of the image-bearing light beams of the first pixel incident upon the diffractive features at a second angle.