Three-Level Grating Waveguide for AR Light Projection
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Solution Overview
Problem
Existing augmented reality systems face challenges in efficiently projecting digital images to the viewer while minimizing light loss and reducing unwanted reflections, such as the second order reflection, which can cause image flare and distract the viewer.
Innovation Solution
The use of a diffractive optical element, specifically a three-level grating, is introduced in the eyepiece. This grating is optically coupled to a waveguide and is designed to diffract a first portion of light toward the eye as a first order reflection and a second portion of light away from the eye as a first order transmission, while minimizing second order reflections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a diffractive optical element with multiple levels is used, then light projection efficiency toward the viewer is improved, but device complexity increases
Solution Approach 1:
The diffractive optical element is segmented into multiple discrete levels (first level, second level, third level) with different heights. Each level segment corresponds to a specific phase modulation range, allowing independent optimization of diffraction efficiency for different orders while maintaining manufacturability through stepped structures.
Solution Approach 2:
The patent optimizes specific parameters of the diffractive optical element including the height differences between levels (first height difference corresponding to first wavelength, second height difference corresponding to second wavelength), the widths of ridges at different levels, and the spacing between adjacent ridges. These parameter variations enable simultaneous control of diffraction efficiency for multiple wavelengths and orders.
2Object-affected harmful factors
If a three-level grating is used to minimize second order reflections, then image clarity is improved, but manufacturing precision requirements increase
Solution Approach 1:
The grating structure is divided into three distinct levels with clearly defined height steps. The first level has a first height, the second level has a second height greater than the first, and the third level has a third height greater than the second. This segmentation creates discrete phase zones that are more tolerant to manufacturing variations compared to continuous profiles.
Solution Approach 2:
The patent specifies optimized parameter ranges for the grating structure including height differences (first height difference, second height difference), ridge widths (first ridge width, second ridge width), and spacing between ridges. These parameter optimizations balance the suppression of second-order reflections with practical manufacturing capabilities.
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
The three-level grating significantly enhances the efficiency of light projection toward the viewer, reduces unwanted light directed toward the world, and minimizes second order reflections, thereby improving the overall performance and clarity of the augmented reality experience.
Implementation Method 1
The diffractive optical element may be configured to diffract a first portion of the light propagating in the waveguide toward the eye as a first order reflection, and to diffract a second portion of the light propagating in the waveguide away from the eye as a first order transmission
Data Source
AI summary
A viewing optics assembly for augmented reality includes a projector configured to generate image light and an eyepiece optically coupled to the projector. The eyepiece includes at least one eyepiece layer comprising a waveguide having a surface, an incoupling grating coupled to the waveguide, and an outcoupling grating coupled to the waveguide. The outcoupling grating comprises a first array of first ridges protruding from the surface of the waveguide, each of the first ridges having a first height in a direction perpendicular to the surface and a first width in a direction parallel to the surface and a plurality of second ridges, each of the plurality of second ridges protruding from a respective first ridge of the first ridges and having a second height and a second width. At least one of the first width or the second width varies as a function of position across the surface.