Variable Index Grating Elements for AR Waveguide Light Coupling
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Solution Overview
Problem
Current augmented reality (AR) devices face challenges in creating high-performance, cost-effective optical waveguides with surface relief gratings for efficient light coupling and expansion, which are crucial for providing a uniform and immersive AR experience.
Innovation Solution
The development of optical waveguides with variable index grating elements, formed vertically on the waveguide substrate, and a method involving actinic radiation of varied intensities to create solubility-changing agents for precise grating formation, allowing for efficient light coupling and expansion through total internal reflection paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional surface relief grating fabrication methods are used, then manufacturing cost is reduced, but light coupling efficiency and uniformity deteriorate
Solution Approach 1:
The patent applies parameter changes by varying the refractive index of the grating elements vertically through the waveguide substrate. Instead of using uniform index gratings, the invention implements variable index gratings where the refractive index decreases from the top surface toward the bottom, creating optimized light coupling conditions that improve efficiency while maintaining manufacturability
Solution Approach 2:
The patent implements local quality by creating grating elements with non-uniform refractive index distribution. Each grating element has different refractive index at different depths, allowing localized optimization of light coupling properties at specific positions within the waveguide structure
2Manufacturing precision
If variable index grating elements are implemented, then light coupling efficiency is improved, but fabrication complexity increases
Solution Approach 1:
The patent replaces complex mechanical fabrication processes with a chemical approach. Instead of mechanically varying groove depths or using multiple lithography steps, the invention uses photosensitive materials that chemically respond to light intensity patterns, allowing variable index gratings to be formed through photochemical reactions rather than complex mechanical processing
Solution Approach 2:
The patent introduces a photosensitive material as an intermediary substance. This material converts optical patterns into chemical changes, enabling the transfer of light intensity information into refractive index variations without requiring direct mechanical manipulation of the grating structure itself
3Manufacturing precision
If actinic radiation of varied intensities is used to create solubility-changing agents, then grating formation precision is improved, but process time increases
Solution Approach 1:
The patent employs periodic action through the use of patterned actinic radiation exposure. By projecting periodic light patterns that correspond to the desired grating structure, the photosensitive material undergoes periodic chemical changes that directly form the grating pattern, enabling precise control of grating geometry through temporal and spatial modulation of the light source
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 enables the creation of low-cost, high-performance surface relief gratings for AR waveguide applications, enhancing light uniformity and efficiency across the eyebox, thereby improving the overall AR experience.
Implementation Method 1
forming the photosensitive material to cover the developable material filled in the grooves between the grating elements, the photosensitive material generating the solubility-changing agent in response to exposure of the actinic radiation of varied intensities
Implementation Method 2
causing the different regions of the solubility-changing agent to diffuse into corresponding underlying regions of the developable material at varied diffusion depths such that the solubility-changing agent changes a solubility of a top portion of the developable material
Implementation Method 3
an input grating coupler configured to couple light to propagate along a total internal reflection (TIR) path in the waveguide substrate
Implementation Method 4
an expansion grating coupler configured to expand the light that propagates in the waveguide substrate
Data Source
AI summary
Aspects of the present disclosure provide a method for fabricating a grating coupler. For example, the method can include providing a substrate, forming a plurality of grating elements and a photosensitive material above the substrate, and projecting actinic radiation of varied intensities to expose different regions of the photosensitive material, causing the photosensitive material to generate a solubility-changing agent. The method can also include removing the solubility-changing agent. The actinic radiation of varied intensities can correspond to depths of grooves between the grating elements.