Non-Uniform Thin-Film Diffractive Elements for Light Guide Brightness
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Solution Overview
Problem
Augmented reality headsets face challenges in maintaining uniform brightness across the display surface due to variations in light intensity as distance increases from the light source, leading to non-uniform brightness levels.
Innovation Solution
The implementation of diffractive elements with varying sizes and shapes over the light guide surface, utilizing thin-film stacks with non-uniform thicknesses, to compensate for brightness differences by adjusting light extraction based on distance from the light source.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If light extraction is increased at greater distances from the light source, then brightness uniformity across the display surface is improved, but the complexity of the diffractive element structure increases
Solution Approach 1:
The diffractive elements are designed with locally varying properties - specifically, the pitch (spacing between diffraction features) changes as a function of distance from the light source. Elements closer to the light source have one pitch value, while elements farther away have a different pitch value. This local variation in pitch allows each region of the light guide to extract the appropriate amount of light, achieving uniform brightness across the display surface without requiring complex additional components.
2Area of stationary object
If the light guide surface area is increased to provide a larger display, then the display field of view is improved, but the brightness non-uniformity worsens due to greater distance variations from the light source
Solution Approach 1:
The pitch parameter of the diffractive elements is changed as a function of position within the light guide. By varying the pitch parameter across different regions, the light extraction efficiency is adjusted to compensate for the inverse square law attenuation. This allows the system to maintain uniform brightness across a large display surface area, enabling extended field of view without sacrificing brightness uniformity.
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 ensures a more uniform brightness level across the display, enhancing the user's experience by maintaining consistent image quality and accuracy regardless of the distance from the light source.
Implementation Method 1
Diffractive elements, distributed over the surface area of the light guide, can extract at least some of the guided light from the light guide and direct the extracted light toward an eye of the user
Data Source
AI summary
In a thin film stack deposited on a substrate, a first layer can have a non-uniform thickness. A second layer, disposed so that the first layer is between the substrate and the second layer, can have a non-uniform thickness. A first pattern can be formed on the second layer to define first areas. The second layer can be etched in the first areas to form first holes having varying depths. A second pattern can be formed on the first layer in the first holes to define second areas. Each second area can be smaller than a corresponding first area. The first layer can be etched in the second areas to form second holes having varying depths. An imprint of the etched thin film stack can be formed such that the first holes and the second holes form a plurality of diffractive elements having varying sizes on the imprint.