Superimposed Diffractive Gratings for AR Waveguides
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Solution Overview
Problem
Existing diffractive gratings in waveguides for head-mounted displays face challenges in efficiently diffracting light, particularly due to the high cost and difficulty in working with high-refractive index materials, and the limitations in using materials that could provide additional benefits like light absorption.
Innovation Solution
The implementation of superimposed diffractive gratings, which combine a buried diffractive grating with a surface relief grating or another buried grating, allows for increased diffraction efficiency using either high-refractive index materials or lower refractive index materials, while also enabling the use of transparent conductive materials for light absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-refractive index materials are used to increase diffraction angle and image quality, then diffraction efficiency is improved, but manufacturing cost and difficulty increase
Solution Approach 1:
The patent divides the diffractive grating into multiple separate gratings positioned at different depths within the waveguide. Each grating can be manufactured independently using standard materials and processes, avoiding the need for difficult-to-manufacture high-refractive index materials while achieving superior diffraction efficiency through the combined effect of multiple gratings.
Solution Approach 2:
The patent uses composite structures consisting of multiple diffractive gratings with different properties positioned at different depths. This composite approach allows each grating to be made from suitable materials optimized for its specific function, rather than requiring all gratings to be made from difficult high-refractive index materials.
2Reliability
If high-refractive index materials are used to increase the difference in refractive indices, then diffraction angle increases and image quality improves, but material cost increases
Solution Approach 1:
By segmenting the diffractive function into multiple separate gratings, the patent enables use of lower-cost materials for each individual grating while achieving the cumulative diffraction effect that would otherwise require expensive high-refractive index materials.
Solution Approach 2:
The patent employs standard, readily available materials for manufacturing diffractive gratings instead of rare or expensive high-refractive index materials, reducing material costs while maintaining or improving performance through the multi-grating configuration.
3Reliability
If high-refractive index materials are used to improve diffraction, then diffraction efficiency increases, but material selection is limited
Solution Approach 1:
The patent segments the diffractive functionality into multiple independent gratings, allowing each grating to be manufactured from materials optimized for specific purposes (e.g., transparent conductive materials for light absorption, different materials for different wavelength ranges), thereby increasing material selection flexibility.
Solution Approach 2:
The multi-grating configuration allows different materials to be used for different gratings to achieve multiple functions simultaneously, such as light absorption, wavelength-specific diffraction, and polarization control, making the system more versatile than single-material approaches.
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 enhances the diffraction of light in waveguides, allows for cost-effective use of materials, and enables the incorporation of materials that provide additional benefits such as light absorption, thereby improving the quality and efficiency of virtual and augmented reality displays.
Implementation Method 1
waveguides include diffractive gratings, such as an input coupler (in-coupling) grating and an output coupler (out-coupling) grating. To diffract the light, waveguides include diffractive gratings
Implementation Method 2
transparent conductive materials which can be used to absorb unpolarized or polarized light
Implementation Method 3
head-mounted displays include waveguides made from glass or plastic which diffract light from an image source to an eye of a user
Data Source
AI summary
Head-mounted displays with waveguides comprising superimposed diffractive gratings and methods for fabricating said waveguides are described herein. In an embodiment, a head-mounted display comprises an optical element and an image source that provides an image beam to an optical element. The optical element comprises two gratings superimposed over each other, at least one of which comprising a buried diffractive grating. The buried diffractive grating comprises a high-refractive index material interspersed with a low-refractive index material or non-solid pockets, such as gas, air or vacuum. Light diffracted by a first of the two gratings is further diffracted by a second of the two gratings without interacting with a surface of the optical element between diffractions.