Gradient Encapsulation in Waveguide Gratings for Efficiency and Directionality
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing augmented reality waveguide combiners face challenges in controlling the diffraction efficiency and directionality of out-coupled light, which affects the overlay of virtual images on the ambient environment.
Innovation Solution
A waveguide combiner design featuring gratings with varying fill ratios of encapsulants between structures, allowing for controlled diffraction efficiency and directionality, achieved through the use of asymmetric structures and encapsulant gradients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If surface relief gratings are used for light coupling in augmented waveguide combiners, then light can be coupled into and out of the waveguide, but the diffraction efficiency and directionality of the out-coupled light cannot be adequately controlled
Solution Approach 1:
The patent applies local quality by varying the encapsulant fill ratio across different regions of the grating structure. Specifically, the encapsulant material is present in some gaps between grating bars while absent in others, creating spatially varying local properties that enable independent control of diffraction efficiency and directionality. This localized variation in encapsulant presence allows different portions of the grating to contribute differently to the out-coupled light characteristics.
Solution Approach 2:
The patent employs asymmetry by creating non-uniform grating structures where adjacent grating bars have different characteristics. The encapsulant is selectively placed in gaps between certain grating bars while omitted from others, creating an asymmetric pattern. This asymmetry breaks the uniformity of conventional gratings and enables precise control over the diffraction properties, allowing simultaneous optimization of efficiency and directionality.
2Ease of manufacture
If grating depth is reduced to simplify fabrication, then manufacturing becomes easier, but diffraction efficiency control is compromised
Solution Approach 1:
The patent applies parameter changes by modifying the encapsulant fill ratio parameter across the grating structure. Instead of changing the grating depth parameter, the invention varies the presence and concentration of encapsulant material in the gaps between grating bars. This parameter variation enables control of diffraction efficiency and directionality while maintaining a consistent, manufacturable grating depth throughout the structure.
3Ease of manufacture
If uniform encapsulant fill is used between grating structures, then fabrication is simplified, but diffraction efficiency and directionality cannot be independently controlled
Solution Approach 1:
The patent applies segmentation by dividing the grating structure into distinct segments with different encapsulant fill characteristics. Individual gaps between grating bars are treated as separate segments, with some containing encapsulant material and others left empty. This segmentation allows independent control of optical properties for different portions of the grating, enabling simultaneous optimization of diffraction efficiency and directionality while maintaining a relatively simple fabrication process.
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 design enables full-range tuning of diffraction efficiency while maintaining directionality, enhancing the overlay of virtual images on the ambient environment without reducing grating depth.
Implementation Method 1
Light is coupled into and out of augmented waveguide combiners using surface relief gratings. The diffraction efficiency and directionality of the out-coupled light may not be adequately controlled.
Implementation Method 2
A first encapsulant is disposed in one or more gaps formed between adjacent first structures, where a fill ratio of the first encapsulant decreases along the first grating.
Data Source
AI summary
Embodiments described herein relate to gradient encapsulation of waveguide outcoupler gratings for control of diffraction efficiency and directionality. A device includes a first grating formed over a substrate, the first grating having a plurality of first structures extending away from the substrate, the first grating corresponding to an outcoupler. The device includes a first encapsulant disposed in one or more gaps formed between adjacent first structures, where a fill ratio of the first encapsulant decreases along the first grating. Also described herein are methods for fabricating the device.