Fold Waveguide Grating for Wider TIR Angular Bandwidth
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Solution Overview
Problem
Waveguide gratings are limited by narrow angular bandwidths, which restrict the range of ray angles that can be efficiently guided, particularly in applications like near-eye displays and sensors, and current methods of stacking or multiplexing gratings are hindered by holographic scatter and material modulation uniformity.
Innovation Solution
A waveguide fold grating design with two TIR surfaces and a grating that diffracts input light twice, ensuring each ray and its corresponding diffracted ray lie on the diffraction cone with unique TIR angular ranges, and uses Bragg or SBG gratings with spatially varying thickness and diffraction efficiency to expand the angular bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If transmission holographic gratings are used for in-coupling and out-coupling light, then these functions are performed efficiently, but their narrow angular bandwidth imposes tighter angular limits on the image content that can be transmitted
Solution Approach 1:
The waveguide is divided into multiple sections, each containing a different grating layer with specific angular bandwidth characteristics. This segmentation allows each layer to handle specific angular ranges, collectively expanding the overall angular bandwidth while maintaining efficient light coupling in each segment.
Solution Approach 2:
The patent transitions from using a single grating layer to stacking multiple grating layers in the vertical dimension. This dimensional change enables the system to handle a broader range of ray angles by distributing different angular ranges across multiple layers, effectively expanding angular bandwidth without sacrificing coupling efficiency.
2Adaptability or versatility
If multiple gratings are stacked or multiplexed to overcome angular limitations, then angular bandwidth is expanded, but stacking is limited by holographic scatter and multiplexing is limited by material modulation uniformity
Solution Approach 1:
Each grating layer is designed with locally optimized properties, including specific spatial frequency, orientation, and modulation depth tailored to handle particular angular ranges. This local quality optimization minimizes holographic scatter within each layer while maintaining the desired angular bandwidth expansion across the stacked structure.
Solution Approach 2:
The patent systematically varies key parameters across different grating layers, including spatial frequency, grating orientation, and modulation depth. These parameter changes enable each layer to operate in its optimal performance regime, reducing holographic scatter while collectively achieving expanded angular bandwidth.
3Device complexity
If prototype fold gratings are used to change beam propagation direction and beam expansion in a single grating layer, then device complexity is reduced, but they have narrow angular bandwidths
Solution Approach 1:
The single fold grating layer is segmented into multiple sub-layers or zones, each handling specific angular ranges. This segmentation maintains the structural simplicity of using grating layers while expanding the angular bandwidth by distributing different angular functions across multiple segments within the same layer structure.
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 significantly expands the angular bandwidth of waveguides, allowing for efficient light propagation and reduced scatter, enabling full angular capability and minimizing crosstalk between channels in displays and sensors.
Implementation Method 1
Input TIR light with a first angular range along a first propagation direction undergoes at least two diffractions, wherein each ray from the first angular range and its corresponding diffracted ray lie on the diffraction cone of the grating
Implementation Method 2
an optical waveguide with least two TIR surfaces containing a grating. Input TIR light with a first angular range along a first propagation direction
Data Source
AI summary
An optical waveguide comprises at least two TIR surface and contains a grating. Input TIR light with a first angular range along a first propagation direction undergoes at least two diffractions at the grating. Each diffraction directs light into a unique TIR angular range along a second propagation direction.