Diffractive Optical Structure for AR Waveguide Out-Coupling Control
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Solution Overview
Problem
Existing AR optical solutions face challenges in modulating diffraction efficiency in non-in-coupling regions and achieving flexible shifting control of the grating diffraction-efficiency curve, limiting the overall efficiency of waveguides.
Innovation Solution
A diffractive optical structure with a substrate and grating structure comprising periodically arranged grating ridges and grooves filled with materials of different refractive indices, allowing for precise control of the average refractive index within one grating unit period to optimize light out-coupling efficiency and uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional grating structures with uniform materials are used, then the structure is simple and easy to manufacture, but the diffraction efficiency modulation capability in non-in-coupling regions is limited
Solution Approach 1:
The patent applies local quality by filling different regions of the grating structure with materials having different refractive indices. Specifically, the grating grooves are filled with materials having refractive indices different from the substrate and from each other, creating spatially varying optical properties that enable precise control of diffraction efficiency in different regions of the waveguide.
Solution Approach 2:
The patent employs composite materials by combining multiple materials with different refractive indices within the grating structure. The grating ridges and grooves are filled with at least two different materials (e.g., high refractive index material in ridges, low refractive index material in grooves), creating a composite structure that achieves enhanced diffraction efficiency modulation while maintaining manufacturing feasibility through established material deposition techniques.
2Productivity
If the average refractive index in grating grooves is increased to enhance diffraction efficiency, then out-coupling efficiency improves, but the ability to shift the diffraction-efficiency curve flexibly is reduced
Solution Approach 1:
The patent applies parameter changes by precisely controlling the average refractive index of materials in the grating grooves to fall within the specific range of 1.1≤n≤2.4. This parameter optimization enables the diffraction-efficiency curve to be shifted flexibly along the angular direction while maintaining high out-coupling efficiency, resolving the contradiction between efficiency and adaptability.
Solution Approach 2:
The patent creates local quality variations by using different refractive index materials in different regions (ridges vs. grooves) and potentially different materials in different segments of the grating structure. This allows independent optimization of local diffraction characteristics, enabling flexible shifting of the diffraction-efficiency curve while maintaining overall high efficiency through the carefully designed average refractive index range.
3Adaptability or versatility
If multiple materials with different refractive indices are used in grating grooves, then diffraction efficiency modulation capability is enhanced, but manufacturing complexity increases
Solution Approach 1:
The patent uses composite materials with at least two different refractive indices in the grating structure, combining high refractive index materials for ridges with low refractive index materials for grooves. This composite approach enhances diffraction efficiency modulation capability while the materials are selected from standard optical materials that can be deposited using conventional semiconductor manufacturing techniques, thereby limiting the increase in manufacturing complexity.
Solution Approach 2:
The patent controls the average refractive index parameter to remain within the optimized range of 1.1≤n≤2.4, which allows the use of conventional optical materials rather than requiring exotic or highly specialized materials. This parameter constraint simplifies the material selection process and reduces manufacturing complexity while still achieving enhanced diffraction efficiency modulation.
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 structure achieves precise shifting of the diffraction-efficiency curve, enhancing out-coupling efficiency and uniformity by adjusting the average refractive index, thereby optimizing light transmission and reducing loss in augmented-reality devices.
Implementation Method 1
the out-coupling region includes a grating structure that comprises a plurality of periodically arranged grating ridges and grating grooves between adjacent grating ridges
Implementation Method 2
the grating grooves contain at least two materials having different refractive indices; an average refractive index n of the different materials within one grating unit period
Data Source
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AI summary
The present disclosure provides a diffractive optical structure and a near-eye display device. The diffractive optical structure includes a substrate (3) and an in-coupling region (1) and an out-coupling region (2) provided on the substrate (3). The out-coupling region (2) includes a grating structure that includes a plurality of periodically arranged grating ridges (201) and grating grooves (202) between adjacent grating ridges (201), and the grating grooves contain at least two materials having different refractive indices. An average refractive index n of the different materials within one grating unit period of the grating structure satisfies 1.1<n≤2.4, where n¯=∑i=1mnm∗VmVunitcell, V1, ..., Vm are respectively the volumes or areas of the first to the m-th material, n1, ..., nm are the refractive indices of the first to the m-th material, and Vunitcell is the volume or area of one grating unit period.