Slab Waveguide Layer for Uniform RGB Grating Diffraction
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Solution Overview
Problem
Existing augmented reality waveguide combiners face challenges in efficiently displaying virtual images overlaid on ambient environments due to disparities in diffraction efficiency across different wavelength channels, leading to misalignment and uneven propagation of light beams.
Innovation Solution
A waveguide structure comprising a waveguide substrate, a slab waveguide layer with specific refractive indices and depths, and gratings with optimized grating structures to enhance diffraction efficiency and minimize angular dispersion, ensuring uniform propagation of blue, green, and red channel lights.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional waveguide structures are used, then the device complexity is reduced, but the diffraction efficiency varies across different wavelength channels causing misalignment
Solution Approach 1:
The waveguide structure is segmented into multiple functional layers: a substrate layer, a slab waveguide layer with specific refractive index (2.0-2.5), and a superstrate layer. Each layer is optimized for specific wavelength ranges, with the slab waveguide layer specifically designed to guide blue light (480-495nm) while the substrate handles other wavelengths. This segmentation allows different wavelength channels to be managed by appropriate layers, ensuring uniform diffraction efficiency across all channels.
Solution Approach 2:
The slab waveguide layer is positioned at a specific depth (50-150 nm) from the grating surface and has a localized refractive index (2.0-2.5) that differs from both the substrate (1.5-1.8) and superstrate (1.4-1.6). This local quality optimization ensures that blue light is efficiently guided and diffracted at the intended location, while other wavelengths propagate through the substrate, preventing cross-channel interference and alignment issues.
2Reliability
If multiple substrates are used to handle different wavelength channels, then the diffraction efficiency for each channel is improved, but the device complexity and number of components increases
Solution Approach 1:
The substrate layer serves multiple functions: it acts as the primary waveguide for red (620-750nm) and green (495-570nm) wavelength channels, provides mechanical support for the entire structure, and serves as the base layer for fabricating the slab waveguide and grating structures. This multi-functionality eliminates the need for separate substrates for different wavelength channels, reducing component count while maintaining alignment precision.
Solution Approach 2:
The slab waveguide layer acts as an intermediary element that selectively interacts with blue light (480-495nm) by providing a refractive index mismatch that guides and diffracts this specific wavelength range. It mediates between the blue light source and the grating structures, ensuring proper coupling and diffraction efficiency without interfering with other wavelength channels that propagate through the substrate.
3Reliability
If the slab waveguide layer has higher refractive index than substrate and superstrate, then the diffraction efficiency for blue channel is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The slab waveguide layer uses a refractive index range (2.0-2.5) that is higher than both the substrate (1.5-1.8) and superstrate (1.4-1.6), creating the necessary condition for total internal reflection and efficient blue light guidance. This parameter optimization ensures that blue light is effectively confined and diffracted at the grating location, significantly improving diffraction efficiency for the blue channel.
Solution Approach 2:
The slab depth is designed to be relatively shallow (50-150 nm) compared to the grating period, which is sufficient to achieve the desired blue light guidance and diffraction enhancement. This partial action approach provides adequate performance improvement without requiring excessive depth that would be difficult to manufacture, thus balancing performance gains with manufacturing feasibility.
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 proposed waveguide structure improves diffraction efficiency, aligns the fields of view for different color channels, and reduces the number of substrates required, enhancing the overall display quality and efficiency of augmented reality devices.
Implementation Method 1
a slab waveguide layer disposed over the waveguide substrate, the slab waveguide layer having a slab RI nswg... The slab RI nswg is greater than the substrate RI nsub and the slab RI nswg is greater than the superstrate RI nsuperstrate
Implementation Method 2
Light is coupled into and out of augmented waveguide combiners using surface relief gratings... at least one grating defined by a plurality of grating structures
Data Source
AI summary
Embodiments of the present disclosure generally relate to augmented reality waveguide combiners. The waveguides includes a waveguide substrate, having a substrate refractive index (RI) nsub, a slab waveguide layer disposed over the waveguide substrate, the slab waveguide layer having a slab RI nswg and a slab depth dswg, the slab depth dswg from a lower surface to an upper surface of the slab waveguide layer, at least one grating defined by a plurality of grating structures, the grating structures are disposed in, on, or over the slab waveguide layer, and a superstrate between and over the grating structures, the superstrate having a superstrate RI nsuperstrate and an interface with the slab waveguide layer. The slab RI nswg is greater than the substrate RI nsub and the slab RI nswg is greater than the superstrate RI nsuperstrate.