Resonant Waveguide Grating for Near-Eye Displays
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Solution Overview
Problem
Current near-eye display technologies face challenges in achieving wide Field Of View (FOV), high lateral image resolution, large RGB gamut, and large exit pupil with minimal chromatic dispersion and interference, while also being compact and lightweight, due to limitations in diffractive optical elements and manufacturing complexities.
Innovation Solution
A resonant waveguide grating with a specific arrangement of subwavelength structures, allowing continuous light beam redirection by incoupling and outcoupling light in a single guided mode at arbitrary angles, using a waveguiding layer with non-regular spacing and varying groove and ridge dimensions to enhance spectral and angular selectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If diffractive optical elements are used to redirect light in near-eye displays, then light redirection is achieved, but chromatic dispersion and interference increase
Solution Approach 1:
The patent changes the operating parameters from conventional diffractive elements to resonant waveguide gratings operating at subwavelength periodicities. By operating in the resonant regime with periodicities significantly smaller than the wavelength (e.g., one-third of the wavelength), the system achieves light redirection while suppressing chromatic dispersion through the resonant coupling mechanism rather than conventional diffraction.
2Reliability
If conventional grating structures are used, then light filtering is achieved, but manufacturing precision requirements increase
Solution Approach 1:
The patent transitions from surface-relief gratings to a three-dimensional waveguide structure with subwavelength periodicity. By embedding the grating within a waveguide layer and utilizing the vertical dimension for resonant mode coupling, the system achieves high optical selectivity through the resonant condition while the subwavelength periodicity provides robustness against manufacturing variations in the lateral dimensions.
3Object-affected harmful factors
If resonant waveguide gratings with subwavelength periodicity are used, then chromatic dispersion is reduced, but device complexity increases
Solution Approach 1:
The patent merges the grating structure with the waveguide layer, creating an integrated resonant waveguide grating where the grating periodicity is embedded within the waveguide medium. This combination eliminates the need for separate diffractive elements and reduces parasitic diffraction by confining the optical field within the waveguide, thereby suppressing unwanted diffraction orders while maintaining a compact structure.
4Adaptability or versatility
If multiple diffractive orders are allowed, then light redirection flexibility increases, but interference and image quality deteriorate
Solution Approach 1:
The patent changes the periodicity parameter to subwavelength scales, which fundamentally alters the diffraction behavior. At subwavelength periodicities, the resonant waveguide grating supports only a single propagating diffractive order due to the resonant coupling condition, thereby eliminating interference from multiple orders while maintaining light redirection flexibility through angular and spectral selectivity control.
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 solution enables high transparency, low parasitic diffraction, and high selectivity, allowing for efficient light redirection with improved FOV, resolution, and color accuracy, while being easier to manufacture and more adaptable to various inter-pupillary distances.
Implementation Method 1
A resonant waveguide grating, also called guided-mode resonance filter, consists of a combination of a subwavelength grating and a thin waveguide. Such structures have a multilayer configuration and a basic arrangement comprises a substrate, a thin dielectric or semiconductor or metallic waveguiding layer and possibly an additional layer in which a grating is formed. A so called resonance occurs when the incident light is diffracted by the grating and matches a mode of the waveguide.
Implementation Method 2
A resonant waveguide grating, also called guided-mode resonance filter, consists of a combination of a subwavelength grating and a thin waveguide. A so called resonance occurs when the incident light is diffracted by the grating and matches a mode of the waveguide.
Implementation Method 3
A resonant waveguide grating, also called guided-mode resonance filter, consists of a combination of a subwavelength grating and a thin waveguide. Such structures have a multilayer configuration and a basic arrangement comprises a substrate, a thin dielectric or semiconductor or metallic waveguiding layer
Data Source
Figure 1~2
Figure 3a~3h
Figure 4a~4b
AI summary
A resonant waveguide grating is disclosed comprising a waveguiding layer, comprising a plurality of subwavelength structures. The waveguiding layer, being in optical proximity to the plurality of subwavelength structures, is configured to guide at most ten wave-guided light modes in a predetermined wavelength range. Said plurality of subwavelength structures comprises at least two adjacent grooves having a subwavelength distance between their groove centers being different than the subwavelength distance between the centers of two adjacent ridges. The plurality of subwavelength structures are configured to couple out of said waveguiding layer resonantly by diffraction, an outcoupled fraction of an incoupled portion of incident light. The resonant waveguide grating is configured to outcouple a fraction of the incoupled portion of incident light having a predetermined central wavelength λ0 in a predetermined wavelength range and has a predetermined spectral width Δλ, said outcoupled fraction being a diffracted part of an incident light beam. The invention is also achieved by a diffractive optical combiner and also by a diffractive optical coupler, both comprising the resonant waveguide grating of the invention. A near-eye display apparatus is also disclosed comprising at least resonant waveguide grating of the invention.