Nanobeam Metasurface Gratings for Compact AR Waveguide Coupling
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Solution Overview
Problem
Challenges exist in creating augmented reality (AR) technology that seamlessly integrates virtual image elements with real-world imagery, providing a comfortable and natural-feeling experience.
Innovation Solution
The use of metasurfaces with nanobeams arranged in specific orientations and spacings to diffract visible light, integrated into waveguides and head-mounted displays, allowing for the projection of AR image content while maintaining a view of the real environment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If conventional optical elements are used in AR displays, then the system can project virtual image elements, but the device becomes bulky and complex
Solution Approach 1:
The patent replaces conventional mechanical optical elements (lenses, mirrors, gratings) with a metasurface that uses sub-wavelength nanobeams to control light through electromagnetic resonance and diffraction. This substitution eliminates the need for bulky optical components while achieving the same light manipulation functions required for AR display, thereby reducing device volume while maintaining AR image integration quality
Solution Approach 2:
The metasurface achieves compact optical control by changing the physical parameters of light interaction at the sub-wavelength scale. By designing nanobeams with specific dimensions (smaller than the wavelength of light) and arranging them in periodic patterns, the system achieves diffraction and light steering effects that would traditionally require much larger optical elements, thus reducing overall device volume
2Volume of moving object
If metasurfaces with sub-wavelength nanobeams are used, then the optical system becomes compact, but the manufacturing precision requirements increase
Solution Approach 1:
The metasurface is divided into discrete unit cells, each containing multiple nanobeams with specific orientations and spacings. This segmentation allows the complex optical function to be achieved through repeated patterns of simpler elements, making the manufacturing process more manageable. Each unit cell can be fabricated using standard lithography processes, and the overall pattern can be generated through computational design tools
Solution Approach 2:
The nanobeam metasurface structure serves multiple optical functions simultaneously: it acts as a diffraction grating for light steering, provides wavelength selectivity through resonant coupling, and enables polarization control. This multi-functionality is achieved within the same compact structure, reducing the need for separate optical components and thereby reducing overall manufacturing complexity despite the sub-wavelength precision requirements
3Productivity
If nanobeams are spaced sub-wavelength apart, then light diffraction is enhanced, but the device complexity increases
Solution Approach 1:
The patent employs asymmetric unit cell designs where nanobeams are arranged in non-uniform patterns with varying orientations and spacings. This asymmetry creates strong diffraction effects and enables control over the direction and polarization of scattered light. The asymmetric design enhances light diffraction efficiency while the periodic repetition of unit cells provides manufacturing regularity, balancing productivity enhancement with device complexity management
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
Enhances the integration of virtual and real-world imagery by diffracting light to propagate under total internal reflection, providing a more immersive AR experience.
Implementation Method 1
a metasurface configured to diffract visible light having a wavelength. The metasurface includes a plurality of repeating unit cells, where each unit cell consists of two to four sets of nanobeams
Implementation Method 2
the one or more first nanobeams and the plurality of second nanobeams are arranged to diffract light at a diffraction angle relative to the direction of an incident light, and to cause the diffracted light to propagate in the substrate under total internal reflection
Data Source
AI summary
Metasurfaces provide compact optical elements in head-mounted display systems to, e.g., incouple light into or outcouple light out of a waveguide. The metasurfaces may be formed by a plurality of repeating unit cells, each unit cell comprising two sets or more of nanobeams elongated in crossing directions: one or more first nanobeams elongated in a first direction and a plurality of second nanobeams elongated in a second direction. As seen in a top-down view, the first direction may be along a y-axis, and the second direction may be along an x-axis. The unit cells may have a periodicity in the range of 10 nm to 1 μm, including 10 nm to 500 nm or 300 nm to 500 nm. Advantageously, the metasurfaces provide diffraction of light with high diffraction angles and high diffraction efficiencies over a broad range of incident angles and for incident light with circular polarization.