Journal
NANO LETTERS
Volume 21, Issue 20, Pages 8642-8649Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.nanolett.1c02612
Keywords
Metalenses; metasurfaces; silicon membrane; high aspect ratio structures; flat optics; infrared optics
Categories
Funding
- Defense Advanced Research Projects Agency (DARPA) [HR00111810001]
- A*STAR Singapore through the National Science Scholarship Scheme
- NWO Rubicon Grant [019.173EN.010]
- Dutch Funding Agency NWO
- National Science Foundation under NSF [ECCS-2025158]
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This study introduces an alternative metasurface geometry based on high aspect ratio via-holes, designing and characterizing metalenses that focus incident infrared light into a diffraction-limited spot. By engineering both transmitted phase and amplitude profiles simultaneously, the impedance match between the incident and transmitted waves is improved, leading to increased focusing efficiency. The holey platform enhances the accessible aspect ratio of optical nanostructures while maintaining mechanical robustness, paving the way for a generation of high aspect ratio ruggedized flat optics.
Free-standing nanofins or pillar meta-atoms are the most common constituent building blocks in metalenses and metasurfaces in general. Here, we present an alternative metasurface geometry based on high aspect ratio via-holes. We design and characterize metalenses comprising ultradeep via-holes in 5 mu m thick free-standing silicon membranes with hole aspect ratios approaching 30:1. These metalenses focus incident infrared light into a diffraction-limited spot. Instead of shaping the metasurface optical phase profile alone, we engineer both transmitted phase and amplitude profiles simultaneously by inverse-designing the lens effective index profile. This approach improves the impedance match between the incident and transmitted waves, thereby increasing the focusing efficiency. The holey platform increases the accessible aspect ratio of optical nanostructures without sacrificing mechanical robustness. The high nanostructure aspect ratio also increases the chromatic group delay range attainable, paving the way for a generation of high aspect ratio ruggedized flat optics, including large-area broadband achromatic metalenses.
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