Polarization-Independent, Narrowband, Near-IR Spectral Filters via Guided Mode Resonances in Ultrathin a-Si Nanopillar Arrays
Abstract
We report the optical properties obtained through experiments, simulation, and theory of ultrathin (<0.1λ), amorphous Si nanopillar arrays embedded in a thin film of SiO_2 designed for narrowband filtering for multi- and hyperspectral imaging in the near-infrared. The fabricated nanopillar arrays are square-packed with subwavelength periodicity, heights of ∼100 nm, and a radius-to-spacing ratio, r/a, of ∼0.2. Specular reflection measurements at normal incidence demonstrate that these arrays behave as narrow stopband filters in the near-infrared (λ = 1300–1700 nm) and attain ∼90% reflectivity in band and a full width at half-maximum as low as 20 nm. Using a combination of full-wave simulations and theory, we demonstrate that these narrowband filtering properties arise from efficient grating coupling of light into guided modes of the array because the nanopillar arrays serve as photonic crystal slabs. This phenomenon is known as a guided mode resonance. We discover that the spectral location of these resonances is passively tunable by modifying array geometry and is most sensitive to nanopillar spacing. Theoretical photonic crystal slab band diagrams accurately predict the spectral locations of the observed resonance and provide physical insights into and support the guided mode resonance formulation. This work demonstrates that these ultrathin all-dielectric nanopillar arrays have advantages over existing hyperspectral filter designs because they are polarization independent, do not suffer from material absorption loss, and have significant implications for minimizing imaging device size.
Additional Information
© 2019 American Chemical Society. Received: September 6, 2018; Published: January 7, 2019. The authors gratefully acknowledge the financial support of Department of Defense through J.R.G.'s Vannevar-Bush Faculty Fellowship and the critical support and infrastructure provided by the Kavli Nanoscience Institute at Caltech. The authors also thank Harry Atwater for computational resources used to calculated a portion of these results. The authors declare no competing financial interest.Attached Files
Supplemental Material - ph8b01253_si_001.pdf
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Additional details
- Eprint ID
- 92240
- Resolver ID
- CaltechAUTHORS:20190114-082742867
- Vannever Bush Faculty Fellowship
- Created
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2019-01-14Created from EPrint's datestamp field
- Updated
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2021-11-16Created from EPrint's last_modified field
- Caltech groups
- Kavli Nanoscience Institute