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Proceedings Paper

Fabrication of ultra-thin Si nanopillar arrays for polarization-independent spectral filters in the near-IR
Author(s): Ryan C. Ng; Julia R. Greer; Katherine T. Fountaine
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Paper Abstract

Sub-wavelength arrays have garnered significant interest for many potential optoelectronics applications. We fabricated sub-wavelength silicon nanopillar arrays with a ratio of radius, r and a center-to-center distance, a, of r/a ≈ 0.2 that were fully embedded in SiO2 for narrow stopband filters that are compact and straightforward to fabricate compared to conventional Bragg stack reflectors. These arrays are well-suited for hyperspectral filtering applications in the infrared. They are ultra-thin (<0.1λ), polarization-independent, and attain greater efficiencies enabled by low loss compared to plasmonic-based designs. The choice of Si as the nanopillar material stems from its low cost, high index of refraction, and a band gap of 1.1 eV near the edge of the visible.

These arrays exhibit narrow near-unity reflectivity resonances that arise from coupling of an incident wave into a leaky waveguide mode via a grating vector that is subsequently reradiated, also known as guided mode resonances (GMRs). Simulations reveal reflectivities of >99% with full width at half maxima (FWHM) of ≈0.01 μm. We demonstrate a fabrication route for obtaining nanopillar arrays that exhibit these GMRs. We experimentally observed a GMR with an amplitude of ~0.8 for filter arrays fabricated on silicon on insulator (SOI) substrates, combined with Fabry-Perot interference that stems from the underlying silicon layer.

Paper Details

Date Published: 21 February 2018
PDF: 6 pages
Proc. SPIE 10541, Photonic and Phononic Properties of Engineered Nanostructures VIII, 105411D (21 February 2018); doi: 10.1117/12.2286804
Show Author Affiliations
Ryan C. Ng, California Institute of Technology (United States)
Julia R. Greer, California Institute of Technology (United States)
Katherine T. Fountaine, Northrop Grumman Corp. (United States)

Published in SPIE Proceedings Vol. 10541:
Photonic and Phononic Properties of Engineered Nanostructures VIII
Ali Adibi; Shawn-Yu Lin; Axel Scherer, Editor(s)

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