Broadband Near-Unidirectional Absorption Enabled by Phonon-Polariton Resonances in SiC Micropyramid Arrays

Abstract

Inspired by moth eyes, nature’s most powerful antireflex, we present a subwavelength SiC micropyramid design, which operates in the reststrahlen band of SiC, namely, the spectral band of strong phonon-photon coupling in the SiC material. While within this band, SiC repels electromagnetic waves, we observe here a broad low-reflectivity window with unique attributes, with distinct characteristics different from typical dielectric moth-eye-like structures. To be specific, while the latter systems are entirely symmetric, the reflection response of our SiC micropyramid system can be highly asymmetric. In particular, the SiC micropyramid system can be near reflectionless for light impinging from the tip side of the micropyramids and can exhibit more than 90% reflection for light impinging from the base side of the micropyramids, over a broad wavelength range in the SiC reststrahlen band. This strongly asymmetric reflection response emanates from the cascaded coupling of vortexlike cavity modes at each of the SiC blocks comprising the micropyramids and translates into a strongly unidirectional absorber response. We discuss how, by virtue of Kirchhoff’s law, this strongly unidirectional superabsorber behavior implies a strongly unidirectional emission profile that is important for one-way infrared sources and passive-radiative-cooling systems.

Ganga Chinna Rao Devarapu

Researcher in Nanophotonics

My research interests include silicon photonics, photonic crystals and biomedical devices.