Regular papers

Broadband Mid-IR superabsorption with aperiodic polaritonic photonic crystals

School of Physics, College of Engineering, Mathematics and Physical Sciences (CEMPS), University of Exeter, Exeter, EX4 4QL, United Kingdom

^* s.foteinopoulou@exeter.ac.uk

Received: 11 December 2013
Revised: 28 January 2014

Abstract

We propose an approach for broadband near-perfect absorption with aperiodic-polaritonic photonic crystals (PCs) operating in the phonon-polariton gap of the constituent material. In this frequency regime the bulk polaritonic materials are highly reflective due to the extreme permittivity values, and so their absorption capabilities are limited. However, we are able to achieve absorptance of more than 90% almost across the entire phonon-polariton gap of SiC with a SiC-air aperiodic one-dimensional(1D)-PC with angular bandwidth that covers the range of realistic diffraction-limited sources. We explore two types of aperiodic PC schemes, one in which the thickness of the SiC layer increases linearly, and one in which the filling ratio increases linearly throughout the structure. We find that the former scheme performs better in terms of exhibiting smoother spectra and employing less SiC material. On the other hand, the second scheme performs better in terms of the required total structure size. We analyze the principles underpinning the broadband absorption merit of our proposed designs, and determine that the key protagonists are the properties of the entry building block and the adiabaticity of the aperiodic sequencing scheme. Further investigation with derivative lamellar sequences,–resulting by interchanging or random positioning of the original building blocks–, underline the crucial importance of the building block arrangement in an increasing order of thickness. If we relax the requirement of near-perfect absorption, we show that an averaged absorption enhancement across the SiC phonon-polariton gap of ~ 10 can be achieved with much shorter designs of the order of two free-space wavelengths. Our findings suggest that our aperiodic polaritonic PC route can be promising to design broadband electromagnetic absorbers across the spectrum.