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.

Highlights

  • Absorbers are crucial components in electromagnetic (EM) wave detection and energy harvesting devices such as photovoltaics [1, 2], thermophotovoltaics [3]–[7], bolometers [8]–[10] and imaging devices [11]–[13]

  • We argue that the performance of the aperiodic photonic crystals (PCs) designs is strongly correlated to the properties of their entry building block

  • We proposed an aperiodic absorbing PC route to engineering broadband EM absorption

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Summary

INTRODUCTION

Absorbers are crucial components in electromagnetic (EM) wave detection and energy harvesting devices such as photovoltaics [1, 2], thermophotovoltaics [3]–[7], bolometers [8]–[10] and imaging devices [11]–[13]. Many current research efforts are focusing on optimizing EM absorption with different mechanisms such as near-field enhancement through plasmonic resonances [1, 2, 14, 15] or impedance-matching by metamaterial structures [16]–[19]. The underlying mechanism was a combination of a quickly vanishing lossy Floquet-Bloch mode [25, 27] and tailoring of the energy velocity at the interface [24, 25] Careful engineering of such phenomenon has led to a compact-superabsorber design where 90% of light gets absorbed within the top absorbing layer of thickness λ/1000 [25]. Based on the determined principles, we present, a shrinked aperiodic PC design which demonstrates an averaged, –within the SiC Reststrahlen band–, absorption enhancement with a value close to 10.

SYSTEM UNDER STUDY
METHODOLOGY
ANGULAR ROBUSTNESS OF THE BROADBAND SUPERABSORPTION
DESIGN OPERATION AND OPTIMISATION
SIGNIFICANCE OF THE APERIODIC PC’S BUILDING BLOCK SEQUENCE
SHRINKING THE SIZE OF THE BROADBAND APERIODIC PC SUPERABSORBERS
Findings
CONCLUSIONS
Full Text
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