Composites of resonant dielectric rods: A test of their behavior as metamaterial refractive elements

TL;DR

This paper investigates the optical behavior of dielectric rod composites at Mie resonances, revealing that negative refraction is diffraction-based and that effective medium theories do not accurately predict their properties, especially when disorder is introduced.

Contribution

It demonstrates that negative refraction in dielectric rod composites is caused by diffraction rather than true metamaterial behavior, challenging previous assumptions.

Findings

Negative refraction arises from diffraction, not effective medium properties.

Disordering the arrays increases transmission losses due to resonant scattering.

Effective medium theory fails to predict the observed optical behavior.

Abstract

We report numerical experiments of optical wave propagation in composites of high refractive index dielectric rods at frequencies where their first electric and magnetic Mie resonances are excited. The arrays of these particles have been extensively studied and proposed as non-absorbing and isotropic metamaterials. We show that negative refraction, observed in ordered particle arrays, is due to diffraction and that an effective medium theory yields constitutive parameters that do not reproduce the observations in these composites, whose transmission also depends on the sample shape. This is further confirmed by disordering the arrays, a case in which large transmission losses appear due to extinction by resonant scattering from the particles. Therefore, these composites although little absorbing have large extinction due to scattering.