Negative index and mode coupling in all-dielectric metamaterials at terahertz frequencies

Eric Akmansoy,Simon Marcellin,Miguel Navarro-Cía,Jiaguang Han

doi:10.1051/epjam/2018006

Abstract

We elucidate the role of the mode coupling of the Mie resonances in all-dielectric metamaterials to ensure a negative effective index at terahertz frequencies. We perform a study as a function of the lattice period and of the frequency overlapping of the modes of resonance. We show that negative effective refractive index requires sufficiently strong mode coupling and that for even more strong mode coupling, the first two modes of Mie resonances are degenerate; the effective refractive index is then undetermined. We also show that it is possible to obtain near-zero, or even null, effective index with a judicious adjustment of the mode coupling. Further, we discuss the mode coupling effect with hybridization in metamaterials.

Highlights

All-dielectric metamaterials (ADMs) are the promising “inflection” of metamaterials to go beyond their limits
The advantages of ADMs come from their low losses and their simple geometry: they do not suffer from Ohmic losses and they may benefit from low energy dissipation, specially, ceramics of high dielectric permittivity and high quality factor [1,2]
3.1 Negative index and mode coupling electric mode coupling effects in ADMs have been separately studied in the microwave by Zhang et al [36]

Summary

Introduction

All-dielectric metamaterials (ADMs) are the promising “inflection” of metamaterials to go beyond their limits. The advantages of ADMs come from their low losses and their simple geometry: they do not suffer from Ohmic losses and they may benefit from low energy dissipation, specially, ceramics of high dielectric permittivity and high quality factor [1,2]. In the microwave, their quality factor is greater than that of metallic metamaterials [3], and it is the case in terahertz (THz) and optical frequencies. We are dealing with a high refractive index bulk material (NTiO2 ⋍ 10)

Negative index and mode coupling

Monomode coupling

Bimodal coupling

Effective parameters

Conclusion