Abnormal wave propagation of high-k modes in tilted linear-crossing metamaterials

TL;DR

This paper introduces tilted linear-crossing metamaterials (TLCMM) with tunable optical axes, revealing unique wave propagation phenomena like abnormal refraction and filtering, supported by experimental validation in circuit-based systems.

Contribution

It proposes a new class of metamaterials with tunable optical axes that exhibit novel wave propagation behaviors, including type-III Dirac cone features and abnormal refraction effects.

Findings

TLCMM can achieve abnormal refraction without reflection.

Experimental demonstration of phenomena in circuit-based TLCMM.

Potential applications in planar photonics for cloaking and switching.

Abstract

In this work, we treat the rotation of the optical axis as a new degree of freedom and theoretically propose a tilted linear-crossing metamaterials (TLCMM). Specifically, the conical dispersions of the NLCMM and TLCMM have the same shapes as type-I and type-II Dirac cones, respectively, in condensed matter physics. Upon rotating the optical axis angle such that it is equal to the cone angle, we find that this special TLCMM has the shape of a type-III Dirac cone. This critical TLCMM can have many unique properties and is of a fundamentally different nature than neighboring phases. When EM waves with large wave vectors are incident to a metamaterial with an open IFC to free space, the incident EM wave is strongly reflected due to wave-vector mismatch. Here, we use boundary conditions and the causality law to reveal that TLCMM high-k modes can achieve abnormal refraction without reflection and filtering. Moreover, these phenomenon are observed experimentally in a planar circuit-based system. The circuit-based TLCMM not only provides a versatile platform for the study of robust negative refraction phenomena in metamaterials, but also has a planar structure that is easier to integrate. Our results regarding the manipulation of EM waves may enable their use in planar-integrated photonics including for directional propagation, cloaking, and switching.