Analysis of Nonlinear Electromagnetic Metamaterials

TL;DR

This paper develops a theoretical framework for analyzing nonlinear electromagnetic metamaterials with embedded nonlinear components, validated by experiments on varactor-loaded split ring resonators demonstrating nonlinear effects like harmonic generation and resonance shifts.

Contribution

It introduces a homogenization method to describe nonlinear metamaterials as continuous media, enabling accurate prediction of nonlinear phenomena in complex structures.

Findings

Theoretical expressions for nonlinear susceptibilities are validated experimentally.

The model accurately predicts intensity-dependent resonance frequency shifts.

Nonlinear effects such as harmonic generation and wave mixing are demonstrated.

Abstract

We analyze the properties of a nonlinear metamaterial formed by integrating nonlinear components or materials into the capacitive regions of metamaterial elements. A straightforward homogenization procedure leads to general expressions for the nonlinear susceptibilities of the composite metamaterial medium. The expressions are convenient, as they enable inhomogeneous system of scattering elements to be described as a continuous medium using the standard notation of nonlinear optics. We illustrate the validity and accuracy of our theoretical framework by performing measurements on a fabricated metamaterial sample composed of an array of split ring resonators (SRRs) with packaged varactors embedded in the capacitive gaps in a manner similar to that of Wang et al. [Opt. Express 16, 16058 (2008)]. Because the SRRs exhibit a predominant magnetic response to electromagnetic fields, the varactor-loaded SRR composite can be described as a magnetic material with nonlinear terms in its effective magnetic susceptibility. Treating the composite as a nonlinear effective medium, we can quantitatively assess the performance of the medium to enhance and facilitate nonlinear processes, including second harmonic generation, three- and four-wave mixing, self-focusing and other well-known nonlinear phenomena. We illustrate the accuracy of our approach by predicting the intensity-dependent resonance frequency shift in the effective permeability of the varactor-loaded SRR medium and comparing with experimental measurements.