Structural second-order nonlinearity in metamaterials

TL;DR

This paper demonstrates a strong bulk second-order nonlinear response in a centrosymmetric plasmonic nanorod metamaterial, advancing understanding and design of integrated nonlinear photonic devices.

Contribution

It introduces a composite metamaterial exhibiting significant second-order nonlinearity and develops an effective-medium theory to describe its physics, highlighting its limitations.

Findings

Strong second harmonic generation in the metamaterial.

Effective-medium theory describes nonlinear polarization well.

Emission of second harmonic light exceeds theoretical predictions.

Abstract

Nonlinear processes are at the core of many optical technologies including lasers, information processing, sensing, and security, and require optimised materials suitable for nanoscale integration. Here we demonstrate the emergence of a strong bulk second-order nonlinear response in a composite plasmonic nanorod material comprised of centrosymmetric materials. The metamaterial provides equally strong generation of the p-polarized second harmonic light in response to both s- and p-polarized excitation. We develop an effective-medium description of the underlying physics, compare its predictions to the experimental results and analyze the limits of its applicability. We show that while the effective medium theory adequately describes the nonlinear polarization, the process of emission of second harmonic light cannot be described in the same framework. The work provides an understanding of the emergent nonlinear optical response in composites and opens a doorway to new nonlinear optical platform designs for integrated nonlinear photonics.