Broadband, electrically tuneable, third harmonic generation in graphene

TL;DR

This paper demonstrates that the third harmonic generation efficiency in graphene can be electrically tuned over two orders of magnitude, enabling broadband, tunable frequency conversion for optical communication applications.

Contribution

It reveals the logarithmic resonances in nonlinear conductivity and shows ultrabroadband electrical tunability due to graphene's linear dispersion.

Findings

Third harmonic generation efficiency can be tuned by over two orders of magnitude.

Logarithmic resonances in nonlinear conductivity are responsible for tunability.

Ultrabroadband electrical tunability enables potential applications in optical communications.

Abstract

Optical harmonic generation occurs when high intensity light ($>10^{10}$W/m$^{2}$) interacts with a nonlinear material. Electrical control of the nonlinear optical response enables applications such as gate-tunable switches and frequency converters. Graphene displays exceptionally strong-light matter interaction and electrically and broadband tunable third order nonlinear susceptibility. Here we show that the third harmonic generation efficiency in graphene can be tuned by over two orders of magnitude by controlling the Fermi energy and the incident photon energy. This is due to logarithmic resonances in the imaginary part of the nonlinear conductivity arising from multi-photon transitions. Thanks to the linear dispersion of the massless Dirac fermions, ultrabroadband electrical tunability can be achieved, paving the way to electrically-tuneable broadband frequency converters for applications in optical communications and signal processing.