Graphene, among other materials, can capture particles of light called photons, combine them, and produce a more powerful optical beam. This is due to a physical phenomenon called optical harmonic generation, which is characteristic of nonlinear materials. Nonlinear optical effects can be exploited in a variety of applications, including laser technology, material processing and telecommunications.

Although all materials should demonstrate this behaviour, the efficiency of this process is typically small and cannot be controlled externally. Now, researchers from the University of Cambridge, Politecnico di Milano and IIT- Istituto Italiano di Tecnologia have demonstrated that graphene not only shows a good optical response but also how to control the strength of this effect using an electric field. Their results are reported in the journal Nature Nanotechnology . All three institutions are partners in the Graphene Flagship, a pan-European project dedicated to bringing graphene and related materials for commercial applications.

Graphene – a form of carbon just a single atom thick – has a unique combination of properties that make it useful for applications from flexible electronics and fast data communication, to enhanced structural materials and water treatments. It is highly electrically and thermally conductive, as well as strong and flexible.

Researchers envision the creation of new graphene optical switches, which could also harness new optical frequencies to transmit data along optical cables, increasing the amount of data that can be transmitted. Currently, most commercial devices using nonlinear optics are only used in spectroscopy. Graphene could pave the way towards the fabrication of new devices for ultra-broad bandwidth applications.

“Our work shows that the third harmonic generation efficiency in graphene can be increased by over 10 times by tuning an applied electric field,” said lead author Giancarlo Soavi, of the Cambridge Graphene Centre.

“The authors found again something unique about graphene: tuneability of third harmonic generation over a broad wavelength range," said Professor Frank Koppens from the ICFO (The Institute of Photonic Sciences)in Barcelona and leader of one of the Graphene Flagship work packages. "As more and more applications are all-optical, this work paves the way to a multitude of technologies.”

Professor Andrea C. Ferrari, Science and Technology Officer of the Graphene Flagship, and Chair of its Management Panel, said: “Graphene never ceases to surprise us when it comes to optics and photonics. The Graphene Flagship has put significant investment to study and exploit the optical properties of graphene. This collaborative work could lead to optical devices working on a range of frequencies broader than ever before, thus enabling a larger volume of information to be processed or transmitted.”

Reference:
Giancarlo Soavi et al. ' Broadband, electrically tuneable, third harmonic generation in graphene .' Nature Nanotechnology (2018). DOI: 10.1038/s41565-018-0145-8

Adapted from a Cambridge Graphene Centre press release .