Electrical control of third harmonic generation (THG) can be obtained in single-layer graphene. In THG three low-frequency photons (red) sum up to generate one high-frequency (blue) photon. For this reason, THG can be used for optical frequency converters. Credit: Giancarlo Soavi, University of Cambridge
Technology could lead to new devices for faster, more reliable ultra-broad bandwidth transfers. For the first time, researchers demonstrated how electrical fields boost the non-linear optical effects of graphene. Graphene, among other materials, can capture photons, combine them, and produce a more powerful optical beam. This is due to a physical phenomenon called the 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 present this behaviour, the efficiency of this process is typically small and cannot be controlled externally. Now, partners of the Graphene Flagship project in Cambridge (UK), Milan, and Genova (Italy) have demonstrated for the first time that graphene not only shows a good optical response, but also how to control the strength of this effect using an electric field.
Researches 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,” explains Giancarlo Soavi, lead author of the paper and researcher at the Cambridge Graphene Centre (University of Cambridge, UK).
“The authors found again something unique about graphene: tuneability of THG over a broad wavelength range. As more and more applications are all-optical, this work paves the way to a multitude of technologies,” said said ICREA Professor Frank Koppens from ICFO (The Institute of Photonic Sciences), Barcelona, Spain, who is the leader of the Photonics and Optoelectronics Work Package within the Graphene Flagship.
Professor Andrea C. Ferrari, Science and Technology Officer of the Graphene Flagship, and Chair of its Management Panel, added how “graphene never ceases to surprise us when it comes to optics and photonics.” He also highlights that “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.”
http://graphene-flagship.eu/tunable-third-harmonic-generation-in-graphene
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