Researchers have demonstrated a tunable optical phenomenon in graphene that could pave the way for a wide range of next-generation optical technology, according to a new report in the journal Nature Nanotechnology.
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Optical harmonic generation is the production of new frequencies or colors when intense light comes into contact with a nonlinear material. Third Harmonic Generation (THG) when this phenomenon generates light with triple the power of the incident light. THG is the result of a nonlinear connection between high-intensity laser light and a material. Nonlinear optical effects such as THG are taken advantage of in various applications, including laser technology, material production, and telecommunications.
In theory, all materials are capable of producing new light frequencies via THG. However, the reality of this occurring is typically minimal and cannot be manipulated externally. Researchers behind the new study said they were drawn to graphene for its strong light interaction and a strong third-order nonlinear response to light.
In the study, researchers showed the first instance of a gate-tunable THG in graphene. The study team revealed the robust THG in graphene can be manipulated by an outside electric field and boosted over a very broad bandwidth. Electrical management of a material’s nonlinear optical response could allow for applications like gate-tunable switches. Such a switch could make more ‘colours’ available for use in spectroscopy, which would allow scientists to achieve a new understanding of various materials and phenomena. Graphene THG optical switches could also take advantage of previously unused optical frequencies to deliver information along optical cables, expanding the quantity of information that can be sent and therefore raising data speeds.
“Our work shows that the third harmonic generation efficiency in graphene can be increased by over 10 times by tuning an applied electric field. Electrical control of the third harmonic enhancement can be achieved over an ultra-broad bandwidth, paving the way to electrically-tunable broadband frequency converters for applications in optical communications and signal processing,” study author Giancarlo Soavi, a researcher from the University of Cambridge in the United Kingdom, said in a news release.
While there are current devices that use nonlinear optics for optical switches, using graphene for THG can make it possible for integration into devices operating over an ultra-broad bandwidth, the study researchers noted.
"Our initial research demonstrates the feasibility of this approach so now we want to move closer to producing integrated devices in optical fibers and waveguides," Soavi said.
Frank Koppens, a professor from ICFO (The Institute of Photonic Sciences) in Barcelona who was not directly involved in the new study said researchers were able to discover yet another one of graphene’s unique qualities: 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,” Koppens said.
Study author Andrea C. Ferrari, who sits on the management panel of the massive European Union initiative Graphene Flagship, said the new research is more proof of graphene’s ability to surprise in the areas of 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.
Andrea C. Ferrari, Study Author
In a similar study released last month, researchers showed altering the temperature of graphene with an embedded photonic crystal could tune its capacity for absorbing light. This discovery could lead to the development of new light sensors, lasers, and technology capable of manipulating optical beams.