A study performed by a research group from Helmholtz-Zentrum Dresden-Rossendorf (HZDR) illustrates that graphene-based materials could be utilized to efficiently transform high-frequency signals into visible light.
A graphene-based material converts incoming terahertz pulses (from above) into visible light in an ultrafast and controllable manner - optimal for data transport in optical fibers. Image Credit: B. Schröder/HZDR
This was done in collaboration with the Catalan Institute of Nanoscience and Nanotechnology (ICN2), the University of Exeter Centre for Graphene Science, and TU Eindhoven.
The newly developed mechanism is tunable and ultrafast. Such outcomes might make way for stimulating applications in near-future information and communication technologies.
The research group has presented their findings in the Nano Letters journal.
The potential to convert signals from one frequency regime to another is important to several technologies, especially in telecommunications, where, for instance, data processed by electronic devices are frequently transmitted as optical signals via glass fibers.
To allow considerably greater data transmission rates, the future 6G wireless communication systems will need to expand the carrier frequency above 100 GHz up to the terahertz range.
Terahertz waves are known to be a part of the electromagnetic spectrum that comes under microwaves and infrared light. But terahertz waves could only be utilized to transport data wirelessly through highly limited distances.
Therefore, a fast and controllable mechanism to convert terahertz waves into visible or infrared light will be required, which can be transported via optical fibers. Imaging and sensing technologies could also benefit from such a mechanism.
Dr. Igor Ilyakov, Institute of Radiation Physics, Helmoltz Zentrum Dresden Rossendorf
Until now, what is missing is a material that has the potential to upconvert the photon energies by a factor of around 1000. Recently, the team has just determined the powerful nonlinear response of alleged Dirac quantum materials, for example, graphene and topological insulators, to terahertz light pulses.
This manifests in the highly efficient generation of high harmonics, that is, light with a multiple of the original laser frequency. These harmonics are still within the terahertz range, however, there were also first observations of visible light emission from graphene upon infrared and terahertz excitation. Until now, this effect has been extremely inefficient, and the underlying physical mechanism unknown.
Dr. Sergey Kovalev, Institute of Radiation Physics, Helmoltz Zentrum Dresden Rossendorf
The Mechanism Behind
The new outcomes offer a physical explanation for this mechanism and display how the light emission could be improved strongly with the help of highly doped graphene or by making use of a grating-graphene metamaterial. It is a material with a customized structure specified by unique electrical, optical, or magnetic properties.
Also, the research group noted that the conversion happens very quickly—on the sub-nanosecond time scale and that it could be regulated by electrostatic gating.
We ascribe the light frequency conversion in graphene to a terahertz-induced thermal radiation mechanism, that is, the charge carriers absorb electromagnetic energy from the incident terahertz field. The absorbed energy rapidly distributes in the material, leading to carrier heating; and finally this leads to emission of photons in the visible spectrum, quite like light emitted by any heated object.
Klaas-Jan Tielrooij, Professor, ICN2’s Ultrafast Dynamics in Nanoscale Systems Group, Eindhoven University of Technology
The speed and tunability of the terahertz-to-visible light conversion obtained in graphene-based materials have a great ability for application in information and communication technologies.
The fundamental ultrafast thermodynamic mechanism could surely produce an effect on terahertz-to-telecom interconnects and also in any technology in which ultrafast frequency conversion of signals is needed.
Journal Reference
Ilyako, I., et al. (2023) Ultrafast Tunable Terahertz-to-Visible Light Conversion through Thermal Radiation from Graphene Metamaterials. Nano Letters. doi.org/10.1021/acs.nanolett.3c00507.