A study carried out by a research team from the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), the Catalan Institute of Nanoscience and Nanotechnology (ICN2), University of Exeter Centre for Graphene Science, and TU Eindhoven demonstrates that graphene-based materials can be used to efficiently convert high-frequency signals into visible light, and that this mechanism is ultrafast and tunable, as the team presents its findings in Nano Letters (DOI: 10.1021/acs.nanolett.3c00507). These outcomes open the path to exciting applications in near-future information and communication technologies.
Photo: A
graphene-based material converts incoming terahertz high-frequency signals into
visible light extremely quickly and controllably - ideal for data transport in
optical fibers. ©Copyright: B. Schröder/HZDR
The
ability to convert signals from one frequency regime to another is key to
various technologies, in particular in telecommunications, where, for example,
data processed by electronic devices are often transmitted as optical signals
through glass fibers. To enable significantly higher data transmission rates
future 6G wireless communication systems will need to extend the carrier
frequency above 100 gigahertz up to the terahertz range. Terahertz waves are a
part of the electromagnetic spectrum that lies between microwaves and infrared
light. However, terahertz waves can only be used to transport data wirelessly
over very 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,” says Dr. Igor Ilyakov of the Institute of Radiation Physics at HZDR.
What
is missing so far is a material that is capable of upconverting photon energies
by a factor of about 1000. The team has only recently identified the strong
nonlinear response of so-called Dirac quantum materials, e.g. 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,” recalls Dr. Sergey
Kovalev of the Institute of Radiation Physics at HZDR. “Until now, this effect
has been extremely inefficient, and the underlying physical mechanism unknown.”
The mechanism
behind
The
new results provide a physical explanation for this mechanism and show how the
light emission can be strongly enhanced by using highly doped graphene or by
using a grating-graphene metamaterial – a material with a tailored structure
characterized by special optical, electrical or magnetic properties. The team
also observed that the conversion occurs very rapidly – on the sub-nanosecond
time scale, and that it can be controlled 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,” explains Prof. Klaas-Jan Tielrooij of ICN2's
Ultrafast Dynamics in Nanoscale Systems group and Eindhoven University of
Technology.
The tunability and speed of the terahertz-to-visible light conversion achieved in graphene-based materials has great potential for application in information and communication technologies. The underlying ultrafast thermodynamic mechanism could certainly produce an impact on terahertz-to-telecom interconnects, as well as in any technology that requires ultrafast frequency conversion of signals.
No comments:
Post a Comment