Plots showing that surface plasmons are more confined when propagating
along on a monolayer of graphene (G) than they are along a thin film of gold
(Au).
Theoretical calculations show graphene’s potential for controlling
nanoscale light propagation on a chip
Semiconductors have
revolutionized computing because of their efficient control over the flow of
electrical currents on a single chip, which has led to devices such as the
transistor. Working towards a similar tunable functionality for light,
researchers from the A*STAR Institute of High Performance Computing (IHPC),
Singapore, have shown how graphene could be used to control light at the
nanometer scale, advancing the concept of photonic circuits on chips1.
Graphene, which is made from a
single layer of carbon atoms, has excellent electronic properties; some of
these are also useful in photonic applications. Usually, only metals are able
to confine light to the order of a few nanometers, which is much smaller than
the wavelength of the light. At the surface of metals, collective oscillations
of electrons, so-called ‘surface plasmons’, act as powerful antennae that
confine light to very small spaces. Graphene, with its high electrical
conductivity, shows similar behavior to metals so can also be used for
plasmon-based applications, explains Choon How Gan of IHPC, who led the
research.
Gan and co-workers studied
theoretically and computationally how surface plasmons travel along sheets of
graphene. Even though graphene is a poorer conductor than a metal, so plasmon
propagation losses are higher, it has several key advantages, says team member
Hong Son Chu. “The key advantage that makes graphene an excellent platform for
plasmonic devices is its large tunability that cannot be seen in the usual
noble metals,” he explains. “This tunability can be achieved in different ways,
using electric or magnetic fields, optical triggers and temperature.”
The team’s calculations indicated
that surface plasmons propagating along a sheet of graphene would be much more
confined to a small space than they would traveling along a gold surface (see
image). However, the team also showed that surface plasmons would travel far
better between two sheets of graphene brought into close contact. Furthermore,
by adjusting design parameters such as the separation between the sheets, as
well as their electrical conductivity, much better control over surface plasmon
properties is possible.
In the future, Gan and his
co-workers plan to investigate these properties for applications. “We will
explore the potential of graphene plasmonic devices also for the terahertz and
mid-infrared regime,” he explains. “In this spectral range, graphene plasmonic
structures could be promising for applications such as molecular sensing, as
photodetectors, or for optical devices that can switch and modulate light.”
The A*STAR-affiliated researchers
contributing to this research are from the Institute of High Performance Computing
References
- Gan, C. H., Chu, H. S. & Li, E. P. Synthesis
of highly confined surface plasmon modes with doped graphene sheets in the
midinfrared and terahertz frequencies. Physical Review B 85, 125431
(2012). | article
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