Electrons in graphene exhibit collective oscillations, known as plasmon polaritons. These waves arise from the close interaction of the electrons confined in the two-dimensional (2D) material and the electromagnetic field around it. While difficult to excite and image on uniform graphene, these wave phenomena become more evident when graphene is patterned into nanoribbons. In this geometry the plasmons are repeatedly reflected back and forward by the edges of the ribbon, leading to a strong resonance.

Harnessing resonance

A multidisciplinary collaboration of researchers from École Polytechnique Fédérale de Lausanne (EPFL) and the University of Minnesota demonstrate that these resonances can be harnessed to control the propagation direction of infrared light. An array of nanoribbons, each resonating at slightly different frequencies, can induce a space-dependent reflection phase to a monochromatic incident infrared wave.

Anomalous reflection

The resulting reflection can then have a different angle with respect to the standard reflected wave (a phenomenon called ‘anomalous reflection’). By applying a voltage on the nanoribbons, the resonance frequency can be shifted and the anomalous reflection can be turned on and off. More complicated geometries should allow more degrees of freedom controlling the beam in a continuous range of angles.


The design is inspired by a class of antennas called ‘reflectarrays’; a technology which has been known for decades at microwave frequencies. The development of improved nanofabrication techniques in recent years has extended its application. It can now function in terahertz, infrared and visible regions of the electromagnetic spectrum, as they require much smaller features. The realization of this device constitutes an important step for telecommunication and for optical computing, where the principle could be used to improve optical switches and routers.

More information can be found in the journal Nanotechnology 26 134002. The article forms part of the Nanotechnology Focus Collection on Nanophotonics to celebrate the International Year Of Light 2015.

Further reading

Focus on Nanophotonics
Patterning technique prepares graphene nanoribbons for photodetector applications (Jan 2014)
Layered semiconductors: thickness changes conductivity (Sept 2014)
Small molecules make big differences to phosphorene (Feb 2015)