Researchers in the UK, China and Germany have come up with a new and useful way to couple light to the surface of a metamaterial. The technique is the first to ensure that the coupling occurs in a single direction and could lead to integrated plasmonic circuits that could be controlled using an electric current.
The coupling involves surface plasmon polaritons (SPPs), which are particle-like quantum phenomena that arise from the interaction of light with a metal's conduction electrons. These quasiparticles are part light and part collective electron wave and are strongly confined at the surface of a metal. SPPs are excited when they interact with light but the problem is that they are then free to propagate in many different directions along the metal surface and cannot be controlled easily. This limits the range of applications possible for these structures.
Now, a team led by Shuang Zhang of the University of Birmingham has shown that SPPs can, indeed, be excited along a single direction on a metal surface provided that the surface is suitably structured first. In this case, they used a "metasurface", which is a metal film with nanometre-sized rectangular holes carefully orientated in a certain way. More importantly, and for the first time, the researchers have confirmed that the direction in which the SPPs travel along the metal surface can be switched by simply flipping the helicity (or circular polarization direction) of the incoming light from left to right and vice versa.
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