Hyperbolic metasurface turns light upside down!

Scientists have developed a new metasurface that is capable of inverting light signals upside down – i.e. wavefronts of light propagate through the surface in an inverted fashion.

To make this more clear, when a stone is thrown in water, the waves generated in the water because of disturbance created by the stone propagate in a circular fashion from inside to outside in a homogenous and isotropic i.e. uniform in all directions. The same is the case with light waves after they are emitted from the source

Previously scientists have predicted surfaces that would invert this behavior and turn the signals upside down. Through a new research scientists at nanoGUNE have managed to create hyberbolic metasurfaces on which the waves emitted from a point source propagate only in certain directions and with open (concave) wavefronts. These unusual waves are called hyperbolic surface polaritons. Because they propagate only in certain directions, and with wavelengths that are much smaller than that of light in free space or standard waveguides, they could help to miniaturize optical devices for sensing and signal processing.

The new metasurface is based on boron nitride, a graphene-like 2D material, and was selected because of its capability to manipulate infrared light on extremely small length scales, which could be applied for the development of miniaturized chemical sensors or for heat management in nanoscale optoelectronic devices. On the other hand, the researchers succeeded to directly observe the concave wavefronts with a special optical microscope, which have been elusive so far.

To see how the waves propagate along the metasurface, the researchers used a state-of the-art infrared nanoimaging technique that was pioneered by the nanoptics group at nanoGUNE. They first placed an infrared gold nanorod onto the metasurface.

The results promise nanostructured 2D materials to become a novel platform for hyberbolic metasurface devices and circuits, and further demonstrate how near-field microscopy can be applied to unveil exotic optical phenomena in anisotropic materials and for verifying new metasurface design principles.


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