Tracking slow nanolight in natural hyperbolic metamaterial slabs
Researchers at CIC nanoGUNE (Basque Country) in collaboration with colleagues at ICFO - The Institute of Photonic Sciences (Catalunya) have imaged how light moves inside an exotic class of matter known as hyperbolic materials. They observed, for the first time, ultraslow pulse propagation and backward propagating waves in deep subwavelength-scale thick slabs of boron nitride - a natural hyperbolic material for infrared light. This work has been funded by the EC Graphene Flagship and was recently reported in Nature Photonics.
Hyperbolic materials are very special because they behave like a metal in one direction, but like an insulator in the other. Until now, these materials have been used to fabricate complex nanostructures that permit subwavelength-scale imaging, as well as the focusing and controlling of light at the nanoscale. However, in order to fully exploit their potential, it is necessary to study and understand how light behaves inside them.
The work lays the foundations for studying the precise manner in which light travels through complex optical systems at the subwavelength scale in extremely high levels of detail. Such a capability will be vital for verifying that future nanophotonic devices, perhaps with biosensing or optical computing applications, are functioning as expected.
“The difficulty in performing the reported experiments is the extremely short wavelength of light when it is inside a hyperbolic material” explains Ikerbasque Professor Rainer Hillenbrand, leader of the nanooptics group at nanoGUNE. When light moves inside the material - in our case mid-infrared light in a 135 nm boron nitride slab - it travels in the form of what we call a polariton, where the light is actually coupled to the vibrations of the matter itself".
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