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Nat Commun. 2015 Apr 22;6:6963. doi: 10.1038/ncomms7963.

Subdiffractional focusing and guiding of polaritonic rays in a natural hyperbolic material.

Author information

1
Department of Physics, University of California, San Diego, La Jolla, California 92093, USA.
2
Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02215, USA.
3
1] Department of Physics, University of California, San Diego, La Jolla, California 92093, USA [2] Department of Physics, Stony Brook University, Stony Brook, New York 11794, USA.
4
National Institute for Materials Science, Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan.
5
Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093, USA.
6
Ludwig-Maximilians-Universität and Center for Nanoscience, 80539 München, Germany.

Abstract

Uniaxial materials whose axial and tangential permittivities have opposite signs are referred to as indefinite or hyperbolic media. In such materials, light propagation is unusual leading to novel and often non-intuitive optical phenomena. Here we report infrared nano-imaging experiments demonstrating that crystals of hexagonal boron nitride, a natural mid-infrared hyperbolic material, can act as a 'hyper-focusing lens' and as a multi-mode waveguide. The lensing is manifested by subdiffractional focusing of phonon-polaritons launched by metallic disks underneath the hexagonal boron nitride crystal. The waveguiding is revealed through the modal analysis of the periodic patterns observed around such launchers and near the sample edges. Our work opens new opportunities for anisotropic layered insulators in infrared nanophotonics complementing and potentially surpassing concurrent artificial hyperbolic materials with lower losses and higher optical localization.

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