Focusing of in-plane hyperbolic polaritons in van der Waals crystals with tailored infrared nanoantennas.

ABSTRACT: Phonon polaritons (PhPs)—light coupled to lattice vibrations—with in-plane hyperbolic dispersion exhibit ray-like propagation with large wave vectors and enhanced density of optical states along certain directions on a surface. As such, they have raised a surge of interest, promising unprecedented manipulation of infrared light at the nanoscale in a planar circuitry. Here, we demonstrate focusing of in-plane hyperbolic PhPs propagating along thin slabs of α-MoO₃. To that end, we developed metallic nanoantennas of convex geometries for both efficient launching and focusing of the polaritons. The foci obtained exhibit enhanced near-field confinement and absorption compared to foci produced by in-plane isotropic PhPs. Foci sizes as small as λ_p/4.5 = λ₀/50 were achieved (λ_p is the polariton wavelength and λ₀ is the photon wavelength). Focusing of in-plane hyperbolic polaritons introduces a first and most basic building block developing planar polariton optics using in-plane anisotropic van der Waals materials.

SUBMITTER: Martin-Sanchez J 

PROVIDER: S-EPMC8500510 | biostudies-literature | 2021 Oct

REPOSITORIES: biostudies-literature