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Nanofocusing of Hyperbolic Phonon Polaritons in a Tapered Boron Nitride Slab

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journal contribution
posted on 25.05.2016, 00:00 by Alexey Yu. Nikitin, Edward Yoxall, Martin Schnell, Saül Vélez, Irene Dolado, Pablo Alonso-Gonzalez, Fèlix Casanova, Luis E. Hueso, Rainer Hillenbrand
Nanofocusing of light offers new technological opportunities for the delivery and manipulation of electromagnetic fields at subdiffraction-limited length scales. Here, we show that hyperbolic phonon polariton (HPP) modes in the mid-infrared as supported by a hexagonal boron nitride (h-BN) slab can be nanofocused (i.e., both field enhanced and wavelength compressed) by propagation along a vertical taper. Via numerical simulations, we demonstrate that field enhancement factors of 90for steep tapersand wavelength compression of more than an order of magnitudefor adiabatic taperscan be expected. Employing scattering-type scanning near-field optical microscopy, we provide, for the first time, proof-of-principle experimental evidence of a significant HPP wavelength compression. We expect these functionalities to provide diverse applications, from biosensing and nonlinear optics to optical circuitry.