Nanofocusing of Hyperbolic Phonon-Polaritons in a Tapered Boron Nitride Slab

TL;DR

This paper demonstrates the nanofocusing of hyperbolic phonon-polaritons in a tapered boron nitride slab, achieving significant field enhancement and wavelength compression, with experimental proof of wavelength compression using SNOM.

Contribution

It introduces a novel method for nanofocusing hyperbolic phonon-polaritons in h-BN slabs via tapering, combining numerical simulations and experimental validation.

Findings

Field enhancement factor of 90 in steep tapers

Wavelength compression of over an order of magnitude in adiabatic tapers

First experimental evidence of HPP wavelength compression using SNOM

Abstract

Nanofocusing of light offers new technological opportunities for the delivery and manipulation of electromagnetic fields at sub-diffraction limited length scales. Here, we show that hyperbolic phonon polarity,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 scatteringtype scanning near field optical microscopy ,s SNOM, 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 non-linear optics to optical circuitry.