Nanofocusing of Hyperbolic Phonon Polaritons in a Tapered Boron Nitride Slab

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-polariton (HPP) modes in the midinfrared 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 (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.

Launching Phonon Polaritons by Natural Boron Nitride Wrinkles with Modifiable Dispersion by Dielectric Environments

“…In order to further study the influence of dielectric environment, we encapsulate a gold antenna between the hBN crystal and SiO 2 substrate, differently from previous report where gold rods are fabricated on top of hBN . Compared with wrinkle‐launching, HPPs launched outside the gold film have the same wavelength (λ p = 280.7 nm for type 1 in Figure b and λ p = 367 nm for type 2 in Figure f, respectively), but exhibit different wavefronts that depend on the shape of the antenna.…”

Probing Mid-Infrared Phonon Polaritons in the Aqueous Phase

“…The strength of the PhP resonance can be further enhanced with specially tailored shapes, such as a circular geometry resonator, [20][21][22] an antenna that localizes electrical fields, 23 or a nanofocusing tapered slab. 24 Heterostructures of h-BN with other metallic or plasmonic materials [25][26] may also enhance the PhPs in the liquid phase to improve the signal strength. Our work opens a new avenue for those applications and the development of polaritonics in the aqueous phase.…”

Tunable Low Loss 1D Surface Plasmons in InAs Nanowires

“…Due to slow charge carrier mobility and large carrier density, plasmons in noble metals cannot simultaneously meet the requirements of high confinement factor, low damping (e.g., λ 0 /λ p ≈ 0.37, p 1 γ − ≈ 10 for a silver nanowire [35] ) and gate-tunability. [9] Hyperbolic phonon polaritons in hexagonal boron nitride (hBN-HPPs), [26,[37][38][39][40] can achieve low damping losses ( p 1 γ − ≈ 20), but with a weak confinement factor (λ 0 /λ p ≈ 17). [7,8,36] But low damping losses ( p 1 γ − ≈ 25) need to be achieved in graphene/hBN heterostructure, which requires a complicated fabrication.…”

“…γ − in various materials such as silver nanowires, graphene, boron nitride (hBN), carbon nanotubes, tungsten diselenide (WSe 2 ), and our InAs nanowires. [26,[37][38][39][40] Orange rhombus and ultramarine triangle are data taken from Ref. [35].…”