Nanoscale Guiding of Infrared Light with Hyperbolic Volume and Surface Polaritons in van der Waals Material Ribbons

Abstract

Van der Waals (vdW) materials host a variety of polaritons, which make them an emerging material platform for manipulating light at the nanoscale. Due to the layered structure of vdW materials, the polaritons can exhibit a hyperbolic dispersion and propagate as nanoscale‐confined volume modes in thin flakes. On the other hand, surface‐confined modes can be found at the flake edges. Surprisingly, the guiding of these modes in ribbons—representing typical linear waveguide structures—is widely unexplored. Here, a detailed study of hyperbolic phonon polaritons propagating in hexagonal boron nitride ribbons is reported. Employing infrared nanoimaging, a variety of modes are observed. Particularly, the fundamental volume waveguide mode that exhibits a cutoff width is identified, which, interestingly, can be lowered by reducing the waveguide thickness. Further, hybridization of the surface modes and their evolution with varying frequency and waveguide width are observed. Most importantly, it is demonstrated that the symmetrically hybridized surface mode does not exhibit a cutoff width, and thus enables linear waveguiding of the polaritons in arbitrarily narrow ribbons. The experimental data, supported by simulations, establish a solid basis for the understanding of hyperbolic polaritons in linear waveguides, which is of critical importance for their application in future photonic devices.

Enhanced Light–Matter Interaction in 10B Monoisotopic Boron Nitride Infrared Nanoresonators

“…The rectangular shapes are useful to better understand the complex field pattern observed for the trapezoidal cross sections. We thus analyze first the field outside the rectangular ribbons (neglecting the complicated pattern inside the structures, which is due to the superposition of hyperbolic rays [ 16 ] ). The effective charge profile corresponding to the observed modes is sketched in Figure 2e.…”

Edge-oriented and steerable hyperbolic polaritons in anisotropic van der Waals nanocavities

“…To further control light with polaritons, we can resort to nanocavities or nanoresonators made of polar vdW materials, offering further enhanced wave confinement and light-matter interactions. For instance, high-quality PhPs exist both in individual hBN nanocones 24 and arrays of polaritonic antennas; 31 Fabry–Perot resonances are sustained in hBN ribbons; 15 , 16 , 31 and deep subwavelength confinement is found in polaritonic crystals of hole arrays in hBN thin films thanks to Bloch modes 24 . However, these studies rely on out-of-plane hyperbolic and uniaxial hBN, and cannot be readily applicable for in-plane hyperbolic nanocavities, which are arguably more accessible and practical.…”

“…ne of the main goals of nanophotonics is to manipulate and control light at the nanoscale [1][2][3][4][5][6][7] . In van der Waals (vdW) nanomaterials and their layers, the interaction of light with different carriers leads to half-light-half-matter quasiparticles, such as plasmon polaritons in graphene [8][9][10][11][12] , exciton polaritons in semiconductor monolayers 13,14 , and phonon polaritons (PhPs) in polar materials 6,[15][16][17][18][19][20][21][22] , which all enable diffraction-less confinement and guiding of light at the nanoscale. In particular, PhPs in polar vdW materials, such as hexagonal boron nitride (hBN) endowed with natural hyperbolic response, offer a low-loss, highly confined and ray-like light propagation, enabling high-quality resonances, hyper-lensing, and nanoimaging [23][24][25][26] .…”

Polariton panorama

“…A special case of Dyakonov polaritons is realized in anisotropic crystals of layered van der Waals materials. One example is that of the hyperbolic surface phonon polaritons propagating along the edges of slabs prepared from hexagonal boron nitride [114][115][116].…”