Negative reflection of nanoscale-confined polaritons in a low-loss natural medium

Abstract

Negative reflection occurs when light is reflected toward the same side of the normal to the boundary from which it is incident. This exotic optical phenomenon is not only yet to be visualized in real space but also remains unexplored, both at the nanoscale and in natural media. Here, we directly visualize nanoscale-confined polaritons negatively reflecting on subwavelength mirrors fabricated in a low-loss van der Waals crystal. Our near-field nanoimaging results unveil an unconventional and broad tunability of both the polaritonic wavelength and direction of propagation upon negative reflection. On the basis of these findings, we introduce a device in nano-optics: a hyperbolic nanoresonator, in which hyperbolic polaritons with different momenta reflect back to a common point source, enhancing the intensity. These results pave way to realize nanophotonics in low-loss natural media, providing an efficient route to control nanolight, a key for future on-chip optical nanotechnologies.

Infrared plasmons propagate through a hyperbolic nodal metal

“…1B) is the hyperboloid, these media are referred to as hyperbolic (8)(9)(10). In the hyperbolic regime, the interaction of light with collective modes of crystals yields hyperbolic polaritons imbuing crystals with exotic optical properties, including negative reflection at interfaces (11) and ray-like waveguiding in the bulk (12,13). Hyperbolic waveguiding has mostly been explored in polar insulators inside their narrow phonon bands, including hBN (14,15), MoO 3 (16,17), V 2 O 5 (18), calcite (19), Ga 2 O 3 (20), and semiconducting WSe 2 (21).…”

Gate-tunable negative refraction of mid-infrared polaritons

“…S3 and note S2), such as those of hyperbolic polaritons in α-MoO 3 (Fig. 1B) ( 35 ). Because the boundary conditions at the interface (between α-MoO 3 with and without covering graphene) only require conservation of the tangential wave vector component k ∥ = k sinθ, where θ is the angle between the wave vector and the direction normal to the interface, the refracted wave can exhibit normal (positive) refraction for k, but negative refraction for S (with S ∥ = S sinφ, where φ is the angle between the Poynting vector and the interface normal).…”

Two-dimensional natural hyperbolic materials: from polaritons modulation to applications

“…(1) Among the four polaritons, experimental research on hyperbolic phonon polaritons (especially those appearing in hBN and α-MoO 3 ) 36,67,70,74,75,[77][78][79][140][141][142][143][144][145][146][147][148][149] is much more than on the other three polaritons. This could be due to the fact that hyperbolic phonon polaritons are the earliest discovered, and hBN and α-MoO 3 are relatively easier to achieve than the other 2D natural HMs.…”