Van der Waals Phonon Polariton Microstructures for Configurable Infrared Electromagnetic Field Localizations

Abstract

Polar van der Waals (vdW) crystals that support phonon polaritons have recently attracted much attention because they can confine infrared and terahertz (THz) light to deeply subwavelength dimensions, allowing for the guiding and manipulation of light at the nanoscale. The practical applications of these crystals in devices rely strongly on deterministic engineering of their spatially localized electromagnetic field distributions, which has remained challenging. The polariton interference can be enhanced and tailored by patterning the vdW crystal -MoO 3 into microstructures that support highly in-plane anisotropic phonon polaritons. The orientation of the polaritonic in-plane isofrequency curve relative to the microstructure edges is a critical parameter governing the polariton interference, rendering the configuration of infrared electromagnetic field localizations by enabling the tuning of the microstructure size and shape and the excitation frequency. Thus, the study presents an effective rationale for engineering infrared light flow in planar photonic devices.

Unidirectionally excited phonon polaritons in high-symmetry orthorhombic crystals

“…We corroborate our experimental near-field images and our interpretation of them in section S7 (fig. S8), where we show calculated near-field images based on a phenomenological interference model ( 27 , 28 ) that excellently reproduces the experimental near-field images shown in Fig. 3 (D to H).…”

High-Q Phonon-polaritons in Spatially Confined Freestanding α-MoO3

“…The remarkably low loss of PhPs in α-MoO 3 , compared to counterparts such as boron nitride and graphene , can potentially lead to practical applications in IR signal processing and heat transfer . Due to strong crystallinity of each layer of α-MoO 3 , twistronics can also be readily experienced in this material. − Twisted double layer α-MoO 3 has been shown to be able to manipulate light at the nanoscale with topological transitions that bring huge potential to nanophotonics and polaritonics. − In addition to twisting the angle between adjacent α-MoO 3 layers, PhPs can also be engineered by other approaches, including patterning their microstructures, , changing the material composition, , and controlling the surrounding dielectric environment. , …”

“…8−10 Twisted double layer α-MoO 3 has been shown to be able to manipulate light at the nanoscale with topological transitions that bring huge potential to nanophotonics and polaritonics. 11−14 In addition to twisting the angle between adjacent α-MoO 3 layers, PhPs can also be engineered by other approaches, including patterning their microstructures, 2,15 changing the material composition, 1,16 and controlling the surrounding dielectric environment. 17,18 Change of the dielectric environment adjacent to α-MoO 3 can modulate its PhP propagation characteristics.…”

Controlling the Propagation Asymmetry of Hyperbolic Shear Polaritons in Beta-Gallium Oxide

“…In orthorhombic lattices with even lower crystal symmetry, all three lattice constants may differ (while remaining orthogonal). In these biaxial materials, such as MoO 3 , it has been shown that in-plane, in addition to out-of-plane hyperbolicity can be realized [15][16][17] , enabling further control over polariton propagation 18 , and even independent control over the wavevector and Poynting vector 19 .…”