Orthogonal canalized polaritons via coupling graphene plasmon and phonon polaritons of hBN metasurface.

Metasurfaces composed of van der Waals materials exhibit extreme anisotropy and strong subwavelength confinement, enabling precise control of mid-infrared and terahertz waves for advanced photonic and optoelectronic applications. Among their intriguing phenomena, canalization - characterized by nearly diffraction-free propagation - offers significant potential for nanoscale light manipulation and enhanced light-matter interactions. Recently, gratings were demonstrated to induce synthetic transverse optical (STO) resonances, facilitating canalization perpendicular to the ribbon axis. In this study, we introduce a novel canalization mechanism by sandwiching a grating of hBN ribbons between graphene layers. The hybrid structure achieves orthogonal redirection of STO-induced canalization through the coupling plasmon polaritons in graphene and phonon polaritons in the hBN ribbons, achieving beam widths of approximately 300 nm (∼λ 0/20, where λ 0 is the free-space wavelength) across the spectral range of 1,470-1,510 cm-1. Detailed analyses were conducted by varying graphene's Fermi energy and geometric parameters, elucidating key field characteristics and spatial evolution of the canalization. Moreover, practical feasibility is demonstrated through simulated experimental antenna-launched excitation. Our finding holds promise for the development of polariton canalizations in diverse vdW material systems and facilitating on-chip photonic applications.