Hybrid phonon-polaritons at atomically-thin van der Waals heterointerfaces for infrared optical modulation

Surface phonon polaritons (SPhPs) in polar dielectrics are potential candidates for infrared nanophotonics due to their low optical loss and long phonon life-time. However, the small confinement factors of bulk SPhPs, limits their applications that require small footprint and strong light-matter interaction. Here, we report that ultrathin van der Waals dielectrics (e.g., MoS₂ and h-BN) on Silicon Carbide enable ultra-confined dielectric tailored surface phonon polaritons (d-SPhPs) where the confinement factor can exceed 100. By creating a heterostructure of these vdW dielectrics with graphene, the d-SPhPs can hybridize with graphene plasmons which can be electrically tuned. By subwavelength patterning of the vdW dielectrics, these hybrid polaritons can be localized into ultra-small antenna volumes (λ0³/v_antenna ³~100³) with high-quality factor resonances (Q~85). Further, electric gating of graphene enables active tunability of these localized resonances which results in an electro-optic modulator with modulation depth exceeding 95%. Our report of manipulating and controlling ultra-confined SPhPs in van der Waals heterostructures, serves as a possible route for non-plasmonic platforms for infrared photodetectors, modulators and sensors.