Traveling Surface Phonon Polariton Modes in One-Dimensional Gratings

Surface phonon polaritons (SPhPs) are a low-loss alternative to surface plasmon polaritons with the potential for mid-infrared to terahertz nanophotonic devices. One requirement for the development of nanophotonic circuitry is the transport of information (i.e., polaritons) from one circuit component to the next. Traveling surface phonon polaritons in isotropic media presents a potential mechanism to achieve the desired interconnects. While localized surface phonon polaritons have been widely implemented, no traveling surface phonon polaritons in nanostructured isotropic ionic crystals have been demonstrated or explored up to date. In this study, we experimentally and theoretically demonstrate traveling surface phonon polaritons in one-dimensional grating. Furthermore, Raman mapping, when compared with phonon distribution based on selection rules, provided additional evidence for the presence of both traveling and localized modes. We provide mechanisms to control the group velocity, propagation length, and confinement of the traveling modes by engineering the geometric parameters of the gratings. Our results demonstrate that we can achieve propagation lengths exceeding 150 μm or confinement below 2 μm. Additionally, the group velocity can be tuned to 4% of the speed of light, enabling slow light for nanophotonic applications.