Leveraging surface phonon polaritons for enhanced Q-factor of mid-infrared BaTiO3 nanoresonators

Abstract

All-dielectric metasurfaces supporting surface phonon polaritons (SPhPs) have lower optical loss and stronger optical confinement than plasmonic systems. However, most polar materials with SPhPs have narrow Reststrahlen bands, typically within a few micrometers, thus limiting their application range. Barium titanate (BTO) is an anisotropic polar dielectric with two Reststrahlen bands supporting SPhPs in the mid-infrared to terahertz range and exhibits high-quality SPhPs characteristics due to its high dielectric function ratio (-/). Herein, we construct BTO anisotropic metasurfaces and investigate the excitation, coupling, and application of SPhPs modes within them. Localized optical modes at subwavelength scales can be excited over a wider range than propagating modes but require large meta-atomic heights (>300 nm). The higher-order hybrid mode predominantly displays monopole characteristics, boasting a high Q-factor of 125, while the transverse dipole mode exhibits robust field enhancement capabilities (|E/E0| = 173, a penetration depth of 404.7 nm). Together, they surpass conventional all-dielectric metasurfaces by nearly a factor of two in correlation performance. These properties are theorized to offer significant advantages in thermal emission, self-referenced sensing, and molecular detection. The findings of this work confirm the considerable contribution of SPhPs to promoting BTO metasurfaces for applications in mid-infrared nanophotonics.