Hybrid long-range mid-infrared hyperbolic phonon polariton waveguide using hexagonal boron nitride

Abstract

For any photonic-on-chip applications long propagation waveguides are critical. The use of plasmon polaritons for near-infrared and optical networks has been extensively studied for the purpose of achieving long propagation lengths, however, due to plasmonic polariton effects being negligible in mid- to long-wave infrared (IR) applications, phonon polaritons are required. In recent years, extensive research has been carried out on hexagonal boron nitride (h-BN), and it has been found that h-BN has naturally occurring sub-range phonon volume-constrained hyperbolic phonon polaritons (HPhPs). The numerical results in this thesis show both the long-range and short-range phonon volume polaritons modes in h-BN. A hybrid long-range phononic waveguide consisting of two identical dielectric cylinder wires symmetrically placed on each side of the h-BN slab is coupled to the long-range HPhP mode. Based on the analysis of coupled-mode theory and computational finite element analysis, the modal characteristics of hybrid long-range phonon-polariton waveguides are studied. Subwavelength confinement can be achieved due to the strong coupling between the high index cylindrical-waveguide mode and the HPhPs in the h-BN thin film. The modal area ranges from 10̄⁻²λ2/0 to 10⁻¹λ2/0, while exhibiting propagation distances 7λ₀-370λ₀.