Mode confinement enhanced by exploiting epsilon-near-zero supercoupling in a mimic transverse electric hybrid phonon polariton waveguide

Abstract

New capabilities in mid- to long-wave infrared sensing and telecommunications require ultracompact waveguides that support long propagation lengths. Hybrid waveguides supporting the coupling between a dielectric strip-waveguide mode (long propagation) and a surface polariton mode (tightly confined mode) are promising candidates. Here, an infrared (λ0 = 10.6 μm) hybrid waveguide design is presented that achieves enhanced mode confinement but with minimal impact on propagation distances. Modal area confinement is enhanced by the integration of a thin layer of epsilon-near-zero material, aluminum nitride near the longitudinal optical phonon resonance, which supports supercoupling, a term that describes the effect of field enhancement caused by squeezing energy into arbitrary-sized regions. While SPhPs are inherently transverse magnetic modes, a transverse electric (TE) mode is sought to best exploit the ENZ supercoupling phenomenon. By adding a thin high index layer (GaAs) over the 4H-SiC substrate, a mimic TE mode is achieved. The epsilon-near-zero supercoupling-enhanced mimic TE hybrid SPhP waveguide presented exhibits modal confinement improvement by as much as a factor of 4 while maintaining more than 95% of the original propagation length.