Low-loss surface-plasmonic nanobeam cavities

One-dimensional surface-plasmonic nanobeam cavities are proposed as a means to confine surface plasmons to a subwavelength-scale mode volume, while maintaining a relatively high Q-factor. By bonding one-dimensional photonic-crystal nanobeam structures to a low-loss metallic substrate, a clear plasmonic TM bandgap can be formed. The introduction of a single-cell defect alongside the engineering of side-airhole shifts to this plasmonic-crystal nanobeam provides subwavelengthscale plasmonic mode localization within the plasmonic TM bandgap. This suppresses radiation and scattering loss to render a maximum Q-factor of 413 and a modal volume of 3.67 × 10^-3 μm³ at room temperature. The possibility of further reduction in the intrinsic loss of the cavity is investigated by lowering the operating temperature and the Q-factor of 1.34 × 10⁴ is predicted at a temperature of 20K for the optimistic case.