Subwavelength confinement in an integrated metal slot waveguide on silicon

We demonstrate propagation losses of less than $0.8\mathrm{dB}∕\mu \mathrm{m}$ in a metal slot waveguide on silicon with a predicted confinement substantially below the optical wavelength $(\sim 1.55\mu \mathrm{m})$. We also show compact and efficient coupling of the high-confinement metal slot waveguide with a standard silicon dielectric waveguide with a coupling efficiency of approximately $2.5\mathrm{dB}$ per facet.