Dielectric nonlinear waveguides have reached their maximum potential in achieving high nonlinearity due to the limitation of mode confinement beyond the diffraction limit. We theoretically demonstrate that a plasmonic waveguide consisted of a nonlinear subwavelength core coated by a metallic nanoshell can achieve ultrahigh nonlinearity and complete mode confinement. Our results show that the subwavelength nanoshell plasmonic waveguide can possess an ultrahigh Kerr nonlinearity up to 4.1 × 104W-1m-1 with nearly 100% of the mode energy residing inside the waveguide at λ = 1.55 μm. The optical properties are explored with detailed numerical simulations and are explained in terms of their dispersive properties.
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