Loss compensation during subwavelength propagation of enhanced second-harmonic generation signals in a hybrid plasmonic waveguide†
Ultracompact coherent light sources with broadband wavelength tunability and subwavelength optical waveguiding have attracted extensive attention due to their potential applications ranging from multicolor detection to multiband on-chip photonic communication. Metal–dielectric nonlinear structures, which comprise nonlinear dielectric materials and metal films, have been widely used to generate nanoscale broadband tunable coherent light sources through the second-harmonic generation process below the diffraction limit. However, restricted by high ohmic losses at the metal–dielectric surface, subwavelength propagation of SHG signals with low loss remains a big challenge. Here, a novel strategy is utilized to reduce the propagation loss of SHG signals based on the coupling between the waveguide mode and plasmonic mode in a hybrid plasmonic waveguide (HPW). The generated hybrid plasmonic mode in the HPW exhibits strong optical confinement around the nonlinear dielectric and insulating gap, which is beneficial for minimizing the ohmic losses at the metal–dielectric interface and enhancing the light–matter interaction below the diffraction limit. Moreover, under the phase matching condition, the propagation loss of SHG signals is partially compensated for by the frequency conversion of the fundamental wave (FW) through the SHG process. As a result, low propagation loss of enhanced SHG signals at a subwavelength scale is realized in HPWs.