Plasmonic modulation and control of optical properties in monolayer TMDCs

Two-dimensional monolayer semiconductors, e.g. transition metal dichalcogenides, have giant second order nonlinearity due to the intrinsic lack of inversion symmetry. However, the sub-nanometer thickness of monolayer limits the conversion efficiency and hence/consequently the potential application. Here, we experimentally show that the second-harmonic generation (SHG) of WS2 can be enhanced by integrating it on a plasmonic metasurface. The SHG enhancement factor of 400 can be realized due to the strong field confinement of the plasmonic dark mode. Meanwhile, the polarization dependence of SHG can also be controlled by the plasmonic mode. An optical information encoding method is demonstrated based on this property. Our results suggest that the planar hybrid structure made by transition metal dichalcogenide and plasmonic metasurface provides an integrated platform for nonlinear optics frequency conversion to generate on-chip tunable light source.