Monolayer transition metal dichalcogenides (TMDCs) have large second-order optical nonlinearity owing to broken inversion symmetry in two-dimensional (2D) crystals. However, despite the strong light–matter coupling in monolayer TMDCs, their nonlinear responses are ultimately limited by subnanometer thickness. Here, a dramatic enhancement of the second-harmonic generation (SHG) is achieved from monolayer tungsten disulfide (WS2) incorporated onto a 2D silver (Ag) nanogroove grating with subwavelength pitch. By tuning surface plasmon mode and second-harmonic frequency in resonance with the C exciton in WS2, a large SHG enhancement factor (≈400) and a large conversion efficiency (≈2.0 × 10–5) can be obtained. Furthermore, the azimuthal angle dependence of polarized SHG from monolayer WS2 can be manipulated by the nanogroove plasmonic mode. Based on this property, a polarization-modulated optical encoding technique is demonstrated. The results suggest that 2D TMDC–plasmonic hybrid metasurface structures can provide an ideal integration platform for on-chip nonlinear photonics and plasmonics.
- 2D materials
- nonlinear optics
- plasmonic metasurfaces
- second-harmonic generation
- transition metal dichalcogenides