Giant enhancement of second-harmonic generation from microcavity-integrated monolayer WS₂

Transition metal dichalcogenide two-dimensional (2D) materials, exhibiting extraordinary properties absent in their bulk forms, have garnered significant attention in the field of nonlinear optical devices. However, the atomic-level thickness limits the light absorption, which makes the intensity of the nonlinear signal extremely weak. Through transferring monolayer WS₂ onto a silica microsphere, we report a giant second-harmonic generation (SHG) enhancement for approximately 1.46 × 10⁷ times. The second-harmonic (SH) signal reaches 2.56 MHz pumped by a continuous wave laser of 2.5 mW. It is attributed to an enhancement of the pump laser due to the whispering gallery mode of the microsphere cavity. This work demonstrates the potential of microcavity-integrated monolayer 2D materials for nonlinear optics in integrated photonics.