Tailoring second harmonic generation in a multilayer WS₂ flake via a silicon circular Bragg grating

Nonlinear emission phenomena observed in transition metal dichalcogenides (TMDCs) have significantly advanced the development of robust nonlinear optical sources within two-dimensional materials. However, the intrinsic emission characteristics of TMDCs are inherently dependent on the specific material, which constrains their tunability for practical applications. In this study, we propose a strategy for the selective enhancement and modification of second-harmonic generation (SHG) emission in a multilayer WS₂ flake through the implementation of a silicon (Si)-based circular Bragg grating (CBG) structure positioned on an Au/SiO₂ substrate. By selectively exciting the region of the circular Bragg grating with the grating oriented either parallel or perpendicular to the linearly polarized pump beam, we successfully achieved wavelength-tunable SHG intensity peaks at 402.5 nm and 425 nm for the respective alignments. Our experimental findings, corroborated by numerical simulations, indicate that the enhancement of SHG intensity is highly sensitive to the orientation of the grating region of the CBG. Power-dependent SHG spectra further validate the quadratic dependence of SHG, while comparative analysis with WS₂ flakes on a bare Si/Au/SiO₂ substrate highlights the critical role of the CBG structure in modulating SHG. This research underscores the potential of CBG-augmented TMDCs for the control of nonlinear optical emissions, suggesting promising applications in photonic devices and selective emission technologies.