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

Area of Science:

• Materials Science
• Optics
• Nanotechnology

Background:

• Nonlinear emission in transition metal dichalcogenides (TMDCs) is key for 2D material optical sources.
• TMDC emission properties are material-specific, limiting tunability for applications.

Purpose of the Study:

• To selectively enhance and modify second-harmonic generation (SHG) in multilayer tungsten disulfide (WS2).
• To investigate the role of silicon-based circular Bragg gratings (CBGs) in controlling SHG emission.

Main Methods:

• Fabrication of a multilayer WS2 flake on a silicon CBG structure atop an Au/SiO2 substrate.
• Selective excitation of the CBG region with specific grating orientations relative to a polarized pump beam.
• Experimental measurements corroborated by numerical simulations of SHG intensity and power dependence.

Main Results:

• Achieved wavelength-tunable SHG peaks at 402.5 nm and 425 nm by altering grating orientation.
• Demonstrated high sensitivity of SHG enhancement to the CBG orientation.
• Confirmed the critical role of the CBG structure in modulating SHG compared to bare substrates.

Conclusions:

• CBG-augmented TMDCs offer a strategy for controlled nonlinear optical emission.
• This approach shows potential for developing tunable photonic devices and selective emission technologies.