Cascaded second-order optical nonlinearities in on-chip micro rings.

Area of Science:

• Photonics and Optical Engineering
• Materials Science
• Nonlinear Optics

Background:

• Whispering-gallery resonators (WGRs) are crucial for nonlinear optical processes.
• Integrated photonic devices require scalable and high-performance fabrication methods.
• Lithium niobate is a key material for nonlinear optics but on-chip fabrication is challenging.

Purpose of the Study:

• To demonstrate cascaded nonlinear optical processes (SRS, SHG, SFG) in integrated WGRs.
• To develop a novel batch fabrication technique for lithium niobate WGRs.
• To achieve high Q-factors and optimize coupling for enhanced nonlinear optical performance.

Main Methods:

• Fabrication of lithium niobate-based WGRs using semiconductor manufacturing techniques.
• Post-processing with specialized polishing for high-quality resonator surfaces.
• Implementation of a flexible and stable optical coupling scheme.

Main Results:

• Successful demonstration of cascaded Stimulated Raman Scattering (SRS), Second-Harmonic Generation (SHG), and Sum-Frequency Generation (SFG).
• Achieved record high Q-factors for on-chip lithium niobate WGRs, up to 3 × 10⁶.
• Validated a novel batch fabrication approach for nonlinear photonic devices.

Conclusions:

• The developed fabrication method enables scalable production of high-performance nonlinear WGRs.
• The achieved Q-factors and coupling scheme are promising for various integrated photonic applications.
• This work paves the way for advanced on-chip optical signal processing and frequency conversion.