Numerical and experimental investigation of Raman-assisted frequency comb in a packaged microbottle resonator...

In this study, the reversible conversion between the Kerr frequency comb and the Raman-assisted frequency comb in a packaged silica microbottle resonator structure is demonstrated both theoretically and experimentally, and the quality factor of this resonator is as high as 1.5 × 10⁸. By deeply probing the gain between four-wave mixing and stimulated Raman scattering, the key role played by dispersion properties in the Kerr frequency comb with different free spectral range spacings and Raman broadening spectra is revealed. In the experiments, by adjusting the pump laser power and detuning amount, the stable excitation and efficient conversion of the Kerr frequency comb and Raman-assisted frequency comb are successfully realized, and broadband frequency combs with a wavelength range of up to 200 nm and tooth spacing as low as 2 nm are obtained. Numerical simulations with the aid of the generalized Lugiato-Lefever equation incorporating the Raman effect accurately reproduce the experimentally observed frequency comb conversion process, further verifying the accuracy of the theoretical model. In addition, the transition from a pure Raman frequency comb to a Raman-assisted frequency comb is observed by changing the coupling position along the axial direction to modulate the cavity dispersion, and a Raman-assisted frequency comb with a continuous bandwidth close to 250 nm is finally obtained. The study in this paper demonstrates that multifunctional optical frequency combs on silica microbottle resonator platforms have unique potential for applications in the fields of frequency conversion, precision measurement and spectroscopy.