Broadband microcomb generation in silica spherical microresonators with engineered dispersive waves in normal and anomalous dispersion regime

Abstract: Expanding the bandwidth of frequency combs in microcavities is currently a prominent research area, and one effective approach is to introduce dispersive waves using higher-order dispersion. 
However, The exploration of high-order dispersion control on quartz microsphere platforms has been limited by the challenge of preserving high Q factors across a broad range of sizes. 
Here, we fabricated quartz microspheres through arc discharge with diameters ranging from 100-260 µm, achieving Q factors in the range of 10⁸. 
We achieved a broadband Kerr frequency comb with dispersive wave radiation by manipulating the dispersion of the microsphere through size adjustment. Our experimental results demonstrate that the spectral span of the dispersive wave frequency combs can be extended up to 360 nm. 
At the same time, we have also demonstrated Raman lasers and Raman-Kerr frequency combs in small microspheres with normal dispersion.This work provides a reference for developing broadband, high-coherence frequency combs on microsphere platforms and offers an efficient implementation scheme for low-noise integrated broadband frequency combs.