Broadband Manipulation of Stokes Raman Frequency Combs Via Mode Division Multiplexing in Optical Microcavities

We theoretically and experimentally investigate broadband manipulation of Stokes frequency comb generation in a silica microbottle resonator. We realize selective excitation of spectrally trapped Stokes combs belonging to distinct transverse mode families and a spectral tuning range up to ∼14.3 nm via coupling engineering by exciting distinct axial mode families with appropriate quality factors (
Q
s). Moreover, radial mode number selection, microcavity diameter control, or injection power adjustment also enables us to shift the Stokes comb wavelength. The tuning bandwidth can be extended to hundreds of nanometers by theoretical prediction using the bottle modal analysis and Coupled Lugiato Lefever (LL) equations simulation. We also show that multiple regimes in two-dimensional (2D) patterns can be selectively triggered depending on the cavity detuning, including Kerr frequency comb, single-frequency Raman lasing, multimode Raman lasing, and soliton crystal-like state. Our approach provides a scheme for greatly extending the wavelength tuning range of compact Raman laser devices with high performance.