Comparative study on pump frequency tuning and self-injection locking in Kerr microcomb generation

The optical frequency comb has attracted considerable interest due to its diverse applications in optical atomic clocks, ultra-low-noise microwave generation, dual-comb spectroscopy, and optical communications. The merits of large frequency spacing, high integration, and low power consumption have shown that microresonator-based Kerr optical frequency combs will become mainstream in the future. Two methods of pump frequency tuning and self-injection locking were used to obtain Kerr combs in the same silicon nitride microresonators with free spectral ranges of 50 GHz and 100 GHz. Singlesoliton combs are realized with both methods. Simplicity, pump power, spectrum bandwidth, conversion efficiency, and linewidth are compared and analyzed. Our results show that the advantages of pump frequency tuning are a wider spectrum and higher soliton power while the advantages of self-injection locking are simplicity, compactness, low cost, significant linewidth narrowing, and high conversion efficiency.