Bidirectional dual-comb fiber laser based on a novel four-port circulator and hybrid mode-locking

Single-cavity dual-comb bidirectional mode-locked laser has the advantages of lower cost, simpler structure, inherent common-mode noise suppression. However, it faces the challenge of gain competition, which makes bidirectional mode-locking difficult to achieve. In this research, we design an integrated module based on PBS and four-port circulator, supporting SESAM and NPR hybrid mode-locking. The partially non-common-path structure of this device enables adjustment of the losses for the two directions independently, thereby balancing the gain competition within the cavity and facilitating bidirectional mode-locking. By changing the length of the non-common-path structure, the repetition rate difference can be flexibly adjusted. Moreover, dual-comb absorption spectroscopy is performed using a hydrogen cyanide gas cell, demonstrating the application prospect of the dual-comb system in gas sensing.