Cascaded injection of semiconductor lasers for optical frequency comb generation

The study focuses on stabilizing subharmonic nonlinear dynamics in semiconductor lasers for optical frequency comb (OFC) generation. The proposed system consists of two cascaded optical injection stages. By injecting the first stage with proper power and frequency, period-one (P1) dynamics are invoked, then leading P1 dynamic injection into the second stage. With adjusted power in the second stage, undamped relaxation oscillations trigger subharmonic nonlinear dynamics. This achieves OFC generation with subharmonic oscillation sidebands, generating over 15 comb lines, and a bandwidth greater than 140 GHz. We have also proposed a cascaded injection-locking scheme to improve microwave comb signal quality limited by laser-induced instability.