Theoretical and experimental development of on-chip colliding pulse mode-locked lasers

We report the successful theoretical and experimental optimization of the absorber length of on-chip colliding pulse mode-locked lasers working at 50 GHz repetition rate. The fundamental approach is that the active-passive integration provides freedom to choose the desired gain section to saturable absorber length ratio in order to obtain stable mode-locked regimes. We have developed four on-chip colliding pulse mode-locked semiconductor laser devices with saturable absorber lengths ranging from 20 μm to 50 μm in steps of 10 μm with fundamental repetition rate at 25 GHz and twice this frequency at 50 GHz due to the fact that the colliding pulse mode-locked structure doubles the fundamental frequency. The agreement in the theoretical and experimental demonstration is that the smallest SA considered (20 μm) exhibits the shortest pulse width, which provides a transform limited time bandwidth product. The theoretical study was carried out by using the simulation tool called FreeTWM which is a free travelling wave model software designed for the study of the dynamics of multi-section semiconductor lasers, while the experimental analysis was executed on the samples fabricated in a multi-project wafer run provided by SMART Photonics foundry service.