Absorber length optimization of on-chip colliding pulse mode-locked semiconductor laser

We present theoretical and experimental results regarding the saturable absorber length optimization for the generation of stable mode-locked regimes of a novel on-chip colliding pulse mode-locked semiconductor laser structure. We have been able to apply the design criteria acquired from previous theoretical and experimental reports to define a suitable gain section length for a given saturable absorber section length. The latter is independent from the cavity length and allows obtaining stable mode-locked regimes with the required repetition rate and pulse width in the range of picoseconds for different applications. We have developed four on-chip colliding pulse mode-locked laser structures with saturable absorber lengths ranging from 20 to 50 μm in steps of 10 μm with fundamental repetition rate at 25 GHz and twice this frequency at 50 GHz when operated in the colliding pulse mode-locked regime. 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 multisection semiconductor lasers, while the experimental analysis was executed on the samples fabricated on a generic InP photonic integrated technology through a multi-project wafer run.