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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 mu m in steps of 10 mu m 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 multi-section semiconductor lasers, while the experimental analysis was executed on the samples fabricated on a generic InP photonic integrated technology through a multi-projectwafer run.