Mode locking in a tapered two-section quantum dot laser: design and experiment

In this Letter, the pulse generation and pulse train stability of a tapered two-section InAs/InGaAs quantum dot laser emitting at 1250 nm are numerically predicted and experimentally verified. Simulations based on a multi-section delayed differential equation model are used to properly design a laser source able to generate stable mode-locked pulses at a 15 GHz repetition rate with picosecond width and output power larger than 1 W, and to identify the device stability regions depending on the bias conditions. Possible instabilities are associated with the existence of a leading or trailing edge net gain window outside the optical pulse. Experimentally, we confirm the existence of different stability regions where instabilities manifest in broadband or multi-periodic pulse train amplitude modulations. Our results confirm the correctness to the design and may be helpful in achieving high-power pulses while avoiding detrimental pulse train instabilities, both being important for time-critical applications.