Detection and Investigation of Pulse Asymmetries in Passively Mode-Locked Quantum-Dot Laser Diodes Using Dispersion-Scan

Mode-locked laser diodes are low-cost, compact and wall-plug efficient sources of ultrashort pulses. However, they suffer from a range of coherence instabilities when trying to achieve higher average powers and lower pulse widths. Existing techniques, such as Frequency-Resolved Optical Gating (FROG), fail when trying to characterize unstable pulses. Here, for the first time, we apply dispersion-scan (d-scan) [1] to the characterization of pulses from mode-locked laser diodes. D-scan is a pulse retrieval technique based on the measurement of a nonlinear signal as a function of the dispersion applied to the pulse, enabling both its full characterization in the time domain, as well as its compression. With this approach, we were able to fully characterize and compress pulses from a quantum-dot (QD) mode-locked laser diode and to achieve pulse widths in the sub-ps regime.