Femtosecond pulse generation from a two-section mode-locked quantum-dot laser using random population

290 fs optical pulses have been demonstrated using a two-section, passively mode-locked InAs quantum dot laser with a proton bombarded absorber, at a repetition rate of 20 GHz, centred around 1220 nm. Optical pulsewidth measurements between 300 K and 20 K, reveal that the pulsewidth decreases by a factor of 29, from 8.4 ps at 250 K to 290 fs at 20 K with a corresponding change in optical bandwidth. Rate equation analysis shows that this is due to the decreased emission rate compared to the recombination rate at 20 K in the random population regime. Random population ensures the dots act as independent oscillators across the entire inhomogeneous distribution thereby allowing access to the full gain spectrum. Proton bombardment of the absorber section shortens the recovery time of the absorber while the dots remain randomly populated