Multiple colliding-pulse mode-locked quantum-well lasers for high repetition rate (up to 375 GHz) short pulse generation

Future high-speed transmission systems and broadband networks demand intense research and development in high-speed short-pulse generation and signal processing. The operation of a monolithic multi-sectioned semiconductor laser is described. The laser can be operated as either single mode, multimode, self pulsation (or Q-switched) and mode-locked in either 1, 2, 3 or 4 pulse operation. This device is a very versatile source of high repetition rated (up to 375 GHz) ultrashort pulses (around 1-3 ps) of light. The various modes of operation of the device is experimentally investigated and we have found experimental indications of the presence of excitonic nonlinearities in its operation. The theoretical results from the frequency domain model strongly suggest that for short monolithic cavities, fast nonlinearities play a major role in mode-locking operation and that the device geometry is highly favourable to multiple colliding-pulse mode (MCPM) operation. Numerical simulations with a time domain model were performed, using saturation coefficients and fast recovery times estimated from the frequency domain model. Good agreement between the models and the experimental results for MCPM operation was obtained, although there are still some features which require further investigation for a complete understanding of the laser