Fundamental limits of sub-ps pulse generation by active mode locking of semiconductor lasers: the spectral gain width and the facet reflectivities

The authors present a numerical simulation of active mode locking of a semiconductor laser amplifier (SCLA) in an external cavity, which includes the finite spectral gainwidth. This is shown to be essential for introducing a lower limit of the pulsewidth, although the gain linewidth is about a factor of 10-50 broader than the inverse pulsewidth. This numerical treatment consistently explains the experimental findings that even SCLA facet reflectivities as low as 10 ^-4 lead to trailing pulses with an intensity almost of the same order of magnitude as the leading one. This theory makes detailed predictions about the influence of the facet reflectivities, the spectral gainwidth, and the injection current on the picosecond pulse generation