Above threshold spectral dependence of linewidth enhancement factor, optical duration and linear chirp of quantum dot lasers

The spectral dependence of the linewidth enhancement factor above threshold is experimentally observed from a quantum dot Fabry-Perot semiconductor laser. The linewidth enhancement factor is found to be reduced when the quantum dot laser operates similar to 10 nm offset to either side of the gain peak. It becomes significantly reduced on the anti-Stokes side as compared to the Stokes side. It is also found that the temporal duration of the optical pulses generated from quantum dot mode-locked lasers is shorter when the laser operates away from the gain peak. In addition, less linear chirp is impressed on the pulse train generated from the anti-Stokes side whereas the pulses generated from the gain peak and Stokes side possess a large linear chirp. These experimental results imply that enhanced performance characteristics of quantum dot lasers can be achieved by operating on the anti-Stokes side, similar to 10 nm away from the gain peak. (C) 2009 Optical Society of America