Optical feedback tolerance of quantum-dot- and quantum-dash-based semiconductor lasers operating at 1.55 μm

This paper reports on the tolerance of low-dimensional InAs/InP quantum-dash- and quantum-dot-based semiconductor lasers to optical feedback in the 1.55 μm window. For this purpose, the onset of coherence collapse (CC) is experimentally determined and systematically investigated as a function of different laser parameters, such as the injection current, differential gain, temperature, and photon lifetime. It is in particular found that for both material systems the onset of CC increases with the injection current in a similar way to bulk or quantum-well-based devices. Of most importance, we experimentally show that the differential gain plays a key role in the optical feedback tolerance. It is indeed shown to determine not only the range of the onset of CC but also the dependence of this threshold both on the temperature and laser cavity length. Increasing the operating temperature from 25°C to 85°C leads to a decrease of the onset of CC by a factor of only ∼3 dB, well accounted for by the variation of the differential gain in this temperature range. We find no difference in the tolerance to external reflections of a truly 3-D confined quantum-dot-based laser and a quantum dash device of the same cavity length, which have similar differential gains. A tentative analysis of our data is finally carried out, based on existing models.