Coherence-collapse threshold of 1.3-μm semiconductor DFB lasers

The onset of the coherence-collapse threshold is theoretically and experimentally studied for monomode 1.3-μm antireflection/high reflection distributed-feedback lasers taking into account facet phase effects. The variation of the coherence collapse from chip to chip due to the facet phase is in the range of 7 dB and remains almost independent of the grating coefficient. Lasers that operate without coherence collapse under -15-dB optical feedback, while exhibiting an efficiency as high as 0.30 W/A, are demonstrated. Such lasers are adequate for 2.5 Gb/s isolator-free transmission without under the International Telecommunication Union recommended return loss.