Tolerance to optical feedback of 10-Gb/s quantum-dash-based lasers emitting at 1.51 mu m

Tolerance to optical feedback is investigated on quantum-dash-based lasers emitting at 1.51 mu m. The onset of coherence collapse regime is experimentally determined using three criteria: optical spectrum broadening, relative intensity noise increase, and bit-error-rate degradation. Measurements were first performed in static operation at different current values, using the first and second criteria. The onset of coherence collapse was found to increase from similar to -41 to -27 dB with the bias current. Then tolerance to optical feedback was assessed in dynamic operation at 10 Gb/s, using the third criterion. In spite of a relatively high linewidth enhancement factor (alpha H similar to 4.5), a -32-dB onset of coherence collapse corresponding to -24-dB maximum optical return loss tolerance was achieved at 10-Gb/s rate.