Effect of optical feedback on fast modulated semiconductor lasers

The authors have studied the numerical response of a singlemode semiconductor laser under modulation of the injection current in the presence of optical feedback for different external cavity lengths. They have restricted the experiment to the nonreturn-to-zero modulation scheme and a modulation frequency of 10 Gbit/s, Observations are made that for short cavities (a few millimetres) the eye diagram aperture and the frequency chirp depend strongly on the phase of the reinjected field. Conversely, for cavity lengths of a few centimetres (pig-tail sizes) neither the eye aperture nor the frequency chirp are appreciably affected by the feedback.