Optimized operation of self-seeded gain-switched laser diode for electrically wavelength-tunable singlemode pulses

A gain-switched Fabry-Perot laser diode at 1.3 μm was self-seeded at different electrical bias and optical feedback rates. With a strong feedback, a comparatively large tuning range and a high sidemode suppression ratio were obtained but multimode emission might occur around the center of the range. Similar phenomenon was observed at a weaker feedback when the electrical bias was sufficiently large. The degradation in tunability was attributed to a broadening of the optical pulses, resulting in temporal overlapping of different longitudinal modes. Our optimized feedback of 2.5% and 3.1 mA bias provided a tuning range of 23.5 nm with a sidemode suppression ratio >10 dB.