We measured the optical linewidths of a passively mode-locked quantum dot laser and show that, in agreement with theoretical predictions, the modal linewidth exhibits a parabolic dependence with the mode optical frequency. The minimum linewidth follows a Schawlow–Townes behavior with a rebroadening at high power. In addition, the slope of the parabola is proportional to the RF linewidth of the laser and can therefore provide a direct measurement of the timing jitter. Such a measurement could be easily applied to mode-locked semiconductor lasers with a fast repetition rate where the RF linewidth cannot be directly measured.
© 2009 Optical Society of America
Lasers and Laser Optics
Original Manuscript: July 6, 2009
Revised Manuscript: September 18, 2009
Manuscript Accepted: September 27, 2009
Published: October 23, 2009
T. Habruseva, S. O'Donoghue, N. Rebrova, F. Kéfélian, S. P. Hegarty, and G. Huyet, "Optical linewidth of a passively mode-locked semiconductor laser," Opt. Lett. 34, 3307-3309 (2009)