Mode coupling and competition in square-racetrack hybrid-cavity semiconductor lasers

Abstract

We propose and demonstrate square-racetrack hybrid-cavity semiconductor lasers to achieve lasing mode control. Strong mode coupling between the modes of the square and racetrack cavities is predicted by finite element method numerical simulation and confirmed by experimental lasing spectra. Mode coupling leads to anti-crossing of the mode wavelengths, crossing of the mode quality factors, and hybrid modes with the field distributing in both square and racetrack cavities, and will affect the competition of lasing modes together with gain distribution induced by separately injected current of the two cavities. Single-mode lasing with a side-mode suppression ratio up to 38 dB and dual-mode lasing with an intensity ratio down to 1 dB are realized by tuning the injection current. Furthermore, increasing racetrack cavity size affects the mode competition process and results in racetrack-mode-dominated lasing for square-racetrack hybrid-cavity semiconductor lasers.