Dynamic Longitudinal Mode Spectral Behavior of Laser Diodes Under Direct High-Frequency Modulation

Abstract

The steady-state longitudinal-mode spectrum of semiconductor lasers has been extensively studied, and major observed features can be understood in terms of modal competition in a common gain reservoir. It was generally agreed that gain saturation in semiconductor lasers is basically homogeneous. Thus, a well-behaved index-guided laser should oscillate predominantly in a single-longitudinal mode above lasing threshold [41, 42]. This has been verified extensively in lasers of many different structures. It was also recognized that a single-mode laser will not remain single-moded during turn-on transients and high-frequency modulation. This can be predicted theoretically from numerical solutions of the multimode rate equations [43]. The optical spectrum of a semiconductor laser during excitation transient has been observed by many researchers [44, 45, 46, 47, 48, 49, 50].