Abstract

Multimode complex electric field equations are employed to numerically simulate the transient process of active mode locking in a semiconductor laser coupled to an external cavity formed by an AlGaAs or InGaAsP waveguide. Langevin noise sources for the complex fields and the carrier population which contribute to the partially incoherent interference among the modes are included. The simulation starts with a free-running multimode laser. The physical mechanism governing the mode coupling is cross saturation of the gain. Use of sinusoidal gain modulation is seen to cause the evolution of a mode-locked pulse. Fluctuations of the mode-locked pulse height and width due to spontaneous emission noise are observed in our simulations. These represent a fundamental limit of the pulse-to-pulse stability that can be attained in a mode-locked laser.

© 1989 Optical Society of America