Abstract

Numerous experimental results^1,2 have shown that the coupling of a nonlinear cavity to a mode-locked laser leads to a drastic reduction of the duration of the emitted pulses. In this paper we present a general model describing the operation of such lasers. Our model identifies the coherent superposition of the pulses propagating in the main laser cavity and in the coupled cavity as the key physical process leading to pulse narrowing; hence, the laser operation is described as interferential mode locking. We have developed a Gaussian pulse theory with simple analytical formulas valid in the weakly nonlinear regime. Numerical simulations of the evolution of the pulse intensity in a laser with a nonlinear, nondispersive fiber inserted in a coupled cavity have revealed the existence of an unstable regime at low pump level and the development of square pulses at higher pump levels.

© 1989 Optical Society of America