Recent developments in additive pulse mode locking of solid state lasers

Additive pulse mode locking (APM) is a means of simulating the action of a fast saturable absorber for passive mode locking of solid state lasers with long gain relaxation times. One way of realizing an APM system is with coupled cavities, as in the original “soliton laser” of Mollenauer and Stolen. Another way is to produce pulse interference via a nonlinear Mach-Zehnder interferometer, or polarization rotation in an all-fiber laser. An analytic theory of APM was developed under the assumption that the change of the pulse within the auxiliary cavity is small. Best APM action is achieved for an interferometric detuning of the auxiliary cavity with respect to the main cavity, in which the auxiliary cavity is a fraction of a wavelength shorter than the main cavity (plus or minus integer multiples of wavelengths)