Theoretical Analysis on Self-Defocusing Mode-Locking in a Ring Resonator

A theoretical analysis of passive mode-locking in a thermal-stable ring cavity containing a Kerr medium and an aperture is presented. The analysis employing the beam propagation theory shows that the power dependence of the cavity loss is extremely sensitive to the relative location of the Kerr medium and the aperture, and is different for the counterpropagating modes, so the unidirectional operation is expected. The combination of Kerr medium with an aperture acts as a p sition feedback, which is similar to the effect of a saturable absorber.