SELF-STABILIZING ADDITIVE-PULSE MODE-LOCKING DUE TO THERMOOPTICAL NONLINEARITY IN AN OPTICAL-FIBER

In additive-pulse mode-locked (APM) lasers, an interferometric phase m atch of both coupled cavities must normally be maintained with the hel p of an electronic servo loop. However, Cheung et al. [Opt. Lett. 16, 1671 (1991)] described a Nd:YLF APM laser which somehow automatically adjusted the relative resonator phase. We reproduce this behavior and analyse its origin. Thermal effects due to the light power guided in t he fiber affect the effective fiber length, which in turn influences t he phase and thus the power level; hence a closed servo loop results. We demonstrate this explanation to be correct in quantitative terms. C onsequences arise for other systems involving fiber-optic loops or int erferometers.