Seminar: Observation of Defect Motions in Active Mode-locked Laser Systems

Ruiling Weng

Abstract: Active mode-locking system achieved by semiconductor lasers has been a popular topic in the field of laser technology. In this work we present experimental results from a fiber ring cavity comprising an intensity modulator, semiconductor amplifier and isolator. This investigation focuses on the complex dynamical regimes near the lasing threshold, particularly at high harmonic resonances. We observed the emergence of three different states of the system: normal mode-locking, period doubling and quasi-periodic behavior. Notably, the quasi-periodic state corresponds to defects in the regular pulse pattern that propagate at a low speed within an otherwise regular crystal of pulses. This quasi-periodic state, while inherently unstable, can be initiated by abrupt changes, for example in semiconductor amplifier pumping current. Furthermore, by tuning to different modulation points, we were able to intentionally induce defects in the system, providing new insights into the dynamics of bifurcation and bistability in active mode-locking laser systems.