Passive mode-locking using multi-mode fiber

The mode-locking of dissipative soliton fiber lasers using large mode area fiber supporting multiple transverse modes is studied experimentally and theoretically. Experiments using large core step-index fiber, photonic crystal fiber, and chirally-coupled core fiber show that when the higher order mode content exceeds -27 dB, the maximum stable single-pulse energy is significantly reduced. The averaged mode-locking dynamics in a multi-mode fiber are studied using a distributed model. The co-propagation of multiple transverse modes is governed by a system of coupled Ginzburg-Landau equations (CGLEs). Simulations show that stable and robust mode-locked pulses can be produced. The maximum stable single pulse energy is found to increase with higher order mode filtering. This work demonstrates that mode-locking performance is very sensitive to the presence of multiple waveguide modes when compared to systems such as amplifiers and continuous-wave lasers, and gives a quantitative estimate of what constitutes effectively single-mode operation. Robust, distributed higher order mode filtering is necessary to maximize single-pulsing energy.