Revealing the soliton buildup dynamics in mode-locked fiber lasers

Passively mode-locked fiber lasers, which have been widely utilized to generate ultrashort pulses in the femtosecond level, can be regarded as the next-generation laser source due to the advantages of high beam quality, high efficiency, etc. On the other hand, ultrafast mode-locking fiber lasers can provide an excellent platform for observing a variety of nonlinear dynamics. Although some steady state phenomena had been observed theoretically and experimentally, many interesting and important transient dynamics properties can only be theoretically predicted, and some are unpredictable. The main reason is that these ultrafast nonlinear dynamics are unrepeatable and have complex transformation in temporal and spectral domain, which cannot be resolved by the current technologies. In recent years, researchers have proposed time-stretched dispersive Fourier transform (TS-DFT) technique [1] - [6] to measure the transient, nonrepeat events. This technique can map the spectral information of optical waves into the time domain, thus provide an elegant way to obtain real-time, single-shot spectrum measurements of ultrafast optical phenomena. Up to now, this technique has helped scientists to experimentally resolve the entire formation dynamics [2] , [3] and localized transient dynamics of solitons in mode-locked fiber lasers [4] - [6] . Besides, a temporal magnifier technique, also known as time lens, was employed to microimaging the ultrafast phenomena in recent years. This technique has been successfully applied to study the real-time full-field characterization of soliton dynamics in mode-locked laser [7] , [8] .