Abstract

Ultrafast fiber lasers have been recognized as the efficient ultrashort pulse sources, which can be applied to various practical fields, such as material processing, fiber sensing, optical communication and medicine. To generate ultrashort pulse, the most efficient approach is the use of passive mode-locking techniques. So far, the passively mode-locked pulse duration ranging from femtosecond to picosecond could be readily achieved in fiber lasers. After achievement of the passive mode-locking operation, it has been demonstrated that the mode-locked soliton pulse could evolve into various patterns, i.e., multi-soliton operation [1], soliton rain [2] and dissipative soliton resonance [3-4]. To date, most of the researches on the mode-locked soliton pulse in the ultrafast fiber lasers are focused on the soliton nonlinear dynamics after the soliton formation. However, the investigations of the soliton build-up during the mode-locking process were rare. Very recently, the build-up of the mode-locked pulse in a Kerr-lens mode-locking Ti:sapphire laser was investigated by virtue of the dispersive Fourier transform (DFT) methods [5], which could enable mapping of single-shot spectra to the temporal domain so as to be captured by a real-time oscilloscope. Regarding the passive mode-locking of a fiber laser, due to the optical waves were localized in the fiber, it can be expected that the nonlinear dynamics would be richer than those of Ti:sapphire laser. Therefore, it would be interesting to see what happens during the build-up of the passive mode-locking in ultrafast fiber laser. In this contribution, we will address this issue. It was found that the high-amplitude waves could be always observed when the mode-locking was starting in the fiber laser. The results would provide an enhanced understanding of the dynamics of passive mode-locking in fiber lasers.

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