Sun, Shijie, Shi, Zhifeng, Wang, Qingbo, Wang, Zhi, Liu, Yan-Ge, Xiang, Dong, and Wang, Pan
• Over the years 2 µm mode-locked fiber laser has been widely developed as an important light source for various significant applications, such as ultrafast mid-infrared spectroscopy. Besides, as the solutions of CGLE governed by the composite balance among dispersion, nonlinearity, gain and loss in dissipative systems, the field of solitons has become subject to extensive study. • Worth to note that, the rise of time-stretched dispersive Fourier transform (TS-DFT) technique has significantly enhanced the understanding of soliton dynamics, including bound solitons, optical rogue waves and others. However, due to the lack of appropriate dispersive components at 2 µm band with low optical transmission loss for TS-DFT measurement, direct real-time observations of ultrafast soliton dynamical phenomena in the 2 µm mode-locked fiber lasers is still limited. • In the present paper, we utilize DFT method to investigate the ultrafast nonlinear soliton dynamics in a 2 µm Tm-doped mode-locked fiber laser. The real-time observation of the nonlinear dynamics of the soliton explosions and pulsations are successively investigated. Moreover, the real-time observation of the soliton explosions associated with soliton pulsations is demonstrated in 2 µm wavelengths for the first time. In addition, soliton rains with dual-wavelength operation are also observed. Our work will benefit the development of 2 µm ultrafast light source, as well as enhance a comprehensive understanding of the soliton nonlinear dynamics in mode-locked fiber lasers. Over the years, 2 μm mode-locked fiber laser has been widely developed as an important light source for various significant applications. Worth to note that, with the help of real-time spectroscopy technique, i.e., time-stretched dispersive Fourier transformation (TS-DFT), various complex nonlinear soliton dynamics have been revealed, such as soliton molecules, soliton explosions and soliton pulsations, enhancing our understanding of the ultrafast physics. However, due to the lack of appropriate dispersive components at 2 μm band with low optical transmission loss for TS-DFT measurement, the investigation of ultrafast soliton dynamical phenomena in the 2 μm mode-locked fiber lasers is still limited. In this work, we demonstrate the direct real-time observation of soliton explosion and pulsation phenomena at 2 μm band mode-locked fiber laser, for the first time as far as we know, by using specially designed linearly chirped fiber Bragg gratings as dispersive component for TS-DFT measurement. For explosions, we observe slight explosion and drastic explosion, respectively. Particularly, the soliton pulsating explosions are also characterized in real time where the explosions occur in the process of soliton pulsation. In addition, dual-wavelength soliton rains are also observed by carefully adjusting the cavity parameters. Our work provides supplements to the current investigation of 2 μm band ultrafast science, and might enrich our understanding of soliton dynamics. [ABSTRACT FROM AUTHOR]