Generation and pulsating behaviors of loosely bound solitons in a passively mode-locked fiber laser

We demonstrate the experimental observation of loosely bound solitons and pulsations in a passively mode-locked fiber laser. The soliton amount inside one soliton bunch typically increases with the increment of pump power, while the average pulse-to-pulse separation in the regime of hundreds of picoseconds decreases in principle accordingly. Besides, by employing the real-time measurement based on the dispersive Fourier-transform technique, we find that some solitons in a single bunch are experiencing a simultaneous pulsating process with a period corresponding to 100 times longer than the cavity round-trip time. The experimental results can be beneficial for better understanding the formation of multiple solitons and pulsating solitons and enriching the nonlinear phenomena in complex soliton systems.