Unveiling Laser Radiation of Multiple Optical Solitons by Nonlinear Fourier Transform

Mode-locked fiber lasers are applied in versatile scientific fields and exhibit a rich diversity of nonlinear dynamics. However, the nontrivial coexistence of solitons and embedded dispersive wave radiation prevents unveiling the real nonlinear dynamics in mode-locked fiber lasers, such as multiple solitons interaction. Here, nonlinear Fourier transform (NFT) is applied as a signal processing tool to reveal nonequilibrium multiple soliton dynamics. It is feasible to isolate solitons from the continuous wave background in a fiber laser. The real-time coherent homodyne detection methodology is used to measure the full-field dynamic evolution of multiple solitons, including multiple solitons buildup and sequentially nonequilibrium evolution with complex splitting, drifting, and collision processes. With the approach of inverse NFT, the corresponding various pure solitons buildup and collision are reconstructed. The eigenvalue probability distributions are used to classify different lasing regimes. Moreover, the controllable multiple solitons drifting is achieved and characterized by using all-optical methods. Experimental results suggest that NFT can be used to identify localized soliton nonequilibrium evolution excluding dispersive wave radiation influence, which provides a new window into the physics of the underlying laser dynamics and uncovers real soliton interaction in dissipative nonlinear systems.