Coexistence of soliton singlets and molecules in a dual-wavelength mode-locked fiber laser

Rapid progress in multi-state pulse generation spreads a new concept of multiplexed fiber laser. The investigations of laser designing and nonlinear soliton dynamics accelerate the discovery with respect to vivid working regimes of ultrashort pulsed lasers, as well as extending the potential application scenarios. Here, we report on the formation of multi-state solitons in a dual-wavelength mode-locked fiber laser. Attributing to the nonlinear polarization rotation (NPR) induced birefringence filtering effect inside the cavity, the fiber laser approaches dual-wavelength working regime, which simultaneously delivers modulation-instability (MI) solitons and conventional solitons in different wavebands. In particular, MI soliton singlets and conventional soliton molecules can be respectively emitted from these two lasing wavebands with asynchronous repetition rates. The soliton molecules exhibit various assembling forms with different bound-pulse number and pulse separations. The findings highlight the feasibility of multi-state soliton generation via waveband multiplexing and bring insight into various behaviors of soliton molecules.