Mid-infrared period-doubled solitons in a few-mode fluoride fiber oscillator

Period doubling bifurcation (PDB) phenomenon, which is prevalent in nonlinear systems, has attracted considerable attention because of its potential application value. As an ideal platform for studying the pulse dynamics of nonlinear systems, the mode-locked fiber laser has been intensively investigated in the near-infrared (NIR) spectral region. However, there is a paucity of relevant reports of pulse dynamics in the mid-infrared (MIR) spectral region. Especially for the MIR large-mode-area (LMA) fluoride fiber oscillator, the existence of multiple transverse modes and a new spatial degree of freedom makes the pulse dynamics phenomenon is more complex, which needs to be further explored. In this paper, a soliton regime with a pulse duration of 404.5 fs, repetition frequency of 45.02 MHz, and average output power of 105.3 mW is obtained in a few-mode fluoride fiber oscillator mode-locked by the nonlinear polarization rotation (NPR) technique. By merely increasing the power of the pump, a period doubled soliton with the pulse intensity varying between two different values can be obtained. This work facilitates a more profound comprehension of the nonlinear dynamics in the mid-infrared multimode fluoride fiber laser, and opens up new opportunities for the chaos, optical frequency combs and all-optical modulation.