Erbium-doped mode-locked fiber laser based on multimode PC auxiliary cavity and NOLM

This paper presents a mode-locked erbium-doped fiber laser (EDFL) based on a nonlinear optical loop mirror (NOLM), incorporating a multimode fiber polarization controller (MMF-PC) in the auxiliary cavity. By introducing the MMF-PC into the auxiliary cavity of the NOLM structure, the polarization state is controlled, enabling switching between single and dual-wavelength mode-locked operations. The structure achieves high stability, with a fundamental repetition rate of 676 kHz and central wavelengths of 1531, 1553, and 1558 nm for conventional solitons, as well as a soliton pulse train at 1553 and 1559 nm. Experimental results indicate that the introduction of the MMF-PC significantly enhances control of the polarization state, gain, and power, balancing the dispersion and nonlinear effects. This optimization facilitates the generation of dual/multi-wavelengths and enables stable switching of the mode-locked pulse central wavelengths. As a result, the system optimizes the laser output performance, addressing a wider range of mode-locked requirements.