Recent research progress of nonlinear multimode interference mode-locking technology based on multimode fibers.

• We reviewed the research progress of NL-MMI mode-locking technology based on multimode fibers. • We gave the theoretical principle of NL-MMI, and the working principles of various SAs based on GIMFs are introduced. • The soliton molecules, noise-like pulse or multi-wavelength operation in NL-MMI mode-locked fiber lasers are discussed. • The present limitation and solutions of using GIMF as the SA are analysized. We review the research status of the mechanism and technology of all-fiber mode-locked ultrafast laser with multimode fiber based saturable absorber. Using novel all-fiber structured mode-locking modulation device with high damage threshold, the single pulse energy and pulse width of conventional soliton can up to the order of nJ and fs in 1 μm, 1.5 μm, 2 μm, switchable and tunable dual or multi-wavelength mode-locked operation can be realized. At the same time, fascinating nonlinear optical phenomena such as soliton molecules and noise-like pulses were achieved, which provided an excellent platform for the study of nonlinear optics. Thus, using the multimode fiber as an all-fiber nonlinear saturable absorber has important research significance and wide application, which further promotes the development of ultrafast laser technology and nonlinear optics. [ABSTRACT FROM AUTHOR]