All-Fiber Saturable Absorbers for Ultrafast Fiber Lasers

The past decade has witnessed tremendous achievements of ultrafast fiber laser technologies due to rapid developments of saturable absorbers (SAs) based on, in particular, nanomaterials such as 0D quantum dot, 1D carbon nanotubes, 2D layered materials, and 3D nanostructures. However, most of those nanomaterials-based SAs are inevitably absence of the high damage threshold and all-fiber integration, therefore challenging their applications on highly integrated and high-energy pulse generations. Recently, the real all-fiber SAs based on the nonlinear multimodal interference (NLMMI) technique using multimode fibers are demonstrated to overcome the above limitations. In this review, a detailed summary of the recent advances in NLMMI-based all-fiber SAs is provided, including the fundamental theory, implementation scenarios, and ultrafast fiber lasers of the all-fiber SAs, covering wide wavelength range of 1, 1.55, and 2 μm. In addition to the state-of-the-art overview, optical rogue waves in the all-fiber SA-based ultrafast fiber laser are extensively analyzed, which reveals the laser physics behind the dynamics from low-energy to high-energy pulses and directs the design of high-energy ultrafast fiber lasers. The conclusions and perspectives of the all-fiber SAs are also discussed at the end.