In this paper,both nonlinear saturable absorption and two-photon absorption(TPA) of few-layer molybdenum diselenide(MoSe_2) were observed at 1.56 μm wavelength and further applied to mode-locked ultrafast fiber laser for the first time to our knowledge.Few-layer MoSe_2 nanosheets were prepared by liquid-phase exfoliation method and characterized by x ray diffractometer,Raman spectroscopy,and atomic force microscopy.The obtained fewlayer MoSe_2 dispersion is further composited with a polymer material for convenient fabrication of MoSe_2 thin films.Then,we investigated the nonlinear optical(NLO) absorption property of the few-layer MoSe_2 film using a balanced twin-detector measurement technique.Both the saturable absorption and TPA effects of the few-layer MoSe_2 film were found by increasing the input optical intensity.The saturable absorption shows a modulation depth of 0.63% and a low nonsaturable loss of ~3.5%,corresponding to the relative modulation depth of 18%.The TPA effect occurred when the input optical intensity exceeds ~260 MW∕cm~2.Furthermore,we experimentally exploit the saturable absorption of few-layer MoSe_2 film to mode lock an all-fiber erbium-doped fiber laser.Stable soliton mode locking at 1558 nm center wavelength is achieved with pulse duration of 1.45 ps.It was also observed that the TPA process suppresses the mode-locking operation in the case of higher optical intensity.Our results indicate that layered MoSe_2,as another two-dimensional nanomaterial,can provide excellent NLO properties(e.g.,saturable absorption and TPA) for potential applications in ultrashort pulse generation and optical limiting. In this paper, both nonlinear saturable absorption and two-photon absorption (TPA) of few-layer molybdenum diselenide (MoSe 2) were observed at 1.56 μm wavelength and further applied to mode-locked ultrafast fiber laser for the first time to our knowledge. Few -layer MoSe_2 nanosheets were prepared by liquid-phase exfoliation method and characterized by x ray diffractometer, Raman spectroscopy, and atomic force microscopy. The obtained few layers MoSe_2 dispersion is further composited with a polymer material for convenient fabrication of MoSe_2 thin films. Chen, we The nonlinear optical (NLO) absorption property of the few-layer MoSe_2 film using a balanced twin-detector measurement technique. By the saturable absorption and TPA effects of the few-layer MoSe_2 film were found by increasing the input optical intensity. saturable absorption shows a modulation depth of 0.63% and a low nonsaturable loss of ~ 3.5%, corresponding to the relative modulation depth of 18%. The TPA effect occ urred when the input optical intensity exceeds ~ 260 MW / cm ~ 2.Furthermore, we experimentally exploit the saturable absorption of few-layer MoSe_2 film to mode lock an all-fiber erbium-doped fiber laser.Stable soliton mode locking at 1558 nm center wavelength is achieved with pulse duration of 1.45 ps.It was also observed that the TPA process suppresses the mode-locking operation in the case of higher optical intensity. Our results indicate that layered MoSe_2, as another two-dimensional nanomaterial, can provide excellent NLO properties (eg, saturable absorption and TPA) for potential applications in ultrashort pulse generation and optical limiting.