γ-MnO2-deposited photonic crystal fiber: Novel photonic devices for multi-state solitons generation

•Low-dimensional materials is introduced into photonics for more than a decade. However, few reports about metal oxide nanoparticles’ integration into photonic devices have been reported till now.•In this manuscript, manganese dioxide (MnO2) nanoparticles are employed to make a robust and reliable saturable absorber for ultrafast fiber lasers. Due to their small band gap of 0.7 eV, tinier size and strong absorption in near-infrared wavelength range, MnO2 nanoparticles show excellent nonlinear optical properties in the proposed femtosecond lasers.•The combination of nanomaterials and hollow photonic crystal fiber provides a simple and reliable approach to optimize compact photonic devices design, which could pave a novel way for its applications in the field of supercontinuum generation, nonlinear applications and fiber sensing.•By inserting a tunable Sagnac filter, conventional solitons, switchable noise-like pulses, soliton molecules and dip-type sidebands solitons could be obtained with identical configuration, which could greatly increase versatility of the proposed fiber laser. Transition metal oxides, especially MnO2 nanoparticles, are often used as cathode of dry batteries and catalysts. They are also promising materials for ultrafast laser applications due to their strong absorption in visible light and near-infrared wavelength range. In this work, high-concentration MnO2 nanoparticles dispersions embedded in the hole cladding of dual-hole photonic crystal fiber is fabricated as a saturable absorber with a modulation depth of 4 % and a saturation intensity of 25 MW/cm2. Strong MnO2-light interaction occurs due to enhanced evanescent-field strength (over 10 cm) of the SA could enable stable mode locking operation at 1.55 μm region. By inserting a Sagnac fiber filter in the cavity, multi-state solitons are experimentally demonstrated with identical layout, respectively, which greatly improves the versatility of this laser. This study proves that MnO2 nanoparticles possess excellent nonlinear optical properties in the near-infrared band. The simple in-line structure of the proposed nanoparticles-deposited device could pave a way for high power and all-fiber applications of photonics.