Black phosphorus Q-switched and mode-locked mid-infrared Er:ZBLAN fiber laser at 3.5 μm wavelength

With the proposal of dual-wavelength pumping (DWP) scheme, DWP Er:ZBLAN fiber lasers at 3.5 mu m have become a fascinating area of research. However, limited by the absence of suitable saturable absorber, passively Q-switched and mode-locked fiber lasers have not been realized in this spectral region. Based on the layer-dependent bandgap and excellent photoelectric characteristics of black phosphorus (BP), BP is a promising candidate for saturable absorber near 3.5 mu m. Here, we fabricated a 3.5-mu m saturable absorber mirror (SAM) by transferring BP flakes onto a Au-coated mirror. With the as-prepared BP SAM, we realized Q-switching and mode-locking operations in the DWP Er:ZBLAN fiber lasers at 3.5 mu m. To the best of our knowledge, it is the first time to achieve passively Q- switched and mode-locked pulses in 3.5 mu m spectral region. The research results will not only promote the development of 3.5-mu m pulsed fiber lasers but also open the photonics application of twodimensional materials in this spectral region. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement