Modelocked Tm-doped Fiber Laser Using Multimode Interference Saturable Absorber in Reflection Mode

We present a reflection mode saturable absorber based on nonlinear multimode interference in a graded index multimode fiber. The saturable absorber provides a modulation depth of 12% at a low saturation intensity of 18.5 MW/cm². The all-fiber structure and reflection mode design of this saturable absorber makes it an ideal device for the fabrication of fiber lasers with linear resonant cavity. When inserted in a linear laser cavity comprising a thulium doped fiber as the gain medium, the saturable absorber triggers modelocked noise like pulses with a center wavelength of 1905 nm and spectral width of 11.2 nm.