Broadband wavelength tunable mode-locked thulium-doped fiber laser operating in the 2 μm region by using a graphene saturable absorber on microfiber

A broadband wavelength tunable mode-locked Tm3+-doped fiber laser operating in the 2 mu m region based on a graphene saturable absorber is experimentally investigated. A section of graphene film is transferred on a microfiber, which allows light-graphene interaction via evanescent field. The microfiber based graphene not only acts as an excellent saturable absorber for mode-locking, but also induces a polarizing effect to form an artificial birefringent filter for wavelength selection. By tuning the polarization states in the laser cavity, the laser exhibits tunable wavelength mode-locked pulses over a wide range from 1880 to 1940 nm. Such a system provides a compact, user friendly and low cost wavelength tunable ultrashort pulse source in the 2 mu m region.