▎ 摘　　要

A saturable absorber based on graphene film covered single-mode fiber with inner short waveguides is proposed and demonstrated for passively mode-locked laser operation. The output laser pulses produced have the center wavelength of 1556.9 nm and pulse width of 830.5 fs at the fundamental repetition rate of 18.7 MHz. Such a saturable absorber is highly robust as the graphene film is covered on the surface of single-mode fiber, instead on tapered fiber or side-polished fiber. Moreover, compared with the saturable absorber based on clamping the graphene film between the two fiber connectors in a fiber adaptor, our device provides a large interaction surface area, thus effectively avoiding the thermal damage and ensuring a long time and stable system operation. The device is attractive for high power ultra-short laser pulse generation.