We present an all-fiber gain-switched thulium (Tm) doped fiber laser operating in the eye-safe region at 1940nm.The fibre Bragg gratings (FBGs) inscribed by phase mask technology are used as cavity mirrors,and the transmission spectra of FBGs are also measured.The output cbaracteristics are studied at pulse repetition frequene cies of 10,20 and 30kHz,and the maximum output powers of 28.9,67.0 and 71.0mW are achieved under incident pump powers of 122,247and 250mW.The narrowest pulse width of29ns and shortest pulse built-time of 140 ns are obtained at 10 kHz.The relation between pulse built-time and cavity length are discussed.
