Abstract：We present an all fiber gain-switched thulium (Tm) doped fiber laser operating in eye-safe region at 1940nm. The FBGs inscribed by phase mask technology are used as cavity mirrors, and the transmission spectrums are also measured. The output characteristics are studied at pulse repetition frequency (PRF) of 10, 20 and 30 kHz. The maximum output powers of 28.9, 67.0 and 71.0mW are achieved under incident pump power of 122, 247 and 250 mW. The narrowest pulse width of 29 ns and pulse built-time of 140ns are obtained at 10 kHz. The relation between pulse built-time and cavity length are discussed in the paper.
