Square-wave pulse with ultra-wide tuning range in a passively mode-locked fiber laser

We report the generation of ultrawide tunable square-wave pulse in an erbium-doped mode-locked fiber laser. The pulse width can be tuned in an ultrawide range of more than 1700 ns by simply increasing the pump power. The pulse-width tuning is 5.1 ns/mW. To the best of our knowledge, this is the widest pulse-width tuning range of any square-wave pulse in an all-fiber passively mode-locked fiber laser. Experimental results show that the fiber nonlinearity plays an important role in the tuning range of the output pulse width. The high nonlinearity helps to increase the tuning range of the pulse width.