Generation of a square pulse with ultra-wide tuning range in a passively mode-locked Yb-doped fiber laser

Abstract

We have experimentally demonstrated a square pulse in a passively mode-locked Yb-doped fiber ring laser operating in the dissipative soliton resonance (DSR) region based on the nonlinear polarization rotation technique. In our experiment, a 1.5-km long single-mode fiber (SMF) is inserted into the cavity to increase the cavity length. The total cavity is 1501.8m. With increasing pump power, the pulse duration can be tuned from 209.8ns to 812.4ns without wave-breaking, and the maximum output single pulse energy is 42.34nJ. To the best of our knowledge, this is the widest pulse in any Yb-doped mode-locked fiber laser. Moreover, the relationship between pulse width and cavity length is investigated. When the total cavity length is decreased to 1001.8m and 501.8m, the tuning range of square pulse is 372.4ns (from 58.6ns to 431ns) and 138ns (from 26ns to 164ns), respectively, and the maximum output single pulse energy is 13.85nJ and 8.75nJ, respectively.