55-fs pulse generation without wave-breaking from an all-fiber Erbium-doped ring laser.

We demonstrate the direct generation of 55 fs pulses from an all-fiber Erbium-doped ring laser oscillator using the nonlinear polarization rotation mode-locking. The average output power is 56.4 mW but limited by available pump power of 330 mW. The linear chirped pulse duration is 55 fs after recompression using standard single-mode fiber. The pulses show to resist optical wave breaking with a smooth spectrum without any side lobe and cw-breakthrough. This all-fiber laser exhibits relatively high transfer efficiency of 17% and the single pulse energy reaches 1.5 nJ.