178 fs, 1.2 nJ pulses from an all-polarization maintaining fiber figure 8 laser based on 3 × 3 coupler at 1 μm

We report on an Yb-doped all-polarization maintaining fiber mode-locked laser based on nonlinear-amplifying-loop mirror and 3 × 3 coupler. Thanks to this coupler inducing a non-reciprocal phase-bias, the mode-locked regime can be easily achieved at the high repetition rate of 52 MHz. The cavity delivers an average power of 62 mW corresponding to a pulse energy of 1.2 nJ. We have finally demonstrated an extra-cavity nonlinear spectral stage induced by the propagation along a standard nonlinear fiber. The pulse can be then compressed down to 178 fs via a grating compressor and the corresponding peak power is then around 6 kW. (letter)