All PM Fiber Laser Mode Locked With a Compact Phase Biased Amplifier Loop Mirror

An Yb-doped, all-polarization-maintaining fiber laser oscillator with a nonlinear amplifying loop mirror is presented in this letter. A new compact non-reciprocal phase shifter biased fiber loop mirror was engaged inside the fiber laser, which results in a low threshold and stable mode locking. With a 2.8-nm filter inside the cavity, the mode locked output power is 4.1 mW with the repetition rate of 31.35 MHz at the pump power of 80 mW. The spectral bandwidth of the pulse is 3.1 nm. The pulsewidth of the direct output and the dechirped pulse are 2.13 ps and 538 fs, respectively. The filter bandwidth plays a significant role in the spectrum bandwidth and the direct output pulse width.