Highly stable 68-fs pulse generation from a stretched-pulse Yb3+-doped fiber laser with frequency shifted feedback

We report on the development of a passively mode-locked and highly-stable stretched pulse laser based on Yb3+-doped silica fiber. Mode-locking is achieved by nonlinear polarization evolution coupled with the frequency-shifted feedback technique for ensuring robust self-starting. The Fabry-Perot (F-P) cavity incorporates also a diffraction grating pair to compensate for the normal dispersion of the fiber. The laser generates chirped pulses with energies of 100 pJ at a repetition rate of 23 MHz (2.3 mW average power) around 1055 nm which were subsequently compressed to near-bandwidth-limited pulses of 68 fs duration.