Ultra-high order harmonic mode-locking of a Raman fiber laser

An ultra-high order harmonically mode-locked Raman fiber laser with a high signal-to-noise ratio has been proposed and demonstrated. We apply the nonlinear polarization rotation (NPR) technique as the mode-locker in the Raman fiber laser. The underlying harmonic mode-locking (HML) mechanism is discussed to achieve ultra-high order HML in the Raman fiber laser. Up to 5044th ultra-high order HML has been obtained with a signal-to-noise ratio of up to 42.5 dB. To the best of our knowledge, this is the highest order of passive HML achieved so far from a Raman fiber laser using NPR or similar techniques.