Observation of diverse passive harmonic mode-locked soliton pulses in an all-normal-dispersion fiber laser

Abstract

Diverse passive harmonic mode-locking were observed in an all-normal-dispersion Yb-doped passively mode-locked fiber laser with a long cavity based on the nonlinear polarization rotation (NPR). Using a cascaded long-period fiber grating as a spectral filter, several modes of passively harmonic mode-locking including passive high-order harmonic mode-locking, passive multiple-pulse harmonic mode locking and passive large-pulse-width harmonic mode locking (over 300 ns ) were obtained by adjusting the tunable CW semiconductor laser (pumping source in the experiment) and polarization controller, in which the intense nonlinear effects, large fiber dispersion and phase bias played an important role. It is expected that the observed various modes of passive harmonic mode-locking may find applications in industrial fields where different pulse widths and repetition rates are needed and provide experimental evidence to the research of ultrafast lasers.