Harmonic Dissipative Soliton Resonance in an Er/Yb Co-Doped Fiber Laser Based On SESAM

Fundamental and harmonic mode-locking in the dissipative soliton resonance (DSR) regime is experimentally investigated in a net-normal-dispersion Er/Yb co-doped fiber laser based on the semiconductor saturable mirror (SESAM), where an equivalent narrow-band spectral filter is used for triggering multi-pulsing. By monotonically increasing the pump power with the fixed polarization controller (PC), the fundamental mode-locking operation of DSR pulses can be transformed into the harmonic mode-locking (HML) under the specific conditions. The main reason is the peak-power-clamping effect induced by the combined effects of the spectral filtering and saturable absorption of the SESAM at higher pump levels, which is applied to achieve the HML in the DSR regime for the first time. The DSR pulse broadens linearly with the pump power in a certain range, no matter whether it is in the fundamental mode-locking or HML state. By incorporating the dispersion compensation fiber (DCF) with different lengths, the pulse characteristics are discussed and compared in detail. The enhanced nonlinearity caused by increasing DCF length can lead to higher orders of HML pulses and even the generation of noise-like pulses (NLPs) with a long-enough DCF.