Stability and Chirp of Tightly Bunched Solitons From Nonlinear Polarization Rotation Mode-Locked Erbium-Doped Fiber Lasers

Investigation of tightly bunched solitons generated from the nonlinear polarization rotation (NPR) governed mode-locked erbium-doped fiber laser (ML-EDFL) is demonstrated. By changing the intra-cavity polarization, the solitons can be switched from the tightly bunched state to coarse bunched state. In the tightly bunched state (stable state), the energy fluctuation of soliton is substantially suppressed to ΔE/E = 2.5 × 10
^-3
with a timing jitter of Δt = 16 ps. In addition, the dynamic evolution of bunched solitons in the NPRML-EDFL is also explored by configuring two output ports at different positions. As compared to the output node before the EDF, the tightly bunched solitons delivered from the output node after the EDF performs the shorter pulsewidth of 380 fs with the lower noises with ΔE/E = 1.6 × 10
^-3
(timing jitter Δt = 12 ps). Enlarging pump power promotes the split number of bunched solitons within one mode-locked pulse envelope. The individual soliton of different orders experiences different amounts of long-range attractive force from solitons, which leads to an unequalized spacing between the adjacent solitons occurred within bunched pulse envelope. The chirp parameter of C = -0.022 is dominated by the cooperation of group-delay dispersion and self-phase modulation effects, which can further compress the EDFL pulse to <;400 fs.