Generation of different mode-locked states in a Yb-doped fiber laser based on nonlinear multimode interference

Abstract

We demonstrated an ultrafast Yb-doped fiber laser with a single mode fiber-graded index multimode fiber-single mode fiber (SMF-GIMF-SMF) structure based saturable absorber. The GIMF was placed in the groove of an in-line fiber polarization controller to adjust its birefringence, enabling the SMF-GIMF-SMF structure to realize efficient saturable absorption based on nonlinear multimode interference without strict length restriction. By adjusting two intra-cavity polarization controllers, stable dissipation solitons and noise-like pulses were achieved in the 1030 nm waveband with pulse durations of 10.67 ps and 276 fs, respectively. We also realized Q-switched mode-locked pulses in the same fiber laser cavity. By the dispersive Fourier transform method, the real-time spectral evolution in the buildup process of the Q-switched mode-locked state was captured, which showed that the continuous-wave in this laser could gradually evolved into the stable Q-switched mode-locked pulses through unstable self-pulsation, relaxation oscillation and rogue Q-switching stage. To the best of our knowledge, our work reveals the buildup dynamics of the Q-switched mode-locked operation in a fiber laser for the first time. And we also studied the real-time spectral evolution of the stable Q-switched mode-locked pulses, which exhibited periodic breathing property.

Revealing the Evolution from Q-Switching to Mode-Locking in an Erbium-Doped Fiber Laser Using Tungsten Trioxide Saturable Absorber

“…This is a transition state of Q-switched and mode-locked regime [31], which could be achieved from QS pulse or evolve to ML pulse by utilizing additional nonlinear saturable absorption. However, at a certain condition, the gain, loss, dispersion, saturable absorption, and other nonlinear effects in the laser reach a balance state, the stable QML operation could be realized [32]. We attribute the evolution in this paper to the additional weak nonlinear saturable absorption introduced by the indeed weak polarization sensitivity of the laser when the PC adjusted, as mentioned in the section of experimental setup.…”

Q-switched Erbium Doped Fiber Laser Generation Using the Kerr Effect of Multimode Interference

“…As a result, the modulation of cavity loss is utilized for the generation of Q-switched pulses [9]. Many reports have shown successful mode-locked laser with SMS structure as SA [10,11], but only a few Q-switched laser with SMS structure as SA were reported.…”

Germanene: demonstration of the conversion from mode-locked to Q-switched mode-locked in Er-doped fiber laser

“…By controlling the energy within the laser cavity, the gain saturation absorption effect of the SA, and nonlinear effects, dynamic instability can be induced within the cavity to generate QML in the laser system. The formation of QML can be summarized as the following stages: unstable self-pulsation stage, relaxation oscillation stage, unstable Q-switched stage, and stable QML stage [59]. Specifically, when the pulse energy within the cavity is small and losses are significant, the SA acts as a Q-switch.…”