Buildup and synchronization regimes of a vector pure-quartic soliton molecule in a fiber laser cavity.

Pure-quartic solitons (PQSs) have recently received increasing attention due to their energy-width scaling over the traditional soliton, which has expanded our understanding of soliton dynamics with high-order dispersion in nonlinear systems. Here, we numerically reveal the asynchronization and synchronization processes of the sub-pulse within the vector PQS molecule in a mode-locked fiber laser by solving the coupled Ginzburg-Landau equations. During the establishment of a vector PQS molecule, the repulsion, attraction, and finally stabilization processes have been observed. Specifically, sub-pulse disappearance, regeneration, and finally synchronization with the other pulses are also investigated. Our analysis of the pulse energy, time interval, and relative phase evolution dynamics with the round trip indicates that the asynchronization and synchronization within the vector PQS molecule associate tightly with the gain competition and the cross-phase modulation. Our findings provide insights into the internal mutual dynamics within the vector soliton molecule and offer guidance for the applications of PQS.

High repetition frequency tunability active Q-switched all-fiber laser by multi-gain sub-rings smoothing multipeak pulse and suppressing ASE self-saturation.

This paper provides a method to effectively suppress the severe ASE self-saturation when achieving high repetition frequency tunability with high output power and narrow pulse width in active Q-switched all-fiber lasers. By studying the regularity of the system's multi-stable state, we first ensured that the laser system operated in a steady state. Then output avoids uneven distribution of pulse energy or missing pulses due to period bifurcation state or chaos state. By adding multiple gain sub-rings within the cavity, the sub-ring structure itself indirectly mitigates the ASE self-saturation while smoothing the pulse. The method will avoid the severe power loss caused by traditional smoothing methods by adjusting the AOM rising edge time. It will also avoid lowering the ASE lasing threshold at high repetition frequency. Meanwhile, the intra-cavity backward ASE can be effectively absorbed by inserting the gain fiber in the sub-rings to directly mitigate the ASE self-saturation. The system's continuously adjustable repetition frequency can be as high as over 300 kHz. It ensures that output power above the watt level and a < 0.2 nm narrow bandwidth can be maintained while tuning the repetition frequency. The narrowest smoothing pulse width of 28 ns has been reached.

Cavity-birefringence-dependent vector pure-quartic soliton fiber laser.

Pure-quartic soliton (PQS) fiber lasers provide a promising avenue for exploring novel soliton interaction dynamics and generating high-energy pulses. Here, we present the numerical observation of vector PQSs generation and the evolution dynamics in a mode-locked fiber laser, using the coupled Ginzburg-Landau equations. We investigate the buildup dynamics of vector PQSs in a mode-locked laser with birefringent fibers, passing through three stages: energy amplification, energy pulsation owing to the cross-phase modulation (XPM) effect, and finally stabilization. Depending on the strength of the cavity-birefringence, the evolution of PQSs in non-polarization-maintaining fibers reveals that both the elliptical-polarization vector PQSs and near-linear-polarization vector PQSs can be formed by the energy conservation and balance between the two orthogonal directions. Additionally, we observe the transition process from vector PQSs to scalar PQSs with higher cavity-birefringence, resulting from the failure compensation of the walk-off via the soliton trapping effect between the two orthogonal components. These results provide valuable insights into the ultrafast transient process of vector solitons and enhance the understanding of PQS generation in fiber lasers.

Controllable multi-stable-state operation in an AOM actively Q-switched all-fiber laser system.

This paper presents a comprehensive experimental study of multi-stable-state output characteristics in an all-fiber laser with an acoustic-optical modulator (AOM) as the Q-switcher. For the first time, in this structure, the partitioning of the pulsed output characteristics is explored, dividing the operating status of the laser system into four zones. The output characteristics, the application prospects, and the parameter setting rules for working in stable zones are presented. In the second stable zone, a peak power of 4.68 kW with 24 ns was obtained at 10 kHz. This is the narrowest pulse duration achieved with an AOM actively Q-switched all-fiber linear structure. The pulse narrowing is attributed to the rapid release of signal power and pulse tail truncated by AOM shutdown.

Demonstration of a 700 W × 2 ports single-stage all-fiber nanosecond amplifier seeded by a multi-cavity passively Q-switched laser.

We demonstrate a single-stage all-fiber nanosecond amplifier with a total average power of greater than 1.4 kW by employing what we believe to be a novel multi-cavity passively Q-switched fiber laser as the seed laser. The multi-cavity seed laser adopts a piece of Yb-doped fiber (YDF) as saturable absorber (SA), and it includes two external cavities resonating at 1030 nm and an internal cavity working at 1064 nm, respectively. Using such a scheme, a stable dual-channel laser output with a total average power of >35 W, a pulse width of 45 ns, and an optical conversion efficiency of 72% operating at 1064 nm is achieved. By power scaling the multi-cavity seed laser, a dual-channel single-stage nanosecond amplifier is obtained with a single-port average power of exceeding 700 W and a pulse energy of about 7.3 mJ. To the best of our knowledge, this work is the highest average power and optical conversion efficiency for passively Q-switched all-fiber laser employing SA fiber, and the highest average power for a single-stage all-fiber nanosecond amplifier.