In this work, we conduct a detailed experimental study on the impact of signal bandwidth on the TMI threshold of fiber amplifiers. Both the filtered superfluorescent fiber sources and the phase-modulated single-frequency lasers are employed to construct seed lasers with different 3 dB spectral linewidths ranging from 0.19 nm to 7.97 nm. The TMI threshold of the fiber amplifier employing those seed lasers are estimated through the intensity evolution of the signal laser, and different criteria have been utilized to characterize the spectral linewidth of the seed lasers. Notably, the experimental results reveal that the TMI threshold of fiber amplifiers grows, keeps constant, and further grows as a function of spectral linewidth of seed lasers. Our experimental results could provide a well reference to understand the mechanism of the TMI effect and optimize the TMI effect in high-power fiber amplifiers.
We found the beam quality factor M 2 of the fundamental mode as a function of wavelength is U-shaped in the working photonic bandgap (PBG) of an all-solid PBG fiber (AS-PBGF) for the first time, to the best of our knowledge, and our simulation results also match well with the phenomenon. The normal band that is near the high-frequency edge of the third PBG integrates the lowest M 2 and single-mode operation simultaneously, while the other two edge regions suffer from anomalous variation of M 2 versus wavelength. The general applicability of this finding can be further extended to other PBGs and also other representative structures in the AS-PBGF field.
High power narrow-linewidth fiber lasers have been highly desired for various applications. In this paper, we presented new considerations of high power narrow-linewidth fiber amplifiers operating within 1030~1060 nm by using newgeometry active fiber, and the power-breakthrough operating at 1050 nm was achieved. We also reported our recent achievements on power scaling of high-power narrow-linewidth fiber lasers which operates within 1060~1080 nm based on system-optimized step-index and confined-doped active fibers, including linear-polarized and stochastic-polarized ones. Meanwhile, our new progress on special designed active fibers assisted high power fiber amplifiers with sub-GHz to within 1.5 GHz were demonstrated. Besides, the basic considerations of end-reflection on the SBS and SRS effects will be discussed, which provide a new insight for the suppression of SBS and SRS effects.
Superfluorescent fiber source (SFS) is a special fiber laser which commonly possesses high temporal stability and wide spectral linewidth. In this work, an all-fiberized linearly polarized SFS with record output power and near-diffraction-limited beam quality is presented. Up to 5.03 kW SFS is achieved at a pump power of 6.18 kW with the corresponding conversion efficiency of ~81.1%. At the maximum output power, the signal-to-noise ratio (SNR) to background spectral noise is over 50 dB, the polarization extinction ratio (PER) is ~17 dB, and the beam quality factor is Mx2=1.49, My2=1.44. Further comparisons confirm the power scalability of fiber amplifiers employing SFSs as seed laser. Overall, this work could provide a well reference for the potential exploration of high-power fiber laser systems.
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