In this study, we compare and illustrate how weak end-facet reflections affect high-power fiber oscillators and fiber amplifiers' stimulated Raman scattering (SRS) threshold. The simulation results reveal that the enhancement of weak end-facet reflections could decrease the SRS threshold of high-power fiber lasers significantly, especially for fiber amplifiers employing phase-modulated single-frequency lasers as seed lasers. Further comparisons point out that weakening reflections at either the input or output end-facet provides an effective approach to improve the SRS threshold of high-power fiber lasers. In addition, weak end-facet reflections could even invalidate the strategy of suppressing the SRS effect through filtering out the Raman component in seed laser. The theoretical approach and findings may serve as a useful guide for designing high-power fiber laser systems with SRS limitations.
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.
Single trench fiber (STF) is one kind of promising novel fibers. In this paper, we design and fabricate a piece of ytterbium-doped STF. The core diameter of the homemade STF is 30 μm and the cladding diameter is 250 μm. Based on this self-developed STF, we have constructed an all-fiberized fiber amplifier that is operating under a continuous-wave regime at 1070 nm wavelength. The maximum output power of the system reaches 1.5 kW, which, to the best of our knowledge, is the highest output power of STF-based laser systems. The M2 is measured to be 1.65 at 1.36 kW and 1.92 at the highest output power respectively. The slope efficiency of amplification system is 68%. The performance of the system can be further enhanced by optimizing the fiber design and system structure.
High power, narrow linewidth all-fiber amplifiers are under intensive investigation in recent years. In this paper, the research status of high power, narrow linewidth all-fiber amplifiers (including those operate at single frequency regime) is briefly summarized. Then the recent progress in our research group is introduced, including more than 500 Watt level single frequency fiber amplifier, more than 4 kW linearly-polarized narrow linewidth all-fiber amplifier and more than 6 kW narrow linewidth all-fiber amplifier. Performance exploring of the operating spectrum property is also discussed.
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