Abstract
Chirped and tilted fiber Bragg gratings (CTFBGs) have attracted a lot of attention in stimulated Raman scattering (SRS) suppression of high-power fiber lasers. However, the laser power handling capacity seriously limits their applications. In this paper, by optimizing the inscription parameters and post-processing strategy, we fabricate a large-mode-area double-cladding CTFBG with a thermal slope of ~0.015 °C/W due to the low insertion loss of about 0.15 dB, which make it possible for direct kilowatt-level application. A 2 kW-level fiber laser oscillator is employed to test the CTFBG, and a series of experiments have been carried out to compare the effect of SRS mitigation in high-power fiber laser long-distance delivery. In addition, the influence of CTFBGs on laser beam quality is studied for the first time. Experimental results indicated that the CTFBG could effectively mitigate SRS and has no obvious influence on laser beam quality. This work opens a new opportunity for further power scaling and the delivery of high-power fiber lasers over longer distances.
Highlights
High-power fiber lasers have been widely used in lots of areas, such as industrial processing, medical treatment, material research, defense technology, and so on, due to their diffraction-limited beam quality, compactness, high efficiency, stability, and robustness [1,2,3]
stimulated Raman scattering (SRS) suppression been For obtained in many high-power fiber laser systems, in inscription technology, the residual hydrogen, thermal stress, and other defects will cause most cases Chirped and tilted fiber Bragg gratings (CTFBGs) were inserted between the seed and the amplification-stage in master power-amplifier (MOPA) systems
CTFBGs are a kind of band-stop filters, which combines characteristics fiber Bragg grating (CFBG) and tilted fiber Bragg grating (TFBG)
Summary
High-power fiber lasers have been widely used in lots of areas, such as industrial processing, medical treatment, material research, defense technology, and so on, due to their diffraction-limited beam quality, compactness, high efficiency, stability, and robustness [1,2,3]. CTFBGs and LPFGs as fiber spectral filters can couple core modes into cladding modes, realizing the filtering of Stokes light, in to gain fibers,and which is anotherHowever, important for power scaling limitation [14].resulting. SRS suppression been For obtained in many high-power fiber laser systems, in inscription technology, the residual hydrogen, thermal stress, and other defects will cause most cases CTFBGs were inserted between the seed and the amplification-stage in master power-amplifier (MOPA) systems [21,22], which mainly limited by the power a large amount ofoscillator heat in CTFBGs when working at a high-power levelis [22]. As several annealing processes are carried out to enhance the power hanmized and some post-process strategies are used in fabrication By this way, a 2 kW-level dling capacity, the CTFBG a designed low measured signal insertion loss ofLMA about. Have few influences on LBQ, which is useful for the longer delivery distance of high-power fiber lasers
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