High-power fiber lasers attracts considerable attentions due to many merits such as high efficiency, excellent beam quality, flexible output wavelength, simple structure which is conducive to thermal management and so on, which have become the representative of the third generation of lasers. With the industrialization of domestic fiber lasers accelerating, 10kW fiber lasers have become the mainstream of industrial laser processing in the future. At present, industrial 10kW fiber lasers are mainly realized by multi-module beam combination. Limited by nonlinear effects, single-module 10kW fiber lasers reported by various research institutions are mainly realized with 976nm wavelength pump source. In this article, we introduce the main factors that limit the power increase of high-power single-module fiber lasers, and analyzes the advantages and disadvantages of using 915nm wavelength and 976nm wavelength pump source from an application perspective. We adopte a new scheme of high-power fiber lasers using the homemade Ytterbium doped fiber, pump combiner and 915nm wavelength pump source in a MOPA system, in which we achieve 12.2kW output power. In addition, the output optical cable is a 30-meter 100/360 output, and the optical efficiency is more than 43%. The cutting speed of medium and thin slab for carbon steel and stainless steel has been significantly improved, the machine is aged for 500 hours at a water temperature of 28°≅, and the output power is not obviously reduced, which is completely satisfied for the requirements of industrial processing.
The pump of fiber laser is a kind of laser diode module with pigtail. In the high power laser diode module, the beams of several diode emitters are shaped by lenses and combined, and coupled into a fiber called pigtail. As the power of fiber laser upgrated, the power of the high power laser diode module needed to be increased, and the tolerance of the pigtail should be higher. And then, the input end of the pigtail becomes to be the weakest part of the high power laser diode module. We developed a kind of pigtail, with high reliability and highly cost-effective, whose power tolerance could be 700W CW.
This paper studies the method of using a high-power fiber combiner to form a Gaussian beam into a flat-top beam, and divides the factors that affect the shaping effect of the flat-top beam. The theoretical analysis model of the fiber power combiner is established based on the waveguide theory, and the excitation characteristics of the fiber mode in the output fiber are analyzed. Based on the beam propagation method, the propagation and superposition characteristics of the highorder modes excited in the fiber combiner are simulated, and the flat-top beam synthesis method is studied. According to the simulation model, a high-power fiber combiner was made, and a high-power laser beam combining experiment was carried out. Finally, a flat-top beam with a beam quality of 10 and an output power of 20kW is obtained. During the experiment, we also found that the uniformity of the flat-top beam increases as the output power of the fiber laser increases.
Using self-designed large core Yb-doped fiber (100 μm / 400 μm)1 and high-power fiber combiner, a laser output with average power of 3 kW, repetition rate of 60 kHz, pulse width of 150 ns, single pulse energy of 50 mJ is achieved by combining three laser modules in an all fiber-fusion structure, where each output power is more than 1000 W; and the beam combining efficiency is 98.3%. By controlling the pulse delay of the three modules, the three pulses are managed to be overlapped completely, and the overlapping rate is more than 97%. This is the highest value among all known fiber pulsed laser output using self-developed fiber and pulse beam combiner.
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