Study On Distributed Side-Coupled Cladding-pumped Fiber Lasers

High power fiber lasers have many applications both in manufacturing industry and military field, such as precision material machined. It becomes an international research hotpot in recent years. Although the conventional double cladding fibers have promoted the development of high power fiber lasers, but the power scaling still faces many challenges. However, the distributed side-coupled cladding-pumped(DSCCP) fiber is a kind of new fiber, which may overcome the limits and get further power promotion. But the international reports of relative research are rarely limited, and the native development is nearly blank. Therefore, this paper will study the transmission characteristic of the DSCCP fiber, and then show the design and drawing the DSCCP fiber. Finally, we will test the DSCCP fiber in the high power fiber lasers experiment.Firstly, we introduced the method to solve the weak-coupling based mode coupling coefficients between two waveguides. The characteristic of pump light in the DSCCP fiber has been analyzed by numerical simulation, and the coupling process of different fiber structures has been given out. It shows that the coupling features in the strong and weak coupling regimes are quite different. The influence of absorption of pump light for twist fiber was also studied. Then we established a simplified pump light coupling model, and give out a method to estimate the average total coupling coefficient, with which we discussed the characteristic of the pump light coupling.Secondly, we established a fiber laser steady rate equation model based on the pump light characteristic of the DSCCP fiber, and also solved the equations analytically and numerically. Then we discuss in detail the characteristic and influent factors of the DSCCP fiber. The comparisons between the DSCCP fiber laser and conventional double cladding fiber laser have been carried out in the aspects of the output efficiency and thermal effect. The results show that through optimizing the design, the DSCCP fiber laser can keep the same high efficiency as conventional double cladding fiber laser, as well as lower the thermal effect of the fiber.Thirdly, we carried out fiber laser experimental validation using the self-designed and drawn DSCCP fiber. By using the drawed 10/125-125 diameter DSCCP fiber, we realized the first natively DSCCP fiber laser with output power of 107 W and the slope efficiency of 51.3%, thus validated the feasibility of bidirectional pumping for the DSCCP fiber. Through the 30/250-250 diameter DSCCP fiber, a two-stage fiber cascaded amplifier with 1009 W output power is achieved. And we validated firstly the feasibility of k W-level DSCCP fiber system. Furthermore, we validated the high power DSCCP fiber oscillator, and got a 1519 W 1080nm oscillator with the slope efficiency of 64.6%. Then we tested the 1018 nm fiber laser tandem pumping with the DSCCP fiber amplifier, and got an output power of 118.7W with the efficiency of 75.6%. We designed two kinds of the DSCCP fiber lasers based on LD pumped and fiber laser pumped, and the simulations show that they both can generate more than 10 k W high power laser.