The Research On The Key Technology Of High Power Ytterbium Doped Fiber Laser

In the field of laser processing, high power Ytterbium doped fiber laser with its great advantages in the structure, efficiency and beam quality is the trend to replace the traditional laser. But the lack of key technologies centered with the Ytterbium doped fiber hamper high power Ytterbium doped fiber laser for further development. This paper focuses on the key technologies of high power Ytterbium doped fiber laser, emphasizes the achievement of high performance Ytterbium doped fiber, considers the breakthrough with the photodarkening of Ytterbium doped fiber and the realization with mode control of large core diameter and multi-mode fiber as key, works with the higher power, better stability, better beam quality of high power ytterbium doped fiber laser.Firstly, basing on the theory of Ytterbium doped double clad fiber laser, the paper expounded the influence of performance parameters of Yb doped fiber on fiber laser providing the basis for the design of Ytterbium doped fiber, and introduced the technological process about using modified chemical vapor deposition technique and solution doping technique to prepare Ytterbium doped optical fiber preform and the drawing technique to prepare ytterbium doped fiber. The process principles were also introduced. Based on these, the specifications of 10/130,30/250,20/400 Ytterbium doped fiber were analyzed, which have huge business potential. A technology roadmap to achieve high performance Ytterbium doped fiber was designed and some test equipments were designed and produced for the three kinds of Ytterbium doped fiber. With the test database, the high performance 10/130,30/250,20/400 Ytterbium doped fiber were achieved.Secondly, the photodarkening that influence the stability of high power Ytterbium doped fiber laser was studied. The special phenomena related to the photodarkening of Ytterbium doped fiber could be explained, when Thulium was considered as the sensitizer for photodarkening. It was proved that the influence of Thulium on photodarkening in our experiments. Furthermore, the intense photobleaching was found, when photodarkened Ytterbium doped fiber was pumped by 793nm, which have potential to suppress the photodarkening. And the influence of Thulium on photobleaching was proved from the difference pumped by 793nm,808nm,1080nm. With these, a new model was proposed to explain the photodarkening and photobleaching of Ytterbium doped fiber.Thirdly, the large core and multi-mode fiber laser was analyzed based on theory about mode competition. There are two ways to achieve the single mode output in large core and multi-mode fiber laser that suppressing the gain of high order mode and increasing the loss of high order mode. They are corresponding to the technology of mode control and mode selection with bend. An Ytterbium doped fiber with 70% doping area whose core diameter is 30?m and numerical aperture is 0.07 was used to construct fiber laser. The beam quality of output laser were achieved as Mx2=1.571, My2=1.583. Another fiber laser constructed by Ytterbium doped fiber with all the doping whose core diameter is 30?m and numerical aperture is 0.07. Its beam quality was optimized from 2.8 to 1.5 by the mode selection with bendFinally, The high power fiber laser technologies were achieve, which include splice with low loss, stripper with cladding light, thermal diffusion. With these,20/400 Ytterbium doped fiber, high power fiber bragg grating, high power pump combiner were combined to achieve a kW level Ytterbium doped fiber laser. The highest power was 1.01kW and the slope efficiency is 80.94%. Its beam quality was measured as Mx2=1.496, My2=1.410. A hectowatt level Ytterbium doped fiber laser was also achieved with systemic technology.