Study On Fabrication Of The Ytterbium Doped Microstructure Fiber Based On High-frequency Plasma And Its Characteristics

It is considered that high concentration Yb3+-doped double-clad microstructure fiberwith large mode area is the most popular gain medium for the high power pulse andcontinuous fiber laser. Nowadays, the general preparation method of Yb3+-dopedmicrostructure fiber is the modified chemical vapor deposition in combination withsolution doping. However, the method has many defectives, such as low dopingconcentration, uneven doping and difficulty in fabricating fiber with large core.Furthermore, because the melting temperature of the Yb3+-doped silica materials is around2000oC, the ordinary resistance furnace is difficult to achieve the temperature. To solvethese problems, it is proposed that the Yb3+-doped silica glass is prepared by the powdermelting technology based on high-frequency plasma in the dissertation. The main researchwork is as follows:Firstly, the composition of the glass is determined by the characteristics of the silicaglass, Yb3+ion and Al3+ion. The formula of the Yb3+-doped silica glass is calculated andoptimized theoretically based on the forming regularity of rare earth doped silica glass andso on. It is proposed that the Yb3+-doped powder is prepared by hydrolysis doping and theYb3+-doped silica glass is prepared by powder melting technology based onhigh-frequency plasma. Furthermore, the problems encountered during the Yb3+-dopedsilica glass preparation, for instance valence state changing mechanism of Yb3+ion, theselection of Yb3+-doped powder size, as well as eliminating the hydroxyl and bubbles,have been researched.Secondly, the structure, the physical properties including density, refractive index,composition, thermal expansion coefficient and doping uniformity, as well as the opticalproperties including absorption and emission characteristics of the Yb3+-doped silica glasshave been tested and researched. The spectrum and laser properties parameters of theYb3+-doped silica glass have also been calculated theoretically and researched. And therelationship between Yb3+ions doping concentration and properties parameters, such asphysical characteristics, optical characteristics, as well as the spectrum and laser properties parameters, have also been studied.Thirdly, the theory research of Yb3+-doped double-clad microstructure fiber withlarge mode area is carried out. The Yb3+-doped double-clad microstructure fibers with theYb3+-doped silica glass as the core are fabricated. The optical properties such asabsorption characteristics, loss characteristics, and emission characteristic, as well as thelaser properties of the fiber are tested. The integrated optical properties of the fiber areobtained, which verifies that the innovation preparation method of the Yb3+-dopedmicrostructure fibers is feasible.Finally, the output power and the working life of the Yb3+-doped fiber laser areseriously influenced by the photodarkening existing in the fiber. The formation mechanismof the photodarkening of the Yb3+-doped microstructure fiber prepared by the powdermelting technology based on the high-frequency plasma is researched.