Design, Simulation And Experimental Study Of Gain-guided-refractive Index-guided Large-mode-field Fibers

Gain-guiding, index-antiguiding (GG-IAG) fiber is a new member in the large area mode fiber family. It can deliver robust large single mode and avoid high power density to cause nonlinear optical effects. Therefore, a new way of obtaining a high power fiber laser may be paved. The article studies this new type fiber in theory and experiment. In theory section, analysing the fiber’s gain-guiding, index-antiguiding characteristic, meanwhile, discussing the coupling characteristic for GG-IAG fiber detailly. In experimental section, the technics of fiber fabricating have been studied. All of these results could give some references for GG-IAG fiber’s designning, manufacture and application.In theory section, first, the pumping technology for GG-IAG fiber has been analysed, including end puming and side pumping. The results give some suggestions for building GG-IAG fiber laser system. Comparing advantage and disadvantage among three different pumping technologies, and founding the side pumping technology is more suitable for GG-IAG fiber laser. Second, suggesting the genernel coupled-mode theory for GG-IAG fiber, and simulating the coupling characteristic between any two fibers. Some interesting phenomena have been found, for instance, the coupler using one index guiding (IG) fiber and one GG-IAG fiber has different coupling characteristics when the RVRID (real part of refractive-index difference between core and cladding) varies. The power will transfer from GG-IAG fiber to IG fiber when the RVRID is large, and perform contrarily when the RVRID becomes much smaller. Such characteristics can be used in laser array, fiber pumping and coupler.In experiment section, first, melting the high pure, low loss Yb3+ glass and host glass, and the process has been described in detail. Some parameters of Yb3+ glass have been mearsured, such as absorption and emission corss sections. And the relationship between absorption (emission) cross section and dopant concentration has been discussed. Second, investigating the fabricating technics of Yb3+ GG-IAG fiber, including preform manufacturing, fiber polishing. And some experience and technology could be used in glass fiber fabricating. Third, the refractive index difference between core and cladding, the fiber loss has been surveyed, and so on. Finally, building the fiber laser system and briefly discussing its thermal managing. Meanwhile, finding the non-laser reason of Yb3+ GG-IAG fiber laser system and giving the solution:need to produce the Yb3+ glass with high-emission cross section, long spontanesous radiative lifetime to match the GG-IAG fiber.