| Fiber lasers can be suitable for optical communication, fiber tensor, advanced manufacture, laser cosmetology,laser weapon, etc, due to their superior performance: low pumping power threshold, high ratio of area to cubage, rapid heat dissipation, single mode running, compactness, and low running costs, so the field is a very important one in the solid laser technology. Among the research hotspots, especially, fiber lasers have aroused people's attention. However, the output power is limited by the nonlinear effects with high power. So it is very important to explore the large mode area single mode fiber, and this fiber can accelerate the development of high-power fiber lasers.Based on the A.E.Sigeman's theory of gain guiding in the fiber, the thesis has designed one fiber with the core diameter lager than 100μm and the mode area diameter over 90μm, which can be single mode running in theory. The paper also has focused on studying the single mode running situation of large-core, gain-guided, index-antiguided fiber lasers. Using finite-difference time-domain(FDTD) method, some bend effects on characteristics of transmissions have been got. Some innovative results have been obtained and presented in our 1 paper and 1 academic report. The main innovative results in our paper are summarized as follows:1. Based on the A.E.Sigeman's theory of gain guiding in the fiber, a large- mode-area, single-mode fiber has been obtained with the mode area diameter large than 90μm, and the lowest-order mode distribution has been studied.2. Combing the gain guiding theory, relationships between mirror reflectivity and core radii, gain and refractive indexes have been discussed for the first time, which offer the theory to select appropriate reflectivity mirror.3. Using finite-difference time-domain method, characteristics of bend of large mode area fibers have been analyzed, including bend effects on modes distribution and bend loss of large mode area fibers. |
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