In this thesis, two kinds of beam combiners for high power fiber lasers were fabricated and their characteristics were studied.
In Part 1, a 4 x 1 signal combiner was fabricated by splicing etched TFB(Tapered Fused Bundle), which is fabricated with hydrofluoric acid, and an output fiber. The input fiber has a core diameter of 20 μm and a cladding diameter of 130 μm, and the output fiber has a core diameter of 105 μm and a cladding diameter of 125 μm. The etched TFB is fabricated by tapering the four input fibers etched by hydrofluoric acid. In this study, two types of etched TFBs were fabricated using input fibers with cladding diameters of 100 and 72.49 μm. We fabricated three 4 x 1 signal combiners by fusing three etched TFBs with two kinds of output fibers. The output fibers has a NA of 0.20 and 0.15, respectively. The average efficiencies of the three signal combiners were measured as 98, 97, and 99%, respectively, and the BPPs(Beam Parameter Product) were measured as 8.44, 7.42, and 6.75 mm mrad, respectively.
In Part 2, we fabricated an fiber optic chip using hydrofluoric acid and fabricated a 7 x 1 pump combiner by fusing 7 input fibers and 1 output fiber on both sides. The optical fiber chip was fabricated by etching a DCF(Double Clad Fiber) with a core diameter of 20 μm and a cladding diameter of 400 μm. The etching time was about 4 hours and 30 minutes. It has a maximum diameter of 375 μm and a minimum diameter of 250 μm, and an output fiber with 25 μm core and 250 μm cladding diameter is spliced to a 250 μm portion of the chip. Next, seven input fibers having a core of 105 μm and a cladding diameter of 125 μm were fabricated in a bundle. The fiber bundle was fabricated by two methods. The first is to polish the fiber bundles with epoxy. The second method is to fix the back side of the cleaved part of the fiber bundle to epoxy and then cleaving the seven optical fibers simultaneously. Two types of 7 × 1 pump combiners were fabricated by splicing the fabricated optical fiber bundles to the 375 μm part of the fiber chip. The average efficiencies of the two 7 x 1 pump combiners were 88.7 and 90.2%, respectively.