Design and fabrication of a fused 7 × 1 35/50 µm into 125/250 µm fiber combiner

We present the design and construction of a fiber combiner comprising 7 × 1 35/50 µm input fibers with thin cladding and an output fiber with 125 µm diameter to maintain the high beam brightness. A transmission higher than 98% between the input fibers and the tapered fiber bundle is achieved. The coupling efficiency between the bundle and the output fiber exceeds 95%. The-near field beam profiles of the fabrication steps are measured and analyzed. Due to the thin cladding of the input fibers, we analyze optical tunneling effects with respect to the numerical aperture of the light.