End cap splicing of photonic crystal fibers with outstanding quality for high-power applications

The application of photonic crystal fibers (PCF), especially in high power fiber laser systems, requires special preparation technologies with some significant differences compared to standard fibers. Features, like air-clad structures, highly rare-earth doped cores with low NA and stress applying parts of the PCFs, require additional steps in fiber preparation and innovative splicing technologies to gain optical properties. Here we discuss a contamination- free carbon dioxide laser splicing device, which is used for defined air-clad collapsing and end cap splicing to get a stable and sealed fiber end face with preserved high beam quality and additional functionality. The special design of the computer-controlled laser splicing process provides a versatile tool with high reproducibility for joining different geometries with an adjustable well-balanced heat distribution. A wide range of PCFs with different diameters, air-clad structures and doped materials up to ~2 mm have been spliced. For selected PCF-end cap splices cleave or polishing requirements as well as results on beam quality, tensile strength and further splicing features are presented.