Fused combiners for photonic crystal bers

The work presented in this Ph.D. thesis focuses on the fabrication of fused combiners for high-power fiber lasers and amplifiers. The main focus of the Ph.D. project was to further develop the fused pump combiners for airclad photonic crystal bers (PCFs), and implement a signal feed-through in these combiners. Such a pump/signal combiner enables the fabrication of all spliced fiber amplifier systems based on the PCFs technology. Amplifier systems interfaced only by standard multi-mode (MM) and single-mode (SM) fibers are easy to use, since all-spliced systems can be made and bulk optics are avoided. Pump/signal combiners were realized in two versions; one with a 12 m mode field diameter (MFD) signal feed-through and one with a 15 m MFD feed-through.
A signal combiner for combining the SM output from multiple fiber lasers into a single MM fiber was also realized. The component was based on a tapered fiber bundle approach and was tested up to 2.5 kW of combined output power.
Two components for the field of astrophotonics have also been developed. The first was a fused fiber bundle, designed to be placed in the focal plane of a telescope. By measuring the spectral content out of the individual fibers in the bundle, more detailed observations of large astronomical objects can be achieved. The second component was a further development of the MM to SM converters or photonic lanterns. These components were developed for the field of astrophotonics, where the transformation of MM starlight into an ensemble of SM fibers enables filtering with advancedfi ber Bragg gratings (FBGs).