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Efficient free space to fiber coupling with tapers

Optical wireless links offer a lot of advantages, and therefore, for Free Space Optics (FSO)-systems a high efficiency at the receiver is important. It can be achieved by using sensitive transmitters and by enlarging the receiver aperture. The receiver aperture can be increased by employing larger lenses, telescopes and mirrors, but also with tapers (glass-cones). Tapers are collecting and guiding the incoming light directly to the fibre. In this contribution, the use of optical tapers as couplers between a light source and a waveguide is being investigated. Optical tapers can concentrate or widen light beams and simultaneously serve as mode filters. Within this work, beside the experimental investigation, various simulations of optical system with tapers were performed. For construction matters a multimode-polymer-fibre was used as a waveguide. Ordinarily, the usage of a single mode fibre should be preferred but its dimensions of 9.2/245 μm core-/cladding-diameter would make the setup of the system considerably more difficult. Polymer-fibres can only be used for short transmission distances, because the attenuation is rather huge. But it is an enormous advantage that the core-diameter of the polymer is about 100 times bigger than the one of the single mode fibre. This simplifies not only the construction of the optical taper but also the connection to the optical waveguide. The new results will play a significant role in future optical wireless communications as information superhighways.