Using tapers for efficient coupling of received FSO-signals into fibres

Sensitive detectors and large receiver apertures offer high efficiency at the receiver of Free Space Optics (FSO) systems. 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 at the receiver. In this contribution, the use of optical tapers as couplers between a light source and a waveguide is being investigated for Optical Wireless links. Of course optical tapers can be used in both directions at the receiver (for light beam concentration) or at the Transmitter (for light beam opening). Firstly, a simulation of an optical system with tapers is done with software and later analysed by experiments. For construction matters a multimode-polymer-fibre was used as a waveguide. 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. In polymer-fibres the attenuation is rather huge, but the core-diameter of the polymer is about 100 times bigger than the one of the single mode fibre and this simplifies the construction of the optical taper and the connection to the optical waveguide.