Glass fiber lightguides with functional interfaces Optical fibers have transformed many areas of modern life from the way we communicate across the globe to the way we detect and treat diseases. Exploitation into new application fields relies on the technological challenge to provide optical functional elements to glass fibers. This thesis assesses novel ways to provide functional interfaces to glass fibers lightguides. To equip the inside of such fibers with optically active species first a modified rod in tube approach was investigated. Here cylindrical glass rods were coated from liquid phase and assembled to preforms by encapsulating them into a glass tube. As functionalities rare earth elements and noble metal nanoparticles were selected and successfully incorporated into fibers. Such fibers showed the characteristic photoluminescence of the rare earths as well as localized surface plasmon resonance related effects from the noble metal particles at the functionalized interface. In a second part the deformation of this noble metal nanoparticles to rotational ellipsoids during the fiber drawing process was investigated. Such fibers showed an optical anisotrop response to light. The ellipticity of the nanoparticles was discussed with respect to particle size and choice of noble metal to understand how the optical properties of such fibers can be controlled. In a third part the effect of silver on the photoluminescence of Eu3+ was investigated. Here sol gel derived co doped coatings were developed that showed strong luminescence enhancement. In these coatings Eu3+ could be excited with non resonant wavelenghts in a broad spectral range below 400 nm. The lateral surface of a glass fiber was functionalized with this coating which could be used to transform guided UV light into luminescent based side emission with the characteristic Eu3+ emission bands.