1. Department of Fiber Photonics Leibniz Institute of Photonic Technology Albert-Einstein-Str. 9 07745 Jena Germany
2. Otto Schott Institute of Materials Research (OSIM) Friedrich Schiller University of Jena Fraunhoferstr. 6 07743 Jena Germany
3. Abbe Center of Photonics and Faculty of Physics Friedrich Schiller University of Jena Max-Wien-Platz 1 07743 Jena Germany