Novel special optical fibers nowadays can take advantage of several new preform production techniques. During the last years we have devoted our attention to the granulated silica method. It is one of the variants of the powder-in-tube technique and potentially offers a high degree of freedom regarding the usable dopants, the maximum possible dopant concentration, the homogeneity of the dopants, the geometry and minimal refractive index contrast. We developed and refined an approach for the production of doped granulated silica material based on the sol-gel process.Here, we present material analysis results of an ytterbium (Yb) doped, aluminum (Al) and phosphorous (P) co-doped glass on the basis of our sol-gel glass based granulated silica method as well as first measurements of two LMA fibers obtained from this material. For the material analysis we used advanced analysis techniques, such as HAADF-STEM and STEM-EDX spectroscopy to determine the composition of the material and the distribution of the dopants and the codopants. The chemical mapping of the STEM-EDX shows an extremely homogeneous distribution of the dopants and co-dopants in nano-scale. Based on self-made LMA fibers, we measured the refractive index contrast of the sol-gelbased granulated silica derived core compared to the pure silica cladding. In addition we quantified optical characteristics such as the emission and absorption spectrum. The measured upper state lifetime of the optical active dopant ytterbium was 0.99ms, which in turn confirms the homogeneous distribution of the Yb atoms. The propagation losses were determined to be 0.2dB/m at 633nm and 0.02414dB/m at1550nm.

Alkalimetallen, Alkoxiden, [(C6H5),X]CI (X = P, As), bipy, Nabipy und Na,bipy untersucht. Inorganic Polyhedron Compounds, I11 ')Ziti's "Polyanionic Salts": Preparation and Properties of the Crystalline Compounds [Na, * 7enlSn9, (Na, -5enlCe,, and ~NP, * 4enjSb, and of their sdutiomThe Crystal Structure of [Na, * 7en]Sn, Alloys of sodium with germanium, tin, lead, antimony, or bismuth when treated with ethylenediamine (en) yield stable solutions of Zintrs so called "polyanionic salts", from which the crystalline compounds "a,. 7en]Sn,, "a4. SenlGe,, and "a3 . 4en]Sb7 are obtained. "a,. 7en]Sn, contains the Sn;--polyhedron (crystal structure determination) with a geometry between the ideal geometries of the tricapped trigonal prism ( 0 9 and the antiprism capped on one square (C4v). The compound is strongly diamagnetic (electron delocalisation). The coordinated en may be completely removed under mild conditions from "a,. 7en]Sn, without a collapse of the polyanionic structure of Na,Sn,. In solution polyhedra of the same composition are found. The compounds are very sensitive against oxygen and water. Apart from these reactions the behaviour of "a,. 7en]Sn9 against the alkali metals, alkoxides, [(C,H,),X]CI (X = P, As), bipy, Nabipy, and Na,bipy is investigated. Die Ergebnisse zeigen, daI3 die zusatzliche Verwendung von 2,2,2-crypt = N(C2H40C2-H40C2H4)3N, die kiirzlich von einer anderen Arbeitsgruppe beschrieben wurde 6-' ), ZUT Stabilisierung nicht notwendig ist. Kryptat bietet nur eine weitere Moglichkeit, aus den in Analogie zu unserer Methode verwendeten khylendiaminlosungen kristalline Verbindungen zu gewinnen.Nachfolgend berichten wir iiber unsere weiteren Untersuchungen auf diesem Gebiet. ErgebaisSe Darstellong der kristallimen VerbindungenIn iihnlicher Weise wie Na/Sn-Legierungen ' ) lost hhylendiamin Legierungen von Natrium und Germanium mit orangeroter Farbe, von Natrium und Blei mit brauner

About 40 years ago Zintl and his co-workers discovered a class of salt-like intermetallic compounds that are soluble in liquid ammonia. This class includes Na4Sn9, Na4Pb9, and Na3Sb7 which exist in solution as Na' cations and complex anions such as Pbt-. At that time Zintl proposed the designation polyanionous salts for such compounds.

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Fabrication of Ytterbium--doped active fibers with different designs, compositions and high Yb concentration has attracted an intense interest. For making highly Yb--doped fibers, co--dopants like phosphorous (P) and aluminum (Al) are also employed in order to modify refractive index and increase Yb solubility, avoiding clusters and phase segregations. Indeed, Yb--clustering results in quenching effects and increased propagation losses due to energy transfer between clustered ions. Therefore, the chemical composition and phase homogeneity of the fiber core have key influences on the performance of an active fiber. However, conventional fabrication techniques such as MCVD (modified chemical vapor deposition) and OVD (outside vapor deposition) are approaching the limit.In this contribution, we have developed an approach for fabrication of such active fibres based on granulated silica derived from the sol--gel process. The advantage of this method is the fabrication of active fibers with high dopant contents and homogeneity. Here, using high angle annular dark--field scanning transmission electron microscopy (HAADF--STEM) in atomic scale, we report the direct, nano--scale and atomic--resolution observation of individual Yb dopant and co--dopant (i.e. Al, P) atoms for different fabricated fibers. The chemical mapping from STEM--EDX shows an extremely homogeneous distribution of the dopants and co--dopants in nano--scale for our fabrication protocol. However in atomic resolution, we also identified the possible Yb clusters in the range of 10 atoms within the core structure. The size, structure, and distribution of these clusters are determined with an Yb--atom detection efficiency of almost 100% by STEM.