A fused optical fiber optical device system comprises at least one optical component comprising optical fibers and at least one other optical component with which light transmitted in the optical fibers interacts, wherein the optical fiber comprises a core glass of the following composition: La.sub.2O.sub.3 1 23 mole %, ZrO.sub.2 1 10 mole %, WO.sub.3.gtoreq.2.5 mole %, ZnO 1 15 mole %, BaO 0 9 mole %, B.sub.2O.sub.3 20 70 mole %, Ta.sub.2O.sub.5 0 3 mole %, CaO 0 7 mole %, PbO 6 35 mole %, SiO.sub.2 0 40 mole %, As.sub.2O.sub.3 and/or Sb.sub.2O.sub.3 0 0.1 mole %, Nb.sub.2O.sub.50 3 mole % and Al.sub.2O.sub.3 0 8 mole %. The core glass is essentially free of CdO, has a refractive index n.sub.d of at least 1.8 and a CTE of .gtoreq.about 74.times.10.sup.-7.