Abstract: A glass when in the form of an optical fiber having an optical loss of not more than 150 dB/km, high transparency, a high numerical aperture, and a high flexural strength, said glass being especially suitable for optical fibers and consisting essentially of:SiO.sub.2 : 65 - 75 mol-%; (38 - 46% by weight);R.sub.2 o: 4 - 17 mol-%; (4 - 13% by weight);PbO: 16 - 25 mol-%; (42 - 55% by weight); wherein R.sub.2 O is Na.sub.2 O, K.sub.2 O or Cs.sub.2 O or mixtures thereof, preferably not more than 3.0 mol % Na.sub.2 O, and with the provision that the molar ratio of SiO.sub.2 : PbO is 2.5 - 4.0.

Abstract: An optical glass with a path length independent of temperature comprises between 40 and 55% by weight P.sub.2 O.sub.5, between 40 and 54% by weight BaO and between 6 and 12% by weight Nb.sub.2 O.sub.5. Part of the BaO may be replaced by SrO or CaO. Minor amounts of SiO.sub.2 or B.sub.2 O.sub.3 may be included as may other metal oxides such as ZnO, Sb.sub.2 O.sub.3 and La.sub.2 O.sub.3.

Abstract: Optical glass with a path length independent of temperature includes SiO.sub.2, B.sub.2 O.sub.3, K.sub.2 O, BaO, ZrO.sub.2, TiO.sub.2, Nb.sub.2 O.sub.5, P.sub.2 O.sub.5 and F in specified percentages by weight, with the sum of the amounts of SiO.sub.2, B.sub.2 O.sub.3 and P.sub.2 O.sub.5 between 38 and 45% by weight and the sum of the amounts of ZrO.sub.2 and TiO.sub.2 between 12 and 27% by weight.