Abstract: The surface quality of halide, preferably fluoride, articles, e.g. articles used in the preparation of halide fibres is improved by cleaning the surface with an aqueous etchant and thereafter removing the etchant by washing the surface with methanol. The aqueous etchant is preferably a solution which contains hydrochloric acid and zirconium oxychloride.

Abstract: A laser has a resonant cavity defined by a pair of mirrors butted to respective ends of a fluorozirconate optical fiber. The fiber has a numerical aperture of 0.205 and an LP.sub.11 mode cut-off of about 2.0 .mu.m. The fibre is co-doped with thulium ions to a concentration of about 0.1%, and with terbium ions to a concentration of about 1%. An optical pump source provides a pump signal at 775 nm which excites the thulium ions into the .sup.1 G.sub.4 energy level to provide lasing at about 475 nm. The pump source is preferably a high power semiconductor laser.

Abstract: Halide glasses having particular utility as hosts for praseodynmium in order to provide optical amplification by laser activity have a halide content provided as a small proportion, e.g., 1-10 percent, of choride with the remainder as fluoride. The metal content is similar to conventional ZBLAN glasses. The replacement of A1 by Y and In and/or the partial replacement of Na by Cs has synergistic benefits. PR.sup.3+ constitutes a good lasing species for amplifying telecommunication signals at 1300 nm using pumped radiation at 1020 nm.

Abstract: Glass fibre suitable for use as the core in fibre lasers and/or amplifiers has a core which consists of a continuous glass phase and a dispersed phase of crystallites. The preferred crystallites are the oxides and phosphates of rare earth metals, e.g. Nd.sub.2 O.sub.3 and NdP.sub.5 O.sub.14. The small size concentration and distribution of the crystallites keeps the attenuation down to acceptable levels.