Optical waveguide article including a fluorine-containing zone

An optical fiber comprising:

• a) a core;
• b) a concentric cladding, the core and the cladding having an core/clad interface;
• and
• c) a fluorine concentration zone extending from the core/clad interface of the core and the cladding and overlapping across at least a portion of the core and the cladding, the zone comprising a highest concentration of fluorine approximately at the core/clad interface.

An optical fiber comprising:

• a) a silicate core;
• and
• b) a cladding concentric to the core,
• wherein the core comprises a halide-doped silicate glass that comprises approximately the following in cation-plus-halide mole percent:
• 85-99 mol % SiO2, 0.25-5 mol % Al2O3, 0-15 mol % GeO2 0.05-1.5 mol % La2O3, 0.0005-0.75 mol % Er2O3, 0.5-6 mol % F, 0-1 mol % Cl.