A doped silica-titania (DST) glass article that includes a glass article having a glass composition comprising a silica-titania base glass containing titania at 7 to 14 wt. % and a balance of silica, and a dopant selected from the group consisting of (a) F at 0.7 to 1.5 wt. %, (b) B.sub.2O.sub.3 at 1.5 to 5 wt. %, (c) OH at 1000 to 3000 ppm, and (d) B.sub.2O.sub.3 at 0.5 to 2.5 wt. % and OH at 100 to 1400 ppm. The glass article has an expansivity slope of less than about 1.3 ppb/K.sup.2 at 20 C. For DST glass articles doped with F or B.sub.2O.sub.3, the OH level can be held to less than 10 ppm, or less than 100 ppm, respectively. In many aspects, the DST glass articles are substantially free of titania in crystalline form.

A doped silica-titania glass article is provided that includes a glass article having a glass composition comprising (i) a silica-titania base glass, (ii) a fluorine dopant, and (iii) a second dopant. The fluorine dopant has a concentration of fluorine of up to 5 wt. % and the second dopant comprises one or more oxides selected from the group consisting of Al, Nb, Ta, B, Na, K, Mg, Ca and Li oxides at a total oxide concentration from 50 ppm to 6 wt. %. Further, the glass article has an expansivity slope of less than 0.5 ppb/K.sup.2 at 20 C. The second dopant can be optional. The composition of the glass article may also contain an OH concentration of less than 100 ppm.

An optical fiber containing an alkali metal and capable of reducing Rayleigh scattering loss is provided. An optical fiber has a core and a cladding made of silica glass and enclosing the core. The cladding contains fluorine and has a refractive index lower than the refractive index of the core. The core contains first group dopants selected from the group of Na element, K element, or a compound thereof at an average concentration of 0.2 ppm or more and 10 ppm or less. The core also contains second group dopants for reducing the viscosity of silica glass and having a diffusion coefficient of 110.sup.12 cm.sup.2/s or more and smaller than the diffusion coefficient of the first group dopants, by an average concentration of 0.2 ppm or more at a temperature of 2000 C. to 2300 C.

An optical fiber has a core region that is doped with one or more viscosity-reducing dopants in respective amounts that are configured, such that, in a Raman spectrum with a frequency shift of approximately 600 cm.sup., the fiber has a nanoscale structure having an integrated D2 line defect intensity of less than 0.025. Alternatively, the core region is doped with one or more viscosity-reducing dopants in respective amounts that are configured such that the fiber has a residual axial compressive stress with a stress magnitude of more than 20 MPa and a stress radial extent between 2 and 7 times the core radius.

According to another aspect of the invention a majority of the optical propagation through the fiber is supported by an identified group of fiber regions comprising the core region and one or more adjacent cladding regions. The fiber regions are doped with one or more viscosity-reducing dopants in respective amounts and radial positions that are configured to achieve viscosity matching among the fiber regions in the identified group.

To obtain a crystallized glass member having a curved shape and provide a method for producing the same. A method for producing a crystallized glass member having a curved shape, including a deformation step for adjusting the temperature of a plate glass to a first temperature zone from higher than [At+40] C. to [At+146] C. or lower, where At is the yield point ( C.) of the plate glass and deforming at least part of the plate glass into a curved shape by external force acting on the plate glass while precipitating crystals from the plate glass.