The optical fiber offered is capable of not only restraining the attenuation due to glass defects, but also reducing the increase of manufacturing cost. The optical fiber is made of silica glass and includes a core and a cladding. The cladding encloses the core and has a refractive index smaller than that of the core. When the core is divided into inner core and outer core at half of the radius of the core, the average chlorine concentration of the inner core is larger than that of the outer core. The core includes any of the alkali metal group.

An optical fiber preform includes a silica-glass core portion, and a cladding portion surrounding the core portion, the cladding portion being composed of a fluorine-containing silica glass having a lower refractive index than the core portion, the core portion including a first region that does not include the central axis thereof, the first region containing a first dopant selected from sodium, potassium, and compounds thereof, and a second region that includes the central axis, the second region containing a second dopant that reduces the viscosity of the silica glass, the second dopant having a diffusion coefficient of 110.sup.12 cm.sup.2/s or more and less than the first dopant at 2,000 C. to 2,300 C., in which the entire core portion has an average first dopant concentration of 10 atomic ppm or more and 2,000 atomic ppm or less and an average second dopant concentration of 10 atomic ppm or more.

Glass compositions having from 50 to 80 mol % SiO.sub.2, less than or equal to 25 mol % Al.sub.2O.sub.3, from 6.5 to 10.0 mol % Li.sub.2O and, optionally, other components, such as alkali metal oxides, alkaline earth metal oxides, zinc oxide, phosphorus oxides, rare earth metal oxides, boron oxide, and small amounts of other species, such as titania, zirconia, and tin oxide. The glass compositions are characterized by zero or positive values of the ratios, in terms of mol %: Al.sub.2O.sub.3-R.sub.2O0, or Al.sub.2O.sub.3-R.sub.2O-RO0, or Al.sub.2O.sub.3-R.sub.2O-ROP.sub.2O.sub.50, where R.sub.2O means alkali metal oxides and RO means divalent metal oxides. The glass compositions may have a liquidus viscosity greater than or equal to 1000 Poises to less than or equal to 300,000 Poises.

The present invention discloses a glass-ceramic article and a glass-ceramic for an electric device cover plate, the glass-ceramic comprises, as a predominant crystalline phase, lithium silicate and the quartz crystalline phase, and has a composition expressed in weight percent including: SiO.sub.2: 65-85%, Al.sub.2O.sub.3: 1-15%, Li.sub.2O: 5-15%, ZrO.sub.2: 0.1-10%, P.sub.2O.sub.5: 0.1-10%, K.sub.2O: 0-10%, MgO: 0-10%, ZnO: 0-10%, and Na.sub.2O: 0-5%, wherein (SiO.sub.2+Al.sub.2O.sub.3+Li.sub.2O+ZrO.sub.2)/P.sub.2O.sub.5 is 40-90, the falling ball test height is 700 mm or more. By reasonable component design, the present invention achieves excellent mechanical properties of the glass-ceramic and the glass-ceramic article of the present invention and obtains the glass-ceramic or the glass-ceramic article suitable for electronic devices at a lower cost.

The optical fiber offered is capable of not only restraining the attenuation due to glass defects, but also reducing the increase of manufacturing cost. The optical fiber is made of silica glass and includes a core and a cladding. The cladding encloses the core and has a refractive index smaller than that of the core. When the core is divided into inner core and outer core at half of the radius of the core, the average chlorine concentration of the inner core is larger than that of the outer core. The core includes any of the alkali metal group.

There are provided an optical glass that has a low temperature coefficient of relative refractive index and that can contribute to correction of the influence on image formation characteristics due to temperature change, and a preform and an optical element that use the optical glass.

The optical glass contains, on a mass % basis, 20.0% to 40.0% of a P.sub.2O.sub.5 component, 25.0% to 50.0% of a Nb.sub.2O.sub.5 component, and 3.0% to 30.0% of a total mass (Na.sub.2O+K.sub.2O), wherein a temperature coefficient (40 C. to 60 C.) of a relative refractive index (589.29 nm) is in the range of +3.010.sup.6 to 10.010.sup.6 ( C..sup.1).

The present invention discloses a glass-ceramic article and a glass-ceramic for an electric device cover plate, the glass-ceramic comprises, as a predominant crystalline phase, lithium silicate and the quartz crystalline phase, and has a composition expressed in weight percent including: SiO.sub.2: 65-85%, Al.sub.2O.sub.3: 1-15%, Li.sub.2O: 5-15%, ZrO.sub.2: 0.1-10%, P.sub.2O.sub.5: 0.1-10%, K.sub.2O: 0-10%, MgO: 0-10%, ZnO: 0-10%, and Na.sub.2O: 0-5%, wherein (SiO.sub.2+Al.sub.2O.sub.3+Li.sub.2O+ZrO.sub.2)/P.sub.2O.sub.5 is 40-90, the falling ball test height is 700 mm or more. By reasonable component design, the present invention achieves excellent mechanical properties of the glass-ceramic and the glass-ceramic article of the present invention and obtains the glass-ceramic or the glass-ceramic article suitable for electronic devices at a lower cost.

Methods of enhanced ion exchange (IOX) include exposing a substrate to a bath mixture that includes a second salt dissolved in a first salt, the second salt includes the same metal ion as the first salt with an anion different from the first salt. The first salts are conventional nitrate salts into which one or more second salts, for example, carbonate, sulfate, chloride, fluorine, borate, or phosphate salts are dissolved. The second salts remain at or below their solubility limits in the first salts. Any poisoning ions remain at or below their solubility limits in the bath mixture. Glass-based articles made therefrom and electronic devices incorporating the glass-based articles are also disclosed.

A silicate-based glass composition includes: 50-70 wt. % SiO.sub.2, 0.01-10 wt. % P.sub.2O.sub.5, 10-30 wt. % Na.sub.2O, 0.01-10 wt. % CaO, 0.01-10 wt. % MO, and 15-30 wt. % R.sub.2O, such that MO is the sum of MgO, CaO, SrO, BeO, and BaO, and R.sub.2O is the sum of Na.sub.2O, K.sub.2O, Li.sub.2O, Rb.sub.2O, and Cs.sub.2O.

A glass substrate and a method for manufacturing the glass substrate are provided. The glass substrate may include a base glass including SiO.sub.2, Al.sub.2O.sub.3, and Li.sub.2O, and nanocrystals having an average diameter in a range from about 5 nm to about 10 nm, thereby exhibiting enhanced surface strength properties while maintaining good transmittance properties. The method may include a step of heat-treating a base glass, thereby providing a glass substrate having enhanced strength properties.