An optical fiber includes a core region of silica glass doped with an alkali metal oxide. A depressed-index cladding region surrounds the core region and comprises silica glass doped with a first concentration of fluorine. The depressed-index cladding region has a minimum relative refractive index Δ.sub.3min in a range from −0.80% to −0.30%. An outer cladding region comprises silica glass doped with a second, lesser concentration. The outer cladding region has a relative refractive index Δ.sub.4, where Δ.sub.4−Δ.sub.3min>0.05%. The optical fiber has a time-to-peak hydrogen aging value at 23° C. of less than 100 hours upon exposure to an atmosphere having a total pressure of 1 atm and containing a partial pressure of 0.01 atm H.sub.2 and a partial pressure of 0.99 atm N.sub.2. The optical fiber exhibits an attenuation <0.16 dB/km.

The present invention relates to a method of forming an optical fiber precursor including: forming an alkali metal doped tube; inserting an optical fiber core rod within the alkali metal doped tube; forming a cladding jacket around the alkali metal doped tube; and diffusing an alkali metal from the alkali metal doped tube through a surface of the optical fiber core rod. The present invention further relates to an optical fiber preform having: an optical fiber core rod; an alkali metal doped tube surrounding the optical fiber core rod; and a cladding jacket surrounding the alkali metal doped tube.

Preparation of halogen-doped silica is described. The preparation includes doping silica with high halogen concentration, sintering halogen-doped silica to a closed-pore state, and subjecting the closed-pore silica body to a thermal treatment process and/or a pressure treatment process. The temperature of thermal treatment is sufficiently high to facilitate reaction of unreacted doping precursor trapped in voids or interstices of the glass structure, but is below temperatures conducive to foaming. Core canes or fibers drawn from halogen-doped silica subjected to the thermal treatment and/or pressure treatment show improved optical quality and possess fewer defects. The thermal treatment and/or pressure treatment is particularly advantageous when used for silica doped with high concentrations of halogen.

A method for manufacturing an SiO.sub.2—TiO.sub.2 based glass upon a target by a direct method, includes a first process of preheating the target and a second process of growing an SiO.sub.2—TiO.sub.2 based glass ingot to a predetermined length upon the target which has been preheated, wherein the target is heated in the first process such that, in the second process, the temperature of growing surface of the glass ingot is maintained at or above a predetermined lower limit temperature.

A co-doped optical fiber is provided having an attenuation of less than about 0.17 dB/km at a wavelength of 1550 nm. The fiber includes a core region in the fiber having a graded refractive index profile with an alpha of greater than 5. The fiber also includes a first cladding region in the fiber that surrounds the core region. Further, the core region has an relative refractive index of about −0.10% to about +0.05% compared to pure silica. In addition, the core region includes silica that is co-doped with chlorine at about 1.2% or greater by weight and fluorine between about 0.1% and about 1% by weight.

A method for producing titanium-doped synthetic quartz glass includes: (A) providing a liquid SiO.sub.2 feedstock material that comprises more than 60% by weight of the polyalkylsiloxane D4; (B) evaporating the liquid SiO.sub.2 feedstock material to produce a gaseous SiO.sub.2 feedstock vapor; (C) evaporating a liquid TiO2 feedstock material to produce a gaseous TiO2 feedstock vapor; (D) converting the SiO.sub.2 feedstock vapor and the TiO2 feedstock vapor into SiO2 particles and TiO2 particles, respectively; (E) depositing the SiO2 particles and the TiO2 particles on a deposition surface while forming a titanium-doped SiO.sub.2 soot body; (F) vitrifying the titanium-doped SiO.sub.2 soot body while forming the synthetic quartz glass, whereby the TiO2 concentration of the synthetic quartz glass is between 5% by weight and 11% by weight. The liquid SiO.sub.2 feedstock material comprises at least one additional component made of the polyalkylsiloxane D3 having a weight fraction of mD3 and one additional component made of the polyalkylsiloxane D5 having a weight fraction of mD5 at a weight ratio of mD3/mD5 in a range of 0.01 to 1, and the liquid SiO.sub.2 feedstock material provided is evaporated while maintaining the weight ratio of mD3/mD5 and at least 99% by weight thereof are evaporated to form the gaseous SiO.sub.2 feedstock vapor.

According to some embodiments a method of processing an optical fiber comprises the steps of: (i) drawing the fiber at a drawing rate of at least 30 m/sec; and (ii) cooling the drawn fiber in a gas at an average cooling rate less than 5000° C./s, such that said cooling reduces the temperature of the fiber from an entering temperature in the range between 1500° C. and 1700° C. to another temperature in the range between 1200° C. and 1400° C., the gas being at a temperature between 800° C. and 1500° C.; and the thermal conductivity κ of the gas being not greater than 1.5×10.sup.−4 cal/cm-s-K for at least one temperature within a range of 800° C. to 1500° C. at one atm (atmosphere) pressure absolute.

A method of producing bi-modal particles includes the steps of igniting a first precursor gas using a primary burner thereby producing a first plurality of particles of a first size, fluidly transporting the first plurality of particles down a particle tube, igniting a second precursor gas using a secondary burner thereby producing a second plurality of particles of a second size, flowing the second plurality of particles into the first plurality of particles, and capturing the first and second plurality of particles.

A method for manufacturing an optical fiber preform including a core part and a cladding part is disclosed. The method includes: adding an alkali metal to an inner surface of a silica-based glass pipe; etching the inner surface of the silica-based glass pipe to which the alkali metal is added; making a glass rod by collapsing the silica-based glass pipe after the etching; and making an optical fiber preform using the glass rod. The silica-based glass pipe is heated in the adding such that a surface temperature of the silica-based glass pipe falls within a temperature range of 1500° C. or higher to lower than 2000° C.

Annealing treatments for modified titania-silica glasses and the glasses produced by the annealing treatments. The annealing treatments include an isothermal hold that facilitates equalization of non-uniformities in fictive temperature caused by non-uniformities in modifier concentration in the glasses. The annealing treatments may also include heating the glass to a higher temperature following the isothermal hold and holding the glass at that temperature for several hours. Glasses produced by the annealing treatments exhibit high spatial uniformity of CTE, CTE slope, and fictive temperature, including in the presence of a spatially non-uniform concentration of modifier.