An optical fiber having an axial direction and a cross section perpendicular to the axial direction, and a method and preform for producing such an optical fiber. The optical fiber is adapted to guide light at a wavelength λ, and includes a core region, an inner cladding region surrounding said core region, and at least one of a first type of feature including a void and a surrounding first silica material. The core, the inner cladding region and the first type of feature extends along said axial direction over at least a part of the length of the optical fiber. The first silica material has a first chlorine concentration of about 300 ppm or less.

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.

One of embodiments relates to an optical fiber in which an alkali metal element is efficiently doped to its core to suppress transmission loss from increasing. A mean concentration or a concentration distribution of the alkali metal element is adjusted such that 0.48 or less is obtained as an weighted value obtained by weighting a distribution of field intensity of guided light at a wavelength of 1550 nm, with respect to a radial direction distribution of a ratio I.sub.D2/I.sub.ω3 of an intensity I.sub.D2 of Raman scattering light by a silica three-membered ring structure and an intensity I.sub.ω3 of Raman scattering light by a Si—O stretching vibration, in a cross-sectional region having a diameter of 20 μm.

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.

An optical fiber preform includes: a core formed of silica glass which does not contain Ge, wherein the core has at least one of characteristics in spectrometry of (1) an absorption peak is present at a wavelength of 240 nm to 255 nm, and (2) a wavelength at which an ultraviolet transmittance is 50% or lower is longer than 170 nm.

A single mode optical fiber having a core made from silica and less than or equal to about 11 weight % germania and having a maximum relative refractive index Δ.sub.1MAX. The optical fiber also has an inner cladding surrounding the core and having a minimum relative refractive index Δ.sub.2MIN, a first outer cladding surrounding the inner cladding and a second outer cladding surrounding the first outer cladding. The viscosity at 1650° C. of the second outer cladding minus the viscosity at 1650° C. of the first outer cladding is greater than 0.1e.sup.7 Poise, and Δ.sub.1MAX>Δ.sub.2MIN. The single mode optical fiber may also have an outer cladding surrounding the inner cladding made from silica or SiON. The first outer cladding has a maximum relative refractive index Δ.sub.3MAX, and Δ.sub.3MAX>Δ.sub.2MIN.

An optical fiber having a core comprising silica and greater than 1.5 wt % chlorine and less than 0.5 wt % F, said core having a refractive index Δ.sub.1MAX, and an inner cladding region having refractive index Δ.sub.2MIN surrounding the core, where Δ.sub.1MAX>Δ.sub.2MIN.

Laser waveguides, methods and systems for forming a laser waveguide are provided. The waveguide includes an inner cladding layer surrounding a central axis and a glass core surrounding and located outside of the inner cladding layer. The glass core includes a laser-active material. The waveguide includes an outer cladding layer surrounding and located outside of the glass core. The inner cladding, outer cladding and/or core may surround a hollow central channel or bore and may be annular in shape.

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.

An optical boroaluminate glass article comprises: from greater than or equal to 10.0 mol % to less than or equal to 30.0 mol % Al.sub.2O.sub.3; from greater than or equal to 10.0 mol % to less than or equal to 55.0 mol % CaO; from greater than or equal to 10.0 mol % to less than or equal to 25.0 mol % B.sub.2O.sub.3; from greater than or equal to 0.0 mol % to less than or equal to 30.0 mol % SiO.sub.2; and from greater than or equal to 1.0 mol % to less than or equal to 20.0 mol % refractive index raising components. The optical boroaluminate glass article has a refractive index of the glass article, measured at 589.3 nm, of greater than or equal to 1.62, and a density of less than or equal to 4.00 g/cm.sup.3.