Abstract: According to one example of the invention an optical fiber comprises: (i) a core comprising Al doped silica but essentially no Er or Yb, and having a first index of refraction n1; (ii) at least one F doped silica based cladding surrounding the core and having a second index of refraction n2, such that n1>n2, wherein the cladding comprises essentially of SiO2 and 0.2-5 wt % F; (iii) a hermetic carbon based coating surrounding said cladding, said hermetic coating being 200 to 1000 Angstroms thick; and (iv) a second coating surrounding said hermetic coating, said second coating being 5 ?m to 80 ?m thick.

Abstract: A low-carbon-type in-flight melting furnace for melting granular raw material for glass production in in-flight state using plasma heating and gas combustion, a melting method using the same and a melting system utilizing the same are provided. The low-carbon-type in-flight melting furnace includes a melting furnace body unit; a melting tank in the melting furnace body unit; a melting unit provided above the melting tank and serving to melt raw material; a raw material feeding unit provided outside the melting unit; a plasma/gas melting device provided around the melting unit and serving to spray high-temperature flames produced by plasma and gas; an exhaust tube provided at one side of the melting tank and serving to discharge exhaust gas; and a tap hole for tapping the melt, formed in the melting unit, through the melting tank, in the form of a slag.

Abstract: A method for producing glass balls, wherein a glass flow is fed between two rollers which are driven synchronously but counter-rotatingly in a flow direction, from a feed tank containing a mass of molten glass. The rollers have hemispherical depressions distributed over the circumference and form spherical beads on a thin glass strip successively in the region of an imaginary contact tangent. A thickness of the glass strip is fixed by the spacing between the rollers externally of the depressions in the region of the contact tangent. Crude balls are separated from the glass strip by a separating device, once the glass strip, containing the spherical beads, is cooled. The crude balls are subjected to a cold surface finishing treatment.