Abstract: A UV light-permeable optical glass consisting of a fluorine-doped synthetic quartz glass, which has a long term reliability.

Abstract: An object of this invention is to provide a mode field diameter conversion optical fiber which can be processed in a short period of time to have a reduced mode field diameter at a desired portion thereof. The optical fiber according to this invention comprises a core of silica glass having a residual tensile stress, and a cladding surrounding the core and having a lower refractive index than that of the core. The desired portion is heated to relax the residual tensile stress in the core, whereby the optical fiber has a reduced mode field diameter at the desired portion.

Abstract: In an apparatus for suspending from a quartz rotary shaft, a glass article to be heat treated in a heating furnace so as to support the glass article, a slot is provided for receiving a cylindrical projection formed at an upper end of the glass article, the slot has an elliptical cross section and is formed at a lower end of the rotary shaft. A pin hole for securing the glass article to the rotary shaft, which is formed on the rotary shaft along a minor axis of the slot; wherein a clearance between a peripheral surface of the slot and that of the cylindrical projection along the minor axis of the slot is set to not more than 0.2 mm, while a clearance between the peripheral surface of the slot and that of the cylindrical projection along a major axis of the slot is set to not less than 0.4 mm. An apparatus for supporting a glass article including first and second dummy rods and a coupling member is also provided.

Abstract: A glass preform for an optical fiber is flame abrased with an oxyhydrogen flame while vertically suspending and rotating the glass preform and relatively moving one or both of the glass preform and the oxyhydrogen flame, whereby a surface of the glass preform is smoothened.

Abstract: There is provided a process of melt drawing an optical fiber from a preform therefor in which a heating furnace comprising a muffle tube inside thereof through which the optical fiber is passed is provided immediately below a melt drawing furnace to further draw the optical fiber while heated, and an interior of the muffle tube is kept in an atmosphere selected from the group consisting of an inert atmosphere, an atmosphere comprising oxygen gas and an atmosphere comprising hydrogen gas.

Abstract: The present invention providesa process for the dehydrating and purifying treatment by heating a porous glass preform for an optical fiber comprising passing the porous glass preform through a muffle tube having a SiC layer at least on its inner surface at a high temperature under an atmosphere comprising an inert gas and a silicon halogenide gas;a process for the fluorine-doping treatment by heating a porous glass preform for an optical fiber comprising passing a porous glass preform through a muffle tube having a SiC layer at least on its inner surface at a high temperature under an atmosphere comprising a fluorine compound gas and an inert gas; anda process for the vitrifying treatment by heating a porous glass preform for an optical fiber comprising passing the preform, which has been previously dehydrated and purified, through a muffle tube having a SiC layer at least on its inner surface at a high temperature under an atmosphere gas.

Abstract: A heating furnace for heating a porous preform made of fine particles of quartz base glass for an optical fiber which comprises a heater and a muffle tube positioned inside the heater to separate a heating atmosphere from the heater, wherein the muffle tube body consists of highly pure carbon and an inner wall and an outer wall of the body is coated with a carbon material selected from the group consisting of pyrolytic graphite and solid-phase carbonized glassy carbon.

Abstract: The invention is a method for producing a porous preform for use in the fabrication of an optical fiber at least two burners synthesize glass soot particles, one of which generates a double-layer flame and one of which is used for forming a core part of the preform. The method comprises the steps of supplying SiCl.sub.4 and optionally GeCl.sub.4 to the inner flame of the double-layer flame, and only SiCl.sub.4 to an outer flame of the double-layer flame to flame hydrolyze the supplied compounds and synthesize glass soot particles. Compounds SiCl.sub.4 and GeCl.sub.4 as glass-forming raw materials are supplied to the burner for forming the core part of the preform by depositing the generated glass soot particles on the lower end of a rotating starting member. The generated porous preform comprises a core part containing at least partly GeO.sub.2, and a surface having a low concentration of GeO.sub.2 which reduces cracking or peeling.

Abstract: The present invention providesa process for the dehydrating and purifying treatment by heating a porous glass preform for an optical fiber by passing the porous glass preform through a muffle tube having a SiC layer at least on its inner surface at a high temperature under an atmosphere containing an inert gas and a silicon halogenide gas;a process for the fluorine-doping treatment by heating a porous glass preform for an optical fiber by passing a porous glass preform through a muffle tube having a SiC layer at least on its inner surface at a high temperature under an atmosphere containing a fluorine compound gas and an inert gas; anda process for the vitrifying treatment by heating a porous glass preform for an opticla fiber by passing the preform, which has been previously dehydrated and purified, through a muffle tube having a SiC layer at least on its inner surface at a high temperature under an atmosphere gas.