Abstract: A method for producing a glass preform for an optical fiber comprising a core and a cladding containing fluorine is fisclosed. The method comprises forming a porous glass layer of substantially pure quartz on an outer surface of a fused glass rod consisting of a central portion of substantially pure quartz and a peripheral portion of quartz glass containing fluorine, and heating a composite of the fused glass rod and the porous glass layer in an atmosphere containing fluorine to add fluorine to the porous glass layer and to make it transparent, by which contamination of glass with hydroxyl groups can be prevented and light transmission characteristics of an optical fiber fabricated from the glass preform are improved.

Abstract: A method of manufacturing a glass fiber preform in which a quartz glass rod having an outer coating containing chlorine and a core doped for higher refractive index has blown thereon a soot formed by a burner fed with quartz glass raw material and a chlorine group gas undergoing flame hydrolysis. The resulting composite is the heated and fused to collapse.

Abstract: A method for producing a glass preform for use in the fabrication of an optical fiber which comprises inserting a core rod made of quartz glass in a cladding tube made of quartz glass added with fluorine, heating them from the outside of the cladding tube to fuse them together to form a primary glass preform comprising a core rod and a first cladding layer around the core rod, depositing SiO.sub.2 soot particles around the primary glass preform and thermally treating the soot deposited glass preform in the presence of a fluorine-containing compound to form a final glass preform from which an optical fiber is fabricated. From the glass preform produced by this method, an optical fiber having low attenuation of light transmission in a wide range of wave-length is fabricated.

Abstract: A heating apparatus for drawing a glass rod having a tapered portion coupled, at its upper end, with a feed bar of an outside diameter smaller than that of the glass rod, including an apparatus housing into which the glass rod is inserted, a first sealing cover which is formed with a bore having such a dimension as to seal a clearance between the glass rod and the bore and is hermetically mounted on an inlet opening of the apparatus housing and a second sealing cover which is movably attached to the feed bar and is formed with an aperture having such a dimension as to seal a clearance between the feed bar and the aperture. The second sealing cover has a hollow portion which is formed with a space for accommodating the tapered portion and is hermetically placed, at its lower end, on the inlet opening.

Abstract: A glass preform for an optical fiber having homogeneous distribution of bulk density in its radial direction is produced by a method comprising forming fine glass particles by jetting a gaseous glass material and a fuel gas from a burner, depositing the fine glass particles on a seed rod to form a soot rod with measuring a temperature of a part of the soot rod on which the glass particles are being deposited so as to control said temperature, and then sintering the soot rod to obtain a transparent glass preform.

Abstract: A method for producing a glass preform for a single mode optical fiber comprising a core and a cladding, which method comprises depositing fine glass particle of a glass raw material on a periphery of a cylindrical seed member having a smooth and clean outer surface by flame hydrolysis to form a soot of the fine glass material, pulling out the seed member from the soot, inserting a core glass rod in a hollow portion of the soot and dehydrating and sintering a complex of a core rod and a cladding to produce a glass preform from which a single mode optical fiber having low attenuation of light transmission, particularly due to absorption by hydroxyl groups can be drawn.

Abstract: A rod-in-tube method for producing a glass preform for use in the fabrication of an optical fiber, which comprises steps of inserting a glass rod as a core material in a glass tube as a cladding material, fusing and closing one end of the cladding material, filling a gap between the core and cladding materials with an atmosphere containing at least one gaseous halogen-containing compound and then heating the core and cladding materials at a temperature not lower than 1,900.degree. C. to collapse the gap between them and to fuse them together, from which glass preform, an optical fiber with low attenuation of light transmission is fabricated.

Abstract: A method of producing a highly pure glass tube having a smooth inner surface, said method comprising the steps ofdepositing by the flame hydrolysis of a glass-forming raw material, a first layer of glass soot particles having a bulk density no greater than 0.2 g/cm.sup.3 on a seed member having a smooth and clean outer surface,depositing on the surface of the first layer of glass soot particles, a second layer of glass soot particles having a bulk density greater than that of the first layer by at least 0.03 g/cm.sup.3,drawing the seed member from the deposited two-layered glass soot preform to form a tube of glass soot particles,removing the first inner layer of glass soot particles from the second layer, either simultaneously with or subsequent to the drawing of the seed member from the soot preform, andheating and vitrifying the tubular glass soot preform to form a transparent solid glass tube.

Abstract: A method for producing a glass preform for an optical fiber by an outside vapor-phase deposition method, which comprises forming fine glass particles by jetting gaseous glass raw material and fuel gas from a first burner to deposit the particles on a seed rod to form a soot rod at such a temperature that a specific bulk density of the soot rod being formed is low and subsequently heating the soot rod by a second burner so as to increase the bulk density of the soot and then sintering the soot rod to obtain a transparent glass preform for an optical fiber, by which method, a highly pure glass preform is produced in a good deposition yield without cracking.