Abstract: A glass preform which is used for fabricating an optical fiber, has substantially no bubbles therein and contains sufficient amount of fluorine is produced by a method comprising steps of: forming a porous glass soot body from a glass-forming raw material, removing trapped gas and water from pores of the soot body by heating the soot body under pressure lower than several ten Torr. at a temperature at which the soot body is not vitrified, filling the pores of the soot body with a gas containing SiF.sub.

Abstract: A method for producing a glass preform for use in the fabrication of an optical fiber, which includes the steps of forming a glass soot preform from a glass-forming raw material and heating the soot preform in an atmosphere containing SiF.sub.4 under a pressure higher than 2 atm. for a period of time sufficient to add fluorine during the time between the formation of the soot preform and the vitrification of it, fluorine is added at a high rate and in a larger amount.

Abstract: A glass preform is produced by forming a glass soot composite body having a core portion consisting of a solid glass and a peripheral portion consisting of a porous glass mass, removing trapped gas and water from pores of the soot composite body by heating the soot composite body under a pressure lower than several ten Torr. at a temperature at which the porous glass mass is not vitrified, filling the pores in the porous glass mass of the soot composite body with a gas containing SiF.sub.4, the partial pressure of which is a function of the desired specific difference of refractive index, thus uniformly adding fluorine to the soot glass mass, and vitrifying the fluorine-added soot glass mass into a transparent glass mass to form a glass preform.

Abstract: A method for producing a glass preform for use in the fabrication of an optical fiber, including the steps of forming a glass soot preform from a glass-forming raw material and heating the soot preform to vitrify it, the soot preform being heated in an atmosphere comprising SiF.sub.4 under pressure higher than 1 atm. for a period of time sufficient to add fluorine, between the formation of the soot preform and the vitrification of it, fluorine being added at a high rate and in a large amount.

Abstract: A refractive index profile in a glass article is easily controlled by heating a solid or hollow cylindrical glass soot preform in an atmosphere comprising a fluorine-containing compound under such conditions that a partial pressure of the fluorine-containing compound is changed as the heating proceeds so as to control a fluorine concentration in a radial direction of the optical glass article.

Abstract: A method of the production of the ceramic superconductor filament comprisesa step including mixing raw materials of ceramic superconductor, subsequently shaping the mixed ceramic superconductor into a ceramic superconductor body of a predetermined shape and preliminarily sintering thereof and further subsequently crushing the sintered ceramic superconductor body into ceramic superconductor powder;a step of filling the ceramic superconductor powder in a glass tube;a step of heating the glass tube including ceramic superconductor powder so that the ceramic superconductor powder is molten; anda step of spinning the glass tube including the ceramic superconductor materialwhereby a ceramic super conductor covered with the glass material can be obtained.

Abstract: A method of heating a quartz glass tube with microwaves, which method comprises supplying a gas for plasma generation in the quartz glass tube, applying microwaves to the quartz glass tube so as to generate a hot plasma in the quartz glass tube and to preheat the quartz glass tube, and then discontinuing the supply of the gas for plasma generation while applying the microwaves, whereby the quartz glass tube absorbs the microwaves to heat the quartz glass tube to a sufficient temperature in a very quick and clear manner.