Abstract: A gas impermeabe coating composed of mainly silicon carbide (SiC) without cracks, comprising of a metallic silicon powder as a silicon source, a phenolic resin as a carbon source, a silicon carbide (SiC) powder and solvent are mixed. A mixture is applied to a graphite substrate material, dried and treated in an inert gas atmosphere at temperature from 1500° C. to 2500° C., preferably around 2000° C., with the silicon carbide powder existence in the coating mixture. The metallic silicon powder and carbon constituting the phenolic resin are reacted to form silicon carbide (SiC), thereby a coating film with no cracks is obtained on the graphite substrate material, such as carbon fiber felt molded heat insulation material.

Abstract: A process of manufacturing a silica glass article comprising the steps of: (1) irradiating a silica glass article with electromagnetic waves to generate defects therein; and (2) immersing the thus irradiated silica glass article in an atmosphere comprising a hydrogen gas, thereby providing the resulting silica glass article with a characteristic that is effective for preventing it substantially from increasing its absorption within an ultraviolet region due to ultraviolet ray irradiation. Also disclosed are a silica glass article or a glass fiber produced according to the manufacturing process.

Abstract: In a single mode optical fiber employed in an optical fiber coupler, letting r be the radial distance from the optical axis center, &Dgr;n(r) be the relative refractive index difference at the position r within a core portion with reference to the refractive index of a cladding portion placed about the core portion, &Dgr;npeak be the peak value of the relative refractive index difference &Dgr;n(r) at the position rpeak, and a be the core radius, the relative refractive index difference &Dgr;n (r) satisfies the relationship of &Dgr;n(r)≦&Dgr;npeak[1−(r/a)3] in the range of rpeak≦r≦a; and the refractive index of the cladding portion gradually decreases outward in its radial direction.

Abstract: In an optical fiber of this invention, the MFD is increased to effectively suppress the influence of nonlinear optical effects. A method of manufacturing the optical fiber effectively prevents bubble occurrence in a transparent preform, deformation of the preform, and flaws on the preform surface during the manufacture. The optical fiber has, from its center to the peripheral portion, a first core having a first refractive index n1, a second core having a second refractive index n2 (<n1), a first cladding having a third refractive index n3 (<n2), and a second cladding having a fourth refractive index n4 (>n3, <n2). The outer diameter of the second core is set to be 25 to 40 &mgr;m. Specifically, the refractive indices of the first and second claddings of the optical fiber preferably increase in the radial direction from the inner side thereof to the peripheral side thereof.

Abstract: A process of manufacturing a silica glass article comprising the steps of: (1) irradiating a silica glass article with electromagnetic waves to generate defects therein; and (2) immersing the thus irradiated silica glass article in an atmosphere comprising a hydrogen gas, thereby providing the resulting silica glass article with a characteristic that is effective for preventing it substantially from increasing its absorption within an ultraviolet region due to ultraviolet ray irradiation. Also disclosed are a silica glass article or a glass fiber produced according to the manufacturing process.

Abstract: In a single mode optical fiber employed in an optical fiber coupler, letting r be the radial distance from the optical axis center, &Dgr;n (r) be the relative refractive index difference at the position r within a core portion with reference to the refractive index of a cladding portion placed about the core portion, &Dgr;npeak be the peak value of the relative refractive index difference &Dgr;n (r) at the position rpeak, and a be the core radius, the relative refractive index difference &Dgr;n (r) satisfies the relationship of &Dgr;n (r)≦&Dgr;npeak [1−(r/a)3] in the range of rpeak≦r≦a; and the refractive index of the cladding portion gradually decreases outward in its radial direction.

Abstract: The present invention relates to a dispersion-shifted optical fiber which comprises a structure for effectively eliminating the causes of deterioration in characteristics at the making stage thereof and is suitable for wavelength division multiplexing transmission. In the dispersion-shifted optical fiber according to the present invention, impurities to be added and the contents thereof are adjusted so as to reduce viscosity difference at each interface between individual glass regions. As a consequence of this structure, occurrence of structural irregularity and glass defect are effectively restrained in the vicinity of the interfaces between the regions.

Abstract: A process of manufacturing a silica glass article comprising the steps of: (1) irradiating a silica glass article with electromagnetic waves to generate defects therein; and (2) immersing the thus irradiated silica glass article in an atmosphere comprising a hydrogen gas, thereby providing the resulting silica glass article with a characteristic that is effective for preventing it substantially from increasing its absorption within an ultraviolet region due to ultraviolet ray irradiation. Also disclosed are a silica glass article or a glass fiber produced according to the manufacturing process.

Abstract: In an optical fiber of this invention, the MFD is increased to effectively suppress the influence of nonlinear optical effects. A method of manufacturing the optical fiber effectively prevents bubble occurrence in a transparent preform, deformation of the preform, and flaws on the preform surface during the manufacture. The optical fiber has, from its center to the peripheral portion, a first core having a first refractive index n1, a second core having a second refractive index n2 (<n1), a first cladding having a third refractive index n3 (<n2), and a second cladding having a fourth refractive index n4 (>n3, <n2). The outer diameter of the second cladding is set to be 25 to 40 &mgr;m. Specifically, the refractive indices of the first and second claddings of the optical fiber preferably increase in the radial direction from the inner side thereof to the peripheral side thereof.

Abstract: A dispersion-shifted fiber includes structure configured to effectively reduce nonlinear optical effects and transmission loss caused by structural mismatching. A core region in the dispersion-shifted fiber includes an inner core and an outer core, which are both glass areas. The inner core is doped with a predetermined amount of fluorine, having an average relative refractive index difference &Dgr;n1. The outer core is disposed between the inner core and the cladding region and is doped with a predetermined amount of germanium dioxide, having an average relative refractive index difference &Dgr;n2(&Dgr;n2>&Dgr;n1), such that the viscosity ratio between the inner core and the outer core at a drawing temperature is set within a predetermined range, thereby effectively restraining structural mismatching from occurring at the boundary between these glass regions.

Abstract: A process of manufacturing a silica glass article comprising the steps of: (1) irradiating a silica glass article with electromagnetic waves to generate defects therein; and (2) immersing the thus irradiated silica glass article in an atmosphere comprising a hydrogen gas, thereby providing the resulting silica glass article with a characteristic that is effective for preventing it substantially from increasing its absorption within an ultraviolet region due to ultraviolet ray irradiation. Also disclosed are a silica glass article or a glass fiber produced according to the manufacturing process.

Abstract: A method for producing an oxide glass thin film is provided, in which volatilization of additives in a porous film from which the thin film is formed is effectively suppressed, and which the oxide glass film has a desired arrangement of refractive index with a low optical loss. According to this method, glass fine particles mainly containing SiO.sub.2 with a first additive are deposited on a substrate to form a porous thin film. A gas containing a second additive is supplied to a first chamber and heated to a first predetermined temperature profile to provide a heated gas containing an oxide. After disposing the substrate in a second chamber communicated with the first chamber, the substrate is heated to make the deposited porous glass into transparent glass while controlling a temperature in the second chamber according to a second temperature profile.

Abstract: A process for forming film structure using Flame Hydrolysis Deposition (FHD) in which (1) glass soot is deposited on a substrate via FHD to form a first porous vitreous layer having a first bulk density, (2) a second porous vitreous layer having a second bulk density that is larger than the first bulk density is formed from a portion of the first porous vitreous layer, and (3) a third porous vitreous layer having a third bulk density is formed by depositing glass soot containing a refractive index increasing dopant on the second porous vitreous layer by FHD. The first, second and third porous vitreous layers are then heated to form an undercladding layer and a core layer, the undercladding layer being formed from the first and second porous vitreous layers and the core layer being formed from the third porous vitreous layer.

Abstract: In the method for forming an optical waveguide according to this invention, an optical waveguide comprising a core of quartz as a main component, and a cladding layers surrounding the core is formed by deposition of glass fine particles by flame hydrolysis deposition and vitrifying the glass fine particle layers. This method includes a step of transiently increasing a feed amount of phosphorus to a flame burner in forming glass fine particle layers to be the cladding layers. Feeding phosphorus in this step for the first time after a glass fine particle layer is deposited without feeding phosphorus to the flame burner, whereby generation of foreign objects near the core dan be suppressed.

Abstract: A method of producing an oxide glass thin film includes a process to obtain a transparent glass film, in which volatilization of additives in a porous film deposited is effectively suppressed and which can provide an oxide glass thin film having a desired arrangement of refractive index with a low optical loss. The method is for producing an oxide glass thin film, in which glass fine particles mainly containing SiO.sub.2 with additives are deposited on a substrate to form a porous thin film and then heated to form a transparent glass film. In the method, vapor of oxides of additive components is mixed in an atmosphere in which the porous thin film is heated to form the transparent glass film, whereby stopping the volatilization of the additives in the porous film deposited, preventing diffusion of the additives added to a core layer, and preventing the volatilization of glass transition temperature lowering components of additives (P.sub.2 O.sub.5, B.sub.2 O.sub.3, GeO.sub.2, etc.).

Abstract: An object of this invention is to provide an optical filter which has higher mass-producibility and economy. This feature can be realized by doped a rare earth element into the region made of a glass material which can transmit light. In a case that Er and Tm are doped as the rare earth element into the region, a ratio .alpha..sub.Er /.alpha..sub.Tm between a contribution .alpha..sub.Er of Er to attenuation and a contribution .alpha..sub.Tm of Tm to attenuation is set in a range from about 1 to 1/25 for a 1.5 .mu.m band range, whereby attenuation in this wavelength range is retained above 50 dB/m to realize required cutoff function.

Abstract: In the first step, a fuel and raw material gases are fed to burner while flames from the burner scan a Si substrate. Synthesized fine glass particles are deposited on the substrate to form a first porous vitreous layer to be an under cladding layer. In the second step, the first porous vitreous layer is heated by the flames. A bulk density of an upper part of the first porous vitreous layer is raised to 0.3 g/cm.sup.3. Having a raised bulk density, this upper part functions as a shield layer against GeO.sub.2. In the third step, a second porous vitreous layer, to be a core layer, is deposited uniformly on the first porous vitreous layer. In the fourth step, the first and the second porous vitreous layers are sintered. In this case, the shield layer with a higher bulk density hinders the GeO.sub.2 component which has evaporated from the second porous vitreous layer from diffusing into the first porous vitreous layer.

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 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.