Abstract: In the process comprising manufacturing a glass fine particle deposit (soot) by injecting glass fine particles generated with a burner for glass fine particle synthesis to a starting material rotating around its central axis as an axis of rotation; and sintering the glass fine particle deposit to vitrify it into transparent glass by suspending and heating the glass fine particle deposit in a furnace core tube, it is characterized that a product of a time period (min) during which a part of the glass fine particle deposit is heated in a heating zone in the furnace core tube and a linear speed (m/min) of sintering gas flowing in the furnace core tube is 15.5 (m) or more.

Abstract: A method of measuring a diameter of a core portion of an optical fiber preform including the core portion having a relatively high refractive index and a clad portion having a relatively low refractive index. The method includes applying parallel light to the optical fiber preform, and measuring the diameter of the core portion from an image captured by receiving the light having transmitted through the optical fiber preform.

Abstract: The present invention provides an optical fiber with improved optical properties such as zero dispersion wavelength by suppressing the volatilization of dopant materials such as germanium dioxide and optimizing the refractive index distribution by adjusting the setting position of the core portion burner for deposition in a larger optical fiber preform. An optical fiber preform includes a core portion with a relatively high refractive index and a clad portion with a relatively low refractive index, wherein a position having a value of 45% of a refractive index difference between a center of the core portion and the clad portion is a boundary rcore (mm) between the core portion and the clad portion; and when a radius position r at which a refractive index difference with the clad portion being a maximum value is rside (mm), rside/rcore is 0.745 to 1.

Abstract: An optical fiber preform manufacturing apparatus comprising a seal member, wherein the seal member is attached to a flange portion formed in an open portion of a reaction chamber into which a burner is inserted, the seal member includes a first sheet that is flexible and includes an open portion that is smaller than an outer diameter of the burner, through which the burner is inserted; a second sheet having the same thickness as the first sheet and including an open portion that is larger than an outer diameter of the first sheet; and two third sheets that each include an open portion that is larger than the outer diameter of the burner and smaller than the outer diameter of the first sheet, the second sheet is arranged in the same plane as the first sheet, and the first and second sheets are sandwiched by the two third sheets.

Abstract: Provided is a method of manufacturing a porous glass deposition body for optical fiber comprising depositing silica powder on a starting member being raised and rotated by using burners with different deposition positions. With a glass raw material flow rate supplied to a core deposition burner represented by F1 and a total flow rate of glass raw material supplied to a cladding deposition burner adjacent to the core deposition burner represented by F2, during an initial deposition stage occurring before gas conditions reach a stable state, glass raw material is supplied to points at the same longitudinal position of the deposition body such that a glass raw material flow rate ratio F2/F1 is no less than 0.69 and no greater than 1.03.

Abstract: A method of measuring a diameter of a core portion of an optical fiber preform including the core portion having a relatively high refractive index and a clad portion having a relatively low refractive index. The method includes applying parallel light to the optical fiber preform, and measuring the diameter of the core portion from an image captured by receiving the light having transmitted through the optical fiber preform.

Abstract: A method is provided for producing a glass fine particle deposit by a VAD method using a core deposition burner and a cladding deposition burner disposed adjacent to the core deposition burner. The cladding deposition burner including five cylindrical tubes having different outer diameters and concentrically superimposed on one another and a group of small-diameter nozzles arranged in a ring shape in a third region from the inner side. The method includes flowing, in the cladding deposition burner, a glass raw material gas and a combustion supporting gas in a first region from the inner side, air in a second region from the inner side, a combustible gas in the third region from the inner side, a combustion supporting gas in the group of small-diameter nozzles, an inert gas in a fourth region from the inner side, and a combustion supporting gas in a fifth region from the inner side, respectively.

Abstract: A method of manufacturing an optical fiber glass base material includes storing a glass particulate deposit prepared through a vapor-phase axial deposition (VAD) method in a storage chamber, wherein a hydrogen chloride concentration in the storage chamber is maintained at 2 ppm or lower, and a humidity in the storage chamber is preferably maintained at 12 g/m3 or lower. The storage chamber has an air supply port and an exhaust port, and a gas discharged from the exhaust port is re-supplied from the supply port into the storage chamber using a blower fan. A chemical filter is provided between the exhaust port and the blower fan. A dehumidifier is preferably provided between the exhaust port and the blower fan.

Abstract: An optical fiber preform manufacturing apparatus comprising a seal member, wherein the seal member is attached to a flange portion formed in an open portion of a reaction chamber into which a burner is inserted, the seal member includes a first sheet that is flexible and includes an open portion that is smaller than an outer diameter of the burner, through which the burner is inserted; a second sheet having the same thickness as the first sheet and including an open portion that is larger than an outer diameter of the first sheet; and two third sheets that each include an open portion that is larger than the outer diameter of the burner and smaller than the outer diameter of the first sheet, the second sheet is arranged in the same plane as the first sheet, and the first and second sheets are sandwiched by the two third sheets.

Abstract: A method is provided for producing a glass fine particle deposit by a VAD method using a core deposition burner and a cladding deposition burner disposed adjacent to the core deposition burner. The cladding deposition burner including five cylindrical tubes having different outer diameters and concentrically superimposed on one another and a group of small-diameter nozzles arranged in a ring shape in a third region from the inner side. The method includes flowing, in the cladding deposition burner, a glass raw material gas and a combustion supporting gas in a first region from the inner side, air in a second region from the inner side, a combustible gas in the third region from the inner side, a combustion supporting gas in the group of small-diameter nozzles, an inert gas in a fourth region from the inner side, and a combustion supporting gas in a fifth region from the inner side, respectively.

Abstract: Provided is a method for producing a glass preform for optical fiber which suppresses occurrences of cracks, coloring and foaming in a surface layer when sintering a glass fine particle deposit to allow a production yield to be improved. A method for producing a glass preform for optical fiber comprising the steps of: spraying glass fine particles containing silicon dioxide and germanium dioxide to a starting material moving upward while rotating to produce a glass fine particle deposit; and sintering the glass fine particle deposit while relatively varying a positional relationship between a heating source and the glass fine particle deposit in a sintering apparatus to produce a transparent glass preform, wherein a germanium dioxide reducing gas is contained in an atmosphere gas in the sintering apparatus.

Abstract: In a device for producing a large-sized porous base material by a VAD process, the cracking and variation of the outer diameter of the base material are suppressed by forming a smooth tapered part, without changing the length of a non-effective part. In producing the porous base material by a VAD process, the time for a gas to reach a flow amount of the gas in a steady state from starting of the deposition is extended more in a burner that deposits glass microparticles on a layer closer to the outside of the base material.

Abstract: In a device for producing a large-sized porous base material by a VAD process, the cracking and variation of the outer diameter of the base material are suppressed by forming a smooth tapered part, without changing the length of a non-effective part. In producing the porous base material by a VAD process, the time for a gas to reach a flow amount of the gas in a steady state from starting of the deposition is extended more in a burner that deposits glass microparticles on a layer closer to the outside of the base material.

Abstract: A glass fine particle synthesis burner comprising a glass raw material gas emission path for emitting glass raw material; a ring-shaped combustible gas emission path for emitting combustible gas arranged outside the glass raw material emission path; a ring-shaped combustion aiding gas emission path for emitting combustion aiding gas arranged outside the combustible gas emission path; and small diameter nozzles for emitting the combustion aiding gas within the combustible gas emission path. In a cross section of the glass fine particle synthesis burner formed by cleaving orthogonal to a central axis thereof, when the glass fine particle synthesis burner is divided into two regions by a predetermined straight line passing through a center of the glass fine particle synthesis burner, a total area of the small diameter nozzles in one of the regions is greater than a total area of the small diameter nozzles in the other region.

Abstract: A glass fine particle synthesis burner comprising a glass raw material gas emission path for emitting glass raw material; a ring-shaped combustible gas emission path for emitting combustible gas arranged outside the glass raw material emission path; a ring-shaped combustion aiding gas emission path for emitting combustion aiding gas arranged outside the combustible gas emission path; and small diameter nozzles for emitting the combustion aiding gas within the combustible gas emission path. In a cross section of the glass fine particle synthesis burner formed by cleaving orthogonal to a central axis thereof, when the glass fine particle synthesis burner is divided into two regions by a predetermined straight line passing through a center of the glass fine particle synthesis burner, a total area of the small diameter nozzles in one of the regions is greater than a total area of the small diameter nozzles in the other region.

Abstract: Provided is a method of manufacturing a porous glass deposition body for optical fiber comprising depositing silica powder on a starting member being raised and rotated by using burners with different deposition positions. With a glass raw material flow rate supplied to a core deposition burner represented by F1 and a total flow rate of glass raw material supplied to a cladding deposition burner adjacent to the core deposition burner represented by F2, during an initial deposition stage occurring before gas conditions reach a stable state, glass raw material is supplied to points at the same longitudinal position of the deposition body such that a glass raw material flow rate ratio F2/F1 is no less than 0.69 and no greater than 1.03.

Abstract: To provide a method for manufacturing a porous glass deposition body for optical fiber without causing deposition unevenness or decreasing the yield, provided is a method of manufacturing a porous glass deposition body by blowing glass fine particles generated from a plurality of burners for glass fine particle synthesis onto a starting member that is moved vertically and rotated on a rotational axis that is a central axis of the starting member. The burners are arranged such that the central axis of each burner shares a plane with the rotational axis of the starting member, and at least two of the planes in which the central axis of one of the burners and the rotational axis of the starting member are arranged form a prescribed angle.

Abstract: A method of manufacturing a fluorine-containing optical fiber base material through a sintering process includes dehydrating a porous glass stack by heating it under a chlorine-based gas atmosphere, adding fluorine into the porous glass stack by heating it under a fluorine source gas atmosphere, and making the porous glass stack transparent by heating it under a fluorine source gas atmosphere at a higher temperature than a temperature at which the porous glass stack is heated in the adding. Here, process temperatures in the dehydrating, adding and making are T1, T2 and T3 (K) respectively, concentrations of the fluorine source gas in the adding and making are C2 and C3 (%) respectively, a parameter Q is represented by the formula: Q=C2×exp(?T2/T1)+C3×exp(?T2/T1), and the process temperatures and the concentrations of the fluorine source gas satisfy the relation Q>0.14.

Abstract: Provided is an optical fiber including: a core at a center thereof; a first cladding adjacent to the core to cover a circumference of the core; and a second cladding adjacent to the first cladding to cover a circumference of the first cladding, where 0.35%?(?1??2)?0.65%, 0.30%??1?0.55%, ?0.20%??2??0.05%, 0.22?a/b?0.34, and 4?b?|?2|?10 hold, and loss increase resulting when the optical fiber is wound on a mandrel having a diameter of 20 mm is 0.

Abstract: Provided is an optical fiber including: a core at a center thereof; a first cladding adjacent to the core to cover a circumference of the core; and a second cladding adjacent to the first cladding to cover a circumference of the first cladding, where 0.35%?(?1??2)?0.65%, 0.30%??1?0.55%, ?0.20%??2??0.05%, 0.22?a/b?0.34, and 4?b?|?2|?10 hold, and loss increase resulting when the optical fiber is wound on a mandrel having a diameter of 20 mm is 0.