Preparation of halogen-doped silica is described. The preparation includes doping silica with high halogen concentration and sintering halogen-doped silica to a closed-pore state in a gas-phase environment that has a low partial pressure of impermeable gases. Impermeable gases are difficult to remove from halogen-doped fiber preforms and lead to defects in optical fibers drawn from the preforms. A low partial pressure of impermeable gases in the sintering environment leads to a low concentration of impermeable gases and a low density of gas-phase voids in densified halogen-doped silica. Preforms with fewer defects result.

A method for sintering of a glass preform with reduced helium gas consumption and with reduced cost without affecting any optical or other parameter of the fiber obtained from glass preform processed in this way. The method includes a first step to perform dehydration of the glass preform inside a dehydration module, a second step to perform down-feeding of the glass preform inside a sintering furnace, a third step to perform sintering of the glass preform inside the sintering furnace, a fourth step to move the glass preform in upward motion, and a fifth step to perform re-sintering of the glass preform inside the sintering furnace. Also, the glass preform undergoes dehydration for time period in range of about 20 minutes to 120 minutes. Also, dehydration of the glass preform is performed in presence of helium gas.

The present invention relates to a method of manufacturing an optical fiber preform for obtaining an optical fiber with low transmission loss. A core preform included in the optical fiber preform comprises three or more core portions, which are each produced by a rod-in-collapse method, and in which both their alkali metal element concentration and chlorine concentration are independently controlled. In two or more manufacturing steps of the manufacturing steps for each of the three or more core portions, an alkali metal element is added. As a result, the mean alkali metal element concentration in the whole core preform is controlled to 7 atomic ppm or more and 70 atomic ppm or less.

Provided is a glass fine particle deposit in which a pH of glass fine particles on a surface of the glass fine particle deposit is 5.5 or more and less than 8.5, in which a color difference ΔE*ab with respect to a white calibration plate when the surface of the glass fine particle deposit is measured by the SCI method using a spectrophotometer is 0.5 or more and less than 5. Provided is a method for manufacturing a glass preform including: manufacturing a transparent glass preform by heating a glass fine particle deposit in which a pH of glass fine particles on a surface of the glass fine particle deposit is 5.5 or more and less than 8.5; and measuring the surface of the deposit by the SCI method using a spectrophotometer and determining whether a color difference ΔE*ab with respect to a white calibration plate is 5 or more.

The present disclosure provides a method for modification of surface of an initial optical fiber preform. The initial optical fiber preform is manufactured using at least one preform manufacturing process. The surface of the initial optical fiber preform is treated with 50-70 liters of chlorine per square meter of the surface of the initial optical fiber preform. The surface of the initial optical fiber preform is flame polished using a flame polishing module. The treatment of the surface of the initial optical fiber preform with chlorine and flame polishing of the surface of the initial optical fiber preform collectively converts the initial optical fiber preform into a modified optical fiber preform.

Provided is a method of fabricating an optical fiber glass base material, the method including a first step for dehydrating an optical fiber porous base material while causing a gas that includes at least a halogen or argon to distribute within a quartz core tube that accommodates the optical fiber porous base material; a second step for, after the first step, at least partially ventilating within the quartz core tube by causing a gas having helium as a main component to distribute within the quartz core tube; and a third step for, after the second step, transparently vitrifying the optical fiber porous base material while causing the gas having helium as a main component to distribute within the quartz core tube.

Methods for manufacturing fluorine-doped glass preforms for optical fibers are disclosed. An exemplary method includes exposing a soot preform to an atmosphere containing a fluorine-containing gas in a first elongated chamber of a first furnace. The first elongated chamber typically has a single isothermal hot zone, which may be maintained at a doping temperature of about 800° C. to 1200° C., to obtain a fluorine-doped soot preform. The exemplary method further includes dehydrating the fluorine-doped soot preform by exposing it to an atmosphere containing a chlorine-containing gas in a second elongated chamber of a second furnace. The second elongated chamber typically has an upper hot zone, which may be maintained at a dehydration temperature of about 1000° C. to 1350° C., and a lower hot zone, which may be maintained at a consolidation temperature of about 1500° C. to 1650° C. Dehydration of the fluorine-doped soot preform typically occurs in the upper hot zone of the second furnace. The exemplary method further includes consolidating the fluorine-doped soot preform within the lower hot zone of the second furnace to form a fluorine-doped glass preform.

A multicore optical fiber comprises a common cladding and a plurality of core portions disposed in the common cladding. Each of the core portions includes a central axis, a core region extending from the central axis to a radius r.sub.1, the core region comprising a relative refractive index Δ.sub.1, an inner cladding region extending from the radius r.sub.1 to a radius r.sub.2, the inner cladding region comprising a relative refractive index Δ.sub.2, and a depressed cladding extending from the radius r.sub.2 to a radius r.sub.3, the depressed cladding region comprising a relative refractive index Δ.sub.3 and a minimum relative refractive index Δ.sub.3 min. The relative refractive indexes may satisfy Δ.sub.1>Δ.sub.2>Δ.sub.3 min. The mode field diameter of each core portion may greater than or equal to 8.2 μm and less than or equal to 9.5 μm.

To provide a method of sintering an optical fiber porous glass base material, capable of sufficient dehydration and reducing a transmission loss caused by residual moisture by efficiently transferring heat from the heater to the base material during a process in dehydration/sintering for an optical fiber porous glass base material, a porous glass base material having a heat shield plate installed in a vicinity of a lower end is vertically inserted into a furnace core tube provided with a heater along an outer circumference, and heating using the heater is performed. The heat shield plate has an outer diameter which is 70% or larger than a diameter of the porous glass base material and smaller than an inner diameter of the furnace core tube.

A method of forming an optical fiber, including: exposing a soot core preform to a dopant gas at a pressure of from 1.5 atm to 40 atm, the soot core preform comprising silica, the dopant gas comprising a first halogen doping precursor and a second halogen doping precursor, the first halogen doping precursor doping the soot core preform with a first halogen dopant and the second halogen precursor doping the soot core preform with a second halogen dopant; and sintering the soot core preform to form a halogen-doped closed-pore body, the halogen-doped closed-pore body having a combined concentration of the first halogen dopant and the second halogen dopant of at least 2.0 wt %.