An optical fiber with low fictive temperature along with a system and method for making the optical fiber are provided. The system includes a reheating stage that heats the fiber along the process pathway to a temperature sufficient to lower the fictive temperature of the fiber by relaxing the glass structure and/or driving the glass toward a more nearly equilibrium state. The fiber is drawn from a preform, conveyed along a process pathway, cooled and subsequently reheated to increase the time of exposure of the fiber to temperatures conducive to lowering the fictive temperature of the fiber. The process pathway may include multiple reheating stages as well as one or more fiber-turning devices.

A single mode optical fiber having a core made from silica and less than or equal to about 6.5 weight % germania and having a maximum relative refractive index .sub.1MAX. The optical fiber also has an inner cladding surrounding the core and having a minimum relative refractive index .sub.2MIN. A difference between a softening point of the core and a softening point of the inner cladding is less than or equal to about 20 C., and .sub.1MAX>.sub.2MIN. The single mode optical fiber may also have an outer cladding surrounding the inner cladding made from silica or SiON. The outer cladding has a maximum relative refractive index .sub.3MAX, and .sub.3MAX>.sub.2MIN. A method for manufacturing an optical fiber includes providing a preform to a first furnace, the preform, drawing the optical fiber from the preform, and cooling the drawn optical fiber in a second furnace.

An optical fiber with low fictive temperature along with a system and method for making the optical fiber are provided. The system includes a reheating stage that heats the fiber along the process pathway to a temperature sufficient to lower the fictive temperature of the fiber by relaxing the glass structure and/or driving the glass toward a more nearly equilibrium state. The fiber is drawn from a preform, conveyed along a process pathway, cooled and subsequently reheated to increase the time of exposure of the fiber to temperatures conducive to lowering the fictive temperature of the fiber. The process pathway may include multiple reheating stages as well as one or more fiber-turning devices.

The present disclosure provides the installation of an apparatus for cooling a manufactured glass rod. The apparatus has at least two cooling chambers arranged along the glass strand for sectional cooling of the glass strand. A gaseous cooling medium is either blown into the cooling chamber or sucked out of the cooling chambers. The glass strand is passed through each cooling chamber, with an orifice provided at each of the pass-through points, whose opening is larger than the cross-section or diameter of the glass strand. As a result, an annular gap forms between the opening and the surface of the glass strand, so that a turbulent flow of the gaseous cooling medium is generated, which enables a high cooling rate.

An optical fiber production method includes: drawing an optical fiber from an optical fiber preform in a drawing furnace; and cooling the optical fiber. The optical fiber is passed through a plurality of annealing furnaces while the optical fiber is cooled. Equation (1) is held in a given period during the cooling, where a time constant of relaxation of a structure of glass forming a core included in the optical fiber is defined as ?(T), a temperature of the optical fiber at a point in time during the cooling is defined as T, a fictive temperature of glass forming the core at the point in time is defined as T.sub.f.sup.0, and a fictive temperature of glass forming the core after a lapse of time ?t from the point in time is defined as T.sub.f.

20? C.<T.sub.f?T=(T.sub.f.sup.0?T)exp(??t/?(T))<100? C.(1)

A cooling system for optical fiber drawing is used for decreasing the temperature of an optical fiber before coating, avoiding the occurrence of bubbles in a coating, ensuring a stable coating state of the optical fiber, and reducing the amount of helium gas used, being suitable for high-speed drawing. The cooling system consists of shutters of the cooling pipe; a helium gas guiding device, a cooling pipe body, a cooling water circulation and cooling device, a coating diameter control system, a cooling water pipe and a gas pipe. Several single-section cooling pipes are connected to each other by the gas intake connection devices. The outer wall of each segment of the cooling pipes is covered with a polystyrene foam thermal insulating layer, and the helium gas guiding device guides the gas within the pipe at a suitable guiding flow rate to achieve the optimal cooling effect.

There is provided a method for producing a low-loss alkali metal-doped silica core optical fiber having excellent hydrogen resistance. The method for producing the optical fiber according to the present invention includes a drawing step of drawing an optical fiber preform in a drawing furnace to produce a silica glass-based optical fiber including a core region containing an alkali metal with an average concentration of 0.5 atomic ppm or more and a cladding region that surrounds the core region and a heating step of heating the optical fiber in a heating furnace through which the optical fiber drawn from the drawing furnace passes.

According to some embodiments a method of processing an optical fiber comprises the steps of: (i) drawing the fiber at a drawing rate of at least 30 m/sec; and (ii) cooling the drawn fiber in a gas at an average cooling rate less than 5000 C./s, such that said cooling reduces the temperature of the fiber from an entering temperature in the range between 1500 C. and 1700 C. to another temperature in the range between 1200 C. and 1400 C., the gas being at a temperature between 800 C. and 1500 C.; and the thermal conductivity of the gas being not greater than 1.510.sup.4 cal/cm-s-K for at least one temperature within a range of 800 C. to 1500 C. at one atm (atmosphere) pressure absolute.

A single mode optical fiber having a core made from silica and less than or equal to about 6.5 weight % germania and having a maximum relative refractive index .sub.1MAX. The optical fiber also has an inner cladding surrounding the core and having a minimum relative refractive index .sub.2MIN. A difference between a softening point of the core and a softening point of the inner cladding is less than or equal to about 20 C., and .sub.1MAX>.sub.2MIN. The single mode optical fiber may also have an outer cladding surrounding the inner cladding made from silica or SiON. The outer cladding has a maximum relative refractive index .sub.3MAX, and .sub.3MAX>.sub.2MIN. A method for manufacturing an optical fiber includes providing a preform to a first furnace, the preform, drawing the optical fiber from the preform, and cooling the drawn optical fiber in a second furnace.

There is provided a manufacturing method for an optical fiber that easily reduces transmission losses in the optical fiber. The method includes a drawing process P1 of drawing an optical fiber from an optical fiber preform 1P in a drawing furnace 110; and a slow cooling process P3 of slowly cooling the optical fiber having been drawn in the drawing process P1 in an annealing furnace 121. The temperature of the optical fiber to be delivered into the annealing furnace 121 is a temperature of 1,300 C. or more and 1,650 C. or less. The temperature of the optical fiber to be delivered out of the annealing furnace 121 is a temperature of 1,150 C. or more and 1,400 C. less.