An optical fiber comprises, from a center to a periphery, a fiber core of undoped silica; a cladding layer; and a coating of polyacrylate, wherein the fiber core has a radius of 5 to 7 m and an ellipticity of less than 1.5%, the cladding layer with an ellipticity of less than 0.4% comprises inner, intermediate, and outer cladding layers, the inner cladding layer being doped with fluorine of 5 to 12 m thickness, and refractive index difference to fiber core of 0.4 to 0.2%, the outer cladding layer being undoped quartz of 25 to 45 m thickness, and the coating comprises an inner coating of 25 to 40 m thickness, and an outer coating of 25 to 35 m thickness and an ellipticity of less than 2%. The optical fiber has high durability and large effective transmission area, a method and system for preparing such optical fiber are also disclosed.

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.

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 method for manufacturing an optical fiber including a glass fiber and a primary resin layer, the method includes: applying an ultraviolet curable resin composition; and forming the primary resin layer by curing the resin composition by ultraviolet irradiation reactor(s), wherein a number N of the ultraviolet irradiation reactor(s), a ratio of normalized output ? for each of the ultraviolet irradiation reactor(s), and an irradiation time t (sec) of each of the ultraviolet irradiation reactor(s) in the forming of the primary resin layer satisfy 6.00?10.sup.?5?N*?*t?2.88?10.sup.?1, wherein a concentration C [mass %] of the photoinitiator in the forming of the primary resin layer is in accordance with formula (1):

[00001]$\begin{array}{cc}C=C0*\exp \left(-N*?*\frac{l}{?}*k\right)*\exp \left(-N*?*\frac{L}{v}*\mathrm{kD}\right)+C0*\left(1-\exp \left(-?*\frac{\mathrm{lk}+\mathrm{LkD}}{v}\right)\right)*\left(1-{\left(1+N*\frac{l}{v}*4\mathrm{kR}*C0*\left(1-\exp \left(-?*\frac{\mathrm{lk}+\mathrm{LkD}}{v}\right)\right)\right)}^{-1}\right)& \left(1\right)\end{array}$

wherein the initiation reaction rate constant k is from 20 to 100, wherein the dark reaction rate constant kD is 0?kD?30, and wherein the reverse reaction rate constant kR is 0?kR?10.

An optical fiber production system includes an annealing furnace having a furnace inlet, a furnace outlet, and a process tube extending between the furnace inlet and the furnace outlet, the process tube having a process tube wall and a heating zone including at least one heating element. The optical fiber production system also includes a gas distribution assembly fluidly coupled to the furnace outlet and structurally configured to induce gas flow from the gas distribution assembly into the process tube such that gas flows within the process tube in an upflow direction.

An optical fiber production method includes: drawing an optical fiber from an optical fiber preform in a drawing furnace; cooling the optical fiber in an annealing furnace; and delivering the optical fiber into the annealing furnace, and controlling a temperature difference between a temperature of the optical fiber and a fictive temperature of glass forming a core included in the optical fiber to be higher than 20 C. and lower than 100 C.

An optical fiber production method includes: drawing an optical fiber from an optical fiber preform; and cooling the optical fiber. When in the cooling process, the optical fiber is passed through a plurality of annealing furnaces and Equation (1) is held. A time constant of relaxation of a structure of glass forming a core in the optical fiber is (T.sub.n). A temperature of the optical fiber at a point in time when the optical fiber is delivered into an nth annealing furnace from an upstream side is T.sub.n. A fictive temperature of glass forming the core at the point in time when the optical fiber is delivered is T.sub.fn. A fictive temperature of glass forming the core after a lapse of time t from the point in time when the optical fiber is delivered is T.sub.f.

20 C.<T.sub.fT.sub.n=(T.sub.fnT.sub.n)exp(t/T(T.sub.n))<100 C.(1)

Optical fibers having low fictive temperature and methods of making such fibers are described. Management of the cooling rate of an optical fiber during fiber draw permits control over the fictive temperature of the fiber. Non-monotonic cooling rates are shown to promote reductions in fiber fictive temperature. The non-monotonic cooling includes slower cooling rates in upstream portions of the process pathway and faster cooling rates in downstream portions of the process pathway. Reduction in fiber fictive temperature is achieved by controlling the ambient temperature of the fiber to slow the cooling rate of the fiber in upstream portions of the process pathway that correspond to the fiber temperature regime in which the fiber viscosity is sufficiently low to permit efficient structural relaxation. Increases in cooling rate in downstream portions of the process pathway permit adjustment of fiber temperature as needed to meet entrance temperature requirements of downstream processing units. Lower fiber fictive temperature and lower fiber attenuation are achieved at faster draw speeds through non-monotonic cooling of fiber temperature.