An optical fiber production method includes: drawing 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. While the optical fiber is cooled, temperatures of the annealing furnaces are set such that the temperature difference is within a range between and including an upper limit and a lower limit of a temperature difference between a temperature of the optical fiber and a fictive temperature of glass constituting a core of the optical fiber at which an increase of a transmission loss of the optical fiber when the fictive temperature of the glass is decreased is less than 0.001 dB/km.

A method of heating an optical fiber, the method including flowing gas from a common gas channel into one or more gas outlets of a burner, the common gas channel encircling an aperture of the burner. The method further including igniting the gas to form a flame and heating the fiber with the flame as the fiber passes through the aperture. The one or more gas outlets opening into the aperture such that each gas outlet has a gas outlet bore terminating at an inward-facing wall of the burner that defines the aperture. And the gas outlet bore being oriented at an angle .sub.1 defined between the gas outlet bore and the inward-facing wall of the burner, downstream of the gas outlet bore, that is greater than or equal to 10 degrees and less than or equal to 70 degrees.

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.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.

Methods, apparatuses and systems of manufacturing an optical fiber are disclosed herein. The methods may include heating an optical preform in a draw furnace, drawing an optical fiber from the optical preform, cooling the optical fiber with a slow cooling device, and annealing the optical fiber by passing the optical fiber through an RF plasma heating apparatus.

A system and method for processing an optical fiber includes a treatment device disposed downstream of a furnace and including a treating zone. The treating zone includes a fiber inlet and fiber outlet and is configured to cool the optical fiber at a reduced pressure below ambient pressure and at a slow cooling rate less than an ambient cooling rate. A nozzle assembly is disposed at one or more of the fiber inlet, the fiber outlet, upstream of the treating zone, and downstream of the treating zone. The nozzle assembly includes multiple baffle plates defining a number of nozzle chambers, each nozzle chamber having a nozzle chamber pressure, wherein each baffle plate includes an orifice having a predetermined effective orifice diameter through which the optical fiber passes. Each nozzle chamber is configured to sequentially change a nozzle chamber pressure between the reduced pressure and ambient pressure.

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 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 method for manufacturing an optical fiber is disclosed. The method for manufacturing an optical fiber includes: drawing an optical fiber by heating an optical fiber preform inside a drawing furnace into which a first gas is introduced; and annealing the optical fiber by causing the optical fiber to pass through an annealing furnace disposed downstream of the drawing furnace and adjusted to a temperature lower than a temperature at which the optical fiber preform is heated. In the annealing, a second gas having a lower heat conductivity than the first gas is introduced into the annealing furnace through one or more gas introduction ports such that a total flow rate becomes 3 slm or higher, and a flow rate of the second gas per gas introduction port is adjusted to 30 slm or lower.

A non-contact direction changer includes: a guide groove that guides an optical fiber and changes a direction of advancement of the optical fiber from a first direction to a second direction; a bottom ejection opening at a bottom of the guide groove; and one or more side ejection openings on at least one of opposite side surfaces of the guide groove. A fluid is ejected into the guide groove through the bottom ejection opening. A fluid is ejected into the guide groove through the one or more side ejection openings.