An eccentric state determining method which is performed by a controller and for determining a state of eccentricity of a coating of a glass fiber with respect to the glass fiber. The coating is formed around the glass fiber. The method includes acquiring measurement values for an outer diameter of the optical fiber at positions along a longitudinal direction of the optical fiber, calculating a standard deviation of the measurement values, and determining the state of the eccentricity based on the standard deviation.

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 κ of the gas being not greater than 1.5×10.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.

Described herein are coated optical fibers including an optical fiber portion, wherein the optical fiber portion includes a glass core and cladding section that is configured to possesses certain mode-field diameters and effective areas, and a coating portion including a primary and secondary coating, wherein the primary coating is the cured product of a composition that possesses specified liquid glass transition temperatures, such as below −82° C., and/or a viscosity ratios, such as between 25° C. and 85° C., of less than 13.9. Also described are radiation curable coating compositions possessing reduced thermal sensitivity, methods of coating such radiation curable coating compositions to form coated optical fibers, and optical fiber cables comprising the coated optical fibers and/or radiation curable coating compositions elsewhere described.

An optical fiber preform includes: a columnar portion having an approximately constant radius of r; and a taper portion located adjacent to the columnar portion in a lengthwise direction and having a radius decreasing along the lengthwise direction. The taper portion includes: a first taper portion including a portion having a radius varying between 0.9r and 0.6r; and a second taper portion including a portion having a radius varying between 0.4r and 0.15r. A diameter of the first taper portion in the portion having the radius varying between 0.9r and 0.6r decreases so as to form a maximum angle θ1 between 40 degrees and 60 degrees with respect to the columnar portion, a diameter of the second taper portion in the portion having the radius varying between 0.4r and 0.15r decreases so as to form an average angle θ2 between 5 degrees and 30 degrees with respect to a central axis in the lengthwise direction, and a volume of the taper portion is smaller than or equal to 45% of a volume of a column having a same outer diameter as a maximum outer diameter of the taper portion and having a same length as the taper portion.

An optical fiber preform includes: a core formed of silica glass which does not contain Ge, wherein the core has at least one of characteristics in spectrometry of (1) an absorption peak is present at a wavelength of 240 nm to 255 nm, and (2) a wavelength at which an ultraviolet transmittance is 50% or lower is longer than 170 nm.

To restrict deterioration of non-circularity in a constricted portion of an optical fiber preform, provided is an optical fiber preform manufacturing method including introducing inert gas along a surface of the optical fiber preform, causing the inert gas to circulate around the optical fiber preform with an axis of the optical fiber preform in a longitudinal direction as a center, and heating the optical fiber preform in an inert gas environment. In this manufacturing method, the inert gas may be introduced in a direction parallel to a tangent line of the optical fiber preform in a plane orthogonal to the axis.

A method for temperature measurement includes measuring intensities of two adjacent wavelengths emitted from a heated optical fiber and calculating the thermal population distribution between associated energy levels.

Aspects of the embodiments are directed to systems and methods for forming an optical fiber in a low gravity environment, and an optical fiber formed in a low gravity environment. The system can include a preform holder configured to secure a preform; a heating element secured to a heating element stage and residing adjacent the preform holder; a heating element stage motor configured to move the heating element stage; a tension sensor; a spool; a spool tension motor coupled to the spool and configured to rotate the spool; and a control system communicably coupled to the heating element stage motor and the spool tension motor and configured to control the movement of the heating element stage based on a rotational speed of the spool. The optical fiber can include a fluoride composition, such ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN), and can be characterized by an insertion loss in a range from 13 dB/1000 km to 120 dB/1000 km.

An optical fiber manufacturing method includes: melting and drawing an optical fiber preform to form a glass fiber; cooling the glass fiber while inserting the glass fiber into a tubular slow-cooling device from an inlet end toward an outlet end thereof, and lowering an inner wall temperature of the slow-cooling device below a temperature of the glass fiber and providing a pressure gradient in which a pressure increases in a direction from the inlet end toward the outlet end inside the slow-cooling device when cooling the glass fiber, wherein the average pressure change dP/dL in a moving direction of the glass fiber inside the slow-cooling device satisfies the following Formula (1) when the tube inner diameter of the slow-cooling device is defined as D [m] and the length of an internal space of the slow-cooling device in the moving direction of the glass fiber is defined as L [m].

(πD.sup.2/4)×dP/dL≦0.03  (1)

A method of controlling the temperature of an optical fiber is provided that includes the steps of: providing an energy transfer member configured to accept or provide thermal energy, the energy transfer member defines an energy transfer surface; passing an optical fiber proximate the energy transfer member such that a gap is defined between the optical fiber and the energy transfer surface; and transferring thermal energy between the optical fiber and the energy transfer member via conduction across the gap.