A method for manufacturing an optical fiber preform includes: producing a core preform including a core portion made of transparent glass and a first cladding layer obtained by adding fluorine to the core portion; and forming, on an outer periphery of the first cladding layer, a second cladding layer made of glass having a refractive index higher than that of the first cladding layer. Further, a refractive index profile is formed in the first cladding layer due to a fluorine concentration profile, the refractive index profile being provided at least near a boundary surface with the second cladding layer and having a profile such that a refractive index difference between a refractive index of the first cladding layer and a refractive index of the second cladding layer decreases in accordance with a reduction in a distance from the boundary surface with the second cladding layer.

A method for manufacturing an optical fiber preform includes: producing a core preform including a core portion made of transparent glass and a first cladding layer obtained by adding fluorine to the core portion; and forming, on an outer periphery of the first cladding layer, a second cladding layer made of glass having a refractive index higher than that of the first cladding layer. Further, a refractive index profile is formed in the first cladding layer due to a fluorine concentration profile, the refractive index profile being provided at least near a boundary surface with the second cladding layer and having a profile such that a refractive index difference between a refractive index of the first cladding layer and a refractive index of the second cladding layer decreases in accordance with a reduction in a distance from the boundary surface with the second cladding layer.

An optical fiber manufacturing method includes: coating an outer periphery of a bare optical fiber with a resin before curing by a coating device; and curing the resin with a coating curing device. The following equations are satisfied: tsin >T1 tan and =tan.sup.1 (d/L), where T1 is a tension in the upstream of the coating device, t is the shear force applied to the bare optical fiber by the resin, d is the design maximum value of a deviation amount of an entry position of the bare optical fiber into the resin in the coating device with respect to the center axis of the die hole of the coating device, and L is the contact length between the resin and the bare optical fiber in the coating device along the center axis.

An optical fiber manufacturing method includes: coating an outer periphery of a bare optical fiber with a resin before curing by a coating device; and curing the resin with a coating curing device. The following equations are satisfied: tsin >T1 tan and =tan.sup.1 (d/L), where T1 is a tension in the upstream of the coating device, t is the shear force applied to the bare optical fiber by the resin, d is the design maximum value of a deviation amount of an entry position of the bare optical fiber into the resin in the coating device with respect to the center axis of the die hole of the coating device, and L is the contact length between the resin and the bare optical fiber in the coating device along the center axis.

A light irradiation device includes at least one irradiation unit including a reflective surface which is disposed in a concave inner surface formed to have a substantially arc shape and into which a wire member is inserted, and a light source which is configured to emit light toward the wire member and is disposed so as to face the reflective surface in a direction of an optical axis of the emitted light, and an insertion portion configured to interiorly form an insertion path for inserting the wire member into the reflective surface. The reflective surface is disposed such that a center of the substantially arc shape is eccentric with respect to a center of the insertion path.

A light irradiation device includes at least one irradiation unit including a reflective surface which is disposed in a concave inner surface formed to have a substantially arc shape and into which a wire member is inserted, and a light source which is configured to emit light toward the wire member and is disposed so as to face the reflective surface in a direction of an optical axis of the emitted light, and an insertion portion configured to interiorly form an insertion path for inserting the wire member into the reflective surface. The reflective surface is disposed such that a center of the substantially arc shape is eccentric with respect to a center of the insertion path.

A high-density optical fiber ribbon is formed by two or more cladding-strengthened glass optical fibers each having an outer surface and that do not individually include a protective polymer coating. A common protective coating substantially surrounds the outer surfaces of the two or more cladding-strengthened glass optical fibers so that the common protective coating is common to the two or more cladding-strengthened glass optical fibers. A fiber ribbon cable is formed by adding a cover assembly to the fiber ribbon. A fiber ribbon interconnect is formed adding one or more optical connectors to the fiber ribbon or fiber ribbon cable. Optical data transmission systems that employ the fiber ribbon to optically connect to a photonic device are also disclosed. Methods of forming the cladding-strengthened glass optical fibers and the high-density optical fiber ribbons are also disclosed.

The present disclosure provides coating compositions that can be cured at fast rates as well as coatings and cured products formed from the coating compositions. The coating compositions include an acylgermane photoinitiator that leads to fast cure speeds. The coating compositions include primary coating compositions and secondary coating compositions. The coating compositions can be cured to form primary and secondary coatings of optical fibers. The primary coatings feature low Young's modulus and high tear strength. The primary coatings provide good microbending performance and are resistant to defect formation during the fiber draw process and subsequent handling operations. The secondary coatings feature high Young's modulus and good puncture resistance.

Various examples and systems are provided for enhancing optical fibers for sensing temperature and/or strain at low temperatures (e.g., 1.8K to 77K or lower). An enhanced optical fiber for distributed sensing can comprise a core, a cladding surrounding the core, and a coating surrounding the cladding. A coefficient of thermal expansion (CTE) of the coating is greater than a CTE of silica and/or a Young's modulus (E) of the coating is greater than an E of silica.

A photoirradiation device includes an insertion path for inserting a wire rod; a first reflector having a circular arc shape centered on a point shifted from a center of the insertion path by a first distance, one side of the first reflector facing the insertion path being a reflective surface; a second reflector disposed adjacent open edges of the first reflector and having a circular arc shape centered on a point shifted from the center of the insertion path by a second distance that is different from the first distance, one side of the second reflector facing the insertion path being a reflective surface; and a light source that is positioned on an opposite side of the insertion path from the first reflector and that projects light toward the wire rod.