An optical fiber according to an embodiment has a structure capable of reducing an increase in transmission loss. The optical fiber includes a glass part extending in a direction of a central axis, and the glass part is comprised of silica-based glass, includes a core and a cladding, and has residual stress approximately uniform throughout a cross section of the glass part orthogonal to the central axis, the core having the central axis and being doped with chlorine with a mass fraction of 1% or more, the cladding surrounding the core and having a refractive index lower than a maximum refractive index of the core.

A radiation-resistant laser optical fiber preform core rod at least includes one type of activated ion (Yb.sup.3+, Er.sup.3+) and one or more types of co-doped ion (Al.sup.3+, P.sup.5+, Ge.sup.4+, Ce.sup.3+, F.sup.−), and —OD group of 16-118 ppm. Irradiation resistance of core rod glass can be effectively improved by sequentially performing pre-treatments, i.e. deuterium loading, pre-irradiation and thermal annealing on a preform core rod. Electron paramagnetic resonance test shows that, under the same radiation condition, the radiation induced color center concentration in a preform core rod treated by the method above is lower than in an untreated core rod by one or more orders of magnitude. The obtained core rod can be used for preparing a radiation-resistant rare earth-doped silica fiber, and has the advantages of high laser slope efficiency, low background loss, being able to be used stably in a vacuum environment for a long time, for example.

A radiation-resistant laser optical fiber preform core rod at least includes one type of activated ion (Yb.sup.3+, Er.sup.3+) and one or more types of co-doped ion (Al.sup.3+, P.sup.5+, Ge.sup.4+, Ce.sup.3+, F.sup.−), and —OD group of 16-118 ppm. Irradiation resistance of core rod glass can be effectively improved by sequentially performing pre-treatments, i.e. deuterium loading, pre-irradiation and thermal annealing on a preform core rod. Electron paramagnetic resonance test shows that, under the same radiation condition, the radiation induced color center concentration in a preform core rod treated by the method above is lower than in an untreated core rod by one or more orders of magnitude. The obtained core rod can be used for preparing a radiation-resistant rare earth-doped silica fiber, and has the advantages of high laser slope efficiency, low background loss, being able to be used stably in a vacuum environment for a long time, for example.

An optical fiber includes a glass fiber and a coating resin layer surrounding the outer periphery of the glass fiber. The coating resin layer has a primary resin layer that surrounds the outer periphery of the glass fiber, and a secondary resin layer that surrounds the outer periphery of the primary resin layer. The primary resin layer has a thickness of 7.5 μm or more and 17.5 μm or less. The primary resin layer has a Young's modulus of 0.10 MPa or greater and 0.50 MPa or less at 23° C. The secondary resin layer has a thickness of 5.0 μm or more and 17.5 μm or less. The secondary resin layer has an outer diameter of 165 μm or more and 175 μm or less. The secondary resin layer has a Young's modulus of 1200 MPa or greater and 2800 MPa or less at 23° C.

An optical fiber includes a glass fiber and a coating resin layer surrounding the outer periphery of the glass fiber. The coating resin layer has a primary resin layer that surrounds the outer periphery of the glass fiber, and a secondary resin layer that surrounds the outer periphery of the primary resin layer. The primary resin layer has a thickness of 7.5 μm or more and 17.5 μm or less. The primary resin layer has a Young's modulus of 0.10 MPa or greater and 0.50 MPa or less at 23° C. The secondary resin layer has a thickness of 5.0 μm or more and 17.5 μm or less. The secondary resin layer has an outer diameter of 165 μm or more and 175 μm or less. The secondary resin layer has a Young's modulus of 1200 MPa or greater and 2800 MPa or less at 23° C.

An optical fiber comprises a glass fiber comprising a core and a cladding, a primary resin layer being in contact with the glass fiber and covering the glass fiber, and a secondary resin layer covering the primary resin layer, wherein the secondary resin layer consists of a cured product of a resin composition comprising a base resin containing a urethane (meth)acrylate oligomer, a monomer, and a photopolymerization initiator and hydrophobic inorganic oxide particles, the content of the inorganic oxide particles is 1% by mass or more and 60% by mass or less based on the total amount of the resin composition, and the glass transition temperature of the secondary resin layer is 60° C. or more and 120° C. or less.

An optical fiber comprises a glass fiber comprising a core and a cladding, a primary resin layer being in contact with the glass fiber and covering the glass fiber, and a secondary resin layer covering the primary resin layer, wherein the secondary resin layer consists of a cured product of a resin composition comprising a base resin containing a urethane (meth)acrylate oligomer, a monomer, and a photopolymerization initiator and hydrophobic inorganic oxide particles, the content of the inorganic oxide particles is 1% by mass or more and 60% by mass or less based on the total amount of the resin composition, and the glass transition temperature of the secondary resin layer is 60° C. or more and 120° C. or less.

An optical fiber comprises a glass fiber comprising a core and a cladding, and a coating resin layer covering the outer periphery of the glass fiber, wherein the coating resin layer has a primary resin layer being in contact with the glass fiber and covering the glass fiber and a secondary resin layer covering the outer periphery of the primary resin layer, the secondary resin layer comprises hydrophobic spherical silica particles, and the content of the silica particles is 7% by mass or more and 60% by mass or less based on the total amount of the secondary resin layer, and the absolute value of the surface potential of the optical fiber is 10 mV or more and 60 mV or less.

An optical fiber comprises a glass fiber comprising a core and a cladding, and a coating resin layer covering the outer periphery of the glass fiber, wherein the coating resin layer has a primary resin layer being in contact with the glass fiber and covering the glass fiber and a secondary resin layer covering the outer periphery of the primary resin layer, the secondary resin layer comprises hydrophobic spherical silica particles, and the content of the silica particles is 7% by mass or more and 60% by mass or less based on the total amount of the secondary resin layer, and the absolute value of the surface potential of the optical fiber is 10 mV or more and 60 mV or less.

A resin composition comprises a base resin containing an urethane (meth)acrylate oligomer, a monomer having a phenoxy group, and a photopolymerization initiator, and hydrophobic inorganic oxide particles, wherein the viscosity is 300 mPa.Math.s or more and 4200 mPa.Math.s or less at 45° C. and the content of the monomer having a phenoxy group is 1% by mass or more and 30% by mass or less based on the total amount of the base resin.