An optical fiber has a core to which chlorine is added and a clad to which fluorine is added, chlorine of 9000 to 13000 ppm is added to the core, a relative refractive index difference Δ1 of the core to a pure silica glass is 0.09 to 0.13%, a relative refractive index difference Δ2 of the clad to a pure silica glass is −0.36 to −0.17%, a difference (Δ1-Δ2) between the relative refractive index difference Δ1 of the core and the relative refractive index difference Δ2 of the clad is larger than or equal to 0.30%, a mode field diameter at wavelength 1.31 μm is 8.8 to 9.6 μm, and a stress difference occurring at an interface between the core and the clad is lower than or equal to 60 MPa.

A manufacturing method for an optical fiber, includes: drawing, while heating in a heating furnace, a lower end of an optical fiber preform that is to be an optical fiber having a core consisting of silica glass containing a rare earth element compound. The heating furnace has a temperature profile in which a temperature of the heating furnace increases to a maximum temperature T.sub.max and then decreases from an upstream side of the heating furnace toward a downstream side of the heating furnace. The temperature profile has a changing point at which the temperature decreases more steeply on the downstream side from a position where the maximum temperature T.sub.max is reached. At the maximum temperature, a temperature of the silica glass is higher than or equal to a glass transition temperature and the silica glass is in a single phase.

The invention relates to an optical fiber preform (20) comprising a primary preform (21) and one or more purified silica-based overclad layers (22) surrounding said primary preform (21), the purified silica-based overclad layers (22) comprising lithium and aluminium, and having a ratio between lithium concentration [Li] and aluminium concentration [Al] satisfying the following inequality:
1×10.sup.−3≤[Li]/[Al]≤20×10.sup.−3.

Methods for synthesizing fibers having nanoparticles therein are provided, as well as preforms and fibers incorporating nanoparticles. The nanoparticles may include one or more rare earth ions selected based on fluorescence at eye-safer wavelengths, surrounded by a low-phonon energy host. Nanoparticles that are not doped with rare earth ions may also be included as a co-dopant to help increase solubility of nanoparticles doped with rare earth ions in the silica matrix. The nanoparticles may be incorporated into a preform, which is then drawn to form fiber. The fibers may beneficially be incorporated into lasers and amplifiers that operate at eye safer wavelengths. Lasers and amplifiers incorporating the fibers may also beneficially exhibit reduced Stimulated Brillouin Scattering.

Methods for synthesizing fibers having nanoparticles therein are provided, as well as preforms and fibers incorporating nanoparticles. The nanoparticles may include one or more rare earth ions selected based on fluorescence at eye-safer wavelengths, surrounded by a low-phonon energy host. Nanoparticles that are not doped with rare earth ions may also be included as a co-dopant to help increase solubility of nanoparticles doped with rare earth ions in the silica matrix. The nanoparticles may be incorporated into a preform, which is then drawn to form fiber. The fibers may beneficially be incorporated into lasers and amplifiers that operate at eye safer wavelengths. Lasers and amplifiers incorporating the fibers may also beneficially exhibit reduced Stimulated Brillouin Scattering.

An optical fiber includes a core, and a cladding. When a refractive index of silica glass is set as no, a refractive index of the core is set as n.sub.1, and a refractive index of the cladding is set as n.sub.2, a relative refractive index difference Δ defined by Expression (1):

Δ[%]=100×(n.sub.1.sup.2−n.sub.2.sup.2)/2n.sub.0.sup.2  (1)

is 0.2% or higher. A ratio of a maximum value of a concentration of the dopant composed of the alkali metal element or the alkaline-earth metal element in the cladding to a maximum value of a concentration of the dopant composed of the alkali metal element or the alkaline-earth metal element in the core is 0.06 or higher and 0.25 or lower.

The optical fiber offered is capable of not only restraining the attenuation due to glass defects, but also reducing the increase of manufacturing cost. The optical fiber is made of silica glass and includes a core and a cladding. The cladding encloses the core and has a refractive index smaller than that of the core. When the core is divided into inner core and outer core at half of the radius of the core, the average chlorine concentration of the inner core is larger than that of the outer core. The core includes any of the alkali metal group.

The optical fiber offered is capable of not only restraining the attenuation due to glass defects, but also reducing the increase of manufacturing cost. The optical fiber is made of silica glass and includes a core and a cladding. The cladding encloses the core and has a refractive index smaller than that of the core. When the core is divided into inner core and outer core at half of the radius of the core, the average chlorine concentration of the inner core is larger than that of the outer core. The core includes any of the alkali metal group.

The present disclosure relates to an optical fiber ribbon in which a plurality of optical fibers are covered with a ribbon resin, wherein the ribbon resin is a cured product of a resin composition including a base resin containing oligomers, monomers and a photopolymerization initiator, and inorganic oxide particles.

The present disclosure relates to an optical fiber ribbon in which a plurality of optical fibers are covered with a ribbon resin, wherein the ribbon resin is a cured product of a resin composition including a base resin containing oligomers, monomers and a photopolymerization initiator, and inorganic oxide particles.