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 having a core comprising silica and greater than 1.5 wt % chlorine and less than 0.5 wt % F, said core having a refractive index Δ.sub.1MAX, and an inner cladding region having refractive index Δ.sub.2MIN surrounding the core, where Δ.sub.1MAX>Δ.sub.2MIN.

A coupled-core multicore optical fiber has a plurality of cores that are doped with alkali metals or chlorine to achieve low attenuation and a large effective area. The cores may be embedded in a common cladding region that may be fluorine doped. The cores may also be doped with chlorine, either with the alkali metals described above or without the alkali metals.

The present disclosure provides an optical fibre. The optical fibre includes a core region, a primary trench region and a secondary trench region. The core region has a radius r.sub.1. In addition, the core region has a relative refractive index Δ.sub.1. Further, the primary trench region has a relative refractive index Δ.sub.3. Furthermore, the primary trench region has a curve parameter α.sub.trench-1. Moreover, the secondary trench region has a relative refractive index Δ.sub.4. Also, the secondary trench region has a curve parameter α.sub.trench-2.

An optical fiber includes: a core portion; a side core layer surrounding a circumference of the core portion; and a cladding portion surrounding a circumference of the side core layer. Relations, Δ1 > ΔClad > Δ2 and 0 > Δ2, hold, where Δ1 denotes an average maximum relative refractive-index difference of the core portion with respect to an average refractive index of the cladding portion, Δ2 denotes a relative refractive-index difference of an average refractive index of the side core layer with respect to the average relative refractive index of the cladding portion, and ΔClad denotes a relative refractive-index difference of the average refractive index of the cladding portion with respect to pure quartz glass, Δ1 is 0.24% or more and 0.30% or less, Δ2 is -0.27% or more and -0.08% or less, (Δ1 - Δ2) is 0.36% or more and 0.57% or less.

It is an object of the present invention to provide a multicore optical fiber, a design method for the multicore optical fiber and an optical transmission method using the multicore optical fiber including four cores having a standard cladding diameter of 125±1 μm for an existing single mode optical fiber covering several thousands of kilometers of transmission. The multicore optical fiber according to the present invention disposes two-stage claddings with different refractive indices around each core, and designates as a predetermined range, a core radius a1, a radius a2 of a first cladding region surrounding each core, specific refractive index Δ1 relative to the core of the first cladding region and a specific refractive index Δ2 relative to the core of a second cladding region including four cores and the first cladding region.

An optical fiber includes: a core portion; a side core layer that surrounds an outer periphery of the core portion; and a cladding portion that surrounds an outer periphery of the side core layer, and in which Δ1>ΔClad>Δ2 and 0>Δ2 hold, where Δ1 is an average maximum relative refractive-index difference of the core portion with respect to an average refractive index of the cladding portion, Δ2 is a relative refractive-index difference of an average refractive index of the side core layer with respect to the average refractive index of the cladding portion, and ΔClad is a relative refractive-index difference of the average refractive index of the cladding portion with respect to pure silica glass.

A coupled-core multicore optical fiber has a plurality of cores that are doped with alkali metals or chlorine to achieve low attenuation and a large effective area. The cores may be embedded in a common cladding region that may be fluorine doped. The cores may also be doped with chlorine, either with the alkali metals described above or without the alkali metals.

An optical fiber includes a core that propagates a light that includes a wavelength equal to or larger than 1000 nm and equal to or smaller than 1100 nm. The light propagates in the core at least in an LP01 mode and an LP11 mode. A difference between a propagation constant of the light in the LP01 mode and a propagation constant of the light in the LP11 mode is 1735 rad/m or larger and 4000 rad/m or smaller.

An optical fiber includes: a core portion made of glass; a side core layer made of glass and enclosing the core portion; a cladding portion made of glass and enclosing the side core layer; and a coating layer including a primary layer made of resin and enclosing the cladding portion, and a secondary layer made of resin and enclosing the primary layer. The relationships Δ1>ΔClad>Δ2 and 0>Δ2 are satisfied where Δ1 represents relative refractive-index difference of average maximum refractive index of the core portion with respect to average refractive index of the cladding portion, Δ2 represents relative refractive-index difference of average refractive index of the side core layer with respect to average refractive index of the cladding portion, and ΔClad represents relative refractive-index difference of average refractive index of the cladding portion with respect to refractive index of pure silica glass.