A multicore optical fiber is provided that includes a first core with silica glass doped with chlorine and/or an alkali metal, a first inner cladding surrounding the first core, and a first outer cladding surrounding the first inner cladding and having a first trench region having a volume of about 30%Δ-micron.sup.2 or greater. The multicore optical fiber also includes a second core with silica glass doped with chlorine and/or an alkali metal, a second inner cladding surrounding the second core, and a second outer cladding surrounding the second inner cladding and having a second trench region having a volume of about 30%Δ-micron.sup.2 or greater. Additionally, a common cladding surrounds the first core and the second core, and the first core and the second core each have an effective area at 1550 nm of about 100 micron.sup.2 or less.

An optical fiber includes a core and a cladding. The core contains silica glass and includes a central portion (part having a diameter of 0.5 μm or more and 4 μm or less). The central portion has the central axis of the optical fiber. The cladding contains silica glass and surrounds the core. The core contains chlorine. A chlorine concentration averaged in the entire core is 10,000 ppm or more and 50,000 ppm or less. The chlorine concentration averaged in the entire core minus a chlorine concentration averaged in the central portion is 4,500 ppm or more and 13,500 ppm or less.

A present embodiment relates to a MDL measurement method and the like including a structure for enabling MDL measurement without increasing a processing load. The present embodiment sequentially executes, for N (≥2) spatial modes, light-input operation of inputting light of a predetermined intensity to an arbitrary spatial mode, and intensity measurement operation of measuring an output light intensity of each of the N spatial modes including the arbitrary spatial mode, to generate a transfer matrix relating to transmission loss in an optical fiber as a measurement target, and determine at least a linear value of MDL per unit fiber length by using each component value of the generated transfer matrix.

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 comprising a core region doped with a first alkali dopant and a second alkali dopant. The first alkali dopant has a first average core concentration of C1 and a first diffusivity D1. The second alkali dopant has a second average core concentration of C2 and a second diffusivity D2. An outer cladding region surrounds the core region. The diffusivities D1, D2 of the first and second alkali dopants satisfy the relation D1>D2. The average core concentrations C1, C2 of the first and second alkali dopants satisfy the relation 0.1C2/C11.

The disclosure provides optical fibers that exhibit low macrobend loss at 1550 nm at bend diameters between 10 mm and 40 mm. The relative refractive index profile of the fibers includes a trench cladding region with small depth, large width and a trench volume configured to minimize macrobend loss at large and small bend diameters. The optical fiber includes an outer cladding region that surrounds and is directly adjacent to the trench cladding region and an optional offset cladding region between the trench cladding region and the core region. In some embodiments, the trench cladding region has a relative refractive index that decreases monotonically from the inner radius to the outer radius. The monotonic decrease in relative refractive index may have a constant slope. The low macrobend loss at large and small diameters makes the optical fibers well suited for space-constrained deployment environments, such as data centers.

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.

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.

A multicore fiber for communication 10 which allows propagation of an optical signal includes: a clad 12; a core 11a which is arranged in a center of the clad 12; and seven to ten cores 11b which are arranged at equal intervals surrounding the core 11a, and the cladding diameter is 230 m, distances between centers of the mutually neighboring cores 11a and 11b are 30 m or more, distances between the centers of the cores 11b and an outer peripheral surface of the clad 12 are 35 m or more and a mode field diameter of light propagating in the cores 11a and 11b is 9 m to 13 m.

A single mode optical fiber, comprising: (i) a silica based core having a graded refractive index profile with an alpha of less than 5, a relative refractive index .sub.1max, and an outer radius r.sub.1, wherein 10 microns>r.sub.16.5 microns, the core comprising Cl, Ge, or a combination thereof; (ii) a first cladding region in contact with and surrounding the core, the first cladding region having a relative refractive index .sub.2min, an inner radius r.sub.1, and an outer radius r.sub.2, wherein r.sub.2<20 microns; and (iii) an outer cladding region surrounding the first cladding region, the outer cladding region having a relative refractive index .sub.3. The fiber has MFD at 1310 nm>than 9 microns, a zero dispersion wavelength <1306 nm; a 22 m cable cutoff wavelength <1260nm; and a bend loss <0.005 dB/turn when the fiber is bent around a 30 mm mandrel; and <0.5dB/turn when the fiber is bent around a 20 mm mandrel.