An optical fiber including a core and a cladding including an inner cladding layer and an outer cladding layer is provided. The refractive index of the core 1, the refractive index of the inner cladding layer 2, and the refractive index of the outer cladding layer 3 have a relationship denoted by the following expressions: 1max>2min and 1max>3, and 0.01%<|2min3|<0.03%. An outer circumference radius r1 of the core, an outer circumferential radius r2 of the inner cladding layer, and an outer circumferential radius r3 of the outer cladding layer have a relationship denoted by the following expressions: r1<r2<r3, and 0.2r1/r20.5. A cable cut-off wavelength cc 1260 nm or less. A mode field diameter at a wavelength of 1310 nm is 8.6 m or more and 9.5 m or less.

An optical fiber including a core and a cladding including an inner cladding layer and an outer cladding layer is provided. The refractive index of the core 1, the refractive index of the inner cladding layer 2, and the refractive index of the outer cladding layer 3 have a relationship denoted by the following expressions: 1max>2min and 1max>3, and 0.01%<|2min3|<0.03%. An outer circumference radius r1 of the core, an outer circumferential radius r2 of the inner cladding layer, and an outer circumferential radius r3 of the outer cladding layer have a relationship denoted by the following expressions: r1<r2<r3, and 0.2r1/r20.5. A cable cut-off wavelength cc 1260 nm or less. A mode field diameter at a wavelength of 1310 nm is 8.6 m or more and 9.5 m or less.

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 .sub.1MAX, and a inner cladding region having refractive index .sub.2MIN surrounding the core, where .sub.1MAX>.sub.2MIN.

One embodiment of the disclosure relates to a method of making an optical fiber comprising the steps of: (i) exposing a silica based preform with at least one porous glass region having soot density of to a gas mixture comprising SiCl.sub.4 having SiCl.sub.4 mole fraction y.sub.SiCl4 at a doping temperature T.sub.dop such that parameter X is larger than 0.03 to form the chlorine treated preform, wherein $X=\frac{1}{1+\left[\left(\frac{}{{}_s-}\right)\frac{0.209748T_{\mathrm{dop}}\mathrm{Exp}\left[-5435.33/T_{\mathrm{dop}}\right]}{y_{\mathrm{SiCl}4}^{3/4}}\right]}$
and .sub.s is the density of the fully densified soot layer; and (ii) exposing the chlorine treated preform to temperatures above 1400 C. to completely sinter the preform to produce sintered optical fiber preform with a chlorine doped region; and (iii) drawing an optical fiber from the sintered optical preform.

A multicore fiber includes a plurality of unit multicore fibers each including: a plurality of core portions; and a clad portion which is formed in an outer circumference of the core portions and has a refractive index lower than a maximum refractive index of the core portions. The plurality of the core portions have substantially same refractive index profile and different group delays at same wavelength in same propagation mode. The core portions of the multicore fiber are configured so that the core portions of the plurality of the unit multicore fibers are connected in cascade, a maximum value of differential group delays between the core portions of the multicore fiber is smaller than a reduced value of a maximum value of differential group delays between the core portions of each unit multicore fiber as a value in terms of a length of the multicore fiber.

An optical fiber with large effective area, low bending loss and low attenuation. The optical fiber includes a core, an inner cladding region, and an outer cladding region. The core region includes a spatially uniform updopant to minimize low Rayleigh scattering and a relative refractive index and radius configured to provide large effective area. The inner cladding region features a large trench volume to minimize bending loss. The core may be doped with Cl and the inner cladding region may be doped with F.

The core region of an optical fiber is doped with chlorine in a concentration that allows for the viscosity of the core region to be lowered, approaching the viscosity of the surrounding cladding. An annular interface region is disposed between the core and cladding and contains a concentration of fluorine dopant sufficient to match the viscosity of the core. By including this annular stress accommodation region, the cladding layer can be formed to include the relatively high concentration of fluorine required to provide the desired degree of optical signal confinement (i.e., forming a low loss optical fiber).

The present embodiment relates to an optical fiber having a W-type refractive index d profile or a trench-type refractive index profile and having reduced microbending loss in a wavelength band to be actually used. The optical fiber includes a center core, an inner cladding surrounding the center core, and an outer cladding surrounding the inner cladding. The inner cladding has a refractive index lower than a refractive index of at least the center core and the outer cladding has a refractive index lower than the refractive index of the center core and higher than the refractive index of the inner cladding. Wavelength dependency of microbending loss has a local maximal value and a shortest wavelength .sub.th where the microbending loss becomes 10% of the local maximal value is longer than 1560 nm.

The present invention relates to a method of manufacturing an optical fiber preform for obtaining an optical fiber with low transmission loss. A core preform included in the optical fiber preform comprises three or more core portions, which are each produced by a rod-in-collapse method, and in which both their alkali metal element concentration and chlorine concentration are independently controlled. In two or more manufacturing steps of the manufacturing steps for each of the three or more core portions, an alkali metal element is added. As a result, the mean alkali metal element concentration in the whole core preform is controlled to 7 atomic ppm or more and 70 atomic ppm or less.

The present disclosure provides optical fiber preforms formed from core canes having large core-clad ratio, intermediate core-cladding assemblies, and methods for making the preforms and core cladding assemblies. The preforms are made with capped core canes. The capping material has a coefficient of thermal expansion less than the coefficient of thermal expansion of the core cane and more closely matched to or lower than the coefficient of thermal expansion of the surrounding cladding monolith in a cane-in-soot process. Presence of the cap reduces stresses that arise from differential thermal expansion of the core cane and cladding materials and leads to preforms having low defect concentration and low probability of failure during subsequent thermal processing steps.