A optical fiber comprising a central core region having an outer radius r.sub.1 of 3 μm to 7 μm, and a maximum refractive index Δ.sub.1 of 0.25% to 0.5% and an alpha (a) profile of 1 to 20; a cladding region comprising (i) a first inner cladding region surrounding the core, having a refractive index Δ.sub.2 of −0.25% to 0.05% and a radius r.sub.2 of 6 μm to 15 μm, (ii) a second inner cladding region, surrounding the first inner cladding region, having a refractive index Δ.sub.3 of −0.1% to 0.2% and a radius r.sub.3 of 7 μm to 15 μm, and (iii) an outer cladding region, surrounding the second inner cladding region, having a refractive index Δ.sub.4 between −0.05% to 0.1%; wherein the optical fiber exhibits a cable cutoff of less than 1260 nm, a mode field diameter at 1310 nm of greater than 8.2 microns.

An optical fiber includes: a core portion made of glass; a cladding portion that is located on an outer periphery of the core portion and that is made of glass having a lower refractive index than a refractive index of the core portion; and a coating portion that covers an outer periphery of the cladding portion. Further, an average value of a relative refractive-index difference of a center core of the core portion is 0.1 to 0.5%, a fiber diameter including the coating portion is equal to or smaller than 220 μm, an effective cutoff wavelength is longer than 1260 nm and smaller than 1530 nm, and a mode field diameter of light at 1550 nm is equal to or larger than 9 μm.

An optical fiber includes: a core portion made of glass; and a cladding portion made of glass, having a refractive index lower than the refractive index of the core portion, and positioned on an outer periphery of the core portion. Further, the cladding portion has an outer diameter smaller than 100 μm, and the core portion has a relative refractive-index difference of 0.32% to 0.40% with respect to the cladding portion.

An MCF according to the disclosure has a structure preventing deterioration in quality of optical transmission signals. The MCF comprises cores, a common cladding, and a coating. Any of the cores has a coating leakage loss of 0.01 dB/km or more at a wavelength within a wavelength range of from 850 nm to 1700 nm. The coating includes a leaked light propagation suppressive coating layer having a first optical property or a second optical property to light with a wavelength within a wavelength range of from 850 nm to 1700 nm or from 1260 nm to 1625 nm. The first optical property is defined by, as an attenuation index of the light, an absorbance per 1 μm thickness being 0.1 dB or more. The second optical property is defined by a product of absorbance per 1 μm thickness and a thickness being 0.1 dB or more.

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.

The optical fibers disclosed have single mode and few mode optical transmission for VCSEL-based optical fiber transmission systems. The optical fibers have a cable cutoff wavelength λ.sub.C of equal to or below 1260 nm thereby defining single mode operation at a wavelength in a first wavelength range greater than 1260 nm and few-mode operation at a wavelength in a second wavelength range from 970 nm and 1070 nm. The mode-field diameter is in the range from 9.3 microns to 10.9 microns at 1550 nm. The optical fibers have an overfilled bandwidth OFL BW of 1 GHz.km to 3 GHz.km at the at least one wavelength in the second wavelength range. VCSEL based optical transmission systems and methods are disclosed that utilize both single core and multicore versions of the optical fiber.

An optical fiber comprising: (a) a core having an outer radius r.sub.1; (b) a cladding having an outer radius r.sub.4<32.5 microns; (c) a primary coating surrounding the cladding having an outer radius r.sub.5, a thickness t.sub.P>8 microns, in situ modulus E.sub.P≤0.35 MPa and a spring constant χ.sub.P<2.0 MPa, where χ.sub.P=2E.sub.P r.sub.4/t.sub.P; and (d) a secondary coating surrounding said primary coating, the secondary coating having an outer radius r.sub.6 and a thickness t.sub.S=r.sub.6−r.sub.5, and in situ modulus E.sub.S of 1200 MPa or greater; t.sub.S>8 microns, r.sub.6≤56 microns. The fiber has a mode field diameter MFD greater than 8.2 microns at 1310 nm; a fiber cutoff wavelength of less than 1310 nm; and a bend loss at a wavelength of 1550 nm, when wrapped around a mandrel having a diameter of 10 mm, of less than 1.0 dB/turn.

Multicore optical fibers with low bend loss, low cross-talk, and large mode field diameters In some embodiments a circular multicore optical fiber includes a glass matrix; at least 3 cores arranged within the glass matrix, wherein any two cores have a core center to core center spacing of less than 29 microns; and a plurality of trench layers positioned between a corresponding core and the glass matrix, each trench layer having an outer radius of less than or equal to 14 microns and a trench volume of greater than 50% Δ micron.sup.2; wherein the optical fiber has a mode field diameter of greater than about 8.2 microns at 1310 nm, and wherein the optical fiber has an outer diameter of less than about 130 microns.

An optical fiber is provided that includes a core region, a cladding region having a radius less than about 62.5 microns; a polymer coating comprising a high-modulus layer and a low-modulus layer, wherein a thickness of the low-modulus inner coating layer is in a range of 4 microns to 20 microns, the modulus of the low-modulus inner coating layer is less than or equal to about 0.35 MPa, a thickness of the high-modulus coating layer is in a range of 4 microns to 20 microns, the modulus of the high-modulus inner coating layer is greater than or equal to about 1.6 GPa, and wherein a puncture resistance of the optical fiber is greater than 20 g, and wherein a microbend attenuation penalty of the optical fiber is less than 0.03 dB/km, and wherein an outer diameter of the coated optical fiber is less than or equal to 175 microns

An optical fiber includes: a central core portion; an intermediate layer; a trench layer; and a cladding portion. Further, Δ1>Δ2>Δ3 and 0>Δ3 are satisfied, where Δ1 is a relative refractive-index difference of the central core portion, Δ2 is a relative refractive-index difference of the intermediate layer, and Δ3 is a relative refractive-index difference of the trench layer with respect to the cladding portion, respectively, and (c−b) is smaller than 4.5 μm when Δ1 is equal to or larger than 0.36% and equal to or smaller than 0.40%, Δ2 is equal to or larger than −0.05% and equal to or smaller than 0.05%, |Δ3| is equal to or smaller than 0.25%, Δ1×|Δ3| is equal to or smaller than 0.08%.sup.2, an inner diameter of the trench layer is 2b, and an outer diameter of the trench layer is 2c.