Provided is a mode controller which includes an optical fiber coupled body and at least one pair of bobbins, and the mode controller is configured so that: the one pair of bobbins includes two bobbins arranged, spaced from one another; the optical fiber coupled body includes a step-index fiber and a graded-index fiber, which are coupled with each other; the step-index fiber and/or the graded-index fiber is/are wound around the at least one pair of bobbins, and twisted to form a helical area(s); light is launched into the step-index fiber, propagates through the step-index fiber, is emitted from the step-index fiber, and is launched into the graded-index fiber; propagation mode of the light is converted to an equilibrium mode distribution during the propagation of the light through the step-index fiber; and the propagation mode of the light launched into the graded-index fiber is converted to a low-order mode.

A single mode optical fiber is provided that includes a core region having an outer radius r.sub.1 and a maximum relative refractive index Δ.sub.1max. The single mode optical fiber further includes a cladding region surrounding the core region, the cladding region includes a depressed-index cladding region, a relative refractive index Δ.sub.3 of the depressed-index cladding region increasing with increased radial position. The single mode optical fiber has a bend loss at 1550 nm for a 15 mm diameter mandrel of less than about 0.75 dB/turn, a bend loss at 1550 nm for a 20 mm diameter mandrel of less than about 0.2 dB/turn, and a bend loss at 1550 nm for a 30 mm diameter mandrel of less than 0.005 dB/turn. Additionally, the single mode optical fiber has a mode field diameter of 9.0 microns or greater at 1310 nm wavelength.

The optical fibers disclosed is a single mode optical fiber comprising a core region and a cladding region surrounding and directly adjacent to the core region. The core region can have a radius r.sub.1 in a range from 3 μm to 7 μm and a relative refractive index profile Δ.sub.1 having a maximum relative refractive index Δ.sub.1max in the range from 0.25% to 0.50%. The cladding region can include a first outer cladding region and a second outer cladding region surrounding and directly adjacent to the first outer cladding region. The first outer cladding region can have a radius r.sub.4a. The second outer cladding region can have a radius r.sub.4b less than or equal to 45 μm and comprising silica based glass doped with titania.

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.

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.

A multicore optical fiber includes an inner glass region having a plurality of core regions surrounded by a common outer cladding, the inner glass region further having at least one marker and an outer diameter in the range of 120 microns and 130 microns, wherein each core region is comprised of a germania-doped silica core and a fluorine-doped silica trench, wherein the trench volume of the fluorine-doped silica trench is greater than 50% Δ microns.sup.2. The fiber has an outer coating layer surrounding the inner glass region, the outer coating layer having a primary coating layer and a secondary coating layer with a diameter of the secondary coating layer equal to or less than 200 microns, wherein each core region has a mode field diameter greater than 8.2 microns at 1310 nm, a cable cutoff wavelength of less than 1260 nm, and zero dispersion wavelength of less than 1335 nm.

The optical fiber according to the present invention includes, in a cross section of the optical fiber, one core region (11) and a cladding region (12) that is arranged on an outer periphery of the core region. The cladding region is a medium that has a lower refractive index than that of the core region and also has a smaller refractive index wavelength dispersion than that of the core region. The optical fiber has a solid core and therefore, allows more reduction in the Rayleigh scattering loss compared to an optical fiber having a hollow core. In addition, since the optical fiber adopts, for the cladding region, a medium that has a smaller refractive index wavelength dispersion than that of the core region, it allows a reduction in the wavelength dispersion of n.sub.eff.

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.

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.