The present invention provides a large-effective-mode-area low-loss optical fiber with optimized cladding components, which comprises a core layer and a cladding comprising, from the inside to the outside, a first sinking layer, a second sinking layer, an optional third sinking layer, and an outer cladding. In the present invention, phosphorus and aluminum are co-doped in the optical fiber cladding, to form a tetrahedron [AlPO.sub.4] in glass, thus optimizing the viscosity of the cladding while effectively reducing the refractive index of the cladding, without causing increased hydrogen loss. The process is simple, and highly repeatable.

A method of manufacturing a glass core preform for an optical fibre comprising: providing a porous soot core preform having an outer surface) and a central hole extending axially therethrough; dehydrating the porous soot core preform at a first temperature by exposing the outer surface of the preform to an atmosphere containing chlorine, and simultaneously consolidating the soot core preform and closing the central hole at a second temperature higher than the first temperature to form a glass core preform, wherein consolidating and closing comprises sequentially alternating flowing chlorine containing gas into the central hole and reducing the internal pressure of the central hole.

An optical fiber includes a core and a cladding surrounding an outer periphery of the core and has a refractive index profile in which a relative refractive index difference with respect to a distance r from a center of the core is represented by (r), where a value of A represented by
A=.sub.0.sup.0.22MFD.sup.1.31((r).sub.ref(r))dr+.sub.0.22MFD.sub.1.31.sup.0.44MFD.sup.1.31((r).sub.ref(r))dr(Formula 1)
is 0.3%.Math.m or less, where a unit of r is m, a unit of a relative refractive index difference (r) is %, .sub.ref(r)=0.064r+0.494, and MFD.sub.1.31 is a mode field diameter at a wavelength of 1.31 m.

A method of making a multi-mode optical fiber that includes: depositing a porous germania-doped silica soot to form a germania-doped porous soot preform; depositing a porous silica layer over the porous soot preform; doping the porous soot preform and the porous silica layer with a fluorine dopant to form a co-doped soot preform having a core region and a fluorine-doped trench region; consolidating the co-doped soot preform to form a sintered glass, co-doped core preform having a refractive index alpha profile between 1.9 and 2.2 measured at 850 nm; depositing a cladding comprising silica over the sintered glass, co-doped preform to form a multi-mode optical fiber preform; drawing the optical fiber preform into a multi-mode optical fiber. Further, the step of doping the germania-doped soot preform and the porous silica layer is conducted according to a doping parameter () that is set between 20 and 300, and given by: $=\frac{1{10}^{14}{R}_{\mathrm{prc}}^2\exp \left(-E/{\mathrm{RT}}_{\mathrm{dop}}\right)T_{\mathrm{dop}}^{1/2}}{x^{3/4}}.$

A method for producing an optical fiber includes heating and melting an optical fiber preform and drawing the optical fiber preform. In this method for producing an optical fiber, the optical fiber is formed to include a core, a surrounding cladding surrounding a periphery of the core, and an outer cladding surrounding the surrounding cladding. In the drawn optical fiber, a maximum compressive stress of at least 100 MPa or more is applied to an optical waveguide region including at least the core.

According to embodiments, an optical fiber may include a core portion comprising an outer radius r.sub.C and a maximum relative refractive index .sub.Cmax. A cladding may surround the core portion and include a low-index trench and an outer cladding. The low index trench may surround the core portion and includes an outer radius r.sub.T and relative refractive index .sub.T. The outer cladding may surround and be in direct contact with the low-index trench. The outer cladding may be formed from silica-based glass comprising greater than 1.0 wt. % bromine and has a relative refractive index .sub.OC, wherein .sub.cmas>.sub.OC>.sub.T. The optical fiber may have a cable cutoff of less than or equal to 1530 nm. An attenuation of the optical fiber may be less than or equal to 0.185 dB/km at a wavelength of 1550 nm.

According to some embodiments a method of processing an optical fiber comprises the steps of: (i) drawing the fiber at a drawing rate of at least 30 m/sec; and (ii) cooling the drawn fiber in a gas at an average cooling rate less than 5000 C./s, such that said cooling reduces the temperature of the fiber from an entering temperature in the range between 1500 C. and 1700 C. to another temperature in the range between 1200 C. and 1400 C., the gas being at a temperature between 800 C. and 1500 C.; and the thermal conductivity of the gas being not greater than 1.510.sup.4 cal/cm-s-K for at least one temperature within a range of 800 C. to 1500 C. at one atm (atmosphere) pressure absolute.

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 from core canes having a contoured end surface. The contoured end surface(s) include a depression that acts to reduce the stress that develops at the junction of the end surface of the core cane with a soot cladding monolith arising from differences in the coefficient of thermal expansions of the core can and soot cladding monolith. The contoured end surface(s) leads to preforms having low defect concentration and low probability of failure during fiber draw.

A technique is described for fabricating one or more optical devices in a carbon-coated optical fiber. A photosensitive optical fiber is provided having a hermetic carbon coating. Further provided is a laser having a beam output that is configured to inscribe one or more refractive index modulations into the optical fiber through the hermetic carbon layer while leaving the hermetic carbon layer intact. The laser is used to inscribe one or more optical devices into the optical fiber through the hermetic carbon layer.

Provided is a method for producing a glass preform for optical fiber which suppresses occurrences of cracks, coloring and foaming in a surface layer when sintering a glass fine particle deposit to allow a production yield to be improved. A method for producing a glass preform for optical fiber comprising the steps of: spraying glass fine particles containing silicon dioxide and germanium dioxide to a starting material moving upward while rotating to produce a glass fine particle deposit; and sintering the glass fine particle deposit while relatively varying a positional relationship between a heating source and the glass fine particle deposit in a sintering apparatus to produce a transparent glass preform, wherein a germanium dioxide reducing gas is contained in an atmosphere gas in the sintering apparatus.