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.

A multicore optical fiber comprises a common cladding and a plurality of core portions disposed in the common cladding. Each of the core portions includes a central axis, a core region extending from the central axis to a radius r.sub.1, the core region comprising a relative refractive index Δ.sub.1, an inner cladding region extending from the radius r.sub.1 to a radius r.sub.2, the inner cladding region comprising a relative refractive index Δ.sub.2, and a depressed cladding extending from the radius r.sub.2 to a radius r.sub.3, the depressed cladding region comprising a relative refractive index Δ.sub.3 and a minimum relative refractive index Δ.sub.3 min. The relative refractive indexes may satisfy Δ.sub.1>Δ.sub.2>Δ.sub.3 min. The mode field diameter of each core portion may greater than or equal to 8.2 μm and less than or equal to 9.5 μm.

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.

An optical fiber includes: a central core portion; an intermediate layer; a trench layer; and a cladding portion. Further, relationships Δ1>Δ2>Δ3 and 0>Δ3 are satisfied, where Δ1, Δ2, and Δ3 are a relative refractive-index difference of the central core portion, the intermediate layer, and the trench layer, respectively, with respect to the cladding portion, Δ1 is equal to or larger than 0.34% and equal to or smaller than 0.37%, |Δ3| is equal to or larger than 0.1% and equal to or smaller than 0.25%, Δ1×|Δ3| is equal to or smaller than 0.08%.sup.2, a mode field diameter at a wavelength of 1310 nm is equal to or larger than 8.8 μm, and a transmission loss at a wavelength of 1550 nm is equal to or smaller than 0.195 dB/km.

Provided is a method for manufacturing an optical fiber glass preform in which a refractive index distribution is stable in a longitudinal direction of the glass preform. A method for manufacturing an optical fiber glass preform includes: depositing a porous glass preform by a vapor phase method; and sintering the porous glass preform in a heating region, when sintering the porous glass preform, the porous glass preform being inserted into a vessel of a sintering furnace, and an inside of the vessel being heated with a heater installed on an outer periphery of the vessel to form the heating region. The sintering is started after a surface temperature difference of the porous glass preform in a longitudinal direction is made 50° C. or lower.

The invention relates to a method and a device for producing a preform for glass fiber production. The method comprises the steps of providing a carrier gas with a desired, precisely adjusted temperature, loading the carrier gas with halide vapor, mixing the loaded carrier gas with additional gases, and producing the preform in a reaction chamber with substrate.

Provided is an optical fiber glass preform in which a starting rod and a dummy glass are hardly separated from each other, and a method for manufacturing the glass preform. In the optical fiber glass preform, the dummy glass is fitted into one end of the starting rod, and a part of the dummy glass and the starting rod are surrounded by a clad glass. In the manufacturing method, at the time of connecting the starting rod and the dummy glass, a shape is adjusted in such a manner that an iron is brought into contact with a connection portion and is moved from a starting rod side toward a dummy glass side with appliance of a load.

An optical fiber manufacturing method includes: a drawing step of heating one end portion of an optical fiber preform to melt and deform the one end portion and drawing an optical fiber, wherein in the drawing step, drawing is performed while applying pressure to a melted-deformed portion that is melted and deformed.

The invention relates to a plasma chemical vapor deposition (PCVD) apparatus for deposition of one or more layers of silica onto an interior wall of an elongated hollow glass substrate tube. The apparatus comprises a microwave generator, a plasma generator receiving microwaves from said generator in use, a cylindrical cavity extending through said generator, and a cylindrical liner positioned in the cavity. The substrate tube passes through the liner in use. The cylindrical liner has at least one section having a reduced inner diameter over a part of the length of the liner, the at least one section providing a contact zone for the substrate tube. The microwave generator is configured to generate microwaves having a wavelength Lw in the range of 40 to 400 millimeters, wherein a length of said at least one section having the reduced inner diameter is at most 0.1×Lw.

An optical fiber includes: a central core portion; an intermediate layer formed around an outer circumference of the central core portion; a trench layer formed around an outer circumference of the intermediate layer; and a cladding portion formed around an outer circumference of the trench layer. Further, when, relative to the cladding portion, a relative refractive-index difference of the central core portion is Δ1, a relative refractive-index difference of the intermediate layer is Δ2, and a relative refractive-index difference of the trench layer is Δ3, relationships Δ1>Δ2>Δ3 and 0>Δ3 are satisfied and Δ1 is equal to or greater than 0.34% and equal to or less than 0.40%, |Δ3| is equal to or less than 0.25%, and Δ1×|Δ3| is less than 0.08%.sup.2.