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.

An exemplary method for preparing a primary preform by etching and collapsing a deposited tube includes mounting a deposited tube on a lathe and introducing the deposited tube into a central aperture of a furnace mounted on the lathe, wherein the furnace and the deposited tube are movable in axial direction with respect to each other, and creating within the furnace a hot zone that moves in translation back and forth over the length of the deposited tube during one or more cycles, wherein (i) during at least one cycle at least part of the outside of the deposited tube is etched by supplying a fluorine-containing etching gas to an annular region between the outer surface of the deposited tube and the central aperture of the furnace, and (ii) during at least one cycle the deposited tube is collapsed.

A method activates the inner surface of a substrate tube via plasma etching with a fluorine-containing etching gas. An exemplary method includes the steps of (i) supplying a supply flow of gas to the interior of a substrate tube, wherein the supply flow includes a main gas flow and a fluorine-containing etching gas flow, (ii) inducing a plasma via electromagnetic radiation to create a plasma zone within the substrate tube's interior, and (iii) longitudinally reciprocating the plasma zone over the length of the substrate tube between a reversal point near the supply side and a reversal point near the discharge side of the substrate tube. The flow of the fluorine-containing etching gas is typically provided when the plasma zone is near the supply side reversal point.

A method of manufacturing an optical fiber, the method including mounting a glass sleeve in a selective etching apparatus. The sleeve comprising one or more axial through-holes, and the etching apparatus comprising a first end cap with a central aperture disposed therethrough, the first end cap being attached to a first surface of the sleeve. The method further including exposing the sleeve to an acid solution such that a first portion of the first surface is exposed to the acid solution and a second portion of the first surface is not exposed to the acid solution. The first portion being adjacent to the central aperture when the sleeve is mounted in the selective etching apparatus, and the second portion being covered by the first end cap when the sleeve is mounted in the selective etching apparatus.

A method for manufacturing a preform for a multicore fiber, including stacking (S1) a plurality of core rods and a plurality of silica-based filler rods in a tube; collapsing (S2) the tube around the stack of core rods and silica-based filler rods, forming a collapsed stack; depositing (S3) a layer of silica around the collapsed stack; removing (S4) at least part of the deposited layer of silica. The preferential process for depositing a layer of silica around the collapsed stack and removing at least part of the deposited layer of silica is Advanced Plasma and Vapor Deposition.

A method for manufacturing an optical fiber preform includes: adding an alkali metal element or an alkaline earth metal element to an inner surface of a glass pipe made of silica-based glass; reducing a diameter of the glass pipe after the adding; etching an inner surface of a continuous section of the glass pipe in a longitudinal direction after the reducing; and collapsing the glass pipe after the etching. At least one of the adding, the reducing, the etching, and the collapsing includes performing a local etching on an inner surface of a section of the glass pipe that is shorter than the continuous section.

A multicore fiber includes: a plurality of first glass regions each including: a core portion; and a first cladding portion having a lower refractive index than a maximum refractive index of the core portion; and a cladding region formed on outer peripheries of the plurality of first glass regions, wherein compressive stress is applied to the plurality of first glass regions.

A method for manufacturing an optical fiber preform made of silica-based glass, the method including: forming a core portion; and forming a cladding portion surrounding the core portion, the cladding portion having a refractive index lower than a refractive index of the core portion, wherein the forming the core portion includes: adding an alkali element group consisting of an alkali metal element and an alkaline earth metal element to an inner surface of a glass pipe made of silica-based glass; and integrating the glass pipe and a glass rod disposed inside the glass pipe to form an integrated rod after the adding.