A method is described for manufacturing an optical fiber preform, including a tube collapsing phase, and including monitoring the concentration of at least one fluid component of a fluid that is exhausted from the tube, to detect structural integrity of the tube. A system is also described for manufacturing optical fiber preforms. The system comprising a holder configured to hold a tube, a heater configured to heat at least part of the tube to a tube collapsing temperature, a fluid exhaust configured to discharge fluid from the tube, held by the holder. The system also includes a tube integrity monitor configured to monitor structural integrity of the tube, during a collapsing phase, by monitoring fluid that is discharged from the tube.

A photodarkening-resistant ytterbium-doped quartz optical fiber and a method for preparing such a fiber are provided. Glass of a photodarkening-resistant ytterbium-doped quartz optical fiber core rod includes at least Yb.sub.2O.sub.3, Al.sub.2O.sub.3, P.sub.2O.sub.5, SiO.sub.2. The proportions of Yb.sub.2O.sub.3, Al.sub.2O.sub.3, and P.sub.2O.sub.5 in the entire substance are Yb.sub.2O.sub.3: 0.05-0.3 mol %, Al.sub.2O.sub.3: 1-3 mol %, and P.sub.2O.sub.5: 1-5 mol %, respectively. In the preparation method for the photodarkening-resistant ytterbium-doped quartz optical fiber, a sol-gel method and an improved chemical vapor deposition method are combined. By using the molecular-level doping uniformity and the low preparation loss thereof respectively, ytterbium ions, aluminum ions and phosphorus ions are effectively doped in a quartz matrix, thereby effectively solving the problems in the optical fiber of high loss, photodarkening caused by cluster or the like, and a central refractive index dip.

The present embodiment relates to an optical fiber preform producing method for effectively suppressing breaking of symmetry of refractive index profile defined on a cross section of an optical fiber preform. In the present embodiment, when producing a center glass rod forming a part of the optical fiber preform, prior to grinding an outer peripheral portion of an intermediate glass rod in which an element-doped region is formed by collapse, an non-defective article determination regarding the intermediate glass rod to be a grinding target is performed.

The present embodiment relates to an optical fiber preform producing method for effectively suppressing breaking of symmetry of refractive index profile defined on a cross section of an optical fiber preform. In the present embodiment, when producing a center glass rod forming a part of the optical fiber preform, prior to grinding an outer peripheral portion of an intermediate glass rod in which an element-doped region is formed by collapse, an non-defective article determination regarding the intermediate glass rod to be a grinding target is performed.

A method for manufacturing an optical fiber preform including a core part and a cladding part is disclosed. The method includes: adding an alkali metal to an inner surface of a silica-based glass pipe; etching the inner surface of the silica-based glass pipe to which the alkali metal is added; making a glass rod by collapsing the silica-based glass pipe after the etching; and making an optical fiber preform using the glass rod. The silica-based glass pipe is heated in the adding such that a surface temperature of the silica-based glass pipe falls within a temperature range of 1500 C. or higher to lower than 2000 C.

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 for preparing a doped optical fibre preform includes formulating, a rare earth material or a functional metal material and a co-doping agent into a doping solution, mixing a high-purity quartz powder with the doping solution, drying same at a temperature of 100 C.-150 C. for 12-48 hours, crushing and screening the same to obtain a doped quartz powder; depositing the doped quartz powder onto the surface of a target rod to form a doped core layer; replacing the doped quartz powder with the high-purity quartz powder, and depositing the high-purity quartz powder onto the surface of the doped core layer to form a quartz outer cladding; and removing the target rod, and gradually collapsing the entirety formed from the doped core layer and the quartz outer cladding at a high temperature to obtain the doped optical fibre preform.

The invention relates to exemplary methods, devices, and systems for heating an elongate silica cylinder to form a core-rod for optical fibers. An exemplary heating device includes an elongate cavity, an elongate liner bounding the cavity, a heating element in a heating element space surrounding the liner, the liner separating the heating element space from the cavity, and a gas flushing device for effecting a flow of gas at least through the heating element space. An exemplary method includes providing the elongate silica cylinder such that it extends through the cavity, heating the cylinder locally beyond its softening temperature, and effecting a flow of argon and nitrogen gas during the heating.

Provided is an optical fiber containing an alkali metal element or the like having a smaller diffusion coefficient than K and having a low Rayleigh scattering loss. An optical fiber is composed of silica glass and includes a core and a cladding arranged to surround the core which has a lower refractive index than the core. The core includes a first core including a central axis and a second core arranged to surround the first core. The average concentration of an alkali metal element or alkaline-earth metal element in the first core is 10 mol ppm or less. The average concentration of chlorine in the first core is 2000 mol ppm or more. The average concentration of an alkali metal element or alkaline-earth metal element in the second core is 10 mol ppm or more. The average concentration of chlorine in the second core is 10 to 600 mol ppm.

The present application provides a process of fabrication of erbium and ytterbium-co-doped multielements silica glass based cladding-pumped fiber for use as a highly efficient high power optical amplifier.