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 invention relates to the production of an anti-resonant hollow-core fiber consisting of a capillary blank and a sleeve tube. The capillary blank comprises an external capillary and a nested internal capillary, and is stretched to a maximum external diameter ODARE_cap and a maximum wall thickness WTARE_caP. The blank is mounted on the inside of the sleeve tube. In order to retain the advantages of the pre-produced capillary blank with respect to ease of assembly and precision, while keeping the associated drawbacks owing to ovality low and predictable, it is proposed that the geometric internal diameter and external diameter of the external capillary and of the internal capillary, as well as ODARE_cap and WTARE_caP, are aligned in relation to one another in such a way that the ARE-external capillary of the capillary blank has a degree of ovality of less than 1.025.

Methods are known for producing an anti-resonant hollow-core fiber which has a hollow core extending along a fiber longitudinal axis and an inner jacket region that surrounds the hollow core, said jacket region comprising multiple anti-resonant elements. The known methods have the steps of: providing a cladding tube that has a cladding tube inner bore and a cladding tube longitudinal axis along which a cladding tube wall extends that is delimited by an interior and an exterior; providing a number of tubular anti-resonant element preforms; arranging the anti-resonant element preforms at target positions of the interior of the cladding tube wall, thereby forming a primary preform which has a hollow core region and an inner jacket region; further processing the primary preform in order to form a secondary preform, including an elongation process; and drawing the secondary preform in order to form the hollow-core fiber. The aim of the invention is to achieve a high degree of precision and an exact positioning of the anti-resonant elements in a sufficiently stable and reproducible manner on the basis of the aforementioned methods. This is achieved in that after the primary preform is elongated, at least some of the formerly tubular anti-resonant element preforms of the primary preform have an oval outer cross-sectional shape with a longest cross-sectional axis A.sub.L and a shortest cross-sectional axis A.sub.K, wherein the ratio A.sub.L/A.sub.K of the length of the axes ranges from 1.01 to 1.27, and the shortest cross-sectional axis A.sub.K runs in a radial direction when viewed from the cladding tube longitudinal axis.

A method for producing a preform of an anti-resonant hollow-core fiber, which has a hollow core extending along a fiber longitudinal axis, and a cladding region surrounding the hollow core and includes at least one anti-resonance element. The method includes (a) providing a cladding tube having a cladding tube inner surface and a cladding tube outer surface, at least one anti-resonance element preform being arranged at the cladding tube inner surface, (b) providing an overlay tube including an overlay tube inner surface, the overlay tube having an inner diameter larger than an outer diameter of the cladding tube, (c) arranging the cladding tube inside the overlay tube, so that the overlay tube inner surface surrounds the cladding tube outer surface, and (d) adding the overlay tube to the cladding tube, so that the overlay tube inner surface connects to the cladding tube outer surface.

A method of manufacturing an optical fiber, the method includes drawing a first optical fiber preform at a first draw tension to produce a first alkali doped optical fiber and drawing the first optical fiber preform at a second draw tension to produce a second alkali doped optical fiber, measuring the attenuation of the first alkali doped optical fiber and the second alkali doped optical fiber such that the second alkali doped optical fiber has a lower attenuation. Additionally, the method includes setting the draw tension to the second draw tension and drawing a second optical fiber preform at the second draw tension to produce a third alkali doped optical fiber. The third alkali-doped optical fiber has an attenuation at 850 nm of about 1.50 dB/km or less and an attenuation at 1550 nm of about 0.155 dB/km or less.

The invention relates to a device, system, and method for forming a core-rod for optical fibers by collapsing a tube comprising deposited layers of silica to form the core-rod. The device comprises an elongate cavity, an elongate cylindrical carbon liner bounding the cavity, the liner connecting to a frame of the device at opposing end portions, a heating element in a heating element space, surrounding the liner, the liner separating the heating element space from the cavity, a ring of a refractory material, fixated to the frame, surrounding a part of a length of the cavity, the liner being provided such that an inner surface portion at a first end portion of the liner mates with a cylindrical outer surface portion of the ring such that the liner can axially move with the first end portion thereof along the outer surface portion of the ring.

Methods for producing glass components and obtainted glass component, e.g. optical fiber preform. A method includes providing a cladding tube (110) with a longitudinal axis including a first and a second bore separated by a chamfered region (114); inserting a spacer (120) into the first bore; inserting a rod (130) into the first bore (116); moving the spacer (120) into the chamfered section (114), causing the spacer (120) to rotate within the chamfered region (114); and rotating the cladding tube (110) into a vertical orientation, whereby the spacer (120) is prevented from entering the second bore (118) and supports the rod (130). Each portion of the chamfered region has a height perpendicular to the longitudinal axis greater than the height of the second bore. The spacer has a length parallel to the longitudinal axis greater than the height of the second bore but less the distance between the deepest point of the bottom of the chamfered region and an intersection of the top of the chamfered region and the first bore.

The present invention relates to a method of manufacturing an optical fiber preform for obtaining an optical fiber with low transmission loss. A core preform included in the optical fiber preform comprises three or more core portions, which are each produced by a rod-in-collapse method, and in which both their alkali metal element concentration and chlorine concentration are independently controlled. In two or more manufacturing steps of the manufacturing steps for each of the three or more core portions, an alkali metal element is added. As a result, the mean alkali metal element concentration in the whole core preform is controlled to 7 atomic ppm or more and 70 atomic ppm or less.

A method for producing substrate tubes of quartz glass includes continuously supplying a hollow cylinder of quartz glass to a heating zone, softening the hollow cylinder zonewise in the heating zone, and drawing off a tubular strand from the softened portion. The hollow cylinder has an outer diameter C.sub.a, an inner diameter C.sub.i and an inner bore. The tubular strand has an outer diameter T.sub.a and an inner diameter T.sub.i. The following parameters are applicable to the hollow cylinder and the tubular strand: C.sub.a>180 mm, C.sub.r>3 with C.sub.r=C.sub.a/C.sub.i, T.sub.r<1.6 with T.sub.r=T.sub.a/T.sub.i and C.sub.i/T.sub.i<2.5. The blow pressure in an inner bore is adjusted to a value in the range of 4 to 10 mbar. Substrate tubes, obtained by cutting the tubular strand to the desired length, serve as semi-finished products for the manufacture of preforms for optical fibers.

A process for manufacturing an MCF preform having a center longitudinal axis, a plurality of core rods each positioned in a respective core hole and extending along the axis, and a common cladding covering each of the plurality of core rods. The process includes the following steps. A cylinder is provided which will form the cladding of the preform and may have a center core hole. Peripheral core holes are created in the cylinder extending along the longitudinal axis. Each of a plurality of core rods is inserted into a respective peripheral core hole. The cylinder with the core rods inserted in the respective core holes is heated by exposing the cylinder and core rods to a heating element, thereby integrating the core rods and the cylinder and forming the preform, wherein the position error of the core holes with respect to the diameter of the preform is ?0.6%.