The present invention relates to a method for manufacturing a preform for optical fibers, which method comprises the sequential steps of: i) deposition of non-vitrified silica layers on the inner surface of a hollow substrate tube; ii) deposition of vitrified silica layers inside the hollow substrate tube on the inner surface of the non-vitrified silica layers deposited in step i); iii) removal of the hollow substrate tube from the vitrified silica layers deposited in step ii) and the non-vitrified silica layers deposited in step i) to obtain a deposited tube; iv) optional collapsing said deposited tube obtained in step iii) to obtain a deposited rod comprising from the periphery to the center at least one inner optical cladding and an optical core; v) preparation of an intermediate layer by the steps of: *deposition of non-vitrified silica layers on the outside surface of the deposited tube obtained in step iii) or deposited rod obtained in step iv) with a flame hydrolysis process in an outer reaction zone using glass-forming precursors, and subsequently; *drying and consolidating said non-vitrified silica layers into a vitrified fluorine-doped silica intermediate cladding layer; and *in case preceding step iv) was omitted collapsing; to C provide a solid rod comprising from the periphery to the center the intermediate layer, at least one inner optical cladding and an optical core; wherein a fluorine-comprising gas is used during the deposition and/or drying and/or consolidating and wherein the intermediate layer has a ratio between the outer diameter of the intermediate cladding layer (C) to the outer diameter of the optical core (A) that is at least 3.5; vi) deposition of natural silica on the outside surface of the intermediate cladding layer of the solid rod obtained in step v) by melting natural silica particles in an outer deposition zone to produce an outer cladding whereby a preform is obtained.

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.

In order to improve the yield of an optical fiber base material, provided is a manufacturing apparatus for manufacturing an optical fiber base material by forming a soot deposition body on a surface of a target rod, including a main burner that generates glass microparticles to be deposited on the target rod while moving in a longitudinal direction of the target rod; a pair of side burners that are arranged outside a movement range of the main burner and heat both ends of the soot deposition body formed on the surface of the target rod; and a shielding member that prevents the glass microparticles generated by the main burner from being deposited on the target rod farther outward than a segment of the target rod sandwiched by the pair of side burners.

Provided is a manufacturing apparatus for manufacturing a soot deposition body, including a main burner that deposits glass microparticles on a target rod while moving parallel to a longitudinal direction of the target rod; and a side burner that is positioned outside of a movement range of the main burner in a movement direction of the main burner, and fires an end portion of the soot deposition body formed on the target rod. The side burner includes a plurality of heating burners arranged distanced from each other in a circumferential direction of the target rod. In the manufacturing apparatus described above, the main burner may include a plurality of deposition burners that are arranged distanced from each other in the circumferential direction of the target rod.

A production method of an optical fiber preform includes first preparing a first preform having a plurality of glass preforms and a first cladding portion disposed between the plurality of glass preforms, and first arranging a second cladding portion to surround the first preform. At the first arranging, a material gas and a combustion gas are ejected from a burner to produce glass particles. The first preform and the burner are moved relative to each other in a longitudinal direction of the first preform. The glass particles are deposited on the first preform.

A known method for producing a tubular quartz glass composite body in an outer deposition process comprises providing and rotating a substrate tube about an axis of rotation, depositing SiO.sub.2 particles on the outer jacket surface of the tube forming a composite consisting of the tube and a SiO.sub.2 soot body, and sintering the composite by heating to form the tubular quartz glass composite body, and using a holding device which is suitable for holding the composite body at least temporarily in the heating zone with the longitudinal axis of the substrate tube oriented vertically. To enable the production on this basis of a tubular composite body consisting of quartz glass with a particularly large inner diameter and with a wall with reduced scrap, it is proposed that a holding device is used which comprises a holding element which is produced in a holding region of the substrate tube.

A method for producing a tubular quartz glass composite body in an outside deposition method comprising the following method steps: providing a substrate tube, rotating the substrate tube about a rotation axis, depositing SiO.sub.2 particles on the outer lateral surface of the substrate tube to form a composite consisting of the substrate tube and an SiO.sub.2 soot body, and sintering the composite by heating at a sintering temperature to form the tubular quartz glass composite body. A substrate tube is provided which consists at least partially of quartz glass of a first quartz glass quality, and that the soot body consist of quartz glass of a second quartz glass quality, wherein the first quartz glass quality has a material-specific viscosity at the sintering temperature that is higher than the material-specific viscosity of the second quartz glass quality.

A device for producing a tubular SiO.sub.2 blank in an external deposition process has a substrate tube and a substrate tube holder comprising a clamping device, which is designed to support the substrate tube and to rotate the substrate tube about an axis of rotation. In order to provide, on this basis, a reproducible and operationally reliable holder for a large-volume, tubular SiO.sub.2 blank in an external deposition process, it is proposed that the substrate tube holder comprise a clamping mechanism which has a first pressure unit abutting the first substrate tube end face, a second pressure unit abutting the second substrate tube end face, and at least one force element which is designed to generate an axial contact pressure with a force component acting in the direction of the longitudinal axis of the substrate tube.

A method of manufacturing synthetic quartz glass through an outside vapor deposition (OVD) process with improved deposition efficiency. When a hollow cylindrical synthetic quartz glass product is manufactured through an OVD method or the like, it is environmentally friendly in view of using a smaller amount of chlorine and is economical in view of requiring no separate treatment equipment, as compared to a conventional technique using silicon chloride (SiCl.sub.4). Also, the method, in which octamethylcyclotetrasiloxane is supplied to a deposition burner while being sprayed in the form of a droplet along with a high-pressure carrier gas and vaporized by the deposition burner, can effectively address the high-temperature heating and slow decomposition involved when octamethylcyclotetrasiloxane ([(CH.sub.3).sub.2SiO].sub.4) is used as a source for depositing silicon dioxide particles.

A method of manufacturing a hollow core optical fiber including (a) a consolidated tube presenting step including presenting a consolidated cladding tube including a consolidated cladding first end, a consolidated cladding second end, a consolidated cladding longitudinal axis, and a consolidated cladding inner surface, the consolidated cladding inner surface defining a consolidated cladding interior and including consolidated cladding recesses (i) positioned around the consolidated cladding longitudinal axis and (ii) extending from the consolidated first end to the consolidated second end; and (b) a capillary tube coupling step comprising coupling preform capillary tubes to the consolidated cladding inner surface within the consolidated cladding recesses thus creating an optical fiber preform, each of the preform capillary tubes disposed within a different one of the consolidated cladding recesses.