A method of manufacturing a porous glass preform includes depositing glass particles on an outer periphery of a target rod while a burner for synthesizing glass particles and the target rod that is rotating are relatively reciprocated, wherein V and r are gradually reduced while a variation in sweeping pitch P [mm] expressed as V/r is caused to be within a range of a central value±10% when a glass particle deposition layer of a portion satisfying a relation 0.5L≦R≦0.8L is synthesized; where a final outer diameter of the manufactured porous glass preform for an optical fiber is L [mm], an outer diameter of a glass particle deposition body in the middle of the manufacture is R [mm], a rotating speed of the target rod is r [rpm], and a relative moving speed between the target rod and the burner is V [mm/min.].

A method of manufacturing a porous glass preform includes depositing glass particles on an outer periphery of a target rod while a burner for synthesizing glass particles and the target rod that is rotating are relatively reciprocated, wherein V and r are gradually reduced while a variation in sweeping pitch P [mm] expressed as V/r is caused to be within a range of a central value±10% when a glass particle deposition layer of a portion satisfying a relation 0.5 L≤R≤0.8 L is synthesized; where a final outer diameter of the manufactured porous glass preform for an optical fiber is L [mm], an outer diameter of a glass particle deposition body in the middle of the manufacture is R [mm], a rotating speed of the target rod is r [rpm], and a relative moving speed between the target rod and the burner is V [mm/min.].

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.

Multi-core optical fiber ribbons and methods for making multi-core optical fiber ribbons are described herein. In one embodiment, a multi-core optical fiber ribbon includes at least two core members formed from silica-based glass and oriented in parallel with one another in a single plane. Adjacent core members have a center-to-center spacing ≧15 microns and a cross-talk between adjacent core members is ≦−25 dB. In this embodiment each core member is single-moded with an index of refraction n.sub.c, and a core diameter d.sub.c. In an alternative embodiment, each core member is multi-moded and the center-to-center spacing between adjacent core members is ≧25 microns. A single cladding layer is formed from silica-based glass and surrounds and is in direct contact with the core members. The single cladding layer is substantially rectangular in cross section with a thickness ≦400 microns and an index of refraction n.sub.cl<n.sub.c.

A shaped tube (50,51) for use as a component in the fabrication of an antiresonant hollow core optical fibre, the shaped tube having a side wall with a transverse cross-sectional shape comprising a number of major curved portions (52) alternating with the same number of minor substantially straight portions (54), each curved portion (52) having an inwardly curving shape, and each straight portion (54) being equidistant from a central longitudinal axis of the shaped tube (50,51).

A shaped tube (50,51) for use as a component in the fabrication of an antiresonant hollow core optical fibre, the shaped tube having a side wall with a transverse cross-sectional shape comprising a number of major curved portions (52) alternating with the same number of minor substantially straight portions (54), each curved portion (52) having an inwardly curving shape, and each straight portion (54) being equidistant from a central longitudinal axis of the shaped tube (50,51).

Provided are such a method of manufacturing a hollow synthetic quartz glass porous preform and method of manufacturing a synthetic quartz glass cylinder as described below: even a soot body having an outer diameter of more than 300 mm can be produced without significantly increasing a load on an apparatus, such as a centrifugal force generated during growth; even when manufactured at low-speed rotation, the soot body is free of any crack or rupture; and a target can be easily extracted. Specifically, provided is a method of manufacturing a hollow porous quartz glass preform by an OVD method, wherein the rotation peripheral speed of the soot body is controlled so as to be practically constant by fluctuating the rotation number of the soot body on the basis of a fluctuating outer diameter of the soot body during growth, and wherein a frequency factor γ calculated by the following equation is set so as to fall within the range of 0.13≤γ<1.0 in a range in which the outer diameter of the soot body is more than 250 mm: γ=S/(L.Math.N.sub.m), where S represents the moving speed (mm/min) of the burners, L represents the moving distance (mm) of the burners, and N.sub.m represents the lowest value (rpm) of the rotation number of the soot body, which is fluctuated.

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 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 for manufacturing an optical fiber preform includes generating glass particles from a glass raw material gas in a flame obtained by combustion of a combustible gas supplied to a burner and depositing the glass particles on an outer circumference of a silica glass pipe to form a hollow porous glass preform, inserting a rod into the silica glass pipe, transparently vitrifying the porous glass preform by heating the porous glass preform after inserting the rod to obtain a transparent glass preform, drawing out the rod from the silica glass pipe after the porous glass preform is transparently vitrified, and removing the silica glass pipe from the transparent glass preform by etching after drawing out the rod.

An apparatus for manufacturing an optical fiber preform, the apparatus including: a reaction vessel in which an initial substrate is arranged; a burner that can be inserted from an opening of the reaction vessel to spray a glass soot on the initial substrate in the reaction vessel; and a sealing member that has an internal space for accommodating the burner, and is extendable in accordance with a position of the burner and airtightly connects the opening and the internal space.