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.

A method of producing photonic crystal fibers (PCFs) is disclosed, the method includes: 1) obtaining an intermediate PCF having an initial outer fiber diameter of less than 1 mm; and 2) elongating the intermediate PCF so as to controllably reduce at least one dimension of the intermediate PCF.

An optical fiber preform of the present embodiment comprises a core portion and a cladding each comprised of silica glass. The core portion has a first dopant region including a central axis of the core portion and a second dopant region away from the central axis. The first dopant region contains a first dopant selected from among Na, K, and their compounds, and a concentration of the first dopant is 10 atomic ppm or more but 2,000 atomic ppm or less. The second dopant region contains a second dopant reducing viscosity of the silica glass. The second dopant has, as a characteristic at a temperature of 2,000 C. to 2,300 C., a diffusion coefficient of 110.sup.12 cm.sup.2/s or higher but lower than that of the first dopant, and a concentration of the second dopant region is 10 atomic ppm or more.

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.

There is provided a method for producing a multicore optical fiber while reducing the mass of a glass block to be connected to a common cladding tube. A production method for a multicore optical fiber includes in order, a preform forming step of forming a common cladding tube having a plurality of holes extending between a first end and a second end, an insertion step of inserting core rods in the holes in a state in which end portions of the core rods are recessed from the first end, a heat shrinkage step of reducing a diameter of the first end by heating, a sealing step of sealing the holes by connecting a glass block to the first end, and a drawing step of depressurizing insides of the holes from the second end and performing spinning from the first end while combining the common cladding tube and the core rods.

A method for producing an optical fiber includes heating and melting an optical fiber preform and drawing the optical fiber preform. In this method for producing an optical fiber, the optical fiber is formed to include a core, a surrounding cladding surrounding a periphery of the core, and an outer cladding surrounding the surrounding cladding. In the drawn optical fiber, a maximum compressive stress of at least 100 MPa or more is applied to an optical waveguide region including at least the core.

A glass base material elongating method of sequentially feeding rod-like glass base materials hung by a glass base material feeding mechanism into a heating furnace, and pulling a glass rod with a smaller diameter by a pulling chuck at a lower part of the heating furnace, includes: aligning, by an alignment guiding device that guides the glass rod, a guiding center of the alignment guiding device with an axis of the glass rod, the alignment guiding device guiding the glass rod between the heating furnace and the pulling chuck.

Systems and methods for drawing high aspect ratio metallic glass-based materials are provided. Methods of drawing a high aspect ratio metallic glass-based material are premised on stably drawing high aspect ratio metallic glass-based material from a preform metallic glass-based composition, accounting for the relationships between: the desired formation of an amorphous structure that is substantially homogenous along the majority of the length of the drawn high aspect ratio material; the desired final geometry of the drawn high aspect ratio material; the nature of the force that is used to draw the molten metallic glass-based composition; the velocity at which the high aspect ratio material is drawn; the viscosity profile of the material along its length as it is being drawn; and/or the effect of temperature on the metallic glass-based material. A precise thermal treatment is imposed along the forming length of the drawn material so as to enable a steady state drawing process, the precise thermal treatment being based on: the desire to develop a substantially same amorphous structure along the length of the drawn material; the desired final geometry for the drawn material; the nature of the force used to draw the material; the velocity at which the material is being drawn; and/or the thermal treatment's impact on the viscosity profile of the material along its length as it is being drawn.

A method for manufacturing an optical preform including the steps of providing a substrate tube having deposited layers of glass on an inside surface thereof, increasing an outer diameter of the substrate tube by means of applying a traversing heat source to heat the substrate tube to above a softening temperature thereof and by providing an internal pressure in the substrate tube higher than an ambient pressure, and collapsing the substrate tube of increased outer diameter by means of applying the traversing heat source to heat the substrate tube to above the softening temperature thereof such that an optical preform is manufactured.

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; and elongating the primary preform in order to form the hollow-core fiber or further processing the primary preform in order to form a secondary preform. 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 the step of providing and/or arranging the anti-resonant element preforms and/or the process of carrying out a hot-forming process includes a fixation measure and/or a sealing measure using an amorphous SiO.sub.2 particle-containing sealing or joining compound.