A manufacturing method that enables stably making a high-quality optical fiber is provided. The manufacturing method of the present invention comprises: a softened portion falling step in which an optical fiber preform is heated in a heating furnace and a dropping part of softened portion of the preform thus heat-softened is allowed to drop; and a drawing step for drawing the preform such that the softened glass is drawn into a fiber by applying a tension with a take-up means after the softened portion falling step, whereas the preform is rotated about its axis at the softened portion falling step.

A method of manufacturing an optical fiber includes heating a distal end portion of an optical fiber preform made of glass; drawing a glass fiber from the distal end portion softened by the heating; and forming a coating layer made of resin on the glass fiber to form an optical fiber. The drawing includes periodically varying a tension that is applied to the glass fiber to vary a diameter of the glass fiber and a residual stress in an axial direction of the glass fiber so as to be in phases opposite to each other along the axial direction.

Provided is a glass base material hanging mechanism that, when hanging a starting member or a glass base material, can tightly (solidly) connect the hanging shaft tube and the hanging component and can vertically align the hanging component and the center of the glass base material.

A gripping mechanism includes: a plurality of chuck claws that, when having come close to each other, generate a gripping force on a gripped body; a chuck body that holds the plurality of chuck claws on a common planar surface, and moves them on the planar surface; and a plurality of chuck plates that, when each of the plurality of chuck claws grips the gripped body, are interposed between each of the plurality of chuck claws and the gripped body, wherein a thermal expansion coefficient .sub.l of the plurality of chuck claws, a thermal expansion coefficient .sub.2 of the plurality of chuck plates and a thermal expansion coefficient .sub.W of the gripped body has a relationship indicated by Equation 1:

.sub.W<.sub.1<.sub.2 (Equation 1)

Capacity of space in a drawing furnace is decreased so as to reduce variations in pressure in the furnace and also the side of an insertion port of a glass perform is stably sealed. When drawing is started, an outer peripheral surface of the optical fiber glass preform 11 is sealed with a first seal part 17 of the seal mechanism. After a vicinity of a taper part of the optical fiber glass preform 11 starts to pass through the first seal part 17, switching to a second seal part 18 arranged above the first seal part 17 is performed, and an outer peripheral surface of a sleeve member 20 fixed so as to surround an outer periphery of the dummy rod 12 is sealed with the second seal part 18.

A method for producing a preform for an antiresonant hollow-core fiber involves providing a cladding tube comprising a cladding tube inner bore with a cladding tube inside and a central cladding tube axis, providing a plurality of tubular antiresonance element preforms (ARE preforms for short), each comprising a longitudinal tube axis and an outer tube surface, initially positioning the ARE preforms in peripheral desired positions of the cladding tube inner side by means of a positioning aid to form a primary preform, and thermally stretching the primary preform to form the hollow-core fiber or further processing the primary preform to form a secondary preform from which the hollow-core fiber is drawn.

A drawing furnace for drawing a glass element includes: a furnace body having an upper end and a lower end. The furnace body includes a top annular plate, an A/C induction coil capable of accepting electrical current and producing an oscillating electronic signal, a cylindrical susceptor capable of producing heat output, a cylindrical quartz beaker, an insulating material disposed between the susceptor and the beaker, and a bottom annular plate housing and supporting at least one of the susceptor, the beaker, and the insulating material. wherein the furnace body comprises a central longitudinal axis; A rotational drive system operably connected to the bottom annular plate by an annular rotation gear system rotates the bottom annular plate along with the susceptor, beaker, and/or insulating material at a frequency between 0.01 to 10 Hz. The electrical current and oscillation frequency determine the heat output of the susceptor.

Provided is an optical-fiber-coating composition. The optical-fiber-coating composition includes: a photo-curing oligomer with 35% to 95% of a weight of the composition, a photo-curing active monomer with 1% to 45% of the weight of the composition, a photo-initiator with 0.5% to 15% of the weight of the composition, and an auxiliary agent with 0.1% to 10% of the weight of the composition, wherein the photo-initiator includes at least one of compounds represented by a following general formula I:

##STR00001##