According to a fabrication method for fabricating a porous glass base material for optical fiber, the orientation of a clad forming burner used to form the outermost layer of a clad-corresponding portion is changed further upward while glass fine particles are deposited during the period between a first timing and a second timing. At the first timing, the outer diameter of the porous glass base material for optical fiber has not reached a target outer diameter. The second timing is later than the first timing, and either a timing at which the outer diameter of the porous glass base material for optical fiber reaches the target outer diameter for the first time, or a timing prior to this timing.

A horizontal lathe for manufacturing a porous optical fiber preform, the horizontal lathe being configured to hold and fix two opposite ends of a target in such a manner that a longitudinal direction of the target is a substantially horizontal direction, and cause the target to be rotated around an axis parallel to the longitudinal direction thereof as a rotation axis. The horizontal lathe includes a thermal expansion absorbing mechanism configured to absorb a change in dimension of the target, the change being due to thermal expansion of the target in a direction of the rotation axis.

A lathe system for producing an optical fiber preform, the lathe system including a rotating bait rod, a burner box configured to deposit silica-containing soot on the rotating bait rod, a hood configured to direct airflow within the lathe system through an exhaust, and a perforated floor configured to expel air within the lathe system as a plurality of air jets from a bottom portion of the lathe system to a top portion of the lathe system.

According to a fabrication method for fabricating a porous glass base material for optical fiber, the orientation of a clad forming burner used to form the outermost layer of a clad-corresponding portion is changed further upward while glass fine particles are deposited during the period between a first timing and a second timing. At the first timing, the outer diameter of the porous glass base material for optical fiber has not reached a target outer diameter. The second timing is later than the first timing, and either a timing at which the outer diameter of the porous glass base material for optical fiber reaches the target outer diameter for the first time, or a timing prior to this timing.

To prevent a lowering of gripping force due to temperature changes, provided is a gripping mechanism including 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. A thermal expansion coefficient .sub.1 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 have a relationship indicated by
.sub.W<.sub.1<.sub.2(Equation 1).

A rotary feed-through for mounting a rotating substrate tube in a lathe and providing a flow of process gas into the tube, said feed-through including a process gas supply line for providing a process gas into said substrate tube, a rotatable holder arranged for receiving and holding said substrate tube for rotating said substrate tube with respect to said process gas supply line, a rotary union provided between said rotatable holder and said process gas supply line for rotatably connecting said rotatable holder to said process gas supply line, a stationary housing connected to said process gas supply line and to said rotatable holder, therewith forming a closed cavity surrounding said rotary union, wherein said stationary housing further includes an auxiliary gas supply line for providing said closed cavity with an auxiliary gas.

A production apparatus capable of suppressing the generation of rusts on a base material gripper and a rotation mechanism is provided in a production of a porous glass preform. In an apparatus for producing a porous glass preform by depositing glass fine particles, produced by a flame hydrolysis reaction using a burner, on a starting member gripped by a base material gripper in a reaction vessel, the base material gripper is covered with a cover, and gas is supplied to the inside of the cover and the gas is caused to flow from the inside of the cover to an inside of the reaction vessel.

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)