Apparatus and method for overcladding optical fiber preform rod and optical fiber drawing method

A method for overcladding an optical fiber preform rod in an optical fiber preform rod overcladding apparatus having a vertical lathe including top and bottom chucks, a ring-shaped oxygen-hydrogen burner, a furnace for heating or preheating a glass tube, and a carriage for vertically moving between both chucks, a vacuum pump disposed at one end of the vertical lathe, a coupler connected between the vacuum pump and one of the chucks, and a controller for controlling for the vertical movement of the carriage, the flow rate of the oxygen-hydrogen, and the rotation of the chucks, the method comprising the steps of

• clamping the preform rod in the top chuck and making vertical the preform rod;
• connecting a glass tube to a support tube;
• mounting the support tube in the bottom chuck and making vertical the glass tube;
• coaxially inserting the preform rod into the glass tube by lowering the top chuck;
• preheating the glass tube by utilizing the furnace and heating the glass tube by utilizing the burner until the glass tube reaches a softening point;
• and
• completely sealing the preform rod in the glass tube by sucking air from a gap between the preform rod and the glass tube by application of a negative vacuum pressure, to thereby complete a preform.

A method for overcladding an optical fiber preform rod in an optical fiber preform rod overcladding apparatus having a vertical lathe including top and bottom chucks, a ring-shaped oxygen-hydrogen burner, a furnace for heating or preheating a glass tube, and a carriage for vertically moving between both chucks, a vacuum pump disposed at one end of the vertical lathe, a coupler connected between the vacuum pump and one of the chucks, and a controller for controlling for the vertical movement of the carriage, the flow rate of the oxygen-hydrogen, and the rotation of the chucks, the method comprising the steps of:

• clamping the preform rod in the top chuck and making vertical the preform rod;
• connecting a glass tube to a support tube;
• mounting the support tube in the bottom chuck and making vertical the glass tube;
• coaxially inserting the preform rod into the glass tube by lowering the top chuck;
• depositing a silica layer having a matching viscosity in a gap between the preform rod and the glass tube, while controlling the viscosity of the preform rod and the glass tube by injecting SiCl.sub.4 and a glass forming material into the gap between the preform rod and the glass tube;
• preheating the glass tube by the furnace and heating the glass tube by the burner until the glass tube reaches a softening point;
• and
• completely sealing the preform rod in the glass tube by sucking air in the clearance between the preform rod and the glass tube by application of a negative vacuum pressure, to thereby complete a preform.

An optical fiber drawing method comprising the steps of:

• sealing one end of a preform rod to one end of a glass tube;
• clamping an unsealed end of the preform rod and an unsealed end of the glass tube in a chuck provided to a feed module in an optical fiber drawing apparatus;
• connecting a vacuum pump to the unsealed ends of the preform rod and glass tube;
• aligning the sealed ends of the preform rod and the glass tube in a hot zone of a furnace in the optical fiber drawing apparatus;
• collapsing the glass tube onto the preform rod by preheating the sealed ends of the preform rod by utilizing the furnace, heating the sealed ends with a burner until the sealed ends thereof are softened, and removing air from a gap between the preform rod and the glass tube by utilizing the vacuum pump, thereby forming a preform;
• drawing an optical fiber from the preform by utilizing the furnace to heat the preform;
• and
• measuring an outer diameter of the optical fiber drawn from the furnace;
• cooling the optical fiber after the measuring step;
• and
• coating the optical fiber with a curing resin, following the cooling step.