Furnace for Drawing Optical Fiber Preform to Make Optical Fiber and Method for Drawing Optical Fiber Using the Same

A furnace for drawing an optical fiber comprising:

• a furnace body having an upper opening through which a preform may enter the furnace and a lower opening for discharging an optical fiber drawn from a preform, the furnace body further comprising an inner wall;
• a first core tube installed spaced apart from the inner wall of the furnace body to form a first passage between the first core tube and the inner wall of the furnace body, the first core tube forming a melting area therein to heat and melt a preform entering the furnace from the upper opening;
• a second core tube installed spaced apart from the inner wall of the furnace body to form a second passage between the second core tube and the inner wall of the furnace body, the second core tube having a diameter smaller than the first core tube, the second core tube being installed partially inserted into a lower end of the first core tube to thereby form a third passage, between the first and second core tubes;
• an upper introduction port formed at an upper portion of the furnace body to permit introducing an inert gas toward a preform, a portion of such inert gas being dischargeable out of the furnace through the upper opening;
• a central introduction port formed at a central portion of the furnace body, the port communicating from outside of the furnace body to the first passage formed between the first core tube and the inner wall of the furnace body, to permit introducing an inert gas into the first passage;
• a lower introduction port formed at a lower portion of the furnace body, the port communicating from outside the furnace body to the second passage formed between the second core tube and the inner wall of the furnace body to permit introducing an inert gas into the second passage;
• a support flange interposed between the first passage and second passage to divide the first passage and second passages;
• and
• an atmosphere blocking tube installed at the lower opening for forming a fourth passage in which inert gas introduced through the second passage can flows between the second core tube and the atmosphere blocking tube, the atmosphere blocking tube permitting the passage of a drawn optical fiber therethrough without immediate exposure of said drawn optical fiber to the atmosphere external to the furnace.

A method for drawing an optical fiber by melting a preform in a furnace which includes a furnace body having an upper opening for supplying a preform, a lower opening for discharging an optical fiber drawn from the preform, and upper, central and lower introduction ports for introducing an inert gas;

• heating means installed in the furnace body to receive and melt the preform in a melting area therein;
• and an atmosphere blocking tube installed at the lower opening to ensure the passage of the drawn optical fiber therein, wherein the method comprises the steps of:
• (a) supplying a preform into the melting area through the upper opening;
• (b) melting the preform by heating the preform with the heating means;
• (c) drawing an optical fiber from a melted portion of the preform at its lower end;
• (d) introducing an inert gas through the upper introduction port so that the inert gas is partially discharged outside through a gap between the preform and the upper opening;
• (e) introducing an inert gas through the central introduction port so that the inert gas flows upward in the melting area and collides with the flow of inert gas introduced through the upper introduction port, and then flows downward along a surface of the preform;
• and
• (f) introducing an inert gas through the lower introduction port so that the inert gas flows upward along the melting area and then collides with the inert gas introduced through the central introduction port, and is then discharged outside through the atmosphere blocking tube along the surface of the drawn optical fiber.