Patent ID: 7823419

Claim:
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.