Patent ID: 9458051
Filing Date: 2016-10-04
CPC Classification: C03B

Claim Text:
1. A method of producing an optical fiber preform, comprising: forming an optical fiber porous preform; dehydrating and sintering the optical fiber porous preform by using a graphite heating furnace of which at least a part of a furnace body is formed with a graphite, wherein the graphite heating furnace includes a reaction container and a furnace body which surrounds the reaction container and in which a heater is displaced; setting, by a purifying equipment, a dew-point temperature of a nitrogen gas supplied into the furnace body to be equal to or lower than −80° Celsius; wherein in the dehydrating and sintering, the reaction container accommodating the optical fiber porous preform therein, supplying, by a supplying unit, the nitrogen gas into the furnace body, and exhausting, by an exhausting unit, a gas including a hydrogen-cyanide gas inside the furnace body to outside of the furnace body, the exhausting unit connected to an exhaust-gas treatment equipment to detoxify the gas exhausted, wherein an interior of the reaction container and an interior of the furnace body are separated by the reaction container with a space provided between an end of the furnace body and the reaction container, wherein the space couples the interior of the furnace body to an atmosphere surrounding the outside of the furnace body such that gas can flow from the furnace body through the space directly to the atmosphere surrounding the outside of the furnace body, wherein the space is to discharge at least a part of the gas including the hydrogen-cyanide gas inside the furnace body directly to the atmosphere surrounding the outside of the furnace body, and wherein a pressure inside the furnace body is equal to or higher than 140 pascals with respect to an atmospheric pressure of the atmosphere outside the furnace body.