The present disclosure generally relates to methods and apparatus for forming optical fibers and, more particularly, relates to an optical fiber production method for capturing and recycling gases used in optical fiber production.
Conventional manufacturing processes for producing optical fibers typically include drawing an optical fiber from an optical fiber preform in a draw furnace, cooling the drawn fiber, and coating the fiber after it has sufficiently cooled. The optical fiber is typically drawn in a furnace at about 2,000° C. and the heat is typically transported to the preform mostly by radiation, but the flow of gas in the furnace, the result of forced flow from blanketing and natural convection, can also affect the glass temperature. The relative contribution of convective heat transfer is significant at the lower part of the fiber forming zone, the region at the optical fiber preform root and below, where the radiative heat transport generally becomes negligible due to the small diameter of the fiber.
The gas flow in the draw furnace, resulting from forced and free convection, typically creates convection cells. These cells can become unstable under certain conditions of temperature gradient and gas density. The resulting unsteady motion affects the heat transfer in the fiber forming zone enough that the fiber clad diameter can vary significantly, which is generally undesirable. To counteract this effect, Helium may be used as the gas in the furnace. Helium reduces the strength of the convection cells and the temperature difference across the cells. This typically results in improved fiber diameter control, but the disadvantage is that Helium, which is expensive, is consumed, thereby adding a significant cost.