Rod in tube method for producing optical fibres, comprises reducing pressure inside cavity between rod and tube during heating and flushing with inert gas

摘要

During the heating step the pressure inside the annular cavity (22) between the rod (11) and tube (12) is reduced and this cavity is flushed with an inert gas (19). A forming method for producing optical fibres (13) comprises placing a tubular mantle around a rod-shaped primary forming part and heating so that the mantle is shrunk onto the rod. During the heating step the pressure inside the annular cavity between the rod and mantle is reduced and this cavity is flushed with an inert gas.