Method and apparatus for manufacturing a rare-earth metal doped optical fiber preform

Abstract

A method and apparatus is disclosed for the manufacture of an optical fiber preform having incorporated therein a comparatively high concentration of rare earth metal dopant material, and which thus can be drawn and processed into an optical fiber having low numerical aperture, low core attenuation, and high pumping power absorption. The high concentrations of rare earth metal dopant material are accomplished through a ''hybrid vapor processing'' (HVP) method or a ''hybrid liquid processing'' (HLP) method, either being practiced in combination or independently of one another. The HVP method involves the vaporization of a rare earth metal halide by the exposure thereof to a sufficiently elevated temperature, independently, or contemporaneously with the transport of the resultant rare earth metal halide laden vapor, into a glass-forming oxidation reaction zone on a flowing stream of essentially an unreactive inert gas, such as helium. According to the HLP method, a first amount of rare earth metal dopant is provided according to the HVP method and/or other vapor source of rare earth metal dopant which is mixed with glass-forming vapors to form a deposited soot layer on the internal surface of a glass tube. The soot-deposited tube is then impregnated with a dopant solution comprising, a second amount of rare earth metal dopant. The tube is then thermally collapsed resulting in an optical preform with an enhanced amount of rare earth metal dopant incorporated at a comparatively high concentration. The apparatus comprises means, such as tubes, for introducing the rare earth metal dopant as a vapor, formed from a solid state form of the dopant, into the main glass deposition tube separately from glass-forming material vapors and oxygen for the reaction within the main tube.

Description

[0001] related application [0002] This application claims priority to provisional application 60 / 091,290, filed June 30, 1998, and provisional application 60 / 091,154, filed June 30, 1998. field of invention [0003] The present invention relates to a method of making an optical fiber preform doped with a predetermined high level of rare earth dopant, in particular wherein the concentration of the rare earth dopant is relatively high and the cross-sectional geometry of the preform promotes good mode disturbance. Background of the invention [0004] Optical fiber is an ultra-thin light guide. Light is drawn into one end, travels forward through the fiber, whether the fiber is curved or straight, and finally exits the other end. By pumping light into fibers in a predetermined manner, large amounts of information can be communicated almost instantaneously (ie, at the speed of light) over large bandwidths across vast geographic distances. Because it is thin, fast and strong, ...

AI Technical Summary

Problems solved by technology

Nevertheless, in current practice, it is difficult to dope high concentrations of rare earth dopants, especially the commonly used rare earth element neodymium (Nd) with limited total doping levels.

[0010] Issues include: The most common method of pre

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