International Telephone and Telegraph Corporation

Shin M Oh

Pablo C Pureza

Dilip K Nath

Hydroxyl free deposition with high efficiency and at a high deposition rate may be achieved, even with use of relatively inexpensive raw materials, by utilizing a ring-shaped plasma activated axial chemical vapor deposition obtaining 100% chemical conversion and fractional volatilization of impurities. The plasma is induced in an annular stream of a plasma-forming gaseous medium, and the reactant or reactants used in the axial chemical vapor deposition are introduced into the center of the ring-shaped plasma to be converted by the heat of the plasma flame into soot which is deposited on a bait. An annular stream of a cooling medium flows outwardly past the plasma flame and is circumferentially centered by an extension of the outer tubular element of a plasma torch in which the plasma is generated. An RF generator which induces the plasma is operated at a frequency exceeding 20 MHz to give the plasma flame the desired ring-sloped configuration.

Fabrication of optical preforms by axial chemical vapor deposition

In order to provide a high power heat source having a very clean and invariable heat flux, a ring plasma is induced in a heating zone of a plasma torch including a plurality of coaxial tubular elements and the optical fiber is drawn through a channel passing axially through the center of the plasma torch and of the ring-shaped plasma. In this manner the preform from which the fiber is drawn can be placed in close proximity to the induced plasma without exposure to non-symmetrical temperature variations. Cooling gas passes through the heating zone either in an annular stream surrounding the plasma or in an annular stream passing through the center of the plasma around the preform and the fiber being drawn, or both. The heating zone is protected from environmental disturbances by an extension of the outer tubular element of the plasma torch which surrounds the heating zone. The plasma is induced by an RF source in an undisturbed stream of a plasma-forming gaseous medium, such as argon or a mixture of argon with oxygen, which flows through the heating zone.

Optical fiber drawing using plasma torch

An oxyhydrogen torch for use in drawing an optical fiber from a preform without axial rotation includes four coaxial tubular elements bounding respective passages. The fiber is coaxially drawn through the innermost passage, and hydrogen, oxygen and an inert gas are respectively individually admitted into the successively outer passages at their upstream ends in the circumferential directions of the respective passages. Oxygen and hydrogen become mixed with one another and combust after leaving the downstream ends of the respective passages to form an annular oxyhydrogen flame in a heating zone of the torch around the portion of the preform from which the fiber is being drawn. The inert gas, such as argon or nitrogen, flows past the flame in the heating zone to shield the flame from environmental disturbances. The outermost tubular element has an extension which surrounds the heating zone and confines the stream of the shielding inert gas to provide an improved shielding effect for the flame, while being cooled by the shielding gas.

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Roanoke, VA, United States of America

Shin M Oh