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Abstract

A single-mode optical waveguide is constructed in a manner such that the core thereof is subjected to a stress-induced birefringence. A coating of core glass soot is deposited on the surface of a cylindrical mandrel, and a coating of inner cladding glass soot is deposited on the core glass soot. The mandrel is removed and the resultant porous preform is consolidated to form a hollow dense glass preform. The preform aperture is closed at both ends. Diametrically opposed slabs are removed from the inner cladding region of the consolidated preform. The resultant article is evacuated, heated and stretched to close the aperture and form a preform foreproduct having two opposed rounded sides and two opposed flattened sides. The foreproduct is coated with a layer of outer cladding glass soot having a thermal coefficient of expansion which differs from that of the inner cladding glass by at least 1.times.10.sup.-7 /.degree.C. The resultant composite structure is consolidated to form a draw blank which can be drawn into an optical fiber.

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First Claim