Method of making polarization retaining single-mode optical waveguide

A method of fabricating an optical waveguide fiber comprising the steps of

• providing a preform foreproduct having an oblong, centrally disposed glass core surrounded by a layer of inner cladding glass, the refractive index of said core glass being greater than that of said cladding glass, the cross-sectional shape of said foreproduct having two opposed rounded sides and two opposed flatter sides,
• depositing a layer of flame hydrolysis-produced soot in nonuniform thickness on the outer surface of said inner cladding layer, the thermal coefficient of expansion of said glass soot being different from that of said inner cladding layer by at least 1.times.10.sup.-7 /.degree. C., the thickness of said soot layer being greatest over the flatter sides of said preform foreproduct,
• heating the resultant article to consolidate said layer of glass soot, thereby forming a solid glass draw blank, and
• drawing said solid glass draw blank to form a polarization retaining single-mode optical waveguide fiber.