Directional coupler for coupling single-polarization optical fibers

Abstract

A directional coupler for coupling two single-polarization optical fibers each comprising a core, a cladding, and an elliptic jacket having a major axis is made by preparing two quartz substrates each of which is formed with a channel on one major surface; embedding and bonding the jacketed single-polarization optical fibers in the channels in the substrates, respectively, such that the major axis of the elliptic jacket extends perpendicular to the substrate surface; abrading away the substrates together with the fiber embedded therein from the major surface to a depth where light traveling in the core of said fiber may leak out; placing one substrate on the other substrate with the abraded surfaces facing each other; and bonding the substrates to keep the cores in sufficiently close relation to establish evanescent wave coupling therebetween. A stress perpendicular to the major axis is preferably applied to the fiber.