Abstract

Polarization-maintaining optical fiber is finding increasing use in various interferometric sensor applications where polarization stability of the guided wave is required. Accordingly, in-line fiber-optic devices such as directional couplers and polarizers have been developed with highly birefringent fibers. In constructing these devices, accurate alignment of the birefringent axes of the fiber at arbitrary points along the fiber becomes important. Accurate alignment can be achieved when using specially shaped (D-or square-type) fibers, but a reliable technique for fibers with circular cross section has not been reported. This paper presents a technique for accurate alignment (<1°) of the birefringent axes of circular fibers, which also identifies the fast and slow axes. When a birefringent fiber is under lateral stress, the resultant birefringence is a combination of the residual builtin birefringence and the externally induced birefringence due to stress. As a result, the orientation and magnitude of the net birefringence deviate, in general, from their original values. This causes a coupling of some of the optical power from one eigenpolarization mode of the fiber to the other mode, unless the direction of external stress is along one of the birefringent axes.

© 1985 Optical Society of America