Asymmetric behavior of polished polarization-maintaining couplers.

Basic asymmetric behavior is experimentally observed in a polished polarization-maintaining fiber coupler. As the two half-couplers are made to slide on top of each other, the output extinction ratio exhibits relatively large variations whose forms depend on the fiber that is selected for the input. We propose that a local distortion of the fiber birefringent axes, which could be caused by the half-coupler polishing process, can generate such features even when the launched light is perfectly polarized along a principal axis of the input fiber.