Polarization-mode-coupling measurements along a spliced polarization-preserving fiber using a backscattering technique

New methods for principal-axis alignment for splicing polarization-preserving fibers and for evaluation of the axis-mismatching angle after splicing have been proposed, which use a backscattering technique. This technique can align the polarization axis within ±1 deg and is advantageous because the axis alignment is attained at one end of the test fiber. For the purpose of obtaining the axis-mismatching angle at a splice point, two kinds of backscattered signals coming through each principal axis of the fiber are utilized. By introducing a measurement technique for both ends, it is shown theoretically and experimentally that the principal-axis mismatch at each splice as well as local polarization-mode coupling along each fiber piece can be measured exactly.