Polarization effects in short length, single mode fibers

The ability to maintain linearly polarized output in single mode fibers is essential for utilization of polarization dependent receiver circuitry. Our measurements with long lengths of fiber (200 m) indicate that we can find input polarization angles which yield essentially linearly polarized output. However, we found that these polarization effects are greatly influenced by the presence of physical stress on the fiber such as stress due to bending, twisting, mounting, and other variations in ambient conditions. We conducted several experiments on short length fibers where special precautions were adopted to assure repeatability of the measurements. Our results indicate the existence of a general theoretical model that predicts the output polarization characteristics as a function of input polarization and fiber length. The model assumes the presence of two asynchronous, orthogonal modes, uniformly coupled over the entire fiber length. The model, however, cannot distinguish between uniformly coupled and uncoupled mode cases based on the output radiation measurements.