Fiber birefringence measurements with an external stress method and heterodyne polarization detection

Precise birefringence measurements on polarization maintaining fibers have been obtained with external pressure scanning along the fiber axis. Output detection has been performed through heterodyne interferometric polarimetry, which allows the use of a simplified technique (avoiding pressure modulation and fiber eigenaxis search). Beat-length evaluation is achieved directly through multiple counting of periodical variations of the two radio-frequency output signals provided by the polarimeter. A theoretical model for the behavior of the fiber output polarization on the Poincare´ sphere, as a function of pressure scanning, has been developed and experimentally tested and the results are in good agreement with the theory.