The change of polarization in single-mode fibers due to external perturbations

The importance of the state of polarization of optical signals propagating through single-mode fibers leads to the study of the effects of microbends and lateral stresses on the signal. The authors examine the change of birefringence as a function of microbending and lateral pressure parameters. In the first case, He-Ne polarized light was injected into a single-mode fiber. About 15 m of the fiber was coiled in a 9-cm diameter. The microbending device was placed about 50 cm from the end of the fiber. Birefringence was measured using a rotating polarized film followed by a photodetector and a voltmeter. Similarly, the same set up was used for the lateral pressure experiment except that the pressure device was used instead of the microbending device. In the latter case the fiber was placed between two samples of polyurethane plates with epoxy in the middle to have a homogeneous system. Based on the measured data, it is possible to determine the birefringence as a function of microbend parameters and lateral pressure exhibited by the environment