Local Birefringence in optical fibers for Low-PMD performances

The introduction of a spinning step in the drawing process is a primary way to improve optical fiber performances in terms of Polarization Mode Dispersion (PMD), by modifying fiber intrinsic birefringence. However, spin profiles actually transferred into fibers may differ from nominally imparted ones, leading to departures from the expected efficiency in PMD reduction. Therefore, for best optimization of low-PMD fibers, it is useful to investigate the effect of spinning, in terms of effectiveness of spin function transfer and modification of local intrinsic birefringence. In this review, after a brief theoretical excursion over different types of spin functions and related effects on PMD, we introduce measurement methods featuring high spatial resolution and enabling the reconstruction of local birefringence evolution along spun fibers. In this way, the overall effect of spinning on birefringence and related PMD can be experimentally verified, as will be summarized.