Polarization Mode Dispersion (PMD) is a form of modal dispersion that affects signal transmission in single-mode fiber. Unlike multi-mode fiber where different modes travel different paths, single-mode fiber ideally supports only one mode. However, due to imperfections in the fiber's geometry and stress-induced birefringence (variation in refractive index depending on the polarization of light), the single mode can split into two orthogonal polarization modes. These two polarization modes travel at slightly different speeds through the fiber. This difference in propagation time between the two polarization modes causes pulse spreading, which is PMD. The....
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