Polarization Mode Dispersion: 1. Polarization mode dispersion is an inherent property of all optical media. It is caused by the difference in the propagation velocities of light in the orthogonal principal polarization states of the transmission medium. The net effect is that if an optical pulse contains both polarization components, then the different polarization components will travel at different speeds and arrive at different times, smearing the received optical signal. 2. Dispersion of an optical signal due to the different polarizations of light traveling at different speeds through optical fiber.