Polarization Changes during a Lightning Strike: Isotropic Zones of Anisotropic Optical Fiber

A numerical experiment for light passing through the section of the optical ground wire during a lightning strike events was carried out. The “isotropy effect” for areas in state of polarization rotation speed time profiles was discovered and explained. This effect consists in the fact that time profiles shapes of anisotropic and isotropic fibers practically coincide in short zones at the beginning and the end of lightning current rapid increase interval (lightning front), but it differ significantly in the middle part. It is shown that such a behavior of time profile is determined by the smallness of the length of interaction of light with the region of rapid change of the magnetic field at the beginning and the end of the lightning front, while the effect of the magnetic field on short sections of the anisotropic fiber practically coincides with the effect on sections of isotropic fiber of the same length. Using the model of light propagation in a fiber with a random distribution of linear birefringence, located in the magnetic field of lightning, a formula for calculating the matrix rotation speed of the polarization state for an extended fiber is obtained.