Variation of the Pauli matrices coefficients in Nd-doped fibers subjected to a magnetic field

The evolution of Pauli matrices coefficients, known as Quaternions, of a Nd³⁺ fibre subjected to a longitudinal magnetic field, that is, to Faraday effect, has been analysed. These parameters change with the electrical current which generates the magnetic field. The obtained values are in general similar to the theoretical ones, although some disagreements have been found, which could be explained by the influence of external parameters, as temperature, pressures or vibrations, by mistakes in the measurement devices (polarizers, retarders,...) or by another factor as optical activity