Polarization preservation in circular multimode optical fibers and its measurement by a speckle method

The first-order statistics of the Stokes parameters (SP\´s) are used to investigate the polarization properties of a circular multimode optical fiber. Linearly polarized light launched into an optical fiber 3 m in length is found to be partially preserved. The degree of polarization was a proper parameter to measure quantitatively the polarization preservation in our experiments. was especially high, when the speckle field produced at the end of the fiber was nonuniform. In all experimental investigations, the probability density functions (PDF\´s) of the Stokes parameters, calculated theoretically, coincide well with the experimental results. The spatial stationarity of the fiber speckle pattern has been verified when all modes ate equally excited.