A simple method is proposed for the experimental calculation of the mode conversion coefficients in multimode optical fibers. It only requires observing the far-field output pattern from a fixed length of fiber as the launching angle changes,as well as the intersection point between two far-field output patterns corresponding to two different input angles. The results obtained with this method are quite insensitive to small variations of the experimental parameters. A good agreement between theoretical and experimental results is also found.
J. Zubia, G. Durana, G. Aldabaldetreku, J. Arrue, M. A. L da, and M. Lopez-Higuera, "New Method to Calculate Mode Conversion Coefficients in SI Multimode Optical Fibers," J. Lightwave Technol. 21, 776- (2003)