The influence on output spot of large core fibers in noncentral incidence

The situation was discussed when the input light is in noncentral incidence theoretically and experimentally. An optical system was built to detect the output light spot and its changes under different radial direction conditions. Fiber disturbing mode and Two Dimensional Fitting method were used here to improve the spot images captured by CCD camera. The results showed noncentral incidence would cause focal ratio degradation (FDR).