Full-set mode analysis of three-mode fibers calculated from polarization components of near-field pattern

We propose and demonstrate a novel mode analysis method that can provide a full set of amplitudes, phases, and polarization states of guided modes including degenerate modes in few-mode fibers. The method is based on the calculation of amplitude components and phase differences from the intensity profiles that passed through a polarizer with angles of 0, 45, and 90°. The accuracies of calculation formulas are shown by simulation to be less than 10−10 for amplitudes and 10−3 rad for phase differences. The method was applied to a graded-index three-mode fiber, and the off-axis mode excitation ratio characteristics were compared with theoretical ones.