Effective mode-field diameter measurement for few-mode fibers

We experimentally investigate the applicability of the conventional near-field patter (NFP), far-field pattern (FFP) and variable aperture (VA) methods for measuring the effective mode-field diameter (MFD) of the higher-order mode which can be used for evaluating the splice loss accurately. We confirmed that the variation in measured MFD values obtained with FFP and VA methods can be converged by considering the minimum scanning angle and minimum numerical aperture (NA) respectively for both fundamental and higher-order modes. We reveal that the FFP and VA methods provide adequate effective MFD values in the FMF, which can be used for evaluating the splice loss based on the traditional Gaussian fitting model. We also found that the minimum NA in the VA method can be determined empirically as a function of the effective MFD.