Mode Field Diameter Definitions for Few-Mode Fibers Based on Spot Size of Higher-Order Gaussian Mode

The spot size at which the electric field distribution for higher-order modes in few-mode fibers (FMFs) is approximated by a higher-order Gaussian profile is a promising parameter for estimating various transmission characteristics. To establish a technique for measuring the mode field diameter (MFD) corresponding to higher-order Gaussian spot size for any-order mode in FMFs, we investigate the relation between the higher-order Gaussian spot size and the values yielded by conventional MFD definitions. We then present formulas that output the MFD values corresponding to higher-order Gaussian spot size. Some examples of the MFD values for typical few-mode fibers determined experimentally and numerically are also shown.