Computing of parameters for scheme of MDM channel precision positioning at the few-mode optical fiber end

This work presents method for computing of parameters for scheme of mode-division multiplexing (MDM) channel precision positioning at the excited few-mode optical fiber end. Proposed solution is based on combination of well-known overlap integral method and earlier on developed modified Gaussian approximation generalized for analysis of silica weakly guiding optical fibers with single solid outer cladding and arbitrary axially-symmetric refractive index profile. This approach provides ability to derive analytical expressions for arbitrary order mode coupling coefficients under particular radial misalignment. Based on developed method launching parameters were computed for 5 modes of MDM channels at the end of few-mode optical fiber (FMF) with core diameter 42 mm and reduced differential mode delay (DMD). According to obtained results, particular combination of MDM channel launched mode field radius and precision offset provides transmission of the almost launched mode power to only one excited FMF mode with the same azimuthal order. Some practical guidelines were developed to select positioning scheme parameters for MDM channel modes placement at the end of FMF 42/125 with low DMD.