Broadband all-fiber mode multiplexer for future MDM-WDM transmission over few-mode fibers

Mode division multiplexing (MDM) over few-mode fibers (FMFs) is considered a promising solution for surpassing the capacity limits of single-mode fiber systems. To meet this objective in capacity increase, MDM should comply with wavelength division multiplexing, i.e. apply over each wavelength. A crucial component for a MDM transmission system is the mode multiplexer (MUX), which should be broadband enough to be used in a WDM context. A broadband all-fiber mode MUX based on cascaded FMF couplers is presented and numerically analyzed. The MUX combines modes LP₀₁, LP_11a, LP_11b, LP_21a, LP_21b, and LP₀₂, with an optimized performance over the C band. By considering polarization multiplexing, an order of magnitude capacity increase is supported.