Performance of Direct-Detection Mode-Group-Division Multiplexing Using Fused Fiber Couplers

We present an end-to-end performance evaluation of a mode-group-division multiplexing system that uses direct detection instead of coherent detection, avoiding complex digital signal processing. The system transmits four data channels through a step-index fiber supporting six spatial modes comprising four mode groups, considering the twofold degeneracy of the LP_lm modes for l ≠ 0. Multiplexing and demultiplexing is performed using two- and three-core fused fiber couplers, each one phase-matched to a group of degenerate modes. These devices are analyzed through a field-based model that describes, for the first time to our knowledge, crosstalk between all the fiber modes. Propagation through the few-mode fiber is modeled considering differential modal attenuation, intermodal dispersion, chromatic dispersion, and both intergroup and intragroup modal coupling. The end-to-end link is described by a concatenation of matrix operators describing the optical field transfer functions for the multiplexer, fiber, and demultiplexer. Error-free transmission of four 32-Gb/s OOK-modulated data channels through a 1-km link proves the feasibility of the proposed direct-detection mode-group-division multiplexing approach.