Routing, Modulation Format, Baud Rate and Spectrum Allocation in Optical Metro Rings with Flexible Grid and Few-Mode Transmission

Application of few-mode transmission (FMT) in transport optical network is currently under scrutiny, especially for metro networks, where shorter distances and pressing traffic increase (e.g., due to a growing need for metro datacenter interconnection) represent promising conditions for FMT deployment. In this paper, we analyze, from a network-level perspective, the benefits introduced by FMT in metro networks. We consider the application in a flexi-grid network of a FMT system employing hybrid optical/digital mode demultiplexer and low-complexity MIMO-based digital signal processing (DSP). Under this system model, we derive the reach values associated to different modulation formats, baud rates, and number of modes. For the first time to the best of our knowledge, we formulate using linear programming the routing, modulation format, baud rate, and mode assignment problem, for two different switching policies (spatially flexible and spatially and spectrally flexible switching). Using our proposed modes, we identify the configurations that ensure minimum spectrum occupation or minimum cost of installed transceivers, and contrast them to the benchmark case of single-mode transmission.