28-GBd 32QAM FMF Transmission With Low Complexity Phase Estimators and Single DPLL

As spatial division multiplexed transmission systems employing few mode fibers (FMFs) rely heavily on digital signal processing (DSP), the impact of computational complexity should be considered. A key DSP process block is the carrier phase estimation (CPE), which consists of a phase estimator and digital phase locked loop (DPLL) per output. In this letter, a low complexity phase estimator is proposed, and the common-mode laser frequency offset is exploited to reduce the number of DPLLs. The combination of a low complexity CPE and single DPLL is experimentally demonstrated for a 28 GBd six-channel transmission over a 41.7-km FMF, carrying up to 32 quadrature amplitude modulation. Thereby, the nonlinear tolerances for the proposed CPE scheme are shown to perform similarly as the more computationally complex conventional CPE scheme.