Nonlinearity-Aware Adaptive Bit and Power Loading DMT Transmission Over Low-Crosstalk Ring-Core Fiber With Mode Group Multiplexing

In this article, based on a specially designed ring-core fiber (RCF) with low inter-mode group (MG) crosstalk, we experimentally demonstrate orbital-angular-momentum (OAM) MG-multiplexing (MGM) transmission with intensity modulation and direct detection (IM/DD) utilizing discrete multi-tone (DMT) modulation. Two adjacent high-order OAM MGs |l| = 2 and |l| = 3 with low inter-MG crosstalk of -24.3 dB over 1-km RCF transmission system are employed for data transmission simultaneously. In addition, a low-complexity frequency-domain polynomial nonlinear equalizer (FD-PNLE) combining with adaptive bit and power loading are implemented to mitigate the modulation/detection related nonlinearities as well as modal dispersion induced high-frequency power fading. Experimental results show that compared with linear equalization, the capacities of MGs |l| = 2 and |l| = 3 using FD-PNLE can be significantly improved by 13% and 11.1% with adaptive bit and power loading DMT modulation over 1-km low-crosstalk RCF at a received optical power (ROP) of -13 dBm, respectively. Based on the nonlinearity-aware adaptive bit and power loading DMT signal, successful 186.4-Gbit/s MGM transmission over 1-km low inter-crosstalk RCF is realized only with 20-GHz electrical signal bandwidth. Therefore, the low-crosstalk RCF-based MGM scheme combined with advanced modulation format shows great potential in large-capacity low-cost short-reach optical interconnects.