Experimental PDM-OFDM Signal Transmission with Shaped Signal Constellations Achieving a Net Spectral Efficiency of 11.15 b/s/Hz over a Distance of 800 km

Abstract:
In this contribution we present a coded coherent optical orthogonal frequency-division multiplex (COOFDM) transmission scheme with reduced guard interval (RGI) and our latest results on achieving highest information spectral densities. In our scheme, a RGI is used to accommodate the intersymbol interference (ISI) with short memory, such as induced by transmitter bandwidth limitations or fiber polarization mode dispersion(PMD), while fiber chromatic dispersion (CD) with long memory and well-defined characteristics is mostly compensated within the receiver by a discrete Fourier transform (DFT)-based electronic dispersion compensation (EDC). We apply strong forward error correction (FEC) coding as an enhancement of bit interleaved coded modulation with iterative decoding (BICM-ID) by using low-density parity-check (LDPC) codes and shaped signal constellations (256-iterative polar modulation (IPM)) on the subcarriers of the OFDM system. We then present our latest experimental results on the generation and FEC-decoding of a polarization-division multiplexed (PDM)- OFDM signal with a net channel data rate of 231.5 Gb/s, occupying a bandwidth of 20.75 GHz. In an experiment on the performance of the developed system, transmission was performed over 800 km of ultra-large-area fiber (ULAF), achieving an intrachannel spectral efficiency (ISE) of 11.15 b/s/Hz with a coding gain of 15.1 dB compared to uncoded 256-QAM at a post-FEC BER of 10-15. Index Terms — Coded Optical Orthogonal Frequency- Division Multiplexing (CO-OFDM), Bit Interleaved Coded Modulation with Iterative Decoding (BICM-ID), Iterative- Polar-Modulation (IPM), Polarization-Division Multiplexing (PDM).