Demonstration of a highly bandwidth-efficient optical interconnection with symbol division multiplexing pulse amplitude modulation

A novel symbol division multiplexing (SDM) technology is proposed in an intensity modulation and direct detection (IM/DD) pulse amplitude modulation (PAM) optical interconnection. The SDM-PAM4 symbol is the multiplexing of two standard 3-bit PAM8 symbols based on many-to-one (MTO) mapping, increasing by an extra 50% the line rate compared with a typical PAM4 under the same symbol rate and channel bandwidth. The forward error correction (FEC) based on low-density parity-check coding establishes a mechanism between the codewords of both intra- and inter-SDM-PAM4 symbols, to theoretically support the iterative decoding of symbol de-multiplexing employing an optimized bit-interleaved coded modulation iterative decoding (BICM-ID) system. Furthermore, since SDM evidently reduces the mapping order of the PAM signal, the transmission reliability can be effectively improved by alleviating the impairments mainly caused by fiber chromatic dispersion and Kerr nonlinearity. The experimental results indicate that the SDM-PAM4 can achieve more than 5 dB superior systematic receiver power sensitivity over 10-km single mode fiber transmission, and thus represent an important development in coding and modulation multiplexing techniques for optical interconnection systems.