Polar coded symbol division multiplexing scheme for bandwidth efficient short-reach optical interconnection

To mitigate the impairments by system bandwidth limitation, a joint polar coded pulse amplitude modulation (PAM) scheme based on symbol division multiplexing (SDM) is proposed and experimentally demonstrated in an intensity modulation and directly detected optical interconnection. The SDM-PAM4 employs a polar coded many-to-one mapping scheme to enhance information capacity per symbol, thus improving the bandwidth efficiency and reducing the symbol rate requirement while maintaining the same data rate. To realize the demultiplexing SDM (De-SDM) without iterative calculation, a systematic polar encoder with the arrangement of ambiguous bits in specific parity bits is proposed to obtain optimal system performance in simultaneous De-SDM and polar decoding. Experimental results show that the proposed scheme improves receiver power sensitivity by 2.5 dB compared with conventional PAM4 under constrained system bandwidth, while achieving the same data rate over 2-km standard single-mode fiber transmission. Benefiting from the short code length and flexible rates, the polar coded SDM is highly promising for bandwidth limited optical interconnection.