High-Capacity Coherent DCIs Using Pol-Muxed Carrier and LO-Less Receiver

Commonly used 4-level pulse amplitude modulation (PAM-4) scheme limits the amount of data traffic that can be handled by the PAM-4 based data center interconnects (DCIs). Coherent links can support much higher data rates, albeit with a higher complexity of the receiver and much higher power consumption of the system. As a compromise solution, we suggest the use of a polarization multiplexed carrier based self-homodyne (PMC-SH) system for DCIs, which can support higher data rates with power consumption comparable to that of a PAM-4 system. Implementation of this scheme has been impeded earlier by the requirement of polarization control for proper separation of the carrier and the modulated signal at the receiver end. The proposed PMC-SH link with adaptive polarization control is a practical solution that facilitates a local oscillator (LO)-less and carrier phase recovery (CPR)-free coherent receiver. Simulation results successfully validate the proposed system for a 200 Gbps (50 Gbaud) PMC-SH 16-ary quadrature amplitude modulation (16-QAM) link. We also experimentally demonstrate a 32 Gbaud (128 Gb/s) PMC-SH 16-QAM link for a standard single-mode fiber channel. Furthermore, we analytically show that the PMC-SH scheme results in a significantly better bit-error-rate for a given transmission bit-rate or can double the data rate for a given bandwidth of electronics (when compared with the PAM-4 system).