Statistical Evaluation of PAM4 Data Center Interconnect System With Slope-Compensating Fiber Bragg Grating Tunable Dispersion Compensation Module

Data center interconnect (DCI) links with high data-rate direct-detection require strict chromatic dispersion compensation. One such solution which has been widely deployed is based on four-level pulse amplitude modulation (PAM4). With this application in mind, we describe in detail a 50-GHz channelized fiber Bragg grating (FBG) tunable dispersion compensation module (TDCM) which can compensate chromatic dispersion slope over the full C-band (4.8 THz) and is thus suitable for dense wavelength division multiplexing (DWDM) PAM4 DCI systems. We then present a comprehensive set of system performance results comprising 1,120 unique link measurements, to characterize the combined effect of statistical variations in component characteristics and link impairments, and show that a statistical approach to link budgeting is advantageous in this type of system. We also analyze the group delay ripple characteristics of the FBG-TDCM device and the corresponding impact on the PAM4 system. Instead of the conventional phase ripple standard deviation, we introduce a novel metric to quantify high-frequency phase ripple, which is better correlated with the impact on the PAM4 system.