Modified low CSPR Kramer–Kronig receivers based on a signal–signal beat interference estimation

Due to their simple structures and high robustness to fibre dispersion, single-sideband transmission systems using Kramer–Kronig (KK) receivers are an attractive solution for 80 km data centre interconnects. However, a major problem with KK receivers is that the optimal carrier signal power ratio (CSPR) needs to be large, due to the existence of signal-signal beat interference (SSBI), but this results in low receiver sensitivity. We propose two modified KK receivers that can estimate and eliminate SSBI and allow for signal detection when the CSPR is less than 0 dB. After transmission over an 80 km optical fibre, our modified KK receivers were able to increase the receiver sensitivity by 3 dB compared with a traditional KK receiver while the CSPR was reduced by 6 dB, and improvements of 1.16 and 1.60 dB in the OSNR were achieved with a reduction in the CSPR of 8 dB. Our improved KK receivers can greatly reduce the carrier power and CSPR necessary for the system, and thus reduce the cost of the system transmitter.