Low-Complexity Nonlinear Tomlinson-Harashima Precoding Based on Absolute-Term for ZR Inter-DCI

Due to the sensitivity to cost and power consumption, the intensity modulation direct detection (IM/DD) transmission system attracts significant interest in inter-data center interconnections. In medium reach IM/DD transmission systems, chromatic dispersion caused power fading effect appears to be a major performance limiting problem for double sideband (DSB) signal. Tomlinson-Harashima Precoding (THP) is an effective method for compensating for the dispersion at the transmitter side. By incorporating nonlinear kernels into the transfer function, the nonlinear THP can compensate both the dispersion and the nonlinear distortion of the signal and improve the performance of the system. However, the added nonlinear kernels will significantly increase the complexity. To reduce the complexity of nonlinear THP, we propose a low-complexity absolute-term kernel based nonlinear THP scheme. Compared with the conventional Volterra kernel based THP scheme, the proposed methods can reduce the number of multipliers by 50%-60% without performance degradation. We successfully demonstrate a 70-km 40-Gbaud and a 90-km 30-Gbaud DSB PAM-4 C-band IM/DD transmission over dispersion-uncompensated links.

I. Introduction

With the proliferation of bandwidth-intensive services such as video streaming, cloud computing, Internet of Things and virtual and augmented reality, the continued growth of data center traffic is driving the need for beyond 100 Gb/s/ extended range (ER) Ethernet for inter-datacenter interconnects (inter-DCI) [1], [2]. Cost and power consumption are important considerations in the data center. Due to the complexity of DSP and optical/electrical components, the coherent systems are inferior to the IM/DD in cost and power consumption. The coherent transceivers consume ~1.5x more power as the IM/DD at the same linear density achieving at 400 Gb/s (<100 km 400G ZR) [3]. For short-reach inter-DCI, O-band IMDD has become the mainstream as no dispersion compensation is required. However, with the distance extend to ZR (80km), due to the lower attenuation of SSMF at 1550 nm, the power budget provided by C-band IM/DD is over 10-dBm larger than that of O-band, which is beneficial for SNR at the receiver end. C-band IM/DD system is hopeful to be the low cost and power consumption solution for future ZR inter-DCI standard.