Abstract

High-speed intensity-modulation direct-detection (IM/DD) fiber optical transmission system is of great interest to the applications of datacenter interconnects (DCI) as well as edge/access networks. However, when the fiber reach is beyond 40 km such as ER or ZR, the power fading induced by chromatic dispersion (CD) in C-band, S-band and even edge-wavelengths of O-band becomes a severe issue with the ever-increasing signal data rate. In this work, we focus on an ultra-low complexity joint optical-electrical feedforward equalization (OE-FFE) scheme to mitigate the CD distortion. We establish a comprehensive theory to jointly model the IM/DD channel, optical circuit and the digital equalizer, which offers analytical bit-error ratio (BER) expressions of pulse amplitude modulation (PAM)-2 and PAM4 formats and guides co-optimization of optical and electrical parts. As proofs of concept, we experimentally demonstrate C-band 60 Gb/s PAM2 over 85.8 km single-mode fiber (SMF) and up to 112 Gb/s PAM4 over 50 km or 61.3 km SMF, enabled by OE-FFE with only a 1-tap optical delay line and lean digital equalizers. For 112 Gb/s PAM4 over 50 km, BER satisfying 7% hard-decision FEC limit is achieved using a symbol-spaced simplified polynomial FFE with only 39 multiplications per PAM-4 symbol. For 60 Gb/s PAM-2, we achieved 85.8 km transmission with symbol-spaced 25-tap linear FFE and KP4 FEC-compliant BER. In addition, investigations on the parameters of the optical delay line are also carried out. The analytical and experimental results show the great potential of proposed OE-FFE approach for CD-constrained beyond-100G/λ ER and beyond-50G/λ ZR IM/DD systems.

High-speed reach-extended IM-DD system with low-complexity DSP for 6G fronthaul [Invited]

Paikun Zhu, Yuki Yoshida, Kouichi Akahane, and Ken-ichi Kitayama
J. Opt. Commun. Netw. 16(1) A24-A32 (2024)

Collaborative FFE-assisted simplified soft-output MLSE with LDPC for high-speed IM-DD transmissions

Xue Zhao, Jing Zhang, Jiahao Zhou, Zhengyu Ma, Shaohua Hu, Bo Xu, Qianwu Zhang, and Kun Qiu
Opt. Express 32(3) 3866-3873 (2024)

Experimental demonstration of pre-electronic dispersion compensation in IM/DD systems using an iterative algorithm

Xiong Wu, Abdullah S. Karar, Kangping Zhong, Alan Pak Tao Lau, and Chao Lu
Opt. Express 29(16) 24735-24749 (2021)

Experimental demonstration of low-complexity trigonometric-memory-polynomial decision-feedback equalizer for nonlinear compensation in IM/DD optical systems

Xing Liu, Yun Liu, Chengju Hu, and Jian Zhao
Opt. Express 32(3) 3329-3341 (2024)

C-band 120-Gb/s PAM-4 transmission over 50-km SSMF with improved weighted decision-feedback equalizer

Junwei Zhang, Xiong Wu, Lin Sun, Jie Liu, Alan Pak Tao Lau, Changjian Guo, Siyuan Yu, and Chao Lu
Opt. Express 29(25) 41622-41633 (2021)