Cost-effective digital coherent short-reach transmission system with D8QAM and low-complexity DSP

Tingting Zhang*, Qian Xiang, Sen Zhang, Lei Liu, Stylianos Sygletos, Tianjian Zuo

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


We propose a cost-effective digital coherent scheme with low-complexity digital signal processing (DSP) for short-reach optical interconnection. Differential 8-ary quadrature amplitude modulation (D8QAM) with 1-decision-aided adaptive differential decoding bypasses carrier recovery and enables cycle-slip-free operation. We experimentally demonstrate that the receiver sensitivity of 400-Gb/s D8QAM is insensitive to the laser type, and is the same as 400-Gb/s 16QAM in the case of 2-km transmission with a distributed feedback (DFB) laser. The proposed adaptive equalizer (AEQ) using real-valued finite impulse response (FIR) filters and shorter tap lengths for the real-imaginary filters allows hardware-efficient implementation with high robustness to the receiver-side timing skew. In the case of 400-Gb/s D8QAM 10-km transmission, our AEQ achieves comparable performance as conventional 4×4 real-valued multi-input multi-output (MIMO) and the existing simplified AEQs with complexity reduction of 50% and 14% respectively.

Original languageEnglish
Pages (from-to)11892-11902
Number of pages11
JournalOptics Express
Issue number8
Early online date31 Mar 2021
Publication statusPublished - 12 Apr 2021

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