Rate Adaptation and Reach Increase by Probabilistically Shaped 64-QAM: An Experimental Demonstration

TLDR

The study proposes an adjustable‑rate single‑carrier coherent optical transmission system that approaches the Shannon limit. The system employs probabilistically shaped 64‑QAM with an adjustable distribution matcher at the transmitter, an inverse matcher at the receiver, and fixed‑QAM modulation combined with a fixed FEC to realize adjustable net data rates over a wide reach. Experimental results show that probabilistically shaped 64‑QAM at 32 Gbaud achieves net data rates of 200–300 Gb/s and extends transmission reach by over 40 % compared with regular 16‑QAM and 64‑QAM.

Abstract

A transmission system with adjustable data rate for single-carrier coherent optical transmission is proposed, which enables high-speed transmission close to the Shannon limit. The proposed system is based on probabilistically shaped 64-QAM modulation formats. Adjustable shaping is combined with a fixed-QAM modulation and a fixed forward-error correction code to realize a system with adjustable net data rate that can operate over a large reach range. At the transmitter, an adjustable distribution matcher performs the shaping. At the receiver, an inverse distribution matcher is used. Probabilistic shaping is implemented into a coherent optical transmission system for 64-QAM at 32 Gbaud to realize adjustable operation modes for net data rates ranging from 200 to 300 Gb/s. It is experimentally demonstrated that the optical transmission of probabilistically shaped 64-QAM signals outperforms the transmission reach of regular 16-QAM and regular 64-QAM signals by more than 40% in the transmission reach.