Exploring and Experimenting with Shaping Designs for Next-Generation Optical Communications

TL;DR

This paper introduces a novel circular 64-QAM modulation combining geometric and probabilistic shaping, demonstrating near-Shannon limit performance and significant transmission gains over traditional schemes in optical communication experiments.

Contribution

It presents a new circular 64-QAM design that outperforms square 64-QAM in various transmission scenarios, offering a promising alternative for next-generation optical systems.

Findings

Close to Shannon limits in AWGN channels

Equivalent or better SNR in WDM simulations

28% distance gain in real-world experiments

Abstract

A class of circular 64-QAM that combines 'geometric' and 'probabilistic' shaping aspects is presented. It is compared to square 64-QAM in back-to-back, single-channel, and WDM transmission experiments. First, for the linear AWGN channel model, it permits to operate close to the Shannon limits for a wide range of signal-to-noise ratios. Second, WDM simulations over several hundreds of kilometers show that the obtained signal-to-noise ratios are equivalent to - or slightly exceed - those of probabilistic shaped 64-QAM. Third, for real-life validation purpose, an experimental comparison with unshaped 64-QAM is performed where 28% distance gains are recorded when using 19 channels at 54.2 GBd. This again is in line - or slightly exceeds - the gains generally obtained with probabilistic shaping. Depending upon implementation requirements (core forward-error correcting scheme for example), the investigated modulation schemes may be key alternatives for next-generation optical systems.