List-encoding CCDM: A Nonlinearity-tolerant Shaper Aided by Energy Dispersion Index

TL;DR

This paper introduces L-CCDM, a new shaper architecture that reduces nonlinear interference in optical transmission by lowering the energy dispersion index, leading to improved SNR and information rate.

Contribution

The paper proposes L-CCDM, a novel shaper with an EDI selecting module compatible with PAS, enhancing nonlinear tolerance in optical systems.

Findings

Achieves 0.35 dB SNR gain over standard CCDM with 256QAM.

Provides 0.22 bit/4D-symbol increase in achievable information rate.

Extends system reach by approximately 8%.

Abstract

Recently, a metric called energy dispersion index (EDI) was proposed to indicate the nonlinear interference (NLI) induced by correlated symbols during optical transmission. In this paper, we propose a new shaper architecture to decrease the EDI of transmitted symbols and thus, increase the signal-to-noise ratio (SNR). We call this shaper the list-encoding constant-composition distribution matcher (L-CCDM). L-CCDM consists of an additional EDI selecting module, which is compatible with standard probabilistic amplitude shaping (PAS) architecture. Numerical results obtained from a multi-span multi-channel system show that when compared to standard CCDM with 256-ary quadrature amplitude modulation (256QAM), the proposed architecture offers an effective SNR gain of 0.35 dB, an achievable information rate gain of 0.22 bit/4D-symbol, or equivalently an 8% reach extension.