Beyond 200 Gb/s/lane: An Analytical Approach to Optimal Detection in Shaped IM-DD Optical Links with Relative Intensity Noise

TL;DR

This paper presents an analytical SER expression for optimal detection in high-speed IM-DD optical links, accounting for RIN effects without distribution assumptions, applicable to shaped modulation schemes.

Contribution

It introduces a universal analytical SER model for IM-DD systems considering RIN, applicable to probabilistically and geometrically shaped constellations, matching simulations accurately.

Findings

Analytical SER expression matches numerical simulations.

Model accounts for signal-dependent RIN effects.

Applicable to general shaped modulation formats.

Abstract

Next-generation intensity-modulation (IM) and direct-detection (DD) systems used in data centers are expected to operate at 400 Gb/s/lane and beyond. Such rates can be achieved by increasing the system bandwidth or the modulation format, which in turn requires maintaining or increasing the signal-to-noise ratio (SNR). Such SNR requirements can be achieved by increasing the transmitted optical power. This increase in optical power causes the emergence of relative intensity noise (RIN), a signal-dependent impairment inherent to the transmitter laser, which ultimately limits the performance of the system. In this paper, we develop an analytical symbol error rate (SER) expression for the optimal detector for the IM-DD optical link under study. The developed expression takes into account the signal-dependent nature of RIN and does not make any assumptions on the geometry or probability distribution of the constellation. Our expression is therefore applicable to general probabilistically and/or geometrically shaped systems. Unlike results available in the literature, our proposed expression provides a perfect match to numerical simulations of probabilistic and geometrically shaped systems.