Robustness of WDM technique for the co-propagation of quantum with classical signals in an optical fiber

TL;DR

This paper presents a theoretical analysis demonstrating that wavelength division multiplexing (WDM) can robustly support the coexistence of quantum and classical signals in optical fibers, with crosstalk mainly limited to nearest channels.

Contribution

It introduces a novel theoretical framework for analyzing quantum-classical signal co-propagation in WDM systems, highlighting the minimal crosstalk impact from distant channels.

Findings

Only the first two nearest channels cause noticeable crosstalk.

WDM is inherently robust for integrating quantum signals with classical traffic.

Crosstalk depends on classical launch power and wavelength separation.

Abstract

Many quantum communication systems operate based on weak light pulses which by design are assumed to operate in isolation from regular data traffic. With the widespread availability and commercialization of these systems comes a need for seamless integration already at the physical layer. In particular for optical fiber links where wavelength division multiplexing (WDM) is the dominant data transmission technique this results in the propagation of very weak quantum signals against a strong data signal background. With this work, we present a novel theoretical approach that studies the evolution of co-propagating quantum and classical signals that are launched using WDM. The important factors that contribute to crosstalk, such as the launch power of the classical signal and the separation between the two signals in terms of wavelength, are comprehensively analyzed. Interestingly, calculations show that only the first two nearest channels from the classical channel experience noticeable crosstalk whereas other distant channels have negligible crosstalk effect. This reflects the WDM technique is in principle robust in the integration of weak quantum links into classical data traffic.