Comparative Study of Co- and Counter Propagation in an Integrated Classical and Quantum Communication System
Year: 2026
Type: conference-paper
Abstract: Quantum Key Distribution (QKD) is now mature and considered a key technology for future secure communication networks. It provides information-theoretic security guaranteed based on the laws of quantum physics. However, high-quality QKD implementations typically require dedicated dark fibers to isolate the quantum channel from high-speed classical traffic, which impedes the spread of this technology. In existing optical communication network infrastructure, the availability of dark fibers cannot always be assumed. Therefore, the coexistence of QKD with classical optical networks becomes essential for widespread deployment. In this scenario, the quantum channel can propagate in the same direction (co-propagation) or in the opposite direction (counter-propagation) alongside the classical, standardized, high-speed channels. Each configuration has a different impact on the performance of the quantum communication system due to noise sources such as Spontaneous Raman scattering and crosstalk. Consequently, a detailed comparative analysis is necessary to determine whether co-propagating or counter-propagating transmission offers more favorable conditions for reliable and efficient QKD operation in shared optical fiber environments. The optimal propagation direction of the quantum channel depends strongly on the targeted network segment, as the dominant noise mechanisms, power levels, and architectural constraints vary significantly across access, metro, and core optical networks.
Author: Eszter Udvary
Institution: Budapest University of Technology and Economics
Language: English
Subfield: Artificial Intelligence
Field: Computer Science
Domain: Physical Sciences
Open Access status: hybrid
OpenAlex ID: W7215033147