Fiber Tapping in Optical Networks: Attack Techniques, Detection, and Mitigation

Initially considered secure against interception, fiber-optic networks were subsequently found susceptible to covert tapping, although such attacks require different coupling mechanisms and components than those used for twisted pair and coaxial cables. Fiber-optic networks carry the majority of data and voice traffic worldwide, including backhaul and fronthaul traffic in 4G and 5G radio networks, connections between data centers, and submarine cable systems. Consequently, physical access to fibers for interception has attracted the attention of intelligence agencies and industrial spies. This vulnerability is facilitated by the fact that single-mode optical fibers (SMFs) used in telecommunication networks have evolved relatively little over the last 40 years. Fibers of substantially different designs—anti-resonant hollow core fibers (HCF) and multi-core fibers (MCF)—made their commercial debut around 2023, and their susceptibility to tapping may differ substantially from that of conventional SMFs. New promising fiber monitoring techniques based on polarization measurements have also been demonstrated recently. While established tapping techniques remain feasible for conventional fibers, new fiber designs and monitoring technologies can make covert interception difficult. This review examines physical fiber tapping techniques and their practical feasibility, with particular emphasis on optical power constraints, introduced loss, detectability, and implementation limitations. It also reviews prevention and monitoring approaches, including optical time-domain reflectometry, received-power monitoring, and state-of-polarization (SOP) monitoring, and provides a prospective engineering assessment of the susceptibility of MCFs and HCFs to physical tapping.