Optical network security: technical analysis of fiber tapping mechanisms and methods for detection & prevention

Increasing emphasis on reliable data transmission for homeland security and network-centric operations makes secure communications a critical component of national security. While fiber optic cables are immune to typical EMI/RFI issues, it is possible to intercept an optical signal successfully if risk areas are not understood and if detection and/or prevention mechanisms are not actively integrated into network management practices. There are several ways to ´tap´ into an optical fiber, including fiber bending, splitting, evanescent coupling, scattering, and V-grooves. Many of these techniques require altering the physical characteristics of the fiber with a significant risk of damaging the fiber and having the optical intercept detected by the end user. Of all the techniques, the bent fiber tap is the most easily deployed with minimal risk of damage or detection. The paper quantifies the bend loss required to tap a signal propagating in a single mode fiber and analyzes the properties of the bend that could be used to detect that a tap is occurring. Understanding the mechanisms used for fiber tapping provides greater insight into ways of actively detecting unauthorized optical intercepts or compromised network security. Enhanced monitoring techniques enable the detection and localization of fiber taps. Monitoring techniques are reviewed with detailed analysis of each method´s effectiveness in detecting bent fiber taps and their cost-effectiveness for integration into optical networks.