Electromagnetic Emission from “Dielectric” Optical Fiber Cables

The conventional wisdom is that optical fiber is dielectric, and thus does not radiate RF emissions. In practice, optical fiber cable connectors have non-negligible amounts of conductive material, for example a ferrule, spring, and crimp ring. As data rates have increased beyond 1 gigabit/second (Gbps), equipment with supposedly “RF tight” enclosures exhibited high levels of RF emissions, failing to meet FCC/European electromagnetic compliance (EMC) requirements. It is hypothesized that these small metallic bits can re-radiate RF emissions due to capacitive coupling, and a model is proposed. Data is presented to support this mechanism for RF emission, and corrective measures are suggested to reduce these emissions.