Novel Multi-Pass E-M System for Locating Buried Optical Cables Using Faraday Rotation of the Transmitted Light

Abstract

We present a novel high-sensitivity location technology for buried dielectric optical cables. A downwardtraveling RF EM wave modulates the state of polarization of the light guided by the buried fibre cable. The cable is located by observing the peak Faraday polarization modulation as the field generator is traversed laterally above the buried cable. We show we can enhance the sensor sensitivity firstly by employing a dual-pass method, giving 6dB SNR improvement, and then a more sophisticated multiple pass system, capable of achieving further SNR improvements. We show our systems demonstrate SNR improvements close to the theoretical limit.