Using fiber optics to detect sound

The Independent : QinetiQ has perfected a technique that transforms a fiber optic cable into a highly sensitive microphone capable of detecting a single footstep from up to 40 km away.The system works by picking up tiny seismic waves detected under the ground by the fiber optic cable which carries an optical pulse sent from a central computer. Virtual “microphones” created remotely every 10 meters along the cable register the vibrations through the ground. The patterns caused by the disturbances are then matched to digitally pre-sampled sounds such as footsteps, cars or diggers and the information fed back to a command center where personnel can assess whether the sound warrants further investigation or not.Trials have already been staged in Europe to use the OptaSense system , as it’s called. It has been deployed by several blue chip oil companies to protect energy pipelines that run through some of the most lawless and remote regions of the world.