Fiber-Optic Distributed Strain and Temperature Sensing With Very High Measurand Resolution Over Long Range Using Coherent OTDR

We describe a novel fiber-optic technique for measuring distributed strain and temperature that uses a coherent optical time-domain reflectometer (OTDR) with a precisely frequency-controlled light source. Using this technique, we achieved temperature measurements in an 8-km-long fiber with a resolution of 0.01 degrees C and a spatial resolution of one meter. This temperature resolution is two orders of magnitude better than that provided by the Brillouin based sensing technique.