Single-Photon Detector Based Long-Distance Brillouin Optical Time Domain Reflectometry

During the last few years, the transport of energy via the development of offshore wind turbines has experienced a strong growth. Monitoring these infrastructures is essential and requires measuring the temperature along several tens of kilometers of submarine cables [1]. One solution is to place an optical fiber along these submarine cables and to monitor the temperature using a Brillouin optical time domain reflectometer (BOTDR) sensor. Here, we present a novel BOTDR using a single-photon avalanche diode (SPAD) [2] in gated mode with the ability to measure the Brillouin frequency shift that gives access to the temperature. In our experiment, the slope of a fibre Bragg grating (FBG) is used to convert the count rate variation into a frequency shift. Measurements until 120 km with a spatial resolution of 10 m are obtained without optical amplification along the optical fibre thanks to the very low noise (-120 dBm) of the SPAD.