Nonlinear spectrum broadening and its impact on performance of Rayleigh-scattering-based distributed strain/temperature fiber optic sensors

Abstract

A Rayleigh-scattering-based distributed strain/temperature fiber optic sensor using low-coherence light is experimentally investigated at probe pulse powers well above the nonlinear effect threshold. OTDR technology is used for special channel interrogation. It is established that for an SMF-28e+ fiber this threshold is about 100 mW. Exceeding this power leads to the degradation of sensor performance and is explained by nonlinear spectrum broadening. The evolution of the probe pulse spectrum is investigated using a tunable MEMS filter. A novel version of the arrangement for the sensor is proposed, which partially overcomes the limitations associated with said effect. As low as 2.2 µε, the RMS noise level for strain is demonstrated at a distance of 25 km. The spatial resolution is estimated as 1.5 m, the data collection time is 20 min, and the average power in the fiber is about 0.2 mW, which allows the sensor to be used for infrastructure monitoring under explosive conditions.