Optimized Hybrid Raman/Fast-BOTDA Sensor for Temperature and Strain Measurements in Large Infrastructures

An optimized hybrid Raman/BOTDA optical fiber sensor based on cyclic Simplex pulse coding is proposed to overcome temperature and strain cross-sensitivity issues, allowing at the same time fast implementation of Brillouin optical time domain analysis with subsecond measurement times. By providing a real-time diagnostic system for safe operation, the proposed sensor can play a key role for in-service monitoring of large critical infrastructures. Experimental results demonstrate the capability of the proposed technique to effectively discriminate the Brillouin frequency shift contributions due to strain and temperature variations simultaneously applied to the same fiber section along 10 km of standard single mode optical fiber, with 1-m spatial resolution and a worst-case strain resolution value of 62 με. The proposed scheme uses a single narrowband laser source and one sensing fiber only.