DAS with 302km sensing range using remote amplification and engineered fiber

We demonstrate extended sensing range of DAS for passive, unrepeatered fiber networks with single-end access. The frequency swept interrogation technique, capable of 154 km DAS sensing range in standard telecom fibers, is taken as the basis for our experiments. Raman amplification is found to extend the sensing range to 202 km, while adding a ROPA to the line further extends the range to 254 km. We also discuss the utilization of engineered fiber for extended sensing range and demonstrate DAS measurements with engineered fiber positioned at 302 km. Based on our results we estimate that a low-loss engineered fiber with gradually increased reflectivity could facilitate interrogation noise below ~30 pε/√Hz throughout the complete 300 km range.