Mitigation of Stimulated Raman Effects in Coded Raman Optical Time-Domain Reflectometry

Distributed temperature sensors based on coded Raman optical time-domain reflectometry (ROTDR) obtain distributed temperature profiles along a sensing fiber by decoding backscattered anti-Stokes and Stokes signals obtained with coded pulse sequences. However, using long sequences or pulses with high peak power can induce backward stimulated Raman scattering (SRS), disrupting the linear superposition of spontaneous Raman scattering responses required for reliable decoding, and causing significant temperature estimation errors. To address this, this paper proposes a compensation method that estimates SRS-induced gain and depletion relative to a low-power coded Stokes and anti-Stokes references acquired under negligible SRS conditions. This correction restores the linearity of Raman traces with minimal added complexity, enabling a correct decoding process that minimizes errors in the retrieved temperature profile. Experimental results over a 24 km fiber using 130-bit genetic-optimized codes and 1 W peak power pulses demonstrate that the method effectively suppresses SRS-induced distortions without compromising the spatial resolution or the SNR improvement provided by the coding gain. Compared to direct decoding, the method reduces temperature errors by up to 18°C (under specific tested conditions) and improves the retrieval temperature accuracy, demonstrating scalability to longer code lengths and higher launch powers.