Raman DTS Based on OTDR Improved by Using Gain-Controlled EDFA and Pre-Shaped Simplex Code

This paper described a distributed temperature sensing (DTS) system based on Raman scattering using pre-shaped simplex code (S code) with erbium-doped fiber amplifiers (EDFAs) transient effects suppression techniques. We investigated these techniques to mitigate the waveform distortion caused by the EDFA when DTS uses S code in an optical time-domain reflectometer (OTDR). We tested the DTS experimentally using two EDFA's transient effects suppression techniques: automatic gain control and pre-shaped S code pulses. The performance of these two techniques working simultaneously was compared with the standard S code technique. In the experimental setup, we tested code word lengths from 3 to 127 b with 100-ns pulsewidth. The temperature measurement demonstration was done in reaches of 40 and 50 km, and in a repeated system of 62 km using standard single-mode fiber and commercial OTDR and EDFA modules, which were properly adapted to this application. Results show that EDFA's transient effects suppression techniques allow increasing the reach of DTS using short S code sequences, reducing the complexity and the processing time.