Ultra-long chaotic FBG sensing with high-order random fiber lasing amplification.

We propose and demonstrate an ultra-long chaotic fiber Bragg grating (FBG) sensing system based on wavelength-scanning correlation optical time-domain reflectometry (COTDR) assisted by sixth-order random fiber lasing amplification (RFLA). Cascaded random Raman fiber lasing generated in the long fiber span can provide up to sixth-order distributed Raman amplification for the chaotic probe light and its echo signal without ruining the chaotic behavior, which can significantly extend the sensing distance of COTDR. As a result, a 152-km-long wavelength-scanning COTDR is experimentally demonstrated to simultaneously realize FBG sensing and location with a spatial resolution as high as 6 cm, which is the longest COTDR to the best of our knowledge. Temperature sensing of the specific FBG is performed, and the temperature sensitivity of the proposed system is 0.25 dB/°C with a good linearity. The proposed chaotic FBG sensing system with high-order RFLA can act as a new platform for ultra-long, large-capacity FBG sensing, which has potential applications in overhead transmission powerline monitoring and structural health monitoring.