Quasi-Distributed Fiber Loop Ring Down Sensing With Random Distributed Multi-Ultrashort Pulse

We propose and demonstrate a quasi-distributed fiber loop ring down (FLRD) sensing system based on the randomly distributed multi-ultrashort pulse. The multi-ultrashort pulse exhibits randomness in the time intervals and delta-like characteristics of the correlation function. The improved structure of the fiber loop can achieve the simultaneous measurement of the transmitted light containing overall loss information and the reflected light carrying location and loss information of individual sensors. The location and loss of any sensor can be obtained through correlation analyses between the transmitted and reflected light, thereby realizing high-precision quasi-distributed FLRD sensing. The minimum distance resolution of 7.6 cm is achieved in the proposed sensing system with a data acquisition bandwidth of 1 GHz. The minimum measurable reflection range of the sensor is −16.58 dB. The system allows the optical signal to traverse the sensors repeatedly to enhance energy utilization and also enables multi-point measurement. We believe the proposed sensing system offers a promising approach for fiber fault diagnosis and the detection of external parameters such as temperature and strain.