Monitoring of FTTH-PON using direct-detection FBG-assisted 𝝋-OTDR

A fiber Bragg grating-assisted phase-optical time domain reflectometer (FBG-assisted φ-OTDR) was developed to interrogate an FTTH network installed over a total distance of 25 km. The network includes a 1x4 splitter at the FAT (Fiber Access Terminal). The sensor interrogates each branch of the aerial section with a probe signal consisting of a double-pulse. In the final meters of each branch, a pair of weakly reflective FBGs was placed and the corresponding interference signal was used to identify a possible cable motion. A mitigation method for polarization fading inherent to FBG-assisted φ-OTDR is also described. The proposed approach allows locating a cable motion at the end of the tree-like structure of the FTTH network, which corresponds to the aerial part of the network. Detection and localization of cable motions enable the repair of a fault before it gives rise to a cable deterioration and a detrimental insertion loss.