Precise Fault Location in TDM-PON by Utilizing Chaotic Laser Subject to Optical Feedback

We propose a method with high spatial resolution to detect fiber faults in a time-division multiplexing passive optical network (TDM-PON). A semiconductor laser serving as the probe light source is subjected to self-feedback caused by reflection at fiber faults. The feedback will induce the laser to generate chaos. Autocorrelation of the output time series shows the external cavity signature and, therefore, indicates the distance between the laser and the fiber fault. Each branch is identified by the marker that is formed by the inserted fiber Bragg grating (FBG) providing the feedback in each branch, and the faulty branch can be distinguished by the marker that has disappeared. Our proof-of-concept experiment demonstrates the identification of the faulty branch and the location of the fault point in an optical network simultaneously. This is achieved with a 6-km feeder fiber and realizes the 8-mm spatial resolution.