Localization of distributed fiber sensor employing a sub-ring

There is a simple distributed optical fiber sensing system which is used to monitor vibration signal, having an additional sub-loop coupled with main ring by a 3dB coupler. This paper compares three outputting interfered beams, each of them traveling in the sub-ring 0, 1, 2 times separately. Using the simultaneous equations produced by those three outputs, it finds the relation between the interference lights and vibration signal's characteristics, such as frequency, amplitude and position. Through simplify and calculating, vibration position of long pipeline is to be achieved finally.