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.