Coherent detected phase-OTDR (CDPO) systems are mainly used in distributed vibration sensing and these systems are preferred over the direct detected phase-OTDR (DDPO) systems due to their inherent property of mitigating a certain type of phase noise. There is a possibility that the existing non-mitigated phase noise can be controlled in CDPO systems only after properly investigating the characteristics of both the CDPO mitigated and CDPO-non-mitigated noise types. Hence, the first and crucial step, i.e, the characteristics of two different phase noise types are determined in this paper. This determination will help in providing ease about finding the real sources of both of the phase noise types and hence can help in mitigating the existing phase noise further.
