Combination of Phase-Sensitive OTDR and Michelson Interferometer for Nuisance Alarm Rate Reducing and Event Identification

In order to obtain low nuisance alarm rate (NAR) and achieve the disturbance event identification, the wavelength-division multiplexing combination of a phasesensitive optical time-domain reflectometer (φ-OTDR) and a Michelson interferometer (MI) is proposed and demonstrated. The disturbance is synchronously detected by a φOTDR and an MI. A true alarm is presented only when a real disturbance is detected by both φ-OTDR and MI. Furthermore, the event identification of the confirmed real disturbance is recognized by an equivalent frequency distribution analysis on the MI signal. It is found that, by the experiment, NAR can be reduced to 1.2% from 13.5% via a single φ-OTDR, with a high detection probability of 92%. Furthermore, four disturbance events can be distinguished with a 90% identification rate. Our proposed wavelength-division multiplexing of a φ-OTDR and an MI is simple and low cost, no complicated algorithm is required, and only one sensing fiber is needed; therefore, it is an interesting exploration of multiplexing of φ-OTDR and interferometers.