| 摘要 |
An optical fiber sensing system (20) applies spectral analysis to time-varying disturbances in the output optical power from a Sagnac interferometer. In particular, harmonically related null frequencies in the spectrum (402) of the output optical power from the Sagnac interferometer are used to uniquely determine the location of a disturbance along a fiber cable (50). An optical signal having relatively high coherence is fed into a splitter (25), which creates a pair of subsignals that are sent in opposite directions around a common optical path. The splitter is effective to recombine the subsignals after they have traveled around the common path. The location of the disturbance is determined by the formula: z is the distance between the locations of the disturbance and the splitter; 2L is the length of the common path; c is the speed of light; ne is the effective index of refraction of the optical fiber path experienced by the subsignals; and OMEGA 0 is the fundamental frequency associated with harmonically related nulls in the spectrum. Preferably, the sensing system is embedded within a communication system (60), which operates at wavelengths that are different than the wavelengths of the sensing system.
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