Real-time quasi-coherent detection and fiber optic detection using multi-frequency signals

Abstract

A distributed acoustic detection (DAS) system for the quasi-coherent detection of at least one multi-frequency signal through an optical fiber, comprising a multi-frequency pulse generator, a circulator, a coherent detector, and a processor; the pulse generator generating at least one multi-frequency pulse train comprising at least two pulses, each with a different frequency; the pulse train comprising a plurality of carriers; the coherent detector receiving at least one backscattered signal from the optical fiber; and the processor for the quasi-coherent aggregation of the carriers into the backscattered signal; wherein the processor channels the backscattered signal into at least one complex signal for each frequency in the carriers, and wherein for each complex signal,The processor extracts at least one amplitude shift and one phase shift for each of the carriers and selectively aggregates at least one of the shifts for the carriers to determine if an event has occurred across the optical fiber.

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