Distributed fiber acoustic sensing system based on random gratings

Abstract

The invention relates to a distributed fiber sensing system based on random gratings. The system structurally comprises a narrow linewidth laser, a pulse modulator, a circulator, a sensing optical fiber and a detector; an output end of the narrow linewidth laser is connected to the pulse modulator, an output end of the pulse modulator is connected to a first port of the circulator, a second port of the circulator is connected with the sensing optical fiber, a third port of the circulator is connected to the photodetector, and the detector is connected with a filter and a demodulator; a plurality of random gratings are engraved on the sensing optical fiber, and the random grating interval is Delta]z; the pulse modulator modulates out two pulse pairs with the frequency difference of [Delta]for a plurality of pulse pairs with different frequency differences, the interval is [Delta]T, and the [Delta]T is twice the random grating interval; the demodulator receives the pulse pairs filteredby the bandpass filter of [Delta]f and then conducts phase demodulation with a local oscillator of [Delta]f. The novel distributed fiber acoustic sensing system can greatly increase the signal-to-noise ratio and response linearity of the system.

Description

technical field [0001] The invention relates to optical equipment, in particular to a novel distributed optical fiber acoustic wave sensing system. Background technique [0002] As a relatively mature and classic measurement system, interferometer has relatively high performance, including accuracy, linearity, signal-to-noise ratio, dynamic range, etc. However, in many applications we need multiple interferometers, or even a large number of interferometers, which leads to the multiplexing system of interferometers, including wavelength division multiplexing (using multiple wavelengths of lasers corresponding to different interferometers) ; Space division multiplexing (using couplers or optical switches to multiplex multiple channels); Time division multiplexing (using pulses to distinguish multiple interferometer systems in time), etc., and their combined systems. [0003] The DAS (Distributed fiber Acoustic Sensing, DAS) system is a variant of a time-division multiplexing ...

AI Technical Summary

Problems solved by technology

However, the distributed optical fiber acoustic wave sensing system has these advantages and also brings some disadvantages: (1) In ordinary single-mode optical fiber, the intensity level of RBS is about -82dB of the incident signal, compared with the original reflector , the signal is much weaker

(2) For short-distance measurement, it is necessary to ensure the signal-to-noise ratio, etc., and the pulse width cannot be too short, which makes it relatively difficult for DAS to achieve relatively high spatial resolution in short distances.

(3) The interferometer in DAS is actually formed by the interference between all Rayleigh backscattering signal components in the fiber segment corresponding to the pulse width. This essence determines that the response linearity of the system to external signals is not enough.

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