Optical fiber distributed vibration sensing system based on envelope detection circuit

Abstract

The invention provides an optical fiber distributed vibration sensing system based on an envelope detection circuit. The system modulates a divided first path of direct current laser into pulsed lightand sends the pulsed light to a sensing optical fiber; the sensing optical fiber carries out vibration detection based on pulsed light to generate Rayleigh scattering light transmitted backwards, then the second path of direct current laser and the Rayleigh scattering light are coupled to generate two paths of scattering light interference signals with the phase difference of 180 degrees; coherent detection is carried out on the two paths of scattering light interference signals; common-mode components are filtered out, and beat frequency electric signals are obtained. After passing through an envelope detection circuit consisting of full-wave rectification and low-pass filtering, the beat frequency electric signals are moved to a baseband from a carrier in a frequency domain, so that therequirement of the system on the sampling rate of an acquisition card is reduced; the envelope of the beat frequency electric signals is obtained in the time domain; digital demodulation in coherentdetection is avoided, and the burden of a processing device is reduced. The full-wave rectification circuit and coherent detection are combined, and the sensing distance is increased while the high signal-to-noise ratio of coherent detection is ensured.

Description

technical field [0001] The invention belongs to the field of optical fiber sensing, and in particular relates to an optical fiber distributed vibration sensing system based on an envelope detection circuit. Background technique [0002] For optical fiber distributed sensors, the entire optical fiber acts as a continuous sensing medium, so a single distributed optical fiber sensor is equivalent to connecting a large number of point sensors together, thereby greatly reducing the cost. Optical fiber distributed vibration sensing can detect the vibration of each position on the entire optical fiber link in a distributed manner, and obtain information such as the position, frequency and magnitude of the vibration signal. [0003] Distributed sensing is typically achieved by techniques such as Optical Time Domain Reflectometry (OTDR) or Optical Frequency Domain Reflectometry (OFDR). Time-domain measurement can be measured within a sensing range of tens of kilometers and its spati...

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Problems solved by technology

[0004] The present invention provides an optical fiber distributed vibration sensing system based on an envelope detection circuit to solve the problems of short transmission distance, low signal-to-noise ratio and the need for a large number of processing devices when optical fiber is used for vibration measurement based on time-domain measurement technology. The problem with digital demodulation

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