Device and method for enhancing phi-OTDR frequency response

Abstract

The invention discloses a device and method for enhancing phi-OTDR frequency response in the technical field of distributed optical fiber sensors. A laser is connected to the input end of a light splitter (1*2); the output end Out1 of the light splitter is successively connected to an acoustic-optic modulator (AOM), an erbium doped optical fiber amplifier 1 (EDFA1) and an optical circulator port 1; an optical circulator port 2 is connected to a sensing cable fiber core 3; and an optical circulator port3 is successively connected to an erbium doped optical fiber amplifier 2 (EDFA2), a photodetector 2, a data acquisition module 2 and a processing server. The device and method are higher in alarm accuracy; when external vibration occurs, a Michelson interference system can detect and capturethe complete spectrum of a vibration event which can be matched with an intrusion event template library, so that the type of the vibration event can be accurately identified, and the accuracy of alarm can be enhanced; and a phi-OTDR system can rapidly detect vibration and vibration source positions, and can simultaneously preserve part of frequency spectrums of vibration point positions.

Description

technical field [0001] The invention relates to the technical field of distributed optical fiber sensors, in particular to a device and method for improving the frequency response of φ-OTDR. Background technique [0002] The distributed optical fiber sensing system has a series of advantages such as small size, passive, anti-electromagnetic interference, and anti-corrosion. The coherent optical time-domain reflectometry technology (φ-OTDR, positioning type vibrating optical fiber system) based on Rayleigh scattering also has long-distance transmission. , high sensitivity, and precise positioning advantages, vibrating optical fibers, especially φ-OTDR systems, are increasingly being used in petroleum, military and security fields. [0003] However, what φ-OTDR measures is pulsed Rayleigh scattered light, and the Rayleigh scattered light of adjacent pulses cannot overlap, which leads to the limitation of the pulse scanning frequency by the length (L) of the sensing cable. The ...

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Problems solved by technology

[0003] However, what φ-OTDR measures is pulsed Rayleigh scattered light, and the Rayleigh scattered light of adjacent pulses cannot overlap, which leads to the limitation of the pulse scanning frequency by the length (L) of the sensing cable. The relationship is According to Shannon sampling theorem, when the scanning frequency of the system is ScanRatemax, the maximum signal frequency that the system can detect is ScanRatemax / 2, which causes the traditional φ-OTDR system to be unable to detect signals with a frequency greater than ScanRatemax / 2. For φ- Based on the OTDR’s typical detection distance of 50km, the maximum scanning frequency is 2kHz, and the maximum detectable frequency of the system is 1KHz. Signal systems above 1kHz cannot be accurately detected, which leads to the inability of the algorithm to accurately judge vibration signals. Reduced system alarm accuracy

At present, there is no good way to deal with it. The disclosed method uses multi-wavelength injection (see "Distributed Optical Fiber Sensing System and Method Based on Multi-Pulse and Multi-Wavelength", Publication No.: 109282839A), although this method can improve system detection. bandwidth, but the system cost is significantly increased (currently in the φ-OTDR system, narrow linewidth lasers, acousto-optic modulators, and φ-OTDR photodetectors account for more than 50% of the total system cost). It will increase the cost by about 50%; if the laser is shared, the load capacity of the system will be reduced, and the transmission distance will be significantly reduced;

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