Research On Optimal Design Of Distributed Optical Fiber Sensing System Based On Φ-OTDR

Optical fiber sensing technology has the advantages of high sensitivity,long detection distance,and strong anti-interference ability,and is widely used in the fields of electricity,oil,construction,transportation,medical,and military.However,distributed fiber optic sensing(DAS)based on Φ-OTDR has problems such as the high cost of optimizing system structure and complex signal processing methods.Therefore,based on the vibration signal detection of the Φ-OTDR system,this paper conducts research on optimizing system structure and signal processing methods,providing a theoretical basis for practical applications.Based on reference to domestic and foreign literature,this paper summarizes the optical fiber sensing system,compares and analyzes the research status of the Φ-OTDR,and studies the sensing principle,signal processing process,and performance indicators of the Φ-OTDR.A simulation experimental system based on Φ-OTDR is built.Through the principle simulation of the heterodyne coherent optical system,the signal transmission mechanism is further studied and the feasibility of the system is analyzed.Qualitative measurement of theΦ-OTDR system is achieved through the simulation of single or multiple frequency disturbances on a 100 m optical fiber.An EDFA optimization design scheme based on Φ-OTDR is proposed.Through optimization simulation of EDFA,it is analyzed that EDFA has the best gain amplification effect when the pump wavelengths are 1550 nm and 990 nm,and the pump length is 5 m.The optimization direction of optical components is pointed out,improving signal quality,and providing a basis for device selection in subsequent experiments.After analyzing the noise source of the Φ-OTDR system,a vibration signal processing method based on compression sensing for the Φ-OTDR system is designed.The sensing matrix is constructed by sparse array and observation array,and a mathematical model of compressed sensing theory is established;Using a reconstruction algorithm to accurately reconstruct the vibration signal with a small number of sampled values;Perform spectrum analysis of the time domain signal composed of scattered light at the vibration source to complete the measurement of the frequency information of the vibration signal.The results are compared with the difference method,empirical mode decomposition(EMD)method,variational mode decomposition(VMD)method,and VSS-NLMS method.A distributed optical fiber sensing system based on Φ-OTDR was built.The specific process was as follows: using PZT to simulate vibration sources,and simulating vibration signals of different frequency bands were set up for experimental verification.Taking100 Hz and 500 Hz as examples,36 scattered light information were continuously collected,and the signal position information denoising was completed.The experimental results showed that this method achieved a signal-to-noise ratio of 40.41 d B and 30.62 d B respectively,which was superior to other traditional denoising methods,Moreover,this method does not need to be performed on the results of the difference method,and can directly process the beat signal,simplifying the signal processing process and reducing signal processing time.After that,frequency demodulation experiments were conducted using this method and the I/Q quadrature demodulation method.The experimental results showed that the relative error of frequency measurement using the compressed sensing method was at least 2.7%,and the demodulation performance in the low-frequency range was good.This method can directly analyze the signal spectrum without undergoing phase unwrapping processing,further meeting the real-time requirements of the system.Finally,the experimental error and its source are analyzed.The performance of this system is excellent: the sensing distance is 10 km,the frequency response range is 15Hz-550 Hz,and the spatial resolution is 11 m.The research on the optimization design of distributed optical fiber sensing system based on Φ-OTDR in this paper effectively improves the detection ability of distributed optical fiber sensing system based on Φ-OTDR,and has a certain reference value.