This paper presents and experimentally demonstrates a novel scheme of Brillouin optical time domain analysis (BOTDA) sensing system to ensure the encoded pulse waveform amplified from EDFA is flat. This system also can eliminate the noise by introducing additional pre-exhausted wavelength at the laser. The experiment results indicate that this dual-wavelength pump light scheme can easily shape the Lorenz curve between Brillouin gain spectrum(BGS) and scan frequencies without any extra processing, compared to normal BOTDA system with single-wavelength pump light. The new scheme can also improve the intensity of Brillouin signal about 50mV as well as the frequency shift accuracy is increased by 5MHz, which is benefit for increasing sensing range and measurement accuracy.
This paper introduces one three-dimensional measurement system which based on structured light. This system has the advantages of high precision, high speed, and simple structure. In the three-dimensional measurement system based on structured light, the solution phase is one of the key steps. Phase jump, shadow and other errors will have a great impact on the final point cloud computing. This paper explains the three-dimensional measurement system, then also made an error analysis and proposed a corresponding solution. The reasons for the phase jump were analyzed and the corresponding solutions were proposed. This paper also analyzes the cause of random error and proposes a solution. The final accuracy was improved. This has important applications in contour extraction in workpiece repair and autopilot.
In order to improve the real-time performance of Brillouin optical time-domain analysis (BOTDA) distributed optical fiber sensing system, this paper proposes an extraction method of Brillouin scattering spectrum based on half-interval search frequency sweep. This method shortens measurement time by reducing the frequency sweep range, and provides a simplified Brillouin gain spectrum. Cross-correlation of this spectrum with a standard Lorentz curve, then the ideal Lorentz line type near the peak of the convolution result is used for frequency shift feature extraction. And the estimated value of Brillouin frequency shift (BFS) can be calculated by the result of frequency shift feature extraction. A 15km Rayleigh BOTDA temperature sensing experiment is designed to verify the reliability of the method. The results show that this method avoids extension of measuring time caused by the complex iterative process, and reduces frequency sweep time. It has better real-time performance and measurement accuracy than traditional Lorenz curve fitting (LCF) which based on the Levenberg-Marquardt (LM) algorithm.
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