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Strain Measurement Method of Optical Fiber Composite Overhead Line Based on Least-squares Fit

To improve the accuracy of measured strain for optical fiber composite overhead line, a strain measurement method based on the pseudo-Voigt profile and least-squares fit is proposed in this paper. Firstly, the principle of Brillouin scattering-based distributed optical fiber strain measurement method is presented. Secondly, the improved quadratic polynomial fit is used to calculate the initial value of variables. Thirdly, the objective function and optimization process of the least-squares fit are presented. Finally, the Brillouin spectra of the optical fiber composite overhead line with different values of SNR (signal-to-noise ratio) are numerically generated, and the corresponding Brillouin frequency shift (BFS) and strain are calculated by using the proposed method. The results show that the pseudo-Voigt profile-based least-squares fit can effectively approximate Brillouin spectrum under different values of frequency sweep span deviation and SNR, and the accuracy in BFS and strain is guaranteed. This work provides a high precision method for strain measurement of optical fiber composite overhead line.