Mach-Zehnder Interferometer Sensor Curvature Demodulation Method Based on the Orthogonal Decomposition of Spectral Curves

Abstract

This paper proposes a curvature demodulation of Mach-Zehnder interferometer (MZI) sensors based on complete spectral information. An MZI sensor composed of two waist-enlarged single mode fibers (SMFs) was fabricated. To research the spectral characteristics of the sensor under different curvatures, an experimental system was built to load curvature and save spectra. By analyzing the influence of light intensity and wavelength on the curvature fitting accuracy, researchers have found that complete spectral information can express curvature accurately. This paper introduced the concept of orthogonal decomposition to extract complete spectral information. A group of Chebyshev polynomials was chosen as the basis to decompose the spectral curve into a vector (spectral curve decomposition coefficients). A support vector machine improved by a genetic algorithm (GA-SVM) was used to fit the relationship between the spectral curve decomposition coefficients and the curvature. This paper introduces a new accuracy estimation parameter ('equivalent absolute error'), which is used to measure the accuracy of demodulation. The equivalent absolute error of the method proposed in this paper is 0.0022494 m-1, which is superior to other methods. The advantage of this demodulation method is that the curvature is demodulated independently of the spectral information about a particular peak (valley). The demodulation method is applicable to a demodulation process of multiple physical quantities based on spectral information.