Abstract
Static strain can be detected by measuring a cross-correlation of reflection spectra from two fiber Bragg gratings (FBGs). However, the static-strain measurement resolution is limited by the dominant Gaussian noise source when using this traditional method. This paper presents a novel static-strain demodulation algorithm for FBG-based Fabry-Perot interferometers (FBG-FPs). The Hilbert transform is proposed for changing the Gaussian distribution of the two FBG-FPs’ reflection spectra, and a cross third-order cumulant is used to use the results of the Hilbert transform and get a group of noise-vanished signals which can be used to accurately calculate the wavelength difference of the two FBG-FPs. The benefit by these processes is that Gaussian noise in the spectra can be suppressed completely in theory and a higher resolution can be reached. In order to verify the precision and flexibility of this algorithm, a detailed theory model and a simulation analysis are given, and an experiment is implemented. As a result, a static-strain resolution of 0.9 nε under laboratory environment condition is achieved, showing a higher resolution than the traditional cross-correlation method.
Highlights
In recent years, fiber Bragg gratings (FBGs)-based Fabry-Perot interferometers (FBG-FPs) formed by two identical FBGs have been used for many applications in several fields, such as deformation/strain monitoring, vibration measurement, temperature sensing, etc. [1,2,3]
The static strain can be demodulated by calculating the wavelength difference of a group of harmonic peaks from the two FBG-based Fabry-Perot interferometers (FBG-FPs)’ reflection spectra in a free spectrum range (FSR)
This paper presents a high-resolution demodulation algorithm based on the Hilbert transform and cross third-order cumulant for FBG-FP static-strain sensors
Summary
FBG-based Fabry-Perot interferometers (FBG-FPs) formed by two identical FBGs have been used for many applications in several fields, such as deformation/strain monitoring, vibration measurement, temperature sensing, etc. [1,2,3]. High-finesse FBG-FP can be applied to ultra-high-resolution static-strain sensing where an extra FBG-FP is used as a reference sensor head [6,7,8]. In these systems, a narrow line-width tunable laser is generally used for interrogating the FBG-FP sensor heads and the reference FBG-FP is used for compensating any temperature disturbances and laser frequency drift. The static strain can be demodulated by calculating the wavelength difference of a group of harmonic peaks from the two FBG-FPs’ reflection spectra in a free spectrum range (FSR). There are many methods to calculate the wavelength difference of two FBG sensors, such as centroid detection algorithm (CDA) [9], the least square method (LSQ) [10], the autocorrelation [11]
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