Design and performance investigation of a highly accurate apodized fiber Bragg grating-based strain sensor in single and quasi-distributed systems

Abstract

In this work, fiber Bragg grating (FBG) strain sensors in single and quasi-distributed systems are investigated, seeking high-accuracy measurement. Since FBG-based strain sensors of small lengths are preferred in medical applications, and that causes the full width at half-maximum (FWHM) to be larger, a new apodization profile is introduced for the first time, to the best of our knowledge, with a remarkable FWHM at small sensor lengths compared to the Gaussian and Nuttall profiles, in addition to a higher mainlobe slope at these lengths. A careful selection of apodization profiles with detailed investigation is performed-using sidelobe analysis and the FWHM, which are primary judgment factors especially in a quasi-distributed configuration. A comparison between the elite selection of apodization profiles (extracted from related literature) and the proposed new profile is carried out covering the reflectivity peak, FWHM, and sidelobe analysis. The optimization process concludes that the proposed new profile with a chosen small length (L) of 10 mm and Δn_ac of 1.4×10^-4 is the optimum choice for single stage and quasi-distributed strain-sensor networks, even better than the Gaussian profile at small sensor lengths. The proposed profile achieves the smallest FWHM of 15 GHz (suitable for UDWDM), and the highest mainlobe slope of 130 dB/nm. For the quasi-distributed scenario, a noteworthy high isolation of 6.953 dB is achieved while applying a high strain value of 1500 μstrain (με) for a five-stage strain-sensing network. Further investigation was undertaken, proving that consistency in choosing the apodization profile in the quasi-distributed network is mandatory. A test was made of the inclusion of a uniform apodized sensor among other apodized sensors with the proposed profile in an FBG strain-sensor network.

A Theoretical Study and Numerical Simulation of a Quasi-Distributed Sensor Based on the Low-Finesse Fabry-Perot Interferometer: Frequency-Division Multiplexing

“…The positions of gratings along the fiber length define the optical path difference. Frequency-division multiplexing, wavelength-division multiplexing, and time-division multiplexing can be implemented [5,6,7,8,9,10,11,12]. …”

Numerical and Experimental Analysis of Matched Filter Interrogation of FBG Sensors with Large Side Lobes

“…Thus, it was possible to compare FBG interrogation systems with different side lobe strengths. The parameter that affects side lobe reflectance is the axial apodization of the Bragg structure [ 1 , 26 ]. Figure 2 presents the apodization profiles used in the calculations.…”

High sensitive and large dynamic range quasi-distributed sensing system based on slow-light π-phase-shifted fiber Bragg gratings

“…The number of sensors in the WDM network can be increased by reducing the FWHM and sidelobes of reflected spectra of multiplexed FBG sensors. In recent years, several apodization profiles have been proposed to optimize the optical characteristics, such as FWHM, maximum side-lobes (MSL), average side-lobes, side-lobes suppression ratio (SLSR), etc., of FBG for dense WDM (DWDM) based quasi-distributed strain and temperature sensing networks [15][16][17].…”

“…For the five-stage temperature sensing network, the obtained dynamic range is of 133 • C. The additional advantage of slow-light -FBG in quasi-distributed sensing networks over the conventional apodized FBG sensing networks is that slow-light peaks are free from the side-lobes. Therefore, slow-light sensing networks do not require a guard band between the two sensors when the external perturbation is applied [16,17].…”