Optimal parameters for fiber Bragg gratings for sensing applications: a spectral study

Abstract

The spectral characteristics viz. reflectivity, bandwidth, and sidelobes’ intensity for uniform and apodized (Gaussian, hyperbolic tangent, apod1, sine, and raised sine) fiber Bragg gratings (FBGs) were studied as a function of grating length and index modulation. The optimal grating length and index modulation to obtain maximum reflectivity and minimum sidelobes were determined, as needed for sensing applications. The impact of various apodization profiles on the spectral response has also been assessed. The results indicate that out of the apodization profiles considered for the study, sine, Gaussian, and raised sine profiles offer the desired output. Article highlights The reflectivity (of main peak) and sidelobes’ intensity increase with grating length and index modulation. The bandwidth decreases with grating length and increases with index modulation. The ideal grating length and index modulation were found to be 5 mm and 0.0008 respectively to obtain maximum reflectivity and minimum intensity for sidelobes. Sine, Gaussian, and raised sine profiles are the best suitable apodization profiles among those considered.

Enhancing FBG Sensing in the Industrial Application by Optimizing the Grating Parameters Based on NSGA-II

“…Therefore, in the end, it comes up with the Pareto front that offers the optimum values of grating parameters for the manufacturing decision makers to select the grating length, grating period, and index modulation by which they can obtain the bandwidth and reflectivity that suit their applications’ requirements. The obtained results are compared to those other studies that yielded the same input parameters for verifying the proposed methods [ 15 , 16 ]. In addition, Thereby, the proposed method’s performance has been validated, the same scenarios are tested using another standard optimization method, such as a genetic algorithm, and a comparison has been conducted.…”

“…In conclusion, it is a multi-objective optimization problem in which the bandwidth and reflectivity are the optimized variables. Moreover, the grating parameters, including the grating length and modulation index, are the control variables considering the conflict between these objectives for some applications, as noted by surveying a couple of studies [ 15 , 16 ]. These studies reported a positive correlation between the reflectivity and the modulation index on one hand and grating length on the other hand.…”

“…As a result, some studies worked on determining the grating parameters for obtaining the maximum reflectivity and the minimum sidelobes intensity. Moreover, other studies determined the relation between bandwidth and reflectivity and the grating parameters [ 15 , 16 ]. These studies contributed some simulation and experimental work for reporting the bandwidth, sidelobe, and reflectivity at different values of grating length and index modulation for determining the optimum bandwidth and reflectivity.…”

Strain Modal Testing with Fiber Bragg Gratings for Automotive Applications

“…Although the refractive index variation is oftentimes illustrated as a square waveform, its shape is better represented by a sinusoidal function [55]. Uniform FBGs (i.e., having constant index modulation and grating period) show undesired sidelobes in the reflected spectrum, which can be reduced through proper apodization profiles of the refractive index [56][57][58]. Monotonically varying the grating period will lead to chirped FBGs [59], whereas tilting the grating planes from their original orthogonal direction with respect to the fiber longitudinal axis will produce a tilted FBG [60].…”

“…lation and grating period) show undesired sidelobes in the reflected spectrum, which can be reduced through proper apodization profiles of the refractive index [56][57][58]. Monotonically varying the grating period will lead to chirped FBGs [59], whereas tilting the grating planes from their original orthogonal direction with respect to the fiber longitudinal axis will produce a tilted FBG [60].…”