Simulation and analysis of Gaussian apodized fiber Bragg grating strain sensor

Abstract

In this paper, the performance of various apodization profiles (uniform, hyperbolic tangent and gaussian) for un-chirped Fiber Bragg Grating is investigated. Apodization techniques are used to get optimized reflection spectra with high side lobe suppression. The simulations are done by solving coupled mode equations in MATLAB using transfer matrix method which explains the relationship between the guided modes. The result shows that Gaussian profile suppresses side lobe level much more efficiently than uniform and hyperbolic tangent profiles. Gaussian apodized Fiber Bragg Grating is used to indicate strain by producing wavelength shift. MATLAB and Opti-grating result gives an idea about the efficiency of the suggested scheme to analyze strain measurements by giving a linear response.

Apodization Optimization of FBG Strain Sensor for Quasi-Distributed Sensing Measurement Applications

“…The reflectivity and side lobe level (SLL) as functions of Δ while maintaining at 10 mm for the different apodization profiles are depicted in Figures 5 and 6, respectively. It can be observed from Figure 5 that our proposed profile provides the highest value compared to Gaussian [3] and Nuttall [4] around Δ = 2 × 10 −4 , where FWHM is in acceptable range according to Figure 4.…”

“…In order to develop the new method of apodization based on the FBG technology, firstly we present a brief overview of Bragg grating reflectivity and how the process of apodization helps to get better reflection spectrum. Then, we compare the main apodization profiles discussed in the literature [3,4] with our proposed method to demonstrate the efficiency of our proposed apodization. FBG is a wavelength selective mirror as can be shown in Figure 1.…”

“…It basically constitutes generalized distributed reflector whose reflection spectrum and dispersion characteristics are wavelength-dependent and can be accurately adjusted by a proper design to measure strain and temperature [2]. The important feature of FBGS is that the sensed information is translated into a wavelength shift, giving reproducible measurements in spite of optical losses and intensity fluctuations [3]. However, FBGS with constant refractive index modulation amplitude show reflection spectrum with large side lobes [4], as well as highly nonlinear dispersion characteristics, which makes them unsuitable for high-performance applications.…”

Closed‐form expression to optimize the fiber Bragg grating sensor apodization performance

“…To design a FBG sensor, uniform function, Gaussian function, Hamming function, and Nuttal function apodization profiles will be used: Uniform: Gaussian function: Nuttal function: where a 0 = 0.3635819, a 1 = 0.4891775, a 2 = 0.1365995, and a 3 = 0.0106411 are the apodization coefficients, L is the grating length, and z is the coordinate of light propagation along the length of FBG.…”

“…An automated MATLAB‐based code has been developed to deal with a higher level of reflectivity and negligible SLL. The proposed approach is based on a new apodization formula that can be customized automatically based on a SLL and full width at half maximum (FWHM), ensuring a superior reflectivity level compared to the apodization profiles proposed by other authors …”