Sampled Fiber Bragg Grating spectral synthesis

Abstract

In this paper, a technique to estimate the deformation profile of a Sampled Fiber Bragg Grating (SFBG) is proposed and experimentally verified. From the SFBG intensity reflection spectrum, any arbitrary longitudinal axis deformation profile applied to a SFBG is estimated. The synthesis algorithm combines a custom defined error metric to compare the measured and the synthetic spectra and the Particle Swarm Optimization technique to get the deformation profile. Using controlled deformation profiles, the proposed method has been successfully checked by means of simulated and experimental tests. The results obtained under different controlled cases show a remarkable repetitiveness (< 50 με) and good spatial accuracy (< 1 mm).

Recovering a fiber Bragg grating axial strain distribution from its reflection spectrum

“…Several approaches have been proposed to obtain the deformation profile along the FBG structure, but most of them require phase measurements of the reflection spectrum [3,4] or a priori knowledge of the strain distribution [5][6][7]. Another approach based on a computational method [8] has been proposed to retrieve the strain distribution of sampled FBGs just from their reflection spectra; however, the spatial resolution of this method is limited by the sampling period of the sampled FBG.In this Letter, the particle swarm optimization (PSO) technique [9,10] has been combined with a geometrical processing method to obtain any arbitrary axial strain profile of an FBG from its reflection spectrum. The geometrical processing is implemented as an error function that compares the desired spectrum (associated with the FBG to be measured) to different synthesized spectra [11] generated from the PSO candidate strain profiles.…”

“…Several approaches have been proposed to obtain the deformation profile along the FBG structure, but most of them require phase measurements of the reflection spectrum [3,4] or a priori knowledge of the strain distribution [5][6][7]. Another approach based on a computational method [8] has been proposed to retrieve the strain distribution of sampled FBGs just from their reflection spectra; however, the spatial resolution of this method is limited by the sampling period of the sampled FBG.…”

“…The large amount of possible spectral shapes makes it difficult to compare between them in an efficient way. Previous related works [8] limit the FBG structure to make easier the comparison task between two spectra by ensuring some spectral artifacts that can be evaluated (i.e., several peaks for the sampled FBGs). The geometrical processing scheme must have enough sensitivity to distinguish between two close spectra and also enough goodness to assign a low error to a synthetic spectrum generated from a strain profile with less spatial resolution than the desired one (usually a continuous profile).…”

Optical strain gauge with high spatial resolution

“…The measured spectrum is compared to simulated (synthetic) ones until they match 13 to get the deformation axial profile of an SFBG. Synthetic spectra are computed using the same SFBG base structure, but being artificially stretched (Figure 3).…”

“…In this study, a FBG-based strain gauge has been improved to retrieve its inner deformation profile. Employing sampled fiber Bragg gratings (SFBGs), a particular type of FBGs, 12 in combination with a spectral synthesis technique, 13 a sensor system has been developed and experimentally verified to retrieve the deformation profile of an asymmetric plate. Using only the intensity of the reflection spectrum of the proposed SFBG transducer, its intragrating strain profile can be obtained, achieving an improvement on the spatial resolution of optical strain gauges.…”