Wavelet-Based Demodulation of Multimode Etched Fiber Bragg Grating Refractive Index Sensor

• Published in: Sensors (Basel, Switzerland) Vol. 19; no. 1; p. 39
• Main Authors: Ayupova, Takhmina, Sypabekova, Marzhan, Molardi, Carlo, Bekmurzayeva, Aliya, Shaimerdenova, Madina, Dukenbayev, Kanat, Tosi, Daniele
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 22-12-2018; MDPI
• Subjects: Biosensors; Bragg gratings; Conflicts of interest; Demodulation; Enlargement; Evanescent field sensors; fiber Bragg grating (FBG); Hydrofluoric acid; Interrogation; Laboratories; optical fiber sensor (OFS); Optics; Photonics; Plasma etching; Propagation modes; Questioning; refractive index sensors; Refractivity; Sensitivity analysis; Sensors; Spectra; Sucrose; Wavelet analysis; wavelet density estimation; Kazakhstan; refractive index sensors; Evanescent field sensors; optical fiber sensor (OFS); fiber Bragg grating (FBG); wavelet density estimation
• DOI: 10.3390/s19010039
• EISSN: 1424-8220

Etched fiber Bragg grating (EFBG)-based sensors are used as evanescent field sensors for refractive index detection. When the fiber thickness is thin and the refractive index sensitivity increases, the number of propagating modes increases, resulting in a spectral enlargement that complicates the interrogation of the sensor. In this work, we present a method to analyze the spectrum of a multimode etched fiber Bragg grating (MMEFBG) in the wavelet domain, which analyzes the amount of spectral density independently from the peak reflectivity value. The proposed interrogation method permits defining the integral of the spectral density as a novel and unconventional estimator. With respect to the conventional estimators based on wavelength shift, this estimator can better exploit the larger amount of information given by the spectral enlargement typical of multimode behavior. Results were obtained by etching an MMEFBG in hydrofluoric acid and using water/sucrose mixtures to evaluate the refractive index sensitivity, validating the interrogation method.