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Detection Limit of Etched Fiber Bragg Grating Sensors

TitleDetection Limit of Etched Fiber Bragg Grating Sensors
Publication TypeJournal Article
Year of Publication2013
AuthorsShivananju, BN, Renilkumar, M, Prashanth, GR, Asokan, S, Varma, MM
JournalJournal of Lightwave Technology
Date PublishedJuly
Keywordsadsorbing molecular layer, adsorption, Assembly, Bragg gratings, Bragg wavelength shift, bulk refractive index, clad etched FBG, detection limit, EFBG, electrostatic layer-by-layer assembly, Etched fiber Bragg grating, etched fiber Bragg grating sensors, etching, FBG, Fiber gratings, fibre optic sensors, finite element analysis, finite element model, layer by layer assembly, layer thickness, LbL films, limit of detection, multiplexing, nominal measurement noise levels, Numerical models, optical fibre cladding, optical fibres, polymer electrolytes, refractive index, refractometry, Sensors, surface adsorption sensing, weak polyelectrolytes

While Fiber Bragg Grating (FBG) sensors have been extensively used for temperature and strain sensing, clad etched FBGs (EFBGs) have only recently been explored for refractive index sensing. Prior literature in EFBG based refractive index sensing predominantly deals with bulk refractometry only, where the Bragg wavelength shift of the sensor as a function of the bulk refractive index of the sample can be analytically modeled, unlike the situation for adsorption of molecular thin films on the sensor surface. We used a finite element model to calculate the Bragg wavelength change as a function of thickness and refractive index of the adsorbing molecular layer and compared the model with the real-time, in-situ measurement of electrostatic layer-by-layer (LbL) assembly of weak polyelectrolytes on the silica surface of EFBGs. We then used this model to calculate the layer thickness of LbL films and found them to be in agreement with literature. Further, we used this model to arrive at a realistic estimate of the limit of detection of EFBG sensors based on nominal measurement noise levels in current FBG interrogation systems and found that sufficiently thinned EFBGs can provide a competitive platform for real-time measurement of molecular interactions while simultaneously leveraging the high multiplexing capabilities of fiber optics.