Abstract
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.
© 2013 IEEE
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