Abstract:
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.