Effect of epoxy bonding on strain sensitivity and spectral behavior of reflected Bragg wavelength

We present the effect of epoxy bonding on strain sensitivity of fiber grating sensors. We show experimentally that, on average, sensors mounted onto aluminum plates by epoxy gluing both ends of the Bragg grating (epoxy free grating zone) display 16% more sensitivity to applied strain compared to those with epoxy covering the length of the grating zone (conventional method). We also show that in the conventional method, the epoxy layer contracts upon curing, forming an additional buffer that extends the breaking point of the sensor. Finally, adopting the conventional approach will also result in both spectral broadening and reduction in peak power of the reflected Bragg wavelength caused by the non-linearly distributed axial strain.