Highly sensitive fiber-optic inclinometer utilizing a polymer waveguide-embedded interferometric sensor

A highly sensitive fiber-optic inclination sensor using a modal interferometer was proposed in the present study, which has a photopolymer embedded in a single-mode-few-mode-single-mode fiber (SMF-FMF-SMF) interferometric structure. The sensing component for inclination measurement consists of a cured ellipsoidal photopolymerized-waveguide (EPW) connecting the ends of the FMF and SMF. The effect of EPW on the transmission spectrum and sensitivity of the sensor is specifically investigated using simulation and experiment. In addition, during the preparation of the sensor, it was found that EPW affects the cladding pattern where the FMF is at a low frequency, and a more stable interference pattern can be obtained by modulating the FMF length. The results demonstrate a notable tilt sensitivity of 4.43 dB per degree within the range of 4.4° to 11.4°. Moreover, a change in inclination angle causes misalignment of the FMF and SMF cores, which results in a variation in fringe contrast (FC), allowing a one-to-one correspondence between fringe contrast and θ to be established over a wider range of 0° to 11.4° with an error of less than 3%. The proposed sensor has low temperature crosstalk and is able to cope with disturbances in complex environments. It is expected to be used for microdeformation monitoring of engineered structures.