Directional Bend Sensor Based on Re-Grown Tilted Fiber Bragg Grating

A novel fiber optic bend sensor is implemented by using a re-grown tilted fiber Bragg grating (TFBG) written in a small core single mode fiber with UV overexposure. The spectrum of the re-grown TFBG contrasts with that of normal TFBG by exhibiting large differences in the amplitude between neighboring symmetric (LP_0m) and asymmetric (LP_1m) cladding mode resonances, moreover each asymmetric cladding mode resonance splits into two peaks (corresponding to two orthogonal polarization states). The differential response of the three individual resonances of such group provides quantitative information about the magnitude and directions of bends in the TFBG. Numerical simulations indicate that the changes in the cladding-mode profiles in a bent fiber are responsible for this behavior through their impact on coupling coefficients. A bend sensitivity of 0.4 dB. m (for the 18th order group of cladding modes) is experimentally demonstrated within a range of 0-10.6 m^{- 1}.