Reflective Optical Fiber Sensors Based on Tilted Fiber Bragg Gratings Fabricated With Femtosecond Laser

The fabrication of tilted fiber Bragg gratings (TFBGs) in non-photosensitized single-mode fiber by infrared femtosecond (fs) laser is reported for the first time to the best of our knowledge. The tilted grating structure is obtained by focusing laser pulses through a phase mask into a tilted positioned fiber sample, which is moving along with the interference fringe to form a grating region covering the entire fiber core and partial cladding. A reflective fiber probe based on the TFBG with a gold mirror sputtered on one end has been fabricated and its maximum refractive index (RI) sensitivity is 12.276 nm/RI unit in the RI range of 1.4091-1.4230 for the cladding mode LP020. A wavelength-power demodulated technique based on the sensors has been proposed to measure axial strain and temperature simultaneously, which is found suited to work in harsh environment, especially at high temperature up to 800°C.