Phase-Shifted Terahertz Fiber Bragg Grating for Strain Sensing With Large Dynamic Range

Recent advances in optical fiber sensing techniques have demonstrated the utility of terahertz (THz) gratings as a modality for strain and temperature sensing. However, these techniques remain reliant on the use of higher order resonant peaks, enhancing their sensitivity at the cost of limited dynamic range. The use of a lower order resonant peak for sensing can lead to a larger dynamic range at the cost of accuracy. This letter reports a π-phase-shifted THz fiber Bragg grating, fabricated using a femtosecond laser, capable of detecting changes in strain over a substantially larger dynamic range than previously reported methods with improved accuracy. A second THz grating without a π-phase-shifted structure, but otherwise identically constructed, was interrogated in series on the same optical fiber. The two devices were simultaneously experimentally investigated using a strain test (~1 mε in total), and the results presented in this letter. In addition, the theoretical models of the devices were created, which closely matched experimentally observed device physics.