| Summary: | A highly sensitive two-axis bending sensor based on long period fiber grating (LPFG) in a dual side-hole fiber (DSHF) is presented and experimentally investigated. The LPFG is fabricated by periodically collapsing a piece of DSHF with automatic arc discharge technology. The existence of the two air holes in the DSHF makes the cladding modes, regardless of the polarization state, concentrate in the area perpendicular to the connection of the two holes. Such a feature leads to quite different bending responses at the directions perpendicular and parallel to the connection of the air holes, which makes the DSHF-based LPFG suitable for two-axis bending measurement. The bending sensitivity of the LPFG are 21.03 nm/m<sup>-1</sup> and 15.77 dB/m<sup>-1</sup> at the orthogonal directions, respectively. Besides, compared with the general arc-induced LPFGs in solid fibers, the size of the DSHF-based LPFG is effectively reduced because the periodic air hole collapse in the DSHF causes a large geometric deformation of the fiber core and increases coupling coefficient between the core and cladding modes. The sensing characteristics of strain, polarization, surrounding refractive index, and temperature are also investigated in our experiment.
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