Double Cladding Fiber Chiral Long-Period Grating-Based Directional Torsion Sensor

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We demonstrated the fabrication of a chiral long-period fiber grating (CLPG) by CO2-laser heating of a twisted double-cladding fiber (DCF). The polarization and sensing characteristics of the DCF-CLPG are investigated experimentally. Due to the helical structure, the grating shows a higher torsion sensitivity of -0.40 nm/(rad/m), and the torsion rate and torsion directions can be measured simultaneously using single DCF-CLPG. The temperature, strain, bending, and surrounding refractive index sensing characteristics are also investigated experimentally. The proposed CLPG has a promising application as high-sensitivity directional torsion sensor.