In-fiber torsion and temperature measurement based on femtosecond-laser-inscribed eccentric fiber Bragg grating

To realize light-weight, compact-size, anti-electromagnetic-interference, and high-sensitivity torsion measurement for applications in structural engineering, biological safety, industrial production, a miniature in-fiber torsion sensor based on an eccentric fiber Bragg grating (EFBG) structure was proposed and demostrated. The EFBG was inscribed with an off-axis distance of 3 μm from the core axis through a point-to-point femtosecond laser inscribing process. Since the coupling efficiency between the fiber core mode and cladding modes can be effectively affected by the torsion angle of the fiber, the torsion can be measured by monitoring the transmission intensity. A torsion sensitivity of 0.03341 dB/° with a high linearity of 0.9986 was experimentally achieved. Simultaneously, temperature can be monitored by the wavelength tracing of the Bragg dip with a sensitivity of 0.0108 nm/°C was realized.