Fabrication and characterization of helical long-period fiber gratings in single-mode fibers

A fabrication method for helical long-period gratings (H-LPGs) in single-mode fibers is experimentally demonstrated. H-LPGs are manufactured by homogenously twisting the melting parts of fibers under indirect CO2 laser beam irradiation. The resonant wavelength attenuation is controlled by monitoring the real-time transmission spectrum during heating and twisting processes. The torsional and thermal characteristics of the fabricated H-LPGs are systematically investigated in experiments. The achieved torsion sensitivity is 96.4 pm/(rad/m) for twisting angles from −240° to 240°, and the temperature sensitivity is 49.2 pm/℃ ranging from 20 ℃ to 120 ℃. Our experimental results exhibit a highly accurate and reliable fabrication method for H-LPGs in fibers that possess high potentials for torsion and temperature sensing applications.