Helical Long-Period Gratings Inscribed in Polarization-Maintaining Fibers by CO2 Laser

We demonstrate the fabrication of helical long-period gratings (HLPGs) in a polarization-maintaining fiber using a CO2 laser. The maximum polarization-dependent loss (PDL) of the grating was measured to be more than 30 dB at the resonance wavelength. The HLPG was found to have a high refractive index sensitivity of -7248.6 nm/RIU when the surrounding refractive index changes in the range of 1.4470-1.4600, temperature sensitivity of 158.8 pm/°C, and strain sensitivity of 3.17 pm/με. The twist sensitivities based on intensity variation were measured to be 5.98 dB/(rad/m) (co-directional twist) and -5.97 dB/(rad/m) (contra-directional twist), respectively. The demonstrated grating devices have promising applications as high-sensitivity fiber sensors, PDL compensator, etc.