Long-period grating inscription on polymer functionalized optical microfibers and its applications in optical sensing

Abstract

We demonstrated long-period grating (LPG) inscription on polymer functionalized optical microfibers and its applications in optical sensing. Optical microfibers were functionalized with ultraviolet-sensitive polymethyl methacrylate jackets and, thus, LPGs could be inscribed on optical microfibers via point-by-point ultraviolet laser exposure. For a 2 mm long microfiber LPG (MLPG) inscribed on optical microfibers with a diameter of 5.4 μm, a resonant dip of 15 dB at 1377 nm was observed. This MLPG showed a high sensitivity of strain and axial force, i.e., −1.93  pm/μϵ and −1.15  pm/μN, respectively. Although the intrinsic temperature sensitivity of the LPGs is relatively low, i.e., −12.75  pm/°C, it can be increased to be −385.11  pm/°C by appropriate sealing. Benefiting from the small footprint and high sensitivity, MLPGs could have potential applications in optical sensing of strain, axial force, and temperature.