Helical Long-Period Fiber Grating-Based OAM Interferometer and Its Application to Fiber Sensing

Orbital-angular-momentum (OAM) beams-based interferometers have recently been attracted significant interest and found various applications in the field of optical precision measurement. Whereas all-fiber OAM interferometers featured with the superior characteristics of the compact size, low cost, extremely-low insertion-loss, and the inherent compatibility with other fiber devices, have less been studied and especially demonstrated in experiment. In this study, we proposed and experimentally demonstrated an all-fiber OAM beams-based interferometer, where the two conjugated OAM beams generated by helical long-period fiber gratings (HLPGs) but with opposite helicities, were particularly utilized as the tested and referenced beams, respectively. The resulted interferograms are of the polarization independence, robust, and particularly suitable for phase-demodulation in azimuthal angle domain. As application examples of the proposed all-fiber OAM beams-based interferometer, changes in temperature ranging from 30 °C to 60 °C and changes in the strain ranging from 0 to 100 μϵ were measured, respectively. The obtained maximum sensitivity in temperature and strain are 26.585 rad/°C and 2.130 rad/μϵ, respectively. The accuracies for temperature and strain measurements are estimated to be 0.0016 °C and 0.0195 μϵ, respectively, which are about 2–3 order higher than those obtained from the conventional optical fiber-based sensors. It is believed that the proposed all-fiber OAM beams-based interferometer would find potential applications to ultra-high precision and sensing measurements.