Polarization-Insensitive Tunable LPFGs Using Magnet-Induced Microbend Under Torsional Stress

Polarization-insensitive operation in magnet-induced long-period fiber gratings is presented by circulating the polarization axis in the fiber under a coil spring. The polarization-dependent loss is reduced <;0.4 dB around the resonance wavelength. The loss amplitude is controlled up to 20 dB by positioning a Nd-Fe-B magnet under the fiber. The band-rejection filter response does not deteriorate during the loss-tunable operation in torsion fibers.