2015 年 81 巻 5 号 p. 466-470
Microbend-induced long period fiber gratings (M-LPFG) are loss- and wavelength-tunable and can be reconfigured as compared to laser-irradiated types. However, they are inherently polarization sensitive due to stress-induced birefringence and coupling nature with asymmetric cladding modes. By analyzing the state of polarization along the M-LPFG, the rotation efficiency of the polarization principal axis due to the torsional fiber is changed by the vertical stress, and the polarization ellipticity is changed simultaneously. The polarization dependency can be sufficiently reduced by twisting the fiber for inducing the microbend. In the experiments, the loss amplitude at the resonance wavelength is controlled by the combination of a coil spring and a neodymium magnet.
