Polarization circulation effect in microbend-induced long-period fiber gratings for polarization-insensitive filter response

Abstract

We analyze the reduction mechanism of polarization dependence in loss-peak wavelength for microbend-induced long-period fiber gratings (M-LPFGs) formed in twisted fibers. The analysis model consists of the stress-induced birefringence associated with the microbend as well as the optical activity induced by the twisted fiber. We verify the analysis model by measuring the variation in the state of polarization through the torsion M-LPFG. We reveal that the efficient circulation of the polarization components occurs in the torsion M-LPFG such that the polarization dependence of the loss-peak wavelengths is reduced. In the experiments, the M-LPFG is controlled by an electromagnet in the combination of a coil spring. The experimental results demonstrate a good agreement with the calculated expectation for the polarization-insensitive M-LPFGs.