Asymmetric Stress Distribution Analysis on the Polarization Dependent Loss in a CO₂ Laser-Written Long Period Fiber Grating

The effect of stress-induced birefringence on the polarization-dependent transmission characteristics was investigated. A long period fiber grating (LPFG) was fabricated by a stress relaxation method with CO₂ laser using a tomographic stress measurement technique. After measuring 2D stress profiles for a complete period of the LPFG, the effect of the asymmetric stress profiles on the polarization dependent transmission loss spectrum of the LPFG was studied. It was found that the polarization dependent transmission characteristics of the LPFG are mostly affected by the asymmetric stress distribution in the cladding region rather than the core region.