Long-period fiber gratings (LPGs) using a high-silica core fiber are presented. A high-silica core fiber has a residual stress in the core, and the grating structure is formed by stress releasing of the core using a focused CO2 laser beam. The dependence of the transmission spectrum on temperature and tensile strength is measured, and low dependence compared with conventional LPGs is observed. These unique characteristics are caused by the difference of temperature and tensile strength changes of the effective indices for the fundamental propagation mode and the cladding mode in the high-silica core fiber.

We investigate a method to suppress the polarization-dependent loss (PDL) of long-period fiber gratings (LPFGs). We study the origins of the PDL and propose an azimuthally isotropic UV exposure to suppress the UV-induced birefringence and to realize low-PDL LPFGs. By using this technique and a low birefringent fiber together, the PDL of LPFGs can be reduced to a sufficiently low level required in high performance communication systems. Moreover, the validity of our theoretical modeling is confirmed by the experimental results.