Bending sensitivity of long-period fiber gratings inscribed in holey fibers depending on an axial rotation angle

We discuss bending properties of a long-period fiber grating (LPFG) inscribed into a holey fiber (HF) depending on an axial rotation angle. High quality of the HF-based LPFG with a high extinction ratio of more than 20 dB is achieved. The proposed HF-based LPFG has bending insensitivity under a certain range of the bending curvature. As the bending curvature is higher than 4 m(-1), the center wavelength of the grating is shifted into the shorter wavelength. Bending sensitivity of the HF-based LPFG is changed by an axial rotation angle, which shows its dependence on the rotational orientation. We measure the transmission characteristics of the HF-based LPFG with the ambient index change. The HF-based LPFG has ambient index insensitivity because of the air holes in the inner cladding.