Bend response of weakly tilted Bragg grating inscribed in all-solid photonic band-gap fibers

Abstract

Weakly tilted fiber Bragg gratings (W-TFBGs) with a certain tilted angle are inscribed in the Ge-doped cladding rods of all-solid photonic band-gap fibers (AS-PBGF) by UV illumination. There are couplings not only forward-propagating LP 01 mode to counter-propagating LP 01 mode but also the couplings to counter-propagating high order supermodes based on tilted refractive index modulation. The responses of the W-TFBGs to temperature and bend are investigated. The results indicate that the resonance peaks will shift red-side with increasing temperatures, and the sensitivities of different resonance peaks are very close in the same grating. When the bend is applied, the grids of W-TFBG will be compressed or stretched. Two resonance peaks will shift with increasing curvatures, which is related to the orientation of curvature. Therefore, it is potential to work as a directional bend sensor. For the fiber grating with high-order supermodes coupling, it could form fiber grating array by different levels. If every grating has individual response to surrounding, such a single W-TFBG could be used for one point and multi-parameter measurement. In addition, this work provides some insights into the mechanisms that contribute to the measured properties of TFBG in the photonic crystal fiber. It is also an effective method to investigate supermode properties of photonic crystal fiber.