Arc-remodified long period fiber grating for monitoring absolute bending condition

Abstract

Abstract In this paper, we propose an arc-remodified long period fiber grating (AR-LPFG) and introduce the ratios of shift-distance of two resonant dips (RSRDs) as a novel distinguishing index to monitor bending absolute condition which refers to detect the curvature and directions of fiber under a stationary status. The AR-LPFG is configured by arc-remodifying the LPFG that prepared from CO2 laser. The refractive index of the fiber is modulated again by the arc-remodification method which results in new resonant dips. Two orthogonal bending directions are distinguished by comparing the RSRDs, which are calculated to be 0.51 and 1.42 for 0° and 90°, respectively. Two opposite bending directions are distinguished by the opposite shift directions of two resonant dips. The stability and reliability of the novel distinguishing method are verified by a series of comparative experiments. The AR-LPFG still contains a conspicuous performance for bending variation sensing with a maximum sensitivity of 17.02 nm m−1. The AR-LPFG, together with the orientation distinguishing index, can be widely applied at the fields that the bending relative variation or absolute condition need to be monitored.