Simultaneous SRI and temperature measurement of FM-LPFG written by CO_2 laser

摘要

To measure surrounding refractive index (SRI) and temperature simultaneously, this paper presents a long period fiber grating in few-mode fiber fabricated by CO2 laser. The few-mode long period fiber grating (FM-LPFG) fabrication method is introduced in detail. Through the dislocation experiment, the resonant peaks formed by the coupling between the cladding modes and core modes LP01 and LP11 are observed and selected. In the sensing experiment, the SRI and temperature are measured by the shift of the two resonant peaks, further the different sensing characteristics of such peaks are studied. The results show that as the SRI increases, such peaks shift toward the short-wave direction, and as the temperature increases, the peaks shift toward the long-wave direction. The SRI and temperature sensitivities are -263.257 nm/RIU and 0.058 nm/degrees C, respectively. By the dual-wavelength matrix method, the SRI and temperature simultaneous measurement can be achieved. This FM-LPFG has great potential application in multi-parameter measurement.