Theoretical analysis of dual-mode long period fiber grating sensor based on dual-peak resonance for dual-parameter measurement

Abstract

A dual-mode long period fiber grating (DM-LPFG) sensor for simultaneous measurement of the surrounding refractive index (SRI) and temperature is proposed and demonstrated theoretically. It is made by inscribing a LPFG based on the dual-peak resonance in a dual-mode fiber. Known from coupled mode theory, the sensing principle of the sensor is originated from the sensibility of the dual peaks to the SRI. There are three peaks corresponding to the dual-peak resonance and single-peak resonance in different core modes in the transmission spectrum, respectively. And the three peaks have a different response to the SRI and temperature. Through the monitoring of the distance change between dual peaks and the wavelength shift of single peak, the dual-wavelength matrix method can be used to simultaneously measure the SRI and temperature. As the results show, the SRI sensitivities corresponding to the distance between the dual peaks and the resonant wavelength of the single peak are 1940.0nm/RIU and 590.0nm/RIU in the SRI range of 1.33 to 1.37, respectively. Besides, the temperature sensitivities corresponding to the distance between the dual peaks and the wavelength of the single peak are -0.42nm/°C and 0.23nm/°C with the temperature changing from 20°C to 120°C, respectively. It has great potential application in chemical and biological sensing fields, owing to its advantages of high sensitivity and multi-parameter measurement.