Temperature self-compensation refractometer based on cascaded SNS-FBG structure for multipoint measurement

Abstract

A fiber optic refractive index (RI) sensor that consists of cascaded single mode fiber-no core fiber-single mode fiber (SNS) structure followed by a fiber Bragg grating (FBG) was proposed and demonstrated. Because the SNS structure and FBG have similar temperature characteristics and the FBG is not sensitivity to the RI, temperature self-compensation during the RI measurement can be realized by calculating the difference between the characteristic wavelengths of the SNS and FBG. Three SNS-FBG-based sensors with different lengths of the NCF and different Bragg wavelengths were cascaded to achieve wavelength division multiplexing (WDM) in the range of 1510nm-1590nm. Experimental results show that three-point independent RI measurement can be accomplished with the maximum sensitivity of 211.088, 243.429 and 242.511nm/RIU (RI unit) in the RI range from 1.333 to 1.405, respectively. The RI errors caused by temperature are only 4.548×10-5RIU/°C, 3.779×10-5RIU/°C and 4.458×10-5RIU/°C respectively. These sensors feature the advantages of good reproducibility, small size, low cost, high sensitivity and very low temperature cross-sensitivity, which have a good practical prospect in the simultaneous multi-point RI measurement application area.