Novel Optical Fiber Sensor Based on SGMS Fiber Structure for Measuring Refractive Index of Liquids and Gases

Abstract

In this paper a single mode-gap-multimode-single mode fiber structure (SGMS) as refractive index sensor is demonstrated. A beam propagation method (BPM) for the circular symmetry waveguide is employed for numerical simulations of the light propagation performance in such fiber devices. The multimode interference effect is revealed to design optical fiber sensor with reasonable linearity in wide range of refractive indices. A simple way to predict and analyze the spectral response of the SGMS structure is presented with the derived approximated formulations. The proposed sensor is realized by using standard optical fibers.Results indicate that the proposed SGMS structure can be exploited for measuring a broad refractive index range with reasonable high resolution. The results achieved for refractive indices in the range of 1.1 to 1.43 have best linearity with correlation coefficient 0.9991 at wavelength of 1550 nm. Therefore, it can be suggested that the SGMS structure fibers are attractive for measuring refractive index of both gases and aqueous solutions such as chemical liquids, biological, and biochemical sensing.