A fiber optic refractive index sensor with temperature compensation based on cascaded Mach-Zehnder interference and Intermodal interference

Optical fiber refractive index (RI) sensor with temperature (T) compensation has important application values in biomedicine and environmental monitoring. In order to solve the problem that the detection accuracy of liquid RI is affected by T in practical applications, a T-compensated RI fiber sensor based on cascaded Mach-Zehnder interference (MZI) and multimode interference (IMI) is proposed in this paper. Experimental results showed the proposed sensor achieved a sensitivity of 797.41 nm/RIU for the measurement of RI in the range of 1.3333-1.3640, and a sensitivity of 0.120 nm/degrees C for the measurement of T in the range of 0-60 degrees C. The resolution (R) of RI and T measurements reached 2.5 x 10(-5) RIU and 0.167 degrees C, respectively. The detection limits (DL) of RI and T measurements are 3.135 x 10(-8) RIU and 1.392 degrees C, respectively. A matrix is obtained to demodulate the cross-sensitivity in RI and T measurements. The proposed sensor shows the advantages of simple structure, low hysteresis, and good stability.