All-Fiber Fabry–Perot Interferometer for Liquid Refractive Index Measurement

We propose and design an all-fiber Fabry–Perot interferometer (FPI) for liquid refractive index (RI) measurements. The sensor comprises a short section of a single-mode fiber (SMF) fused between the end sections of two longer SMFs with a large intentional lateral offset. The open FPI cavity is obtained by adjusting the lateral offset. Experimental results show that the liquid to be measured can freely enter and leave the cavity without residual bubbles. The RI sensitivity of this sensor is 1,013.8 nm/RIU in the RI range from 1.3464 to 1.3777 with good linearity. Only cleaving and fusion splicing are used in its making; thus the fabrication of the sensor is relatively simple and cost effective. This sensor has potential applications in the chemical and biomedical domains.