Three-parameter sensing of liquid level–refractive index–temperature (LRT) based on micro/nanofiber coupling ring (MFCR)

Abstract All-optical fiber liquid level–refractive index–temperature (LRT) sensor was proposed the basis of micro/nanofiber coupling ring (MFCR). Two twisted conventional communication optical fibers are tapered, merged, and refined in the preparation of MFCR. By detecting the sensing dips, the liquid level, refractive index and temperature can be measured respectively. The coupler will form two interference paths (odd and even modes) in x and y polarization states and the two slightly different lights superimpose to form the interference using strong evanescent field characteristics of fiber coupling in the process of gradual tapering. Results showed that maximum sensitivities of liquid level, refractive index, and temperature are 81.78 p m / m m , 586.74 n m / R I U , and 443.66 p m / °C, respectively, in the optical fiber coupler with a width of 8 μ m . The proposed sensor has the advantages of simple fabrication process, compact structure, low cost, and important application prospects in the detection of biomedical and chemical liquid level.