High resolution measurement of refractive index with resistance to temperature crosstalk through an all fiber MZI-PMF structure

Abstract

A simple cascaded structure composed of all-fiber Mach-Zehnder interferometer (MZI) and polarization-maintaining fiber (PMF) is proposed and experimentally demonstrated for simultaneous refractive index (RI) and temperature measurement. By splicing a section of thin no-core fiber (TNCF) between two conventional no-core fibers (NCFs) with large lateral offset, a part of the light in the MZI structure can interact directly with the external environment to obtain a high RI sensitivity. A Panda-type PMF is cascaded with the MZI to eliminate temperature crosstalk in the RI measurement. The experimental results show that the RI sensitivity of MZI is as high as −13862 nm/RIU, and the temperature sensitivities of MZI and PMF are −0.4 nm/℃ and 1.47 nm/℃, respectively. With the help of a sensitivity matrix, the change of RI and temperature can finally be demodulated. The RI and temperature resolutions of the cascaded structure can achieve 1.83 × 10−6 RIU and 0.014 ℃ respectively, to the best of our knowledge, which are the highest among all fiber structures without special materials coating or filling for simultaneous measurement. This structure presents outstanding advantages of easy fabrication, low cost and less sample consumption, which has great potential for integrated biochemical analysis systems.