Cascaded fiber non-adiabatic taper and Sagnac loop for refractive index sensing

We propose and experimentally demonstrate a refractive index sensor by cascading a fiber non-adiabatic taper and a fiber Sagnac loop. The modal interference of the non-adiabatic taper produces a regular interference spectrum, which shifts with the refractive index change of the external medium. The interference spectrum of the Sagnac loop can be tuned by changing the polarization state and length of polarization maintaining fiber (PMF). Cascading the two interferometers with different free spectral ranges (FSRs) will generate the superimposed envelope. The cascade structure will change the sensing capability of the single interferometer. Experiment results show that the refractive index sensitivity of our proposed sensor can be adjusted from 921.43 nm/RIU (single tapered fiber) to 787.24 nm/RIU (cascaded configuration). The low cost and easy fabrication of the proposed method highlight a beneficial choice for changing the refractive index sensitivity. 0 2021 Elsevier Science. All rights reserved. 0 2021 Elsevier B.V. All rights reserved.

Automated summary

The paper proposes and experimentally demonstrates a refractive index sensor using a fiber non-adiabatic taper and a fiber Sagnac loop. Experimental results show that the refractive index sensitivity of the sensor can be adjusted by cascading the two interferometers, highlighting a low-cost and easy fabrication method for changing sensitivity.