Simultaneous measurement of temperature and refractive index with F–P microcavity sensor based on graded-index few mode fiber

Abstract

In this paper, a Fabry–Perot (F–P) microcavity sensor based on graded-index few mode fiber is proposed and fabricated. One end of the graded-index few mode fiber is etched by hydrofluoric(HF) acid to form an air microcavity. The end with air microcavity is spliced with single-mode fiber, and another end is cut flat to make sensing head. Due to the generation of reflection surface, the F–P microcavity structure is formed between the surfaces of microcavity and the fiber tip. Simulation and experimental results show that the reflection spectrum will shift regularly with the change of external temperature, and the extinction ratio of that will also change regularly with the change of external solution concentration. The temperature and refractive index can be measured by detecting the wavelength shift and extinction ratio change in spectrum. When the temperature changes between 30∘C∼90∘C, the temperature sensitivity can be up to 10.52pm/∘C. When the refractive index changes between 1.3331∼1.3568, the maximum refractive index sensitivity is -16.03dB/RIU. This fiber F–P microcavity sensor has different responses to the change of temperature and liquid refractive index, it can be used to measure both parameters simultaneously.