Dual-parameter four-beam interferometric sensor for the measurement of temperature and strain with a double air-gaps structure based on graded-index few mode fiber

Abstract

In this paper, a dual-parameter sensor for the measurement of temperature and strain with a double air-gaps structure based on graded-index few mode fiber (GI-FMF) is proposed and fabricated. Two sections of GI-FMF are used: one end of them is etched with HF acid to form an air-gaps, and the other end is cut flat. Next, the single-mode fiber and these two GI-FMFs are spliced successively to form a sensor with double air-gaps structure. A four-beam interferometer is formed and the sensing principle is established. The temperature and strain response characteristics of the sensor are analyzed in the experiment. The reflection spectrum is divided into a low-frequency band affected by the air-gap and a high-frequency band affected by the compound cavity. Experimental results show that the sensor in low-frequency band is insensitive to temperature, and the strain sensitivity is 2.72pm/µɛ. In high-frequency band, the temperature sensitivity of the sensor is 10.81pm/°C, and the strain sensitivity is 1.03pm/µɛ. Simultaneous measurement of temperature and strain is achieved by solving the matrix coefficient equation. The proposed four-beam interferometric sensor has the advantages of compact structure, easy fabrication, and high sensitivity; it can be used to measure the temperature and strain simultaneously.