High-performance all-fiber Mach-Zehnder interferometer based on D-shaped two-mode fiber coated with polydimethylsiloxane for temperature sensing

Abstract

A novel fiber sensor, an all-fiber Mach-Zehnder interferometer based on D-shaped two-mode fiber (DTMF-MZI) coated with polydimethylsiloxane (PDMS), is proposed and demonstrated. When light is incident from a single-mode fiber (SMF) to a two-mode fiber (TMF), two modes will be excited in the TMF and interfere with each other, just like a two-beam fiber Mach-Zehnder interferometer (MZI). Due to the high negative thermo-optical coefficient, the proposed sensor is sensitive to temperature. Our theoretical analysis and experimental results prove that as the temperature increases, the dips in the transmitted spectrum of DTMF-MZI will blue-shift. Furthermore, we demonstrate the influences of the distance from the center of the fiber core to the polished plane (parameter h) and the length of the polished area (parameter Lpo) of TMF on the temperature sensitivity. In the experiments, the maximum temperature sensitivity of the proposed sensor reaches −305.6 pm/°C in the temperature range of 30 ∼ 80 °C, and the linearity is as high as 0.9890. In addition, the sensor shows good stability at 30 °C and 80 °C in 60 min with the maximum variations of 0.16 nm. The proposed sensor has many advantages, such as being highly temperature-sensitive, compact, and stable.