Research on MZI sensor for refractive index and temperature based on D-shaped no core fiber

A novel multi-mode Mach-Zehnder interferometer (MZI) for refractive index (RI) and temperature measurement based on D-shaped no core fiber (DNCF) is proposed. DNCF is produced by polishing the no core fiber (NCF). The sensor is formed by splicing a piece of DNCF between two sections of single mode fiber (SMF). The multiple interference dips observed in the experiment are caused by implement multi-mode interference (MMI) due to the coupling between SMF and no core fiber (NCF). Three types of sensors with different thicknesses of D-shape structures are prepared and the effects of the thickness on the sensitivities of these sensors are investigated. The experimental results show that the DNCF with the thickness of D-shape structure of 54.3 μm exhibits the highest sensitivity of 265.502nm/RIU in the RI range of 1.34–1.39. The highest temperature sensitivity is 0.0861 nm/°C from 25 °C to 80 °C. The experiments also indicate that the sensitivities of RI and temperature can be further enhanced by reducing the thicknesses of D-shape structure. Furthermore, the sensor demonstrates strong stability during experiments involving RI and temperature. The designed sensor possesses advantages such as high sensitivity, good stability and excellent linearity. The proposed sensor can be widely used in the fields of biology, chemistry, medicine and environmental condition monitoring.