We demonstrated a compact fiber sensor for the Refractive Index (RI) and temperature measurement based on a balloon-shaped Mach-Zehnder interferometer (MZI) with no need of special fibers or coating sensitizer material. To enhance the sensitivity and structural stability of the sensor, a spherical structure is added on both sides of the balloon-shaped single mode fiber (SMF). The fiber length between the two spherical structures is L, three kinds of spherical MZI with L of 3 cm, 3.5 cm and 4 cm were prepared, and their sensing performance was studied. The experimental results show that the RI and temperature sensitivity of the sensor increase with the increase of L. We get maximum RI sensitivity of 965.1 nm/RIU (refractive index unit) in the RI range of 1.3350-1.3965 and a temperature sensitivity of 178.6 pm/degrees C in the temperature range of 30-80 degrees C. Compared with other balloon-shaped sensors, the proposed sensor has higher sensing sensitivity and stronger structural stability, which is conducive to promoting the development of balloon-shaped MZI to satisfy practical demands.
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