The purpose of this work is to evaluate the sensing capabilities of a device based on a single mode fiber-thin core fiber-single mode fiber Mach-Zehnder interferometer for high temperature, curvature, and refractive index measurements. A femtosecond laser is used to produce a straight line on the entire thin core, and the fiber core is destroyed to increase the sensor′s sensitivity to the changes in external parameters. With a temperature sensitivity of 15.5 pm/℃ and a linear fitting of 0.988 in the range of temperature to 330 ℃, experimental results show that this sensor is well-suited for high-temperature measurement. Temperature sensitivity increases to 40.9 pm/℃ with a linear fitting of 0.996 in the temperature range of 330 ℃ to 580 ℃. The sensor also has a curvature sensitivity of 2.35 7 dB/m-1 with a linear fitting of 0.971 7 in the curvature range of 0.362 2 m-1 to 1.145 4 m-1, as well as a refractive index sensitivity of -24.327 nm/RIU with a linear fitting of 0.989 9 in the refractive index range of 1.333 0~1.365 2. This sensor is easy to make, extremely sturdy, compact, and capable of monitoring high temperatures, curvature, and refractive index.