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Abstract. In the single-mode fiber, the cascaded symmetric taper was pulled out and it has formed Mach-Zehnder interferometer(MZI), which was put into the optical fiber loop mirror and a different refractive index environment. Theoretical and experimental study on the improvement of the filter characteristics and the sensing characteristics of the sensor. The interferometer has a low insertion loss, stable performance, compatibility, etc, which can be used in optical fiber communication and fiber sensing field.