Research On Two Abrupt-tapers MZI Sensor Based On Twin-core Fiber

With the rapid development of science and technology,the gradual improvement of economic level,as well as the national attention to the quality problems of large-scale buildings,optical fiber sensing has gradually come into people’s attention.In recent years,the research of optical fiber sensing in China has covered many fields,and optical fiber grating have achieved many research results.Compared with traditional sensors,optical fiber sensors have many advantages.It can achieve a wide range of high accuracy detection,especially phase modulation sensors.In view of this research hotspot,starting from the Mach-Zehnder interferometer(MZI)sensing structure,and with the help of the special refractive index distribution of the twin-core optical fiber,a novel two concatenated abrupt-tapers strain sensor based on the twin-core optical fiber is proposed in this paper.The main research work is as follows:(1)This paper briefly introduces the background and significance of the research on optical fiber sensors,as well as the current development status of optical fiber sensors and twin-core optical fibers both here and abroad.The basic principle of optical fiber sensor is described,and the advantages and disadvantages of various types of strain sensors are analyzed.(2)Based on the structure characteristics of twin-core optical fiber and coupled mode theory,the coupling principle of Dual-Waveguide model is studied.The coupling characteristics of twin-core optical fiber are analyzed by MATLAB simulation software.For symmetrical twin-core optical fiber,the mutual coupling coefficients of the two cores are the same.For asymmetric twin-core optical fiber,the coupling factor represents the coupling strength of the two cores.(3)Starting from the optical fiber structure and the fusion method between the optical fibers,the influence of the structure parameters and the offset displacement of the twin-core optical fiber on the transmission energy distribution and spectral characteristics of the optical fiber sensor is studied and simulated.The principle of twin-core optical fiber strain sensing based on MZI are analyzed and studied.(4)Besed on the above simulation analysis of the taper structure and bias structure,a double abrupt-taper in twin-core optical fiber strain sensor based on MZI principle is proposed.The strain sensing characteristics of the double abrupt-taper cascaded with bias structure and the double abrupt-taper cascaded with weak taper structure are investigated through experiments.The experimental data show that the structure of the strain sensor is not only simple to fabricate but also highly sensitive.Further analysis of the experimental data shows that the strain sensitivity of the sensor structure cascaded with a double abrupt-taper and offset structure is 7.6 pm/με at 1716.5 nm,and the maximum extinction ratio is 19.3 dB at 1446.2 nm,and the strain sensitivity here is 6.39 pm/με.Compared with other strain sensors,the sensor performance of this structure has been greatly improved,and its sensitivity is about twice as high as before.The strain sensitivity of the sensor structure tapered with single-mode fiber is 2.66 pm/με at the wavelength of 1455.5 nm,the sensitivity is 2.36 pm/με at the wavelength of 1665.9 nm.