Research On High-sensitivity Fiber-optic Mach-Zehnder Dual-parameter Sensor Based On Vernier Effec

With many excellent properties such as low cost,small size,high sensitivity and anti-electromagnetic interference,optical fiber Mach-Zehnder sensor has been widely valued by researchers and has been developed rapidly.Since research on the optical fiber Mach-Zehnder sensor has been intensified,how to improve measurement sensitivity on its basis has become one of the research hot spots in field of optical fiber sensing.Vernier effect as an effective way to amplify the sensitivity of the optical fiber sensor provides a good idea to solve this problem.In this thesis,we designed and prepared a parallel optical fiber Mach-Zehnder sensor with the Vernier effect to improve strain sensitivity of all-fiber Mach-Zehnder sensor and realize dual-parameter measurement,and then studied strain and temperature sensing characteristics of the sensor separately.The main work of the thesis are as follows:1.A parallel optical fiber Mach-Zehnder sensor based on the Vernier effect was proposed.The sensor consists of two optical fiber Mach-Zehnder interferometers with similar free spectral range connected in parallel.One individual interferometer is composed of single-mode fiber,no-core fiber,few-mode fiber,and single-mode fiber.Strain and temperature response based on the single-mode-no-core-few-mode-single-mode interference structure was analyzed theoretically,and principle of the Vernier effect of parallel structured optical fiber Mach-Zehnder sensor was investigated on this basis.By optimizing design of the parallel optical fiber Mach-Zehnder strain sensor,a method of dual parametric demodulation of the parallel optical fiber Mach-Zehnder sensor based on the Vernier effect was proposed.A reference interferometer was used to detect the temperature for purpose of eliminating cross-sensitivity.2.Separate optical fiber Mach-Zehnder interferometers with different interference lengths were fabricated and connected in parallel to form the parallel optical fiber Mach-Zehnder sensor.Frequency component of envelope was analyzed and determined by performing a fast fourier transform on the spectra.Experimental measurements of strain sensing characteristics of the interferometer and the parallel sensor were carried out separately.The experimental result shows that strain sensitivity of the parallel sensor is improved from-1.90 pm/με to 12.06 pm/με in the range of 0-166.667 με with an amplification factor of-6.3.The parallel sensor with a different amplification factor was designed and prepared,and spectra were analyzed in frequency domain to determine the band-pass filtering range.Finally,the two interferometers and parallel sensor were measured separately for temperature and strain,and simultaneous measurement of dual parameters was achieved with the demodulation method.The experimental results show that temperature sensitivity of the sensor is increased from-26.91 pm/°C to 139.06 pm/°C with the amplification factor of-5.17,and the strain sensitivity is amplified from-1.48 pm/με to 7.77 pm/με with the amplification factor of-5.25.