Study On The Liquid Level Sensor Based On Core-offset Fusion Splicing Method Of Polarization-maintaining Fiber

With the improvement of automation in science, the acquisitions of liquid level information become more and more important in much fields. Optical fiber liquid level sensor receives extensive attention due to its excellent properties. In this thesis, in order to obtain a higher sensing performance, focusing on the in-line Mach-Zehnder optical interferometer based on polarization maintaining fiber (PMF), we mainly completed the following work:1. The background of liquid level sensing technology and the classifications of optical fiber liquid level sensor were introduced.2. The polarization characteristics of optical fiber and principle of fiber intermodal interference were analyzed. Based on optical fiber wave theory, the analyses of optical fiber mode were presented. Then, the polarization characteristics of single mode optical fiber and the PMF were introduced. Finally, the mechanism of fiber intermodal interference was deduced through the introductions of the traditional optical fiber Mach-Zehnder interferometer and in-line optical fiber Mach-Zehnder interferometer.3. A liquid level sensor based on core-offset splicing fusion of polarization-maintaining fiber was proposed. The fabrication process of the interferometer was also introduced. The size and direction of core-offset (fast axis, slow axis and axis alignment of fast and slow axis direction of 45°) were analyzed experimentally by the sandwich structure of SMF-PMF-SMF. The interferometer was made using a fast axis aligned method. The cladding modes were excited through core-offset fusion splicing method and the liquid level information was obtained through the analyses of the interference spectrum. Experimental results showed that the sensitivities of wavelength shifts and intensity variations were-0.4956nm/mm and 0.2204dB/mm, respectively. The temperature sensitivity of the proposed sensor was about 13pm/℃.4. The model scrambling of polygonal fiber was analyzed by computer simulation. This paper expounds the application of polygonal fiber on astronomical observation and the basic theory of polygonal fiber. We verify the excellent properties of polygonal fiber and the parameter of the fiber about model scrambling by simulating the square and octagonal fiber.