Analysis Of Extrinsic Fabry-Perot Interferometer Fiber Optic Sensors For White-Light Systems Using Mode Theory

In this dissertation, Mode theory of extrinsic Fabry-Perot interferometer (EFPI) fiber optic sensors, including both single mode fiber and multimode fiber are systematic studied. By Mode theory, the output signal interference spectrum'function is obtained. Through research on the relationship between the interference spectrum and its parameters, the results benefit on the design, production and application of high-performance EFPI fiber sensors., which is of great significance.For single-mode EFPI fiber sensors, using Mode theory, a new output signal interference spectrum function is proofed. By analyzing this function, it shows that the interference spectrum's phase is relevant with not only the FP cavity length but also the incident fiber end's mode coupling factor's phase. Compared with the analysis of interference spectrum by the geometric optics, it is concluded that the mode coupling factor, which effects the output signal interference spectrum, is essential to improving the accuracy and high-resolution of sensors.In addition, the mode theory of single-mode EFPI fiber sensors under none-ideal structure of FP cavity is also researched. There are two typical none-ideal structure of cavity. One is that the cavity's two lateral faces are a slight dislocation with each other in vertical direction. The other is that cavity's two lateral faces have a wedge angle between each other. According the simulation data, it shows that the former is only impact the interference fringes visibility slightly, while the latter not only effect the interference fringes visibility but also the interference spectrum's phase, which has a direct impact on the sensor's accuracy and resolution.For multimode EFPI fiber sensors, relevant research is less now. In this paper, through the mode theory, multi-mode fiber sensors'output signal interference spectrum is also analyzed. Comparing the spectrum function between single mode and multi-mode, it is proofed that single mode fiber sensor's fringe visibility is relevant with mode coupling factor's amplitude, while multi-mode fiber sensor's fringe visibility is relevant not only with multi mode coupling factor's amplitude but also with its phase, which is one of reason that the single mode fiber sensor's performance is better than multi-mode fiber sensor on the same condition.