Study On Demodulation Method Of Extrinsic Fabry-Perot Interferometer Fiber Optic Sensors For White-Light Systems

Optical fiber Fabry-Perot sensor is one of the widely applied optical fiber sensor due to the advantages such as miniature,high sensitivity, stable performance, immunity from electro-magnetic interference, the possibility of multiplexing and so on. In the optical fiber Fabry-Perot sensor system, demodulation technique is the key factor. In this dissertation, systematic study of the feasibility of application and the performances such as measuring accuracy, dynamic measuring range, response time etc of several curve fitting methods with white light source will be presented, according to the basic principle of the single mode fiber (SMF) and multimode fiber (MMF) extrinsic Fabry-Perot interferometer (EFPI) sensor systems, respectively.For the single mode extrinsic Fabry-Perot interferometer (SMF-EFPI) sensor system, the importance of the mode coupling phase shift to the high precision demodulation is firstly analyzed and then three novel curve fitting methods are presented according to the basic principle. Based on this, simulations are carried out to study the performances of the new curve fitting methods and compare them with the informed curve fitting methods. The results have shown that the new curve fitting methods not only achieve the advantages such as high accuracy, high resolution, large dynamic range, and the capability of absolute measurement at the same time of the informed curve fitting methods, but also greatly increase the operational speed, reduce the response time of the post processing.For the multimode extrinsic Fabry-Perot interferometer (MMF-EFPI) sensor system, using the experience of the demodulation principle of the curve fitting method in the SMF-EFPI system, we adequately modify the first and second curve fitting functions. After that, simulations are carried out to study the performances of several curve fitting methods in detail and compare them with results in the SMF-EFPI system. The results have shown that although the measurement errors increase, all the curve fitting methods also keep the high precision and are able to satisfy the requirements of signal demodulator in the majority of sensor systems.