System model identification of a Fabry-Perot fiber optic sensing system

A Fabry-Perot fiber optic temperature sensing system is presented in this paper. It uses a Fabry-Perot interferometer (FPI) to transform the environmental temperature into modulated reflected light. This light is directed to a patented light cross-correlator that locates the position of the maximum interference fringe intensity, which is detected by a linear CCD array. Therefore, the actual observed data is the position of the CCD pixel detecting the maximum interference fringe intensity rather than the light intensity itself. Consequently, this sensing mechanism is tolerant to the loss of light power that may result from external effects. Based on an analysis of the entire sensing system, a theoretical dynamic model was developed, which shows that the system dynamic response depends on the heat transfer process in the sensor head and the signal processing in the signal conditioner. An experimental method was developed to validate the theoretical model. Two empirical dynamic models are also obtained from the experimental data. Comparing the theoretical model with the empirical models, the poles result from the heat transfer process in the sensor head.