Combined Interrogation Algorithm of Phase Function and Minimum Mean Square Error for Fiber-Optic Fabry-Perot Micro-Pressure Sensors Based on White Light Interference

In this paper, a demodulation algorithm using the phase function of the Fabry-Perot (FP) cavity combined with the minimum mean squared error (MMSE) is proposed for the pressure measurement with low-pressure sensitivity fiber-optic FP micro-pressure sensors, which exhibits reasonable demodulation results. In this algorithm, the initial phase variation during the measurement process is focused, which is usually disregarded in traditional demodulation, and then, use the phase change features of phase function to achieve precise pressure demodulation. A functional relation between the reference pressure and the amount of phase function displacement is developed for demodulation based on interferometric spectra of reference pressures at 0 kPa and 35 kPa. The algorithm has been investigated theoretically and experimentally. The experiment results demonstrate that the measurement accuracy is $\pm$ 0.2 kPa in the pressure measurement range from 0 kPa to 35 kPa, the pressure resolution is up to 0.0218 kPa, and the reading error is $\pm 3\%$ in the pressure range from 6.7 kPa to 35 kPa, which indicate that the proposed algorithm can meet medical pressure analysis standards in the cardiovascular sector for low-pressure sensitivity sensors. Moreover, this work illustrates that inaccurate reference pressure calibration would cause substantial demodulation errors. These errors can be mitigated by appropriately increasing the number of reference pressures to keep the reading error at a reasonable level according to the specific application.