A fast real-time demodulation method based on the coarsely sampled spectrum is proposed for transient signals of fiber optic extrinsic Fabry-Perot interferometers (EFPI) sensors. The feasibility of phase demodulation using a coarse spectrum is theoretically analyzed. Based on the coarse spectrum, fast Fourier transform (FFT) algorithm is used to roughly estimate the cavity length. According to the rough estimation, the maximum likelihood estimation (MLE) algorithm is applied to calculate the cavity length accurately. The dense wavelength division multiplexer (DWDM) is used to split the broadband spectrum into the coarse spectrum, and the high-speed synchronous ADC collects the spectrum. The experimental results show that the system can achieve a real-time dynamic demodulation speed of 50 kHz, a static measurement root mean square error (RMSE) of 0.184 nm, and a maximum absolute and relative error distribution of 15 nm and 0.005% of the measurement cavity length compared with optical spectrum analyzers (OSA).

The optical path length (OPL) of the Fabry-Perot cavity may change during the spectrum acquisition; it introduces demodulationerror or even causes demodulation failure based on traditional algorithms. To address this problem, the relationship between the dynamic OPL and instantaneous frequency is investigated. Demodulation of the dynamic OPL based on instantaneous frequency analysis is proposed. By combining spectrogram (SP) and Wigner-Ville Distribution (WVD), an effective time-frequency (TF) analysis method is investigated to calculate the dynamic OPL at each sampling point in a period of a sweeping laser. Experimental results show that the demodulation speed is 4.8 MHz at a 2 KHz sweeping rate, the max deviation of a sinusoidal variation of OPL is around 0.14 μm, and the max deviation of a triangular variation of OPL is around 0.13 μm.

The development of high-speed dynamic demodulation methods for dynamic Fabry-Perot sensors is essential for high-speed measurements. A new double-sideband microwave modulation demodulation algorithm is proposed. After microwave signal modulation, the envelope of the double-sideband signal generated by dynamic Fabry-Perot interferometry contains dynamic interference phase information. By combining the dynamic interference phase information within the envelope with arctangent operation, high-speed dynamic demodulation of the dynamic cavity length can be achieved. Experimental results demonstrate that the dynamic cavity length demodulation rate can reach up to 10.2 MHz, and it is capable of demodulating the resonant cavity length of a pressure Fabry-Perot sensor at a frequency of 332 kHz in shock wave pressure measurement experiments.

To improve the precision of dynamic distance measurement based on the frequency-swept interferometry (FSI) system, a Doppler-induced error compensation model based on a scheme increasing the frequency sweeping rate is proposed. A distance demodulation method based on a Fourier transformation is investigated when the defined quasi-stationary coefficient approaches a constant. Simulations and experiments based on dynamic distance with a sinusoidal change demonstrate that the proposed method has a standard deviation of 0.09 μm within a distance range of 4 μm at a sweeping rate of 60 KHz.

The blackbody radiation can provide light source for the fiber Fabry-Perot sensor system, but the output signal is difficult to demodulate. Because the signal of Fabry-Perot sensor is modulated by spectrum of blackbody radiation and SNR of signal is low. In this paper, the characteristics of the fiber Fabry-Perot sensor signal based on the blackbody light source were investigated. Effect of spectrum of blackbody radiation and low SNR on demodulation was analyzed. Strain experimental results show that correlation-like algorithm can accurately demodulate the signal when the temperature of the blackbody light source is equal to or higher than 800 °C. The maximum mean square error is 8.375με after separating influence of temperature by the relationship between center wavelength of blackbody radiation and temperature. Higher the temperature, higher the demodulation accuracy.

To improve the fringe contrast and the sensitivity of Fabry-Perot (FP) pressure sensors, a silicone rubber FP pressure sensor based on a spherical optical fiber end face is proposed. The ratio of silicone rubber ingredients and the diameter and thickness of silicone rubber diaphragm were optimized by a simulation based on experimental tests that analyzed elastic parameters, and the influence of the radius of a spherical optical fiber and the initial cavity length of the sensor on the fringe contrast was investigated and optimized. Pressure sensor samples were fabricated for pressure test and temperature cross-influence test. Gas pressure experimental results within a pressure range of 0~40 kPa show the average sensitivity of the sensor is −154.56 nm/kPa and repeatability error is less than 0.71%. Long-term pressure experimental results show it has good repeatability and stability. Temperature experimental results show its temperature cross-sensitivity is 0.143 kPa/°C. The good performance of the proposed FP pressure sensor will expand its applications in biochemical applications, especially in human body pressure monitoring.