Dynamic Demodulation of Low-Finesse Fabry-Perot Sensors Based on Instantaneous Frequency Analysis

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.