A Multiwavelength Diversity Demodulation Method Based on Five-Step Phase Shift Algorithm for Extrinsic Fabry-Perot Interferometer Sensor

In this article, a multiwavelength diversity demodulation method based on a five-step phase shift algorithm is proposed for interrogating extrinsic Fabry-Perot interferometer (EFPI) sensors. A white-light interferometry (WLI) technology is employed to collect the interference spectrum of EFPI sensors, and the five-step phase shift signals with continuous variation of the operating point are subsequently extracted. By averaging the diversity demodulation results of numerous groups of five-step phase shift signals, it achieves multiwavelength diversity demodulation of the interferometric spectrum. The demodulation method effectively utilizes spectral information to optimize the signal demodulation performance by diversity demodulation of five-step phase shift signals at multiple operating points. Simulations and experiments have shown the feasibility of the multiwavelength diversity demodulation method. This method offers several advantages over the conventional single-wavelength demodulation scheme, particularly in terms of suppressing harmonics and reducing total harmonic distortion (THD) by up to 20 dB. Additionally, it effectively addresses signal demodulation errors resulting from increased demodulation parameter errors, thereby ensuring accurate signal demodulation. Moreover, the method employs straightforward addition and subtraction operations, ensuring fast demodulation of dynamic signals while improving demodulation performance. In the future, the multiwavelength diversity demodulation has the potential to be applied in the large-scale multiplexing of EFPI sensor arrays. This application could facilitate the development of a miniaturized, low-noise, and high-precision fiber distributed array system (DAS).