Wideband fiber-optic Fabry-Perot acoustic sensing scheme using high-speed absolute cavity length demodulation

In this paper, a novel method used for Fabry-Perot cavity length's demodulation in high-speed and large scope measurement was proposed. Principle of the method is based on uniqueness of intensity of multiple wavelengths in the scope of Fabry-Perot vibration. This technique offers flexibility of selecting incident wave length and enhances the scope of demodulation of cavity length, compared with that popular triple wave length demodulation. In experiment, multi-wavelength demodulation is demonstrated for measurement of cavity length varying from 110um to 115um and the strain resolution was higher than 0.1um.

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A High-Speed Demodulation Technology of Fiber Optic Extrinsic Fabry-Perot Interferometric Sensor Based on Coarse Spectrum

Sensors ◽

10.3390/s21196609 ◽

2021 ◽

Vol 21 (19) ◽

pp. 6609

Author(s):

Peng Zhang ◽

Ying Wang ◽

Yuru Chen ◽

Xiaohua Lei ◽

Yi Qi ◽

...

Keyword(s):

Real Time ◽

High Speed ◽

Cavity Length ◽

Fiber Optic ◽

Likelihood Estimation ◽

Time Dynamic ◽

Wavelength Division ◽

Broadband Spectrum ◽

Fabry Perot ◽

Interferometric Sensor

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).

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A Zero-Cross Detection Algorithm for Cavity-Length Interrogation of Fiber-Optic Fabry–Perot Sensors

Sensors ◽

10.3390/s19183868 ◽

2019 ◽

Vol 19 (18) ◽

pp. 3868

Author(s):

Ma ◽

Song ◽

Huang ◽

Guo ◽

Yuan ◽

...

Keyword(s):

Power Density ◽

Cavity Length ◽

Fiber Optic ◽

Spectral Power ◽

Spectral Power Density ◽

Maximum Error ◽

Detection Algorithm ◽

Slow Variation ◽

Fabry Perot ◽

And Performance

A zero-cross detection algorithm was proposed for the cavity-length interrogation of fiber-optic Fabry–Perot (FP) sensors. The method can avoid the inaccuracy of peak determination in the conventional peak-to-peak method for the cavity-length interrogation of fiber-optic FP sensors caused by the slow variation of the spectral power density in peak neighboring regions. Both simulations and experiments were carried out to investigate the feasibility and performance of the zero-cross detection algorithm. Fiber-optic FP sensors with cavity lengths in the range of 150–1000 μm were successfully interrogated with a maximum error of 0.083 μm.

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