Absolute Single Cavity Length Interrogation of Fiber-Optic Compound Fabry–Perot Pressure Sensors Through a White Light Non-Scanning Correlation Method

Abstract

A white light non-scanning correlation interrogation system was proposed and built to interrogate absolute length of the air cavity of fiber-optic compound Fabry–Perot pressure sensors for the extraction of pressure value. By carefully choosing thickness range and tilt angle of the optical wedge used for cavity length matching, correlation interferometric signal of the basal cavity can be naturally filtered out. Based on peak positioning by Fourier transform, bandpass filtering in frequency domain, inverse Fourier transform back to time domain, envelope fitting and zero fringe finding through a gravity center method, cavity length can be determined with an accuracy of 0.04%. The system was used for the interrogation of a fiber-optic compound Fabry–Perot pressure sensor under different pressures. For a pressure range of 0.1~2.9 Mpa, the linear relationship between the air cavity length and the gas pressure imposed was successfully extracted.

Recent Progress in MEMS Fiber-Optic Fabry–Perot Pressure Sensors

“…Sapphire has a high melting temperature up to 2050 °C and a wide transmission spectral range. The development of sapphire-based fiber-optic FP pressure sensors has been a long-term concern of researchers [ 50 , 51 , 52 , 53 , 54 , 55 ]. Figure 4 illustrates the recent progress of sapphire diaphragm-based fiber-optic FP sensors.…”

“…In 2016, Jiang et al [57] realized an all-SiC diaphragm-based fiber-optic pressure sensor using the nickel diffusion bonding technique. In order to reduce the device size and improve the device's structural firmness and strength, researchers have been striving to develop an all-sapphire wafer-based FP cavity by the MEMS lithography process and direct bonding technique [51][52][53][54]. The fabrication method provides precise control of the film thickness by means of the silicon oxide-masked wet or inductively coupled plasma (ICP) etching process.…”

Extended centroid position method in liquid-crystal-based interrogation system for electric-field-modulated Fabry-Perot sensing

“…Considering the maximum or peak value of this envelope as the peak position (t 0 ) of the interferogram, the estimated cavity length L 0 = ∆n 0 .t 0 /2 at this point is 19.9810 µm which does not correspond to the actual value of the cavity length. Now for the initial compensation of the asymmetrical nature of the interferogram or the envelope, a centroid position (t c ) of the envelope is determined by using the following relation [27,30,33],…”

Silicone Rubber Based Highly Sensitive Fiber-Optic Fabry–Perot Interferometric Gas Pressure Sensor

“…The response of the sensor is shown in Figure 7. The sensor shows a sudden leap in the wavelength for an increase in the gas pressure as can be seen from the inset of Figure 7 where the experimental response time is less than 2 s. FPI Structure Sensitivity FPI embedded in pressure fitting [17] 0.24 nm/MPa Pendant polymer droplet-based FPI [2] 1.13 nm/MPa FPI based on concave well on fiber end [18] 1.53 nm/MPa FPI with open cavity [19] 2.46 nm/MPa FPI based on dual capillaries [20] 4.15 nm/MPa Hollow-core bandgap fiber with a side opened channel FPI [8] 4.24 nm/MPa PVC-diaphragm based FPI [21] 65.5 nm/MPa FPI sensor based on cavity length measurement [22] 0.42 nm/kPa Silicone rubber-diaphragm based FPI −680 nm/MPa (−0.68 nm/kPa)…”