Extrinsic Fabry-Perot Interferometer, EFPI, is a versatile device for many fiber optic sensing applications including one in harsh environments such as oil and gas wells. Due to its unique structure, the EFPI could be designed to have an extremely small temperature cross-sensitivity (TCS), by matching the coefficients of thermal expansion (CTE's) of the outer gage capillary tube and the inner fibers. Even though it is relatively easy to get a matching condition at the atmospheric pressure, it is not a good design because the CTE of the capillary tubing is expected to change under high pressure conditions. In this paper, the method and the experimental results for the study to minimize the temperature cross-sensitivity (TCS) of the EFPI pressure sensor are presented. Test results have confirmed that the CTE of the capillary tube slightly increases under high pressure, changing the original TCS at the atmospheric pressure. By manipulating the design of the sensor to have a higher negative slope of TCS for the air-gap (dG/dT) at the atmospheric pressure, the zero TCS point can be deliberately shifted to any point of interest within the pressure range.
A setup using wavelength tuning of a pulsed DFB laser to get reflectivity profiles of each FBG element in a low reflectivity FBG array has been tested. For crosscheck purpose, the array under test was rechecked in reversed connection, and the corresponding profiles over wavelength variation showed good agreement.
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