A fiber optic high-temperature sensor with a low-fineness Fabry-Perot cavity formed by dielectric films on sapphire fiber tip is proposed and demonstrated. Experimental investigation shows that the sensor exhibits a sensitivity of 40.7pm/℃ when the ambient temperature changes from 400℃ to 1000℃.
It is well known that using a single-mode lead-in fiber, a multi-mode fiber section as a Fabry-Perot cavity, and an
additional single-mode fiber as the tail results in a structure that generates strong interference fringes while remaining
robust. Due to their compact size, sensitivity, and ability to be multiplexed, intrinsic Fabry-Perot interferometers (IFPIs)
are excellent candidates for almost any multi-point temperature or strain application. Four of these sensors were to be
installed on a 2"x2" coupon for installation in a simulated gas turbine environment. Though the basic principles behind
these sensors are well known, serious issues associated with geometric constraints resulting from the size of the test
coupon, sensor placement, and mechanical reinforcement of the fiber arose; fabricating a sensor chain with appropriate
sensor spacing and excellent temperature response characteristics proved a significant challenge. Issues addressed
include inter-sensor interference, high-temperature mechanical reinforcement for bare fiber sections, and high bending
losses. After overcoming these problems, a final sensor chain was fabricated and characterized. This chain was then
subjected to a battery of tests at the National Energy Technology Laboratory (NETL). Final results are presented and
analyzed.
This article introduces an approach for modeling the fiber optic low-finesse extrinsic Fabry-Pérot Interferometers
(EFPI), aiming to address signal processing problems in EFPI demodulation algorithms based on white light
interferometry. The main goal is to seek physical interpretations to correlate the sensor spectrum with the interferometer
geometry (most importantly, the optical path difference). Because the signal demodulation quality and reliability hinge
heavily on the understanding of such relationships, the model sheds light on optimizing the sensor performance.
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