compared to bulky sensors in many applications where
restricted space or minimum measurement interference is a
concern, for example, invasive blood pressure measurement
[1], [2] and embedded material strain monitoring [3]. In the
past 15 years, a number of Fabry–Pérot interferometric (FPI)
fiber-optic sensors have been developed, which are classified
as intrinsic Fabry–Pérot interferometers (IFPIs) [4] or extrinsic
Fabry–Pérot interferometers (EFPIs) [5], [6]. Generally, the
sensing element of an IFPI sensor is a short section of fiber
sandwiched between two Fabry–Pérot (FP) mirrors. For a
conventional EFPI sensor, the sensing elements are lead-in and
reflecting fibers and a tubing holding them. IFPI sensors are
often more sensitive to temperature changes and a little smaller
than EFPI sensors while the latter make it easier to adjust the
FP cavity length and often have higher pressure sensitivities. In
addition to the sensors mentioned, an in-line fiber etalon sensor
has also been reported [7], in which the sensing element is a
short section of hollow fiber.