Abstract
A microcavity extrinsic Fabry–Perot interferometric (EFPI) fiber-optic sensor is presented for measurement of strain. The EFPI sensor is fabricated by micromachining a cavity on the tip of a standard single-mode fiber with a femtosecond (fs) laser and is then self-enclosed by fusion splicing another piece of single-mode fiber. The fs-laser-based fabrication makes the sensor thermally stable to sustain temperatures as high as 800°C. The sensor exhibits linear performance for a range up to 3700 με and a low temperature sensitivity of only 0.59 pm/°C through 800°C.
Highlights
Different types of optical fiber instruments like fiber Bragg grating sensors, extrinsic Fabry–Perot interferometric (EFPI) sensors, intrinsic Fabry–Perot interferometric (IFPI) sensors, long-period fiber grating sensors, and related hybrid combination sensors have been used for monitoring strain, stress, temperature, and pressure.[3,4,5,6,7]
The EFPI-type sensors are better suited for strain monitoring applications with high ambient temperatures as opposed to Bragg gratings and IFPI sensors
The sensor has a low cross sensitivity due to low thermal expansion of the silica glass, i.e., the wavelength shift with temperature is small up to at least 800°C
Summary
Optical fiber-based sensors have gained wide application for strain monitoring due to their compact size, immunity from electromagnetic interference, multiplexing capabilities etc. offering an alternative to traditional electrical sensors and conventional pneumatic-based sensors.[1,2,3] Different types of optical fiber instruments like fiber Bragg grating sensors, extrinsic Fabry–Perot interferometric (EFPI) sensors, intrinsic Fabry–Perot interferometric (IFPI) sensors, long-period fiber grating sensors, and related hybrid combination sensors have been used for monitoring strain, stress, temperature, and pressure.[3,4,5,6,7] Temperature sensitivity and temperature maximums are important practical limitations for many of these sensors. The EFPI-type sensors are better suited for strain monitoring applications with high ambient temperatures as opposed to Bragg gratings and IFPI sensors These rugged sensors have excellent noise-free performance and fatigue characteristics.[10] The most widely used method for realizing the EFPI sensor is by epoxying two pieces of fiber, with cleaved ends, inside a hollow tube (glass or ceramic) and controlling the separation distance between the two fiberends.[11,12,13,14,15] In addition to the cumbersome fabrication process and the calibration issues related to controlling the cavity gap, this design has limited thermal performance due to the thermal expansion of the tube and the temperature limitation of the epoxy, e.g., Loctite epoxy extra time pro (slow setting) is effective up to 150°C once cured.
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