We demonstrated a high-sensitivity strain sensor based on an in-fiber Fabry–Perot interferometer (FPI) with an air cavity, which was created by splicing together two sections of standard single-mode fibers. The sensitivity of this strain sensor was enhanced to 6.0  pm/μe by improving the cavity length of the FPI by means of repeating arc discharges for reshaping the air cavity. Moreover, such a strain sensor has a very low temperature sensitivity of 1.1  pm/°C, which reduces the cross sensitivity between tensile strain and temperature.

High-sensitivity strain sensor based on in-fiber improved Fabry–Perot interferometer

In-line fiber optic interferometers have attracted intensive attention for their potential sensing applications in refractive index, temperature, pressure and strain measurement, etc. Typical in-line fiber-optic interferometers are of two types: Fabry-Perot interferometers and core-cladding-mode interferometers. It's known that the in-line fiber optic interferometers based on single-mode fibers can exhibit compact structures, easy fabrication and low cost. In this paper, we review two kinds of typical in-line fiber optic interferometers formed in single-mode fibers fabricated with different post-processing techniques. Also, some recently reported specific technologies for fabricating such fiber optic interferometers are presented.

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In-Line Fiber Optic Interferometric Sensors in Single-Mode Fibers

We investigated a novel and ultracompact polymer-capped Fabry-Perot interferometer, which is based on a polymer capped on the endface of a single mode fiber (SMF). The proposed Fabry-Perot interferometer has advantages of easy fabrication, low cost, and high sensitivity. The variation of the Fabry-Perot cavity length can be easily controlled by using the motors of a normal arc fusion splicer. Moreover, the enhanced mechanical strength of the Fabry-Perot interferometer makes it suitable for high sensitivity pressure and temperature sensing in harsh environments. The proposed interferometer exhibits a wavelength shift of the interference fringes that corresponds to a temperature sensitivity of 249 pm/°C and a pressure sensitivity of 1130 pm/MPa, respectively, around the wavelength of 1560 nm.

Simultaneous measurement of pressure and temperature by employing Fabry-Perot interferometer based on pendant polymer droplet

We fabricate and experimentally demonstrate a hybrid structured Fabry-Perot interferometer (FPI) embedded in the middle of a fiber line for simultaneous measurement of axial strain and temperature. The FPI is composed of a silica-cavity cascaded to a spheroidal air-cavity, both of which are formed in a hollow annular core fiber (HACF). The fabrication process of the FPI includes only a fusion splice between a single-mode fiber and a HACF and several electrical arc discharges at the HACF near the splice point. Experimental results show that the strain and temperature sensitivities of the air-cavity can be 5.2 pm/μe and 1.3 pm/C°, respectively, and those of the silica-cavity can be 1.1 pm/μe and 13 pm/C°, respectively. The different sensitivities of silica-cavity and air-cavity to strain and temperature enable us to implement simultaneous sensing in strain and temperature.

Hybrid structured fiber-optic Fabry-Perot interferometer for simultaneous measurement of strain and temperature

Internal strain and temperature discrimination with optical fiber hybrid sensors in Li-ion batteries

We demonstrate an all-fiber optical Fabry–Perot interferometer (FPI) strain sensor whose cavity is a microscopic air bubble. The bubble is formed by fusion splicing together two sections of single-mode fibers (SMFs) with cleaved flat tip and arc fusion induced hemispherical tip, respectively. The fabricated interferometers are with bubble diameters of typically ∼100  μm. Strain and temperature sensitivities of fabricated interferometers are studied experimentally; a strain sensitivity of over 4  Pm/μe and a thermal sensitivity of less than 0.9  Pm/°C is obtained.

Yu-Song Hou

Papers

Microbubble based fiber-optic Fabry-Perot interferometer formed by fusion splicing single-mode fibers for strain measurement.