Abstract
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.
Highlights
Optical fiber sensors have been widely used in sensing applications of various physical, chemical, and even biological measurements, owing to their compact, small size, fast responses, high resolution, high sensitivity, good stability, good repeatability, and resistance to electromagnetic interference
We focus on two typical in-line fiber optic interferometers, Fabry-Perot interferometers (FPIs) and core-cladding-mode interferometer (CCMI), formed only by single mode fibers (SMFs)
In the past few decades, optical fiber sensors have been widely used in sensing applications of various physical, chemical, and even biological measurements
Summary
Optical fiber sensors have been widely used in sensing applications of various physical, chemical, and even biological measurements, owing to their compact, small size, fast responses, high resolution, high sensitivity, good stability, good repeatability, and resistance to electromagnetic interference. To form the local cavity of the intrinsic FPI, several techniques have been introduced, such as internal film coating [24,25], refractive-index mismatch between two fibers in the splicing joint [26,27,28], fiber Bragg grating (FBG) [29], laser irradiated points [30,31,32], chemical etching [33,34,35], etc. The two beams are propagating along the loop in counter directions with different polarization states [55,56] These fiber optic interferometers with two arms have their own limitations, such as complicated structure, big size, high susceptibility to environmental fluctuations, etc. We focus on two typical in-line fiber optic interferometers, FPI and CCMI, formed only by single mode fibers (SMFs). Some specific examples of recently reported in-line fiber optic sensor technologies based on SMFs are presented in detail to show their advantages and the great potential sensing applications
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