Abstract
A review of refractive index measurement based on different types of optical fiber sensor configurations and techniques is presented. It addresses the main developments in the area, with particular focus on results obtained at INESC Porto, Portugal. The optical fiber sensing structures studied include those based on Bragg and long period gratings, on micro-interferometers, on plasmonic effects in fibers and on multimode interference in a large spectrum of standard and microstructured optical fibers.
Highlights
In 1983, Cooper et al [1] proposed the first optical fiber refractometer to measure the refractive index (RI) in several liquids
When the fiber grating was immersed in a liquid sample, this resulted in a wavelength response of the Bragg grating that was affected by the refractive index of the solution to be measured
Long-period gratings (LPGs) can be considered a special class of fiber Bragg gratings in which the period of the index modulation is such that it satisfies a phase matching condition between the fundamental core mode and a forward propagating cladding mode of an optical fiber
Summary
In 1983, Cooper et al [1] proposed the first optical fiber refractometer to measure the refractive index (RI) in several liquids This configuration is very complex and combines two technologies (bulk and fiber). A review of the developments in fiber optic based refractive index sensing undergone at INESC Porto/Portugal is presented. It provides an integrated overview of fiber sensing structures targeting such measurand, with presentation of selected results published elsewhere along the years. Result presentation comprises section on sensors based on: FBG, LPG; multimodal interference; fiber micro cavities; cladding modes and plasmonic structures
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