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Pressure Sensing in High-Refractive-Index Liquids Using Long-Period Gratings Nanocoated with Silicon Nitride

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Author(s): Mateusz Smietana | Wojtek J. Bock | Predrag Mikulic | Jiahua Chen

Journal: Sensors
ISSN 1424-8220

Volume: 10;
Issue: 12;
Start page: 11301;
Date: 2010;
Original page

Keywords: optical fiber sensors | pressure sensor | long-period gratings | plasma deposition | thin films | silicon nitride

ABSTRACT
The paper presents a novel pressure sensor based on a silicon nitride (SiNx) nanocoated long-period grating (LPG). The high-temperature, radio-frequency plasma-enhanced chemical-vapor-deposited (RF PECVD) SiNx nanocoating was applied to tune the sensitivity of the LPG to the external refractive index. The technique allows for deposition of good quality, hard and wear-resistant nanofilms as required for optical sensors. Thanks to the SiNx nanocoating it is possible to overcome a limitation of working in the external-refractive-index range, which for a bare fiber cannot be close to that of the cladding. The nanocoated LPG-based sensing structure we developed is functional in high-refractive-index liquids (nD > 1.46) such as oil or gasoline, with pressure sensitivity as high as when water is used as a working liquid. The nanocoating developed for this experiment not only has the highest refractive index ever achieved in LPGs (n > 2.2 at λ = 1,550 nm), but is also the thinnest (

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Tangokurs Rapperswil-Jona

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