title: Pressure sensing in high-refractive-index liquids using long-period gratings nanocoated with 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 (<100 nm) able to tune the external-refractive-index sensitivity of the gratings. To the best of our knowledge, this is the first time a nanocoating has been applied on LPGs that is able to simultaneously tune the refractive-index sensitivity and to enable measurements of other parameters.
authors.affiliation: Centre de Recherche en Photonique, Université du Québec en Outaouais, 101 rue Saint-Jean-Bosco, Gatineau, QC, J8X 3X7, Canada. M.Smietana@elka.pw.edu.pl
authors.forename: Mateusz
authors.initials: M
authors.lastname: Smietana
authors.forename: Wojtek J
authors.initials: WJ
authors.lastname: Bock
authors.forename: Predrag
authors.initials: P
authors.lastname: Mikulic
authors.forename: Jiahua
authors.initials: J
authors.lastname: Chen
mesh_terms: D015374:Biosensing Techniques / Q000295:instrumentation / Q000379:methods*; D004595:Electroplating / Q000379:methods; D004867:Equipment Design; D005336:Fiber Optic Technology / Q000295:instrumentation / Q000379:methods; D055616:Microtechnology; D049329:Nanostructures / Q000737:chemistry*; D011312:Pressure; D012031:Refractometry / Q000379:methods; D017655:Silicon Compounds / Q000737:chemistry*; D012996:Solutions / Q000032:analysis / Q000737:chemistry; D013499:Surface Properties
chemical_list: D017655:Silicon Compounds; D012996:Solutions; C032734:silicon nitride