title: Fiber optic hot-wire flowmeter based on a metallic coated hybrid long period grating/fiber Bragg grating structure.
abstract: In this work an all-optical hot-wire flowmeter based on a silver coated fiber combining a long period grating and a fiber Bragg grating (FBG) structure is proposed. Light from a pump laser at 1480  nm propagating down the fiber is coupled by the long period grating into the fiber cladding and is absorbed by the silver coating deposited on the fiber surface over the Bragg grating structure. This absorption acts like a hot wire raising the fiber temperature locally, which is effectively detected by the FBG resonance shift. The temperature increase depends on the flow speed of the surrounding air, which has the effect of cooling the fiber. It is demonstrated that the Bragg wavelength shift can be related to the flow speed. A flow speed resolution of 0.08  m/s is achieved using this new configuration.
authors.affiliation: Instituto de Engenharia de Sistemas e Computadores do Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal. pcaldas@inescporto.pt
authors.forename: Paulo
authors.initials: P
authors.lastname: Caldas
authors.forename: Pedro A S
authors.initials: PA
authors.lastname: Jorge
authors.forename: Gaspar
authors.initials: G
authors.lastname: Rego
authors.forename: Orlando
authors.initials: O
authors.lastname: Frazão
authors.forename: José Luís
authors.initials: JL
authors.lastname: Santos
authors.forename: Luís Alberto
authors.initials: LA
authors.lastname: Ferreira
authors.forename: Francisco
authors.initials: F
authors.lastname: Araújo
mesh_terms: D004867:Equipment Design; D005336:Fiber Optic Technology / Q000295:instrumentation*; D045268:Flowmeters; D007834:Lasers; D008027:Light; D055100:Optical Fibers; D012031:Refractometry / Q000295:instrumentation* / Q000379:methods; D013696:Temperature; D014159:Transducers