title: Simultaneous measurement of partial pressure of O2 and CO2 with a hybrid interferometer.
abstract: In this Letter, a hybrid interferometer for simultaneous measurement of the partial pressures of O2 and CO2 mixtures is reported. The sensing head consists in the combination of two interferometric structures, one a Fabry-Pérrot cavity and the other a modal interferometer. The intrinsic Fabry-Pérot was formed by splicing a single mode fiber with a graded index fiber length that was then subjected to chemical etching creating an air cavity. The second interferometer is based on a splice of a pure silica tube in series with the Fabry-Pérot. It was observed for a particular gas that its refractive index changes with pressure variation in a specific way, a characteristic that permitted the simultaneous measurement of partial pressures of CO2 and O2 with rms deviations of ~±48.7 kPa and ~±20.1 kPa, respectively.
authors.affiliation: INESC Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal.
authors.forename: Luís
authors.initials: L
authors.lastname: Coelho
authors.forename: Paula A R
authors.initials: PA
authors.lastname: Tafulo
authors.forename: Pedro A S
authors.initials: PA
authors.lastname: Jorge
authors.forename: José L
authors.initials: JL
authors.lastname: Santos
authors.forename: Diana
authors.initials: D
authors.lastname: Viegas
authors.forename: Kay
authors.initials: K
authors.lastname: Schuster
authors.forename: Jens
authors.initials: J
authors.lastname: Kobelke
authors.forename: Orlando
authors.initials: O
authors.lastname: Frazão