Simultaneous Measurement of Partial Pressure of O2 and CO2 with a Hybrid Interferometer

In this work, 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-Perot 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 its refractive index changes with pressure variation in a specific way, characteristic that permitted the simultaneous measurement of partial pressures of CO2 and O2 with rms deviations of ~ ± 0.079 kPa and ~ ± 0.029 kPa for, respectively.