Photonic bandgap fiber optical correlation spectroscopy gas sensor

Abstract

We present results obtained from the first all-fiber, lensless, optical correlation spectroscopy gas sensor for acetylene (C₂H₂). In the reported sensing configuration, hollow-core photonic bandgap fiber (PBGF) is employed to contain all gas samples required for optical absorption measurements. This sensor relies upon comparison of the absorption spectrum of acetylene held in a 'reference gas cell' to that of a gas sample under test, which is contained in the 'measurement gas cell'. Ingress of the test gas mixture into the measurement cell is achieved via femtosecond laser-machined micro-channels running from the surface of the PBGF to its hollow core. Stable, lensless optical interrogation of the measurement cell is guaranteed by means of arc fusion splices to standard (solid-core) single-mode fiber (SMF). The reference cell is filled with acetylene at atmospheric pressure, and is permanently sealed at both ends by splices to SMF. Therefore, being constructed entirely from optical fiber, both the reference and measurement gas cells are inherently compact and coilable, and dispense with the need for lenses or other free-space optics for connection to the correlation spectroscopy system. We quantify the acetylene concentration of various test gas mixtures and compare our sensor's measured results with computer simulations.