High sensitivity gas detection using Hollow Core Photonic Bandgap Fibres designed for mid-IR operation

We report on the use of novel low loss Hollow Core Photonic Bandgap Fibres (HC-PBGFs) operating in the mid-IR for broadband absorption measurements of low-level concentrations of Acetylene and Ethane gas around 3 and 3.3 μm, respectively. The availability of improved HC-PBGFs operating in the 3-3.6 μm wavelength range with ~0.05-0.1 dB/m loss enables accessing the strongest fundamental ro-vibrational bands (e.g. C-H, O-H, N-H), thus opening up the possibility of absorption based gas sensing with much higher sensitivity than has been demonstrated to date utilizing fibres optimized for near-IR operation. We present for the first time spectroscopic absorption measurements of C₂H₂ at ~3.05 μm (2.5 vol% concentration) and of C₂H₆ at 3.35 μm (50 ppmV concentration) using HC-PBGF cells. Results indicate that sub-ppm sensitivities can easily be achieved using fiber lengths of a few meters and simple detection schemes.