High Sensitivity Gas Detection with Microstructured Optical Fibres

We report recent development in laser spectroscopic gas sensing with microstructured hollow-core optical fibres and sub-wavelength-diameter optical nanofibers. The spectroscopic methods employed are photothermal spectroscopy for gases with strong absorption and stimulated Raman gain/dispersion spectroscopy for Raman-active gases. Compared with open-path systems, the use of microstructured optical fibres as sensing elements enables compact all-fibre systems with high performance. With photothermal interferometry, parts-per-billion (ppb) to parts-per-trillion (ppt) level detection of acetylene, methane and ammonia are demonstrated with dynamic range up to seven orders of magnitude. With stimulated Raman spectroscopy, parts-per-million (ppm) level detection of hydrogen is achieved with dynamic range of five orders of magnitude.