Miniature infrared gas sensors using photonic crystals

The sensitivity of an infrared gas sensor depends on the interaction length between radiation and gas, i.e. a reduction in cell size generally results in a reduced sensitivity, too. However, low group velocity regions in the bandstructure of photonic crystals should enable the realization of very compact gas sensors. Using photonic crystals based on macroporous silicon experimental results with CO2 show an increase of the gas sensitivity in the photonic crystal compared to an empty cell of same dimensions. For practical applications the results are compared with gas measurements using conventional multireflection cells and hollow fiber setups.