Photonic crystal slot waveguide absorption spectrometer for on-chip near-infrared spectroscopy of xylene in water

We experimentally demonstrate a 300 mu m long silicon photonic crystal slot waveguide near-infrared absorption spectrometer. Based on Beer-Lambert absorption law, our on-chip absorption spectrometer combines slow light in a photonic crystal waveguide with a high electric field intensity in a low-index 75 nm wide slot, which effectively increases the optical absorption path length of the analyte. We demonstrate near-infrared absorption spectroscopy of xylene in water, with a polydimethyl siloxane sensing phase for xylene extraction from water. Xylene concentrations up to 100 ppb (parts per billion) (86 mu g/l) in water were measured. (c) 2011 American Institute of Physics. [doi:10.1063/1.3531560]