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

We experimentally demonstrate a 300 μ 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 μ g / l ) in water were measured.