Abstract
We experimentally demonstrate a 300 μm 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 μg/l) in water were measured.
Highlights
A simple and reliable technique for detection and identification of toxic volatile organic contaminants in water is infrared absorption spectroscopy
Infrared spectroscopy relies on fundamental molecular vibrations and does not require costly analyte labeling, which makes the technique very attractive for sensing and identification compared to other methods
The principle of infrared absorption spectroscopy is based on Beer–Lambert law
Summary
A simple and reliable technique for detection and identification of toxic volatile organic contaminants in water is infrared absorption spectroscopy. While electric field enhancement by slot is nearly constant across the entire bandwidth of a guided mode, as observed in the group index simulation, slow light effects exist over a bandwidth ϳ20 nm.
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