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17 January 2011 Photonic crystal slot waveguide spectrometer for the detection of methane
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Defect engineered photonic crystals, with sub-micron dimensions have demonstrated high sensitivity to trace volumes of analytes; however exact identification of analyte through spectroscopic signatures had not been demonstrated. We demonstrate a 300micron long photonic crystal slot waveguide device which combines slow light phenomenon in photonic crystal waveguides with large optical field intensity in a low index narrow slot at the center of the photonic crystal waveguide for highly sensitive spectroscopic detection of methane on-chip at 100 parts per million (ppm) or 0.2% permissible exposure limit. Photonic crystal slot waveguide provides a factor of 1000 reduction in interaction length compared to free-space infrared spectroscopy leading to enhanced optical absorption by analytes in the optical path. By measuring absorption differences in presence and absence of methane, near-infrared absorption spectrum of methane is determined.
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Swapnajit Chakravarty, Wei-Cheng Lai, Xiaolong Wang, Cheyun Lin, and Ray T. Chen "Photonic crystal slot waveguide spectrometer for the detection of methane", Proc. SPIE 7941, Integrated Optics: Devices, Materials, and Technologies XV, 79410K (17 January 2011);

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