Chip-scale Mid- Infrared chemical sensors using air-clad pedestal silicon waveguides

    Authors

    P. T. Lin; V. Singh; J. J. Hu; K. Richardson; J. D. Musgraves; I. Luzinov; J. Hensley; L. C. Kimerling;A. Agarwal

    Comments

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    Abbreviated Journal Title

    Lab Chip

    Keywords

    SURFACE-PLASMON RESONANCE; BIOLOGICAL ANALYSIS; OPTICAL SENSORS; SPECTROSCOPY; FILM; Biochemical Research Methods; Chemistry, Multidisciplinary; Nanoscience; & Nanotechnology

    Abstract

    Towards a future lab-on-a-chip spectrometer, we demonstrate a compact chip-scale air-clad silicon pedestal waveguide as a Mid-Infrared (Mid-IR) sensor capable of in situ monitoring of organic solvents. The sensor is a planar crystalline silicon waveguide, which is highly transparent, between lambda = 1.3 and 6.5 mu m, so that its operational spectral range covers most characteristic chemical absorption bands due to bonds such as C-H, N-H, O-H, C-C, N-O, C=O, and C=N, as opposed to conventional UV, Vis, Near-IR sensors, which use weaker overtones of these fundamental bands. To extend light transmission beyond lambda = 3.7 mu m, a spectral region where a typical silicon dioxide under-clad is absorbing, we fabricate a unique air-clad silicon pedestal waveguide. The sensing mechanism of our Mid-IR waveguide sensor is based on evanescent wave absorption by functional groups of the surrounding chemical molecules, which selectively absorb specific wavelengths in the mid-IR, depending on the nature of their chemical bonds. From a measurement of the waveguide mode intensities, we demonstrate in situ identification of chemical compositions and concentrations of organic solvents. For instance, we show that when testing at lambda = 3.55 mu m, the Mid-IR sensor can distinguish hexane from the rest of the tested analytes (methanol, toluene, carbon tetrachloride, ethanol and acetone), since hexane has a strong absorption from the aliphatic C-H stretch at l = 3.55 mu m. Analogously, applying the same technique at lambda = 3.3 mm, the Mid-IR sensor is able to determine the concentration of toluene dissolved in carbon tetrachloride, because toluene has a strong absorption at lambda = 3.3 mm from the aromatic C-H stretch. With our demonstration of an air-clad silicon pedestal waveguide sensor, we move closer towards the ultimate goal of an ultra-compact portable spectrometer-on-a-chip.

    Journal Title

    Lab on a Chip

    Volume

    13

    Issue/Number

    11

    Publication Date

    1-1-2013

    Document Type

    Article

    Language

    English

    First Page

    2161

    Last Page

    2166

    WOS Identifier

    WOS:000318514400018

    ISSN

    1473-0197

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