10 November 2005 Photonic crystal microcavity source-based chemical sensor
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An ultra-small photonic crystal (PC) optical microcavity to detect small changes in concentration of chemical analytes in solutions is demonstrated. The high electric field concentration in small modal volumes of PC microcavities leads to high quality factor and efficient light-matter interaction with ultrasmall volumes of analyte and makes PC microcavities very sensitive to changes in refractive index of the surrounding medium. A linear PC microcavity was fabricated with four missing holes in a triangular lattice of air rods in a GaAs slab with an embedded quantum-dot active region on a GaAs substrate. The detection scheme depends upon the shifts of the sharp resonances supported by polymer-coated PC microcavities, due to change in refractive index, when in contact with a solution with a particular ionic concentration. For ClO4- anions, the resonance peaks shift by 20nm over the concentration range 10-3M to 10-6M. A smaller shift of 5nm is observed for Ca2+ ions over the same range. The device is a demonstration of PC microcavities in ion sensing. The microcavity sensing area is smaller than in microsphere-based detection or surface plasmon resonance imaging techniques and the devices are ideal as optical sensors for "lab-on-a-chip" microfluidic applications with minuscule volumes of analyte.
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S. Chakravarty, S. Chakravarty, Y. Kang, Y. Kang, J. Topolancik, J. Topolancik, P. Bhattacharya, P. Bhattacharya, M. E. Meyerhoff, M. E. Meyerhoff, S. Chakrabarti, S. Chakrabarti, } "Photonic crystal microcavity source-based chemical sensor", Proc. SPIE 6005, Photonic Crystals and Photonic Crystal Fibers for Sensing Applications, 600504 (10 November 2005); doi: 10.1117/12.631340; https://doi.org/10.1117/12.631340

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