Browsing by Author "Cheung, Sammy C."

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    Fiber optic long period grating sensors with a nanoassembled mesoporous film of SiO2 nanoparticles
    (Optical Society of America (OSA), 2010-06-07T00:00:00Z) Korposh, Sergiy; James, Stephen W.; Lee, Seung-Woo; Topliss, Stephen M.; Cheung, Sammy C.; Batty, William J.; Tatam, Ralph P.
    A novel approach to chemical application of long period grating (LPG) optical fibers was demonstrated, which were modified with a film nanoassembled by the alternate deposition of SiO2 nanoparticles (SiO2 NPs) and poly(diallyldimethyl ammonium chloride) (PDDA). Nanopores of the sensor film could be used for sensitive adsorption of chemical species in water, which induced the changes in the refractive index (RI) of the light propagating in the cladding mode of the optical fiber, with a concomitant effect on the transmission spectrum in the LPG region. The prepared fiber sensor was highly sensitive to the change in the RI of the surrounding medium and the response time was very fast within 10 s. In addition, chemical infusion into the film was tested using a porphyrin compound, tetrakis-(4-sulfophenyl)porphine (TSPP), which could be saturated within a few min. The lowest detectable concentration of the TSPP analyte was 10 mu M. The TSPP infusion led to the development of well-pronounced dual resonance bands, indicating a large increase in the optical thickness of the film. The RI of the film was dramatically increased from 1.200 to ca. 1.540.
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    Response of a fibre optic long period grating operating at the phase matching turning point to the deposition of a nanostructured coating
    (International Society for Optical Engineering; 1999, 2009-12-31T00:00:00Z) James, Stephen W.; Topliss, Stephen M.; Cheung, Sammy C.; Tatam, Ralph P.; Jones, Julian D. C.
    The response of the transmission spectrum of a fibre optic long period grating operating near the phase matching turning point to the deposition of a nanostructured coating is investigated. The dual-resonant bands characteristic of operation in this regime are observed to show a high sensitivity to the thickness of the coating, but with opposite signs. Appropriate design of the device, based on the grating period, the refractive index and thickness of the coating and the fibre composition, can allow the sensitivity of the device to the optical thickness of the coating to be optimised.