Browsing by Author "Topliss, Stephen M."

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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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    Optical fibre long period grating based selective vapour sensing of volatile organic compounds
    (Elsevier Science B.V., Amsterdam., 2010-01-07T00:00:00Z) Topliss, Stephen M.; James, Stephen W.; Davis, Frank; Higson, Seamus P. J.; Tatam, Ralph P.
    The chemical sensing capabilities of an optical fibre long period grating (LPG) coated with a functional material are explored. The LPG period and coating thickness are chosen such that the mode transition region, characteristic of LPGs coated with nanostructured coatings, corresponds with the phase matching turning point, ensuring optimum sensitivity. The functional material is a calixarene, which is shown to exhibit sensitivity to the aromatic compounds toluene and benzene, while being relatively insensitive to the aliphatic hydrocarbon hexane. A nanoscale cavity in the calixarene molecule entraps the VOC molecule, thereby altering the refractive index of the coating and influencing the transmission spectrum of the LPG. A sensitivity to toluene of 231 ppmv has been achieved, based on a spectrometer resolution of 0.3 nm. This is a weak molecular interaction thereby ensuring the sensor gives a reversible response when the VOC is removed. The recovery time is of the order of 15 s.
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    Optical fibre long period grating sensors with nanostructured coatings
    (Cranfield University, 2011-06) Topliss, Stephen M.; James, Stephen W.; Tatam, Ralph P.
    The dual resonant response of long period fibre gratings (LPG) operating near the phase matching turning point to the deposition of nanostructured coatings is explored. A broad range of LPGs have been fabricated with grating periods ranging from 80m to 180m, and these have been characterized with three different coating materials,-tricosensoic acid, undecyl-calix[4]resorcarene and tert-butyl-calix[8]arene carboxylic acid. The dual resonant response has been exploited with the construction of an LPG based sensor coated with a quinolinium dye forming a pH sensor. The wavelength response of this device was measured with a sensitivity of -0.55pH/nm. Furthermore, length apodised phase shifted long period gratings have been characterized, and the effect on the dual resonant response has been recorded. Partial coating of this device has resulted in the observation of a bandgap feature in the wavelength response. The use of calixarenes as a functional coating for long period fibre gratings is also investigated. Calixarene is applied in a thin layer with a thickness of several hundred nm’s to the cladding of the fibre in the region containing the LPG sensor. The chemical sensing capabilities of a long period fibre grating sensor is presented for the detection of the volatile organic compounds; hexane, cyclohexane, benzene and toluene. The wavelength response was measured and the sensitivity to toluene vapour was recorded at 1600ppmv/nm. Using intensity detection of the central maxima in the wavelength response, the chemical selectivity is demonstrated showing sensitivity to toluene vapour over 13 times greater compared to hexane vapour.
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    Properties of length-apodized phase-shifted lpgs operating at the phase matching turning point
    (IEEE Institute of Electrical and Electronics, 2012-07-01T00:00:00Z) James, Stephen W.; Topliss, Stephen M.; Tatam, Ralph P.
    The characteristics of length-apodized phase-shifted fiber optic long period gratings with full and partial nanostructured coatings have been explored theoretically and experimentally. The twin rejection bands that are characteristic of length-apodized phase-shifted long period gratings are studied for a long period grating (LPG) operating at the phase matching turning point. When one half of the length of the LPG is coated, complex bandgap like structure appears within the transmission spectrum, which may be of benefit to spectral filter design and for sensing applications.
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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.
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    Response of fibre optic long period gratings operating near the phase matching turning point to the deposition of nanostructured coatings.
    (Optical Soc- America, 2008-01-01T00:00:00Z) Cheung, C. S.; Topliss, Stephen M.; James, Stephen W.; Tatam, Ralph P.
    The response of the dual resonant bands 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 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 to be optimized. A sensitivity of 1.45 nm / nm is observed experimentally.