Browsing by Author "Wong, Rebecca"

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    Advanced fibre optic long period grating sensors; design, fabrication and sensing
    (Cranfield University, 2014-05) Wong, Rebecca; James, Stephen W.; Tatam, Ralph P.
    This thesis describes the process and technique used to fabricate reproducible optical fibre long period gratings (LPG) of various types. It explores how they can be exploited for use as highly selective and sensitive sensors. A versatile method for fabricating LPG sensors has been demonstrated. The single system has the capability of fabricating LPGs of different configurations, such as uniform period, those operating at the phase matching turning point (PMTP), as well as phase shifted and chirped. LPGs were characterised for their sensitivities to temperature, axial strain and surrounding refractive index. The gratings at the PMTP were found to show higher sensitivities to external influences. Novel sensing configurations that exploit the properties of LPGs were also constructed. An LPG coated with a molecularly imprinted ceramic coating was demonstrated to offer a selective method for porphyrin detection. A composite nanoscale of a titanium oxide (TiO2) matrix and 5, 10, 15, 20 Tetrakis-(N-methyl-piridinium4- yl)-21H, 23H-porphine tertakis (p-toluenesulfonate) [TMPyP] porphyrin template film was deposited on the LPG via liquid phase deposition. Attempts to rebind porphyrins to the matrix were carried out. The LPGs transmission spectrum exhibited a higher sensitivity to the target TMPyP template than it did to other, structurally similar porphyrins, showing high selectivity. A continuously chirped long period grating (CCLPG) sensor for monitoring directional flow and cure of an epoxy resin is also presented. The asymmetric properties of the CCLPG were exploited to facilitate the measurement of the direction of the flow. The CCLPG was also used to monitor changes in the refractive index of the resin during its cure, showing close agreement with a fibre optic Fresnel refractometer.
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    Long period grating based toluene sensor for use with water contamination
    (Elsevier Science B.V., Amsterdam., 2014-11-01T00:00:00Z) Partridge, Matthew; Wong, Rebecca; James, Stephen W.; Davis, Frank; Higson, Seamus P. J.; Tatam, Ralph P.
    A demonstration of the use of a calix[4]resorcinarene coated optical fibre long period grating sensor for the detection of toluene in water is presented. Monitoring water quality both for domestic use and around industrial sites is critical to the preservation of clean water provision. Here we show that, by using a fibre optic based sensor system, water quality monitoring can be carried out without the requirement for water sampling or pre-concentration. The results presented demonstrate that this proof-of-concept sensor is capable of sensing ∼100ppm concentrations of toluene with semi-selectivity and low (<10ppm) variation.
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    Modifying monolayer behaviour by incorporating subphase additives and improving Langmuir–Blodgett thin film deposition on optical fibres
    (Elsevier, 2014-01-17) Partridge, Matthew; Wong, Rebecca; Collins, Mike; James, Stephen W.; Davis, Frank; Tatam, Ralph P.; Higson, Seamus P. J.
    Experiments showing the possibility of modifying the behaviour of calix[4]resorcinarene monolayers at the air–water interface and optimising the deposition of multilayer coatings onto optical fibres are presented. The nature of the subphase is fundamental to the behaviour of monolayers and their utility in coating and sensing applications. Here we show initial studies exploring the modification of the calix[4]resorcinarene monolayer–water interaction through the introduction of dipole altering alcohol additives to the aqueous subphase. We explored the effect of this modification for three small alcohols. The resulting isotherms of the materials showed a reduction in the surface pressure and area per molecule required in order for the monolayer to reach its point of collapse. Incorporation of alcohols shifted the point of collapse, leading to the application of ethanol being successful in improving the transfer of material via Langmuir–Blodgett coating onto optical fibres at lower pressures. This method may prove useful in allowing greater control over future sensor surface coatings.