Browsing by Author "Ashwell, Geoffrey J."
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Item Open Access Fiber-optic chemical sensing with Langmuir-Blodgett overlay waveguides(Osa Optical Society of America, 1999-12-20T00:00:00Z) Flannery, D.; James, Stephen W.; Tatam, Ralph P.; Ashwell, Geoffrey J.Fiber-optic chemical sensing has been demonstrated with a side-polished single- mode optical fiber, evanescently coupled to chemically sensitive Langmuir- Blodgett (LB) overlay waveguides. The sensors exhibit a channel-dropping response centered on a wavelength that is dependent on the thickness and the refractive index of the overlay waveguide. It has been shown that pH-sensitive organic dyes proved to be suitable materials fur the formation of an overlay waveguide whereas LB deposition provides the required thickness control. A theoretical model of the sensor response, based on the Kramers-Kronig relations and phase matching of the guided modes within the optical fiber and overlay waveguide, shows good agreement with experimental results.Item Open Access Modification of the refractive index response of long period gratings using thin film overlays.(Elsevier Science B.V., Amsterdam., 2005-06-01T00:00:00Z) Ishaq Imran, M; Quintela, Antonio; James, Stephen W.; Ashwell, Geoffrey J.; Tatam, Ralph P.The response of a fibre optic long period grating (LPG) to the surrounding refractive index is shown to be modified by the deposition of a thin film of thickness of order 100 nm onto the cladding. The LPG becomes sensitive to surrounding refractive indices greater than that of silica, and exhibits an enhanced sensitivity to external refractive indices lower than that of silica.Item Open Access pH sensor using Langmuir-Blodgett overlays on polished optical fibers(Optical Society of America, 1997-04-15T00:00:00Z) Flannery, D.; James, Stephen W.; Tatam, Ralph P.; Ashwell, Geoffrey J.Evanescent coupling between a side-polished single-mode optical fiber and a single-mode, pH-sensitive Langmuir-Blodgett overlay is used to demonstrate an intrinsic fiber-optic pH sensor. The sensor shows a wavelength sensitivity of 18.8 ± 0.8 nm/pH and a transmission sensitivity of 9.7 ± 0.8 dB/pH when operating at 750 nItem Open Access Second-harmonic generation in Langmuir-Blodgett waveguide overlays on single- mode optical fiber(Optical Society of America, 1999-09-30T00:00:00Z) Johal, S. S.; James, Stephen W.; Tatam, Ralph P.; Ashwell, Geoffrey J.Second-harmonic radiation has been obtained from Langmuir-Blodgett films of E-N- octadecyl-4-[2-(4-dibutylaminophenyl)ethenyl] quinolinium octadecylsulfate, deposited as a waveguide overlay upon optical fiber that is single mode at the pump wavelength (lambda = 1064 nm). A quadratic relationship between the pump power and second-harmonic intensity was observed.Item Open Access Submicrometer fiber-optic Fabry-Perot interferometer formed by use of the Langmuir-Blodgett technique(Optical Society of America, 2001-12-01T00:00:00Z) Rees, N. D.; James, Stephen W.; Staines, Stephen E.; Tatam, Ralph P.; Ashwell, Geoffrey J.The fabrication of an optical cavity at the distal end of an optical fiber has been achieved by Langmuir-Blodgett (LB) deposition of tricosanoic acid. This technique allows nanometer-scale control over the cavity length to a total thickness of ~0.5 à µm. The cavity has been shown to act interferometrically and, thus, has potential sensing applications