303 research outputs found

    Novel technique for measuring dispersion and detuning of a UV written silica-on-silicon waveguide

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    We shall present a new method of measuring the dispersive properties of UV written waveguides in the silica-on-silicon platform used to fabricate planar Bragg gratings. The technique involves direct measurement of the modal refractive index of a waveguide produced in the material. The data obtained also provides additional information about the spectral range of Bragg grating inscription. This direct writing technique reported previously differs from fibre Bragg grating fabrication by the small spot size of the writing beam and permits detuning of the Bragg wavelength from 1250nm to 1625nm. The fabrication technique provides the exact period of the grating and thus interrogation of the gratings produces information on the effective index of the mode. A series of integrated gratings were fabricated in a direct UV written waveguide via the direct grating writing technique in order to measure the wavelength dependence of the refractive index of the material. The Sellmeier curve obtained is shown

    Monitoring the deflection of a membrane using direct UV written planar Bragg gratings

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    A thin (~100 µm thick) silica-on-silicon square membrane (10 mm x 10 mm) has been fabricated and its deflection monitored through a 100 Bragg grating array defined within the membrane

    Affective issues in learning technologies: emotional responses to technology and technology's role in supporting socio-emotional skills

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    This paper focuses on some of the author's research studies over the past thirty years and places these in a wider context to reflect on research into affective issues in learning technologies over this period, and to consider whether and how the issues uncovered by research have changed as technologies have developed over time. Three issues are given particular attention: firstly the reasons for learners' use or lack of use of technologies for their learning; secondly adult learners' attitudes towards using technology for learning and thirdly how technology might support socio-emotional development and expression in children. The discussion of these issues is framed by two of the author's research projects. For the first two issues this is an early study of students' perceptions and attitudes towards using computers for tutorial learning in 1980. The factors that influenced the students' use of the computer tutorials are discussed (including access, assessment and anxiety about using computers) and also the extent to which some of these factors persist for many learners using (or not using) technologies today. The discussion of the third issue draws on a series of studies conducted in the 1990s to investigate whether educational technology could support children and young people's emotional expression and communication and development of socio-emotional skills. Finally the paper considers how these kinds of issues have been taken forward and how they are represented in contemporary research and suggests that trust is an important factor in using learning technologies

    An integrated optofluidic Bragg grating device to measure the dynamic composition of a fluid

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    Strong transitional mixing effects were observed by a planar Bragg grating sensor within a microfluidic system. This property was used to develop an integrated optofluidic sensor for detection of the composition of mixed solvent systems

    Optofluidic integrated Bragg grating chemical sensor: Utilising a sodium-elective receptor surface to enhance detection

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    Planar waveguides can be written with a UV-laser into photosensitised silica to produce a wide range of optical devices. Careful modulation of two interfering beams allows Bragg gratings to be directly written into the channel. These Bragg gratings are inherently sensitive to temperature and strain, however etching away the surface exposes the mode within the grating to its surroundings. The corresponding observed shift in Bragg wavelength can be used to detect changes in this environment [1]. It has been previously reported [2] that the sensitivity of such a refractometer can be enhanced by over an order of magnitude through use of a high-index overlayer of tantalum pentoxide. This enhanced sensor has shown the potential to detect a single molecular monolayer upon the sensor surface [2]. This sensitivity was confirmed through the successful attachment and detection of a single molecular monolayer of a fluorescein-based organic dye to the sensor surface [3

    An integrated Bragg grating oxygen sensor using a hydrophobic sol-gel layer doped with an organic dye

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    Oxygen sensing is required for the understanding of many chemical processes across a diverse set of fields including medicine, environmental science and chemical synthesis. Oxygen sensing can be achieved through the use of electronic sensors. However, there are limitations associated with electronic sensors including susceptibility to electromagnetic interference and presenting a spark risk in flammable environments. Optical fiber and integrated optical chemical sensors overcome these limitations of electrical based sensing methods

    An integrated reconfigurable Bragg grating utilising a photoresponsive co-polymer

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    Reconfigurable Bragg grating devices are of significant interest for telecomm applications. Such devices can be fabricated by combining a UV-written silica Bragg grating with an azobenzene-based polymer - a photoresponsive material that undergoes reversible refractive index change on exposure to ultraviolet light. The preliminary 17 GHz tuning response suggests future applicability

    Integrated temperature compensated Bragg grating refractometer

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    UV written planar Bragg grating sensors have been shown to form effective refractometers. Here we show that by using the birefringence of an integrated waveguide a temperature insensitive Bragg grating refractometer can be realised

    Terahertz bandwidth photonic Hilbert transformers and implementations in ultra wideband single-sideband filters

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    Planar Bragg grating based photonic Hilbert transformers (PHTs) with THz bandwidths are proposed and practically demonstrated. An X-coupler, PHT, and a flat-top reflector are incorporated, demonstrating 2THz all-optical single-sideband filters. Devices are fabricated via a direct UV grating writing technique on a silica-on-silicon platform

    Integrated planar Bragg grating oxygen sensor

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    We demonstrate an integrated planar Bragg grating sensor for the detection of oxygen by modification of the surface with a silica sol-gel containing immobilized methylene blue