Integrated Optical Fibre (IOF) is a passive optical platform that directly integrates optical fibre to a planar substrate, illustrated in Fig 1(a). It possess advantages associated with optical fibre such a low propagation loss, whilst enabling planar functionality commonplace with integrated optics. Planarization is uniquely achieved through a modified Flame Hydrolysis Deposition (FHD) technique that forms a robust glass alloy between the fibre and substrate. The binding medium is of optical quality and resistant against common solvents, chemicals and elevated temperatures of up to 1000 o C. Furthermore as fibre can be brought seamlessly on-off chip there is no need for glues or cumbersome coupling arrangements, which are typically a point of mechanical weakness when monitoring harsh environments. Thus far, developments in IOF have largely utilised either the environmental stability [1] and/or physical robustness [2] of the platform and not the optical quality of the binding medium. This work reports for the first time and evanescent field based refractometer using IOF, in which the optical mode directly interacts with the deposited FHD glass and the external environment. The concept for design is based largely on so termed thinned-FBGs [3], in which an optical fibre is wet etched using buffered HF. Through applying a similar geometry to the IOF format one can achieve external refractive index sensitivity, but with an enhanced mechanical integrity and capacity for integration. Fig. 1 (a) a cross-section profile of an Integrated Optical Fibre with SMF-28. (b) A cross-section profile of an Integrated Optical Fibre with a wet etched SMF-28 fibre (fibre 8 µm in diameter). (c) The optical response of a Bragg grating in construct (b), under exposure to Cargille refractive index matching liquids. This work reports a proof-of-concept refractometer design, fabricated through wet etching SMF-28 fibre in a buffered HF solution then applying it in an IOF format. For the device depicted in Fig 1 (b), etching is continued until a diameter of 8 µm is reached. This etched fibre is then subsequently transferred and layered-up onto a silicon wafer that has a thick thermally grown oxide (15 µm). The purpose of the oxide is to act as an optical buffer layer (clad), ensuring the final device maintains a guided mode. To form the IOF and maintain as much evanescent field exposure to the external environment a 0.5 µm FHD layer is deposited and consolidated at 1250 o C, leaving the cross sectional geometry shown in Fig 1 (b). The FHD recipe is a silicate, doped with boron and phosphorus that once consolidated has a refractive index of 1.4452 (at a wavelength of 1553 nm). Changes in external refractive index were inferred through use of a Direct UV Written fibre Bragg grating [2]. The grating was inscribed at a fluence of 30kJcm-2 into the fibre core, after the FHD had been consolidated. To enhance UV photosensitivity the chip was hydrogen loaded at 120 bar for 7 days. Cargille refractive index matching liquids (series AA and AAA) were ...

Fresnel refractometry was used to follow the changes in the refractive index during the isothermal curing of a simple difunctional epoxy resin, a commercial formulated multifunctional epoxy blend, and the same two resin systems modified by the addition of multiwalled carbon nanotubes. The refractive index change, monitored via an embedded optical fiber, was correlated with the degree of cure established from isothermal differential scanning calorimetry measurements. A good correlation was established in all cases, indicating the potential of the technique to be used for online cure monitoring in thermosetting resin carbon nanocomposites.

The use of optical fibre Bragg grating (FBG) strain sensors to monitor the condition of safety critical rail components is investigated. Fishplates, switchblades and stretcher bars on the Stagecoach Supertram tramway in Sheffield in the UK have been instrumented with arrays of FBG sensors. The dynamic strain signatures induced by the passage of a tram over the instrumented components have been analyzed to identify features indicative of changes in the condition of the components.

The commissioning of superconducting magnet coils was monitored using embedded optical fibre Bragg grating sensors (FBG) fabricated in highly linearly birefringent (HiBi) fibre. The HiBi FBG sensors monitored the internal strain developed in the coils during the energisation of the coils. The development of multiple components of strain in the coils when the magnet was energised and quenched was monitored, revealing phenomena that it had not been previously possible to measure using other sensor technologies.

Optical fibre Bragg grating sensors have been field-trialed for the monitoring of dynamic loading of fish-plates, stretcher bars and switchblades on a tram network, with the aim of developing a condition monitoring system. This paper provides preliminary data showing the ability to identify changes in track/component condition.