Abstract:We report on the thermal characteristics of Bragg gratings fabricated in polymer optical fibers. We have observed a permanent shift in the grating wavelength at room temperature which occurs when the grating has been heated above a threshold temperature. This threshold temperature is dependent on the thermal history of the grating, and we attribute the effect to a shrinking of the fiber. This effect can be avoided by annealing the fiber before grating inscription, resulting in a linear response with temperature and an increased linear operating temperature range of the grating.

Abstract.A series of in-line curvature sensors on a garment are used to monitor the thoracic and abdominal movements of a human during respiration. These results are used to obtain volumetric tidal changes of the human torso in agreement with a spirometer used simultaneously at the mouth. The curvature sensors are based on long-period gratings ͑LPGs͒ written in a progressive three-layered fiber to render the LPGs insensitive to the refractive index external to the fiber. A curvature sensor consists of the fiber long-period grating laid on a carbon fiber ribbon, which is then encapsulated in a low-temperature curing silicone rubber. The sensors have a spectral sensitivity to curvature, d / dR from ϳ7-nm m to ϳ9-nm m. The interrogation technique is borrowed from derivative spectroscopy and monitors the changes in the transmission spectral profile of the LPG's attenuation band due to curvature. The multiplexing of the sensors is achieved by spectrally matching a series of distributed feedback ͑DFB͒ lasers to the LPGs. The versatility of this sensing garment is confirmed by it being used on six other human subjects covering a wide range of body mass indices. Just six fully functional sensors are required to obtain a volumetric error of around 6%. © 2007 Society of Photo-Optical Instrumentation Engineers.

The procedures currently used for isolating legionellae from environmental samples recommend filtration through a 0.2-,im-pore-size polycarbonate filter. In this study we evaluated the performance of 23 other filters composed of various materials and having various pore sizes. We prefer the 0.2-,im-pore-size Gelman Supor filter because of its high level of recovery, faster filtration rate, and ease of handling.

We describe recent research into devices based on fibre Bragg gratings in polymer optical fibre. Firstly, we report on the inscription of gratings in a variety of microstructured polymer optical fibre: single mode, few moded and multimoded, as well as fibre doped with trans-4-stilbenmethanol. Secondly, we describe research into an electrically tuneable filter using a metallic coating on a polymer fibre Bragg grating. Finally we present initial results from attempts to produce more complex grating structures in polymer fibre: a Fabry-Perot cavity and a phase-shifted grating.Keywords: Polymer optical fibre, fibre Bragg grating, sensor, filter. INTRODUCTIONAt the moment there is considerable interest in the use of polymer optical fibre (POF) in a variety of applications. In several countries POF is seen as a good candidate as a digital transmission medium in fibre-to-the-home applications and for home networking. POF is also increasingly being used in automotive data buses, while one of the largest markets, in terms of the sheer length of fibre used, is in illumination applications. All of these markets are possible because POF based systems are seen as being low cost; this applies to both the intrinsic production cost of the fibre itself as well as the cost of its installation, including the making of connections. The communications applications mentioned all involve short transmission distances where the much higher loss of POF in comparison with silica fibre and its high intermodal dispersion are not serious disadvantages. The high intermodal dispersion in these systems arises because of the predominant use of very large core multi-mode fibres, which makes it easy and therefore cheap to couple to low cost, large-area sources and to make fibre-to-fibre connections.A number of workers have developed techniques for sensing using POF which also follow this low cost paradigm 1 and some of these devices are beginning to be commercialised. At the same time, there have been some recent technological developments which open up new possibilities for POF based sensors and devices. These are:• the development of single-mode step index optical fibre; 2• the demonstration of the recording of fibre Bragg grating (FBG) filters in POF; 3• the production of microstructured or photonic crystal polymer optical fibre (mPOF). 4 Whilst, as we shall explore in this paper, these technologies offer tremendous scope for the realisation of novel devices, for the foreseeable future they are unlikely to offer very low costs. This is partly due to the underlying cost of production but also often due to the need for sources compatible with single mode fibre, and the difficulty (and hence expense) of connecting single mode polymer fibres. To justify work in this area, one then has to look for other advantages over the very much more mature silica fibre technology. Fortunately it is not difficult to find several major factors that can act in POF's favour for certain applications.

We present a thorough study on the development of a polymer optical fibre-based tuneable filter utilizing an intra-core Bragg grating that is electrically tuneable, operating at 1.55 µm. The Bragg grating is made tuneable using a thin-film resistive heater deposited on the surface of the fibre. The polymer fibre was coated via the photochemical deposition of a Pd/Cu metallic layer with the procedure induced by VUV radiation at room temperature. The resulting device, when wavelength tuned via Joule heating, underwent a wavelength shift of 2 nm for a moderate input power of 160 mW, a wavelength to input power coefficient of −13.4 pm mW−1 and time constant of 1.7 s−1. A basic theoretical study verified that for this fibre type one can treat the device as a one-dimensional system. The model was extended to include the effect of input electrical power changes on the refractive index of the fibre and subsequently to changes in the Bragg wavelength of the grating, showing excellent agreement with the experimental measurements.