DFB

1. PD SMF28 DFB PCF PD Depress plunger (via screw/thread arrangement) to increase pressure Conclusions We have demonstrated a microstructured fibre that has enhanced pressure sensitivity due to a high air-fraction in the cladding. We have tested this experimentally and used finite element modelling to predict the sensitivity enhancement, and as a means to suggest future developments of the fibre to further enhance the pressure sensitivity. Fibres surrounded by water - high pressure, low energy system. To Interrogation System Finite element analysis and experimental results for a microstructured fibre with enhanced hydrostatic pressure sensitivity William N MacPherson, Euan J. Rigg and Julian DC Jones (Heriot-Watt University) V.V. Ravi Kanth Kumar, Jonathan C. Knight and Philip St. J. Russell (University of Bath) Experimental Measurements FiniteElement Modelling Abstract In this paper we present a comparison of pressure sensitivity between a microstructured fibre and SMF28. Initial measurements show an enhanced pressure sensitivity for the microstructured fibre. Finite element modeling of both fibres confirm our observations. . • Complex shape of microstructured fibre does not lend itself to simple analytical analysis. • Use Lusas modelling software for hydrostatic pressure loading of 3D structure • Pressure loading force evenly distributed along structure surface. • Forces perpendicular to surface. • 3D model is long to minimise ‘end’ effects: look at effect in centre of cross section of model. A single wavelength interrogation technique was adopted, using a stabilised DFB laser as the optical source. The cavity response was quickly tested by heating both cavities - this information is used to interpret the fringe information from the pressure cycling. We wish to determine whether a very high air fraction fibre will exhibit increased pressure sensitivity (literature seems to suggest so). Also we wish to see if this can be realistically modelled using Finite Element (FE) techniques. Both Fabry Perot cavities formed from length of uncoated fibre. Cavity formed between reflective splices  Modelled hydrostatic pressure by applying uniform load perpendicular to mesh In this work we compare SMF-28 with a microstructured fibre (pictured) to model and measure the sensitivity to hydrostatic pressure. In general terms as the exterior of the fibre is subject to pressure this results in a change in the optical path length of the core due to strain-optic effect. We can measure this by considering a finite length of fibre which forms a Fabry-Perot cavity.  Optical configuration for interrogation of two Fabry-Perot cavities. Circulators used to increase optical signal detected and to minimise light coupling back into DFB laser  Microstructure fibre used in this experiment. Fabricated at University of Bath. Core ~6 mm diameter, supporting strands ~ 1.6 mm width Reflected Intensity (Bar) Reflected Intensity (Bar)  EZ strain results due to hydrostatic pressure  Mesh describing microstructured fibre Pressure (Bar) Pressure (Bar)  Pressure cycling results  Quick heating to check cavity operation and measure max. and min. reflected intensities When corrected for different cavity lengths the hydrostatic pressure sensitivity of the microstructured fibre was found to be 7.86 radians/bar/m and 2.37 radians/bar/m for SMF-28 fibre. Thus we observe a pressure sensitivity enhancement of ~3.3. • Model Results for 100 bar hydrostatic loading: • SMF-28 gives value 77.4 me (Z dir) • Microstructured fibre gives 145.1 me (Z dir) • Factor of ~1.9 increase in sensitivity. • Model has some limitations: • Symmetric model not an exact copy of actual fibre, • Limits due to mesh size, • Inherent limits associated with FE modelling. • However model still gives insight into effect of hydrostatic pressure on fibre. • Expect to see some enhanced pressure sensitivity from the microstructured fibre. Hydrostatic Test Facility  Hydrostatic test chamber - 0 to 100 Bar range. An electrical pressure gauge (Keller) is used to monitor the chamber pressure. The chamber is filled with water, which surrounds the fibre. In this way the fibre temperature is unchanged during pressure cycling. Acknowledgements W MacPherson wishes to acknowledge the UK Engineering and Physical Sciences Research Council for provision of funding under the Advanced Fellowship Scheme. E Rigg wishes to thank EPSRC and AWE for provision of PhD funding. School of Engineering and Physical Sciences (Physics), Heriot-Watt University, Edinburgh, EH14 4AS, UK Website: http://www.aop.hw.ac.uk