Development of low and high birefringence optical fibres

The polarization properties of single-mode optical fibers are easily modified by environmental factors, While this can be exploited in a number of fiber sensor devices. it can be troublesome in applications where a stable output polarization-state is required. Fibers with both low and high birefringence have been developed to enhance or diminish their environmental sensitivity, and recent progress in each area is reviewed. Low-birefringence fibers are described which are made by spinning the preform during the draw. In addition. developments in high-birefringence fibers which maintain a polarization state over long lengths are summarized. The effect on performance of external factors such as bends, transverse pressure, and twists is analyzed. Consideration is also given to polarization mode-dispersion as a potential limiting factor in ultrahigh bandwidth systems

Optical fiber fabrication using novel gas-phase deposition technique

We report a highly versatile chemical-in-crucible preform fabrication technique suitable for gas-phase deposition of doped optical fibers. Aluminosilicate and ytterbium-doped phosphosilicate fibers are presented demonstrating the technique and its potential for realizing complex fiber designs that are suitable for the next generation of high-power fiber devices. The results show aluminum-doped fiber with numerical aperture of 0.28 and ytterbium-doped fiber with a measured slope efficiency of 84% with respect to pump launch power

The use of a cephalonium containing dry cow therapy and an internal teat sealant, both alone and in combination

AbstractThe dry period is a critical time in the lactation cycle, being the optimum time to cure existing intramammary infection (IMI) as well as encompassing the periods of highest susceptibility to new infection. Currently, IMI in the dry period is controlled with antibiotic dry cow therapy. The aim of this randomized control trial was to investigate different dry cow therapy regimens by stratifying cows by likely infection status at drying off in herds with low somatic cell count (SCC; bulk milk SCC <250,000 cells/mL) in southwest England. All quarters in 890 cows were recruited. The recruited cows were categorized as either infected or uninfected on the basis of SCC and clinical mastitis history. Ipsilateral quarters within each cow were randomly allocated to receive 1 of 4 different treatment regimens according to their infection category. Quarters in high-SCC infected cows were allocated to receive antibiotic dry cow therapy either alone or in combination with an internal teat sealant; quarters in low-SCC uninfected cows were allocated to receive teat sealant either alone or in combination with antibiotic dry cow therapy. All quarters were sampled for bacteriology at drying off and again within 10 d post-calving. Quarters were subsequently monitored for clinical mastitis for the first 100 d of lactation. The mass of residual sealant was assessed immediately post-calving to allow assessment of the association of sealant retention with treatment efficacy. Models were constructed to assess the efficacy of the different regimens in preventing IMI. Apparent cure rates of existing IMI with major pathogens were consistently >90% in quarters receiving antibiotic. Combination treatment of high-SCC infected cows resulted in an increased likelihood of being pathogen free post-calving (odds ratio=1.40; 95% credibility interval=1.03–1.90). The benefits of combination treatment of low-SCC uninfected cows were less clear. With respect to clinical mastitis, combination treatment of high-SCC infected cows resulted in a decreased likelihood of developing clinical mastitis in the first 100 d of the subsequent lactation (odds ratio=0.68; 95% credibility interval=0.48–0.98). The retention of the internal sealant was adversely affected by its use in combination with antibiotic dry cow therapy

The inertial dynamics of thin film flow of non-Newtonian fluids

Consider the flow of a thin layer of non-Newtonian fluid over a solid surface. I model the case of a viscosity that depends nonlinearly on the shear-rate; power law fluids are an important example, but the analysis here is for general nonlinear dependence. The modelling allows for large changes in film thickness provided the changes occur over a large enough lateral length scale. Modifying the surface boundary condition for tangential stress forms an accessible base for the analysis where flow with constant shear is a neutral critical mode, in addition to a mode representing conservation of fluid. Perturbatively removing the modification then constructs a model for the coupled dynamics of the fluid depth and the lateral momentum. For example, the results model the dynamics of gravity currents of non-Newtonian fluids even when the flow is not very slow

Measurements of fibre polarisation properties using a photo-elastic modulator

Single-mode fibres with controlled polarisation properties are required for many fibre applications. For example, high-birefringence fibres are able to transmit linearly-polarised light, a property which is useful in interferometric fibre sensors and in coherent transmission systems. Low-birefringence fibres, on the other hand, have negligible intrinsic birefringence and are suited to conventional communications, polarisation-control devices and polarimetric sensors

The stress-optic effect in optical fibres

The importance of the photoelastic effect in controlling polarization in optical fibers is discussed. Measurements of the stress-optic coefficient, its dispersion, and temperature dependence are reported using a fiber measurement method. The results compare closely to data obtained for bulk silica by an extrapolation technique. It is shown that the dispersion of the stress-optic coefficient can have a significant effect on the performance of birefringent fibers and of fiber birefringent devices. Furthermore, the temperature dependence is sufficiently large to be troublesome in fiber sensors

Birefringence testing in single-mode fibres manufactured with controlled polarisation characteristics

Single-mode fibres with well-defined polarisation properties are required to interface to integrated-optical components and in fibre sensors and the Faraday current monitor. The development of fibres with closely controlled polarisation characteristics is critically dependent on the ability to accurately measure and interpret complex birefringence properties. A number of test methods for this purpose have been investigated and are described in this paper, together with an indication of the precautions necessary to minimise external effects

Polarisation optical-time-domain reflectometry : experimental results and application to loss and birefringence measurements in single-mode optical fibres

Optical time-domain reflectometry is now a well established means of examining the length-dependence of attenuation in multimode optical fibres. Theoretical work has shown that the technique is similarly applicable to monomode fibres and experimental results have lately appeared in the literature. It has recently been noted that in monomode fibres the scatter return contains additional information concerning the local state of polarisation (SOP) in the fibre, since at any point the scattered light mirrors the SOP at that position. A polarisation optical time-domain reflectometry technique (POTDR) has thus been proposed, in which the backscattered light is analysed by means of a polariser to reveal the variation of polarisation along a mononode fibre. Such a technique would be invaluable in the study of the properties of polarisation-maintaining fibres for sensor applications (e.g. gyroscopes, hydrophones) and of low-birefringence fibres for the Faraday Current Monitor and telecommunications. In the latter case, information could be obtained relating to the polarisation dispersion in the fibre and to the variation of the SOP with time, an effect which is expected to produce problems when interfacing to integrated-optics devices. We present here the first measurement to be made using POTDR. Our results clearly establish the feasibility of the technique and, furthermore, show that polarisation effects can cause substantial errors in conventional backscatter attenuation measurements on monomode fibres. Consequently, care must be taken to eliminate the polarisation sensitivity of the measurement and caution exercised in the interpretation of backscatter curves

Polarisation measurements on monomode fibres using optical time-domain reflectometry

The feasibility of polarisation optical time-domain reflectometry in single-mode fibres is demonstrated. Polarisation analysis of the backscattered light clearly shows the evolution of the state of polarisation in the fibre. It is further shown that the polarised nature of the scatter return from single-mode fibres can cause errors in conventional backscatter measurements

Reconstructing glacier-based climates of LGM Europe and Russia - Part 3: Comparison with previous climate reconstructions

Understanding past climates using GCM models is critical to confidently predicting future climate change. Although previous analysis of GCM simulations have shown them to under calculate European glacial temperature anomalies (the difference between modern and glacial temperatures) such analyses have focused primarily on results from glacial simulations alone. Here we compare glacial maximum GCM results with the palaeoenvironment derived from glacier-climate modelling. The comparison confirms that GCM anomalies are not large enough, and that this is due to modern conditions that are modelled too cold and glacial temperatures that are too warm. The result is that GCM results, if applied to a glacier mass balance model, over predict the extent of glaciers today, and under calculate their extent at the last glacial (as depicted in glacial geological reconstructions). Effects such as seasonality and model parameterisation change the magnitude of the under calculation but still fail to match expected glacial conditions