957 research outputs found
Semiconductor filled microstructured optical fibres with single mode guidance
Microstructured optical fibre (MOF) technology has generated new opportunities for the implementation of optical fibres with novel properties and functions [1]. It has been shown that silica MOFs make excellent 3D templates for semiconductor material deposition inside the capillary voids [2]. Recently a silicon MOF was designed and fabricated that had a high refractive index micron sized core, but yet only supported two guided modes [3]. This structure was realised via the complete filling of a hollow core photonic bandgap fibre (PBGF) with silicon so that the original air guiding PBGF was converted to a total internal reflection guiding fibre. Here, we extend the investigation by using a finite element method to model the optical properties of semiconductor filled MOFs of similar structures, with the aim to achieve broadband single mode guidance. Strategies to achieve single mode guidance both through the MOF template design and the selective filling of the voids of the original PBGF with semiconductor materials of different indices (silicon, silicon nitride, germanium) are proposed and investigated numerically. In particular, by selectively filling MOF templates with cladding rods that have a slightly raised index over that of the core, index guiding single mode operation can be observed in high index micron sized cores. Small index differences are achievable by controlling the nitrogen content in SiNx and an example of a single mode semiconductor MOF is shown in Figure 1, where the confinement loss of the fundamental mode is ~106 lower than the lowest order cladding mode
Fast and broadband fiber dispersion measurement with dense wavelength sampling
We report on a method to obtain dispersion measurements from spectral-domain low-coherence interferograms which enables high accuracy (~ps/(nm·km)), broadband measurements and the determination of very dense (up to 20 points/nm over 500 nm) data sets for both dispersion and dispersion slope. The method exploits a novel phase extraction algorithm which allows the phase associated with each sampling point of the interferogram to be calculated and provides for very accurate results as well as a fast measurement capability, enabling close to real time measurements. The important issue of mitigating the measurement errors due to any residual dispersion of optical elements and to environmental fluctuations was also addressed. We performed systematic measurements on standard fibers which illustrate the accuracy and precision of the technique, and we demonstrated its general applicability to challenging problems by measuring a carefully selected set of microstructured fibers: a lead silicate W-type fiber with a flat, near-zero dispersion profile; a hollow core photonic bandgap fiber with strongly wavelength dependent dispersion and dispersion slope; a small core, highly birefringent index guiding microstructured fiber, for which polarization resolved measurements over an exceptionally wide (~1000 nm) wavelength interval were obtained
Rotating Solution of Einstein-Maxwell Dilaton Gravity with Unusual Asymptotics
We study electrically charged, dilaton black holes, which possess
infinitesimal angular momentum in the presence of one or two Liouville type
potentials. These solutions are neither asymptotically flat nor (anti)-de
Sitter. Some properties of the solutions are discussed.Comment: 11 pages, Accepted (Int. J. Theor. Phys.
The use of out-of-plane high Z patient shielding for fetal dose reduction in computed tomography: Literature review and comparison with Monte-Carlo calculations of an alternative optimisation technique.
When performing CT examinations on pregnant patients, great effort should be dedicated towards optimising the exposure of the mother and the conceptus. For this purpose, many radiology departments use high-Z garments to be wrapped around the patient's lower abdomen for out-of-plane organ shielding to protect the fetus. To assess their current protection efficiency, we performed a literature review and compared the efficiencies mentioned in the literature to Monte-Carlo calculations of CT protocols for which the overall scan length was reduced. We found 11 relevant articles, all of them reporting uterus exposure due to CT imaging performed for exclusion of pulmonary embolism, one of the leading causes of peripartum deaths in western countries. Uterus doses ranged between 60 and 660âŻÂ”Gy per examination, and relative dose reductions to the uterus due to high-Z garments were between 20 and 56%. Calculations showed that reducing the scan length by one to three centimetres could potentially reduce uterus dose up to 24% for chest imaging, and even 47% for upper abdominal imaging. These dose reductions were in the order of those achieved by high-Z garments. However, using the latter may negatively influence the diagnostic image quality and even interfere with the automatic exposure control system thus increasing patient dose if positioned in the primary beam, for example in the overranging length in helical acquisition. We conclude that efforts should be concentrated on positioning the patient correctly in the gantry and optimising protocol parameters, rather than using high-Z garments for out-of-plane uterus shielding
Quality requirements for cross-border care in Europe: a qualitative study of patientsâ, professionalsâ and healthcare financiersâ views
In the past decade the issue of patient mobility has emerged on the European health policy agenda. Although the volume of patients crossing borders to obtain healthcare is low, it is increasing continuously and, due to its legal, financial and medical implications, has generated considerable interest among health policy and other decision makers. However, there is little information available on the safety and patient-centredness of cross-border care and neither governments nor citizens have an explicit basis for comparing healthcare delivery in Europe. This study investigated the viewpoints of patients, professionals and healthcare financiers on the safety and patient-centredness of cross-border care. Qualitative interviews were carried out during 2005 and early 2006 with 40 patients, 30 professionals (doctors, nurses and managers) and 3 healthcare-financing bodies. Although cross-border care has become a common issue in many European countries, there remain uncertainties on the side of each of the parties addressed-patients, professionals and financiers-with regard to the provision of cross-border care. One of the most striking results of this project is the current lack of research on systematic knowledge on the quality of cross-border care. Many of the issues identified through this research may have a potential impact on the quality and safety of cross-border care and will support further investigation and help shape the health policy agenda on patients crossing borders in European Union countries
Advances and limitations in the modelling of fabricated photonic bandgap fibers
Copyright © 2006 IEEEWe model fabricated silica photonic bandgap fibers and achieve good agreement between simulated and measured properties. We identify the size of the SEM bitmap image as the ultimate limit to the accurate calculation of surfaces modes within the bandgapF. Poletti, M. N. Petrovich, R. Amezcua-Correa, N. G. Broderick, T. M. Monro and D. J. Richardsonhttp://eprints.soton.ac.uk/47883
Brillouin suppression through longitudinal structural variation in high nonlinearity silica holey fibers
Copyright © 2006 IEEEWe consider longitudinal variation in the fiber structure as a method of increasing the Brillouin linewidth and threshold within high nonlinearity silica holey fibers. Strategies to control the associated variation in nonlinearity and dispersion along the fiber length are described.http://www.ofcnfoec.org/materials/06AbstractsWednesday.pd
New hairy black hole solutions with a dilaton potential
We consider black hole solutions with a dilaton field possessing a nontrivial
potential approaching a constant negative value at infinity. The asymptotic
behaviour of the dilaton field is assumed to be slower than that of a localized
distribution of matter. A nonabelian SU(2) gauge field is also included in the
total action. The mass of the solutions admitting a power series expansion in
at infinity and preserving the asymptotic anti-de Sitter geometry is
computed by using a counterterm subtraction method. Numerical arguments are
presented for the existence of hairy black hole solutions for a dilaton
potential of the form , special attention being paid to the case of
gauged supergravity model of Gates and Zwiebach.Comment: 12 pages, 4 figures; v2:references added, typos corrected, small
changes in Section
Devices and Fibers for Ultrawideband Optical Communications
Wavelength-division multiplexing (WDM) has
historically enabled the increase in the capacity of optical
systems by progressively populating the existing optical bandwidth
of erbium-doped fiber amplifiers (EDFAs) in the C-band.
Nowadays, the number of channelsâneeded in optical
systemsâis approaching the maximum capacity of standard
C-band EDFAs. As a result, the industry worked on novel
approaches, such as the use of multicore fibers, the extension
of the available spectrum of the C-band EDFAs, and the
development of transmission systems covering C- and L-bands
and beyond. In the context of continuous traffic growth,
ultrawideband (UWB) WDM transmission systems appear
as a promising technology to leverage the bandwidth of
already deployed optical fiber infrastructure and sustain the
traffic demand for the years to come. Since the pioneering
demonstrations of UWB transmission a few years ago, long
strides have been taken toward UWB technologies. In this
review article, we discuss how the most recent advances in
the design and fabrication of enabling devices, such as lasers,
amplifiers, optical switches, and modulators, have improved
the performance of UWB systems, paving the way to turn
research demonstrations into future products. In addition,
we also report on the advances in UWB optical fibers, such as
the recently introduced nested antiresonant nodeless fibers
(NANFs), whose future implementations could potentially provide
up to 300-nm-wide bandwidth at less than 0.2 dB/km loss
A retrospective study on acute health effects due to volcanic ash exposure during the eruption of Mount Etna (Sicily) in 2002
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