Three-core weakly-guiding mode-selective fibre couplers

The coupling behaviour of two-core mode-selective couplers (MSC) depends on the spatial-orientation of the asymmetric higher-order modes. This restricts their use for mode de-multiplexing in few-mode fibre networks. The use of three-core MSC's is presented as a solution

Wavelength-independent mode-selective couplers for few-mode fibre networks

A novel type of tapered fibre coupler is proposed and simulated that enables wavelength-independent directional coupling between a higher-order mode and a fundamental mode for application to few-mode optical fibre networks

Digitally range-gated optical frequency domain reflectometry

We present a new optical frequency domain reflectometry technique which permits high frequency sweep repetition rates without sacrificing range. This technique could thus be adapted for remote and distributed acoustic sensing over long lengths of fibre

Predicting the whispering gallery mode spectra of microresonators

The whispering gallery modes (WGMs) of optical resonators have prompted intensive research efforts due to their usefulness in the field of biological sensing, and their employment in nonlinear optics. While much information is available in the literature on numerical modeling of WGMs in microspheres, it remains a challenging task to be able to predict the emitted spectra of spherical microresonators. Here, we establish a customizable Finite- Difference Time-Domain (FDTD)-based approach to investigate the WGM spectrum of microspheres. The simulations are carried out in the vicinity of a dipole source rather than a typical plane-wave beam excitation, thus providing an effective analogue of the fluorescent dye or nanoparticle coatings used in experiment. The analysis of a single dipole source at different positions on the surface or inside a microsphere, serves to assess the relative efficiency of nearby radiating TE and TM modes, characterizing the profile of the spectrum. By varying the number, positions and alignments of the dipole sources, different excitation scenarios can be compared to analytic models, and to experimental results. The energy flux is collected via a nearby disk-shaped region. The resultant spectral profile shows a dependence on the configuration of the dipole sources. The power outcoupling can then be optimized for specific modes and wavelength regions. The development of such a computational tool can aid the preparation of optical sensors prior to fabrication, by preselecting desired the optical properties of the resonator.Comment: Approved version for SPIE Photonics West, LASE, Laser Resonators, Microresonators and Beam Control XV

Method for predicting whispering gallery mode spectra of spherical microresonators

A full three-dimensional Finite-Difference Time-Domain (FDTD)-based toolkit is developed to simulate the whispering gallery modes of a microsphere in the vicinity of a dipole source. This provides a guide for experiments that rely on efficient coupling to the modes of microspheres. The resultant spectra are compared to those of analytic models used in the field. In contrast to the analytic models, the FDTD method is able to collect flux from a variety of possible collection regions, such as a disk-shaped region. The customizability of the technique allows one to consider a variety of mode excitation scenarios, which are particularly useful for investigating novel properties of optical resonators, and are valuable in assessing the viability of a resonator for biosensing.Comment: Published 10 Apr 2015 in Opt. Express Vol. 23, Issue 8, pp. 9924-9937; The FDTD toolkit supercomputer scripts are hosted at: http://sourceforge.net/projects/npps/files/FDTD_WGM_Simulator

Association between conventional risk factors and different ultrasound-based markers of atherosclerosis at carotid and femoral levels in a middle-aged population

Ultrasound detection of sub-clinical atherosclerosis (ATS) may help identify individuals at high cardiovascular risk. Most studies evaluated intima-media thickness (IMT) at carotid level. We compared the relationships between main cardiovascular risk factors (CVRF) and five indicators of ATS (IMT, mean and maximal plaque thickness, mean and maximal plaque area) at both carotid and femoral levels. Ultrasound was performed on 496 participants aged 45-64years randomly selected from the general population of the Republic of Seychelles. 73.4% participants had ≥1 plaque (IMT thickening ≥1.2mm) at carotid level and 67.5% at femoral level. Variance (adjusted R2) contributed by age, sex and CVRF (smoking, LDL-cholesterol, HDL-cholesterol, blood pressure, diabetes) in predicting any of the ATS markers was larger at femoral than carotid level. At both carotid and femoral levels, the association between CVRF and ATS was stronger based on plaque-based markers than IMT. Our findings show that the associations between CVRF and ATS markers were stronger at femoral than carotid level, and with plaque-based markers rather than IMT. Pending comparison of these markers using harder cardiovascular endpoints, our findings suggest that markers based on plaque morphology assessed at femoral artery level might be useful cardiovascular risk predictor

Control algorithm for a residential photovoltaic system with storage

High penetration of photovoltaic (PV) electricity could affect the stability of the low-voltage grid due to over-voltage and transformer overloading at times of peak production. Residential battery storage can smooth out those peaks and hence contribute to grid stability. A feed-in limit allows for the easy setting of a maximum power injection cap and motivates PV owners to increase their self-consumption. A simple control strategy for a residential battery system coupled with a PV system that maximizes selfconsumption and minimizes curtailment losses due to a feed-in limit is presented. The algorithm used in this strategy does not require a forecast of insulation conditions. The performance of this algorithm is compared to a second algorithm—a control strategy based on linear optimization using a forecast. Assuming an exact forecast, this second algorithm is very close to the maximum self-consumption and minimum curtailment losses achievable and can be used to benchmark the simple strategy. The results show that the simple strategy performs as well as the second algorithm with exact forecasts and performs significantly better than the second algorithm using real forecasts. Moreover, it is shown that this result is valid for a large range of storage capacities and PV sizes. Furthermore, it is shown that with a time resolution of 15 min for the input data (the resolution of most PV production and load data) selfconsumption is overestimated by about 3% and curtailment losses are underestimated by the same amount. Load sensitivity simulations show that different load curve shapes do not fundamentally change the results. Finally, to assess the effect of load aggregation, the case where the strategy is applied separately to 44 households with storage is compared to the case where it is applied to a centralized storage system of the same size as the total storage of the 44 households. The reduction of the curtailment losses with the number of aggregated houses is showed

Effect of the Fluctuations of PV Production and Electricity Demand on the PV Electricity Self-Consumption

The electricity self-consumption level of a family household is determined both experimentally and by modelling. The effect of rapid fluctuation in PV production and electricity demand, and especially the effect of the temporal resolution of their measurements, are studied. For accurate determination of the self-consumption level, temporal resolution of at least 30 s for the load profile and at least 10 min for the PV production measurements are suggested. The effect of temporal resolution becomes negligible when a local electricity storage system is added. Keywords: Small Grid-connected PV Systems, storage, gird integratio

Microalbuminuria, but not cystatin C, is associated with carotid atherosclerosis in middle-aged adults

Background. Cystatin C, a marker of renal function, has been shown to be an independent predictor of cardiovascular disease (CVD) in older adults, but few data are available in middle-aged adults. Moreover, no study has compared cystatin C and microalbuminuria as risk factors for CVD outcomes in middle-aged adults, and it is not known whether cystatin C is related to an early stage of atherosclerosis. Methods. We evaluated the relationships between serum creatinine, estimated glomerular filtration rate (GFR), serum cystatin C (all divided into tertiles), microalbuminuria and carotid atherosclerosis in a population-based random sample of 523 adults aged 35-64 years from the Seychelles (Indian Ocean). GFR was estimated using the modification of diet in renal disease (MDRD) equation. Intima-media thickness (IMT) was assessed by B-mode ultrasound. Results. The mean age of the study sample was 52 years, and 55% were women. Carotid IMT was higher in participants with microalbuminuria (802 vs 732 μm, P < 0.001) and was inversely associated with GFR tertiles (from 728 to 809 μm, P for trend = 0.002). IMT was not associated with cystatin C or creatinine (P for trend = 0.10 and 0.16, respectively). In multivariate analyses adjusted for cardiovascular risk factors, the association between microalbuminuria and IMT remained (P = 0.047), while the association between GFR and IMT disappeared (P for trend = 0.33). Conclusions. Microalbuminuria, but not cystatin C, is associated with carotid atherosclerosis beyond traditional cardiovascular risk factors among middle-aged adults. Cystatin C does not have a stronger relationship with carotid atherosclerosis in middle-aged adults than creatinin

Holey fibre mode-selective couplers

Mode-selective coupling in an asymmetric holey fibre coupler is demonstrated both numerically and experimentally for the first time. The coupler's performance is shown to be ultrabroadband, with significant potential existing for the use of such couplers in high bandwidth few-mode fibre networks