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Wavelength Division Multiplexing, WDM, is a technology developed for applications in telecommunications with the purpose of combining numerous wavelength signals into one single fibre. The aim of this research is the characterization of WDM systems of ring resonators with planar optical waveguides. The optical responses for different configurations, dimensions, and materials are analysed by doing a parametric study both considering analytical expressions and a Finite Element Tool. The results are from add-drop topologies with one, two and three rings. The main difference between topologies with the same parameters is the number of resonance wavelengths, which is higher due to the increase in the number of ring-shaped waveguides. It is concluded that adjusting the rings’ dimensions, the resonant wavelengths are tuned. Furthermore, the higher the rings’ radius the lower is the free spectral range, that can take values from 40 nm to 90 nm. Then, the number of resonant peaks in a wavelength range may change. Also, 1500–5000 describes the values computed for the quality factor, whereas the full width at half maximum varies within some units of nanometres. For models with different core materials, the higher transmittances decrease with lower core refractive indexes and the resonance width increases. These are new degrees of freedom to tune the response of the device that can definitely work as optical wavelength multiplexer, having losses from 20% to 40% considering the transmitted optical power.

New phenomena have been discovered at the nanoscale that allow us to manipulate light and design devices. Evanescent waves such as Surface Plasmon Polaritons are excited in dielectric–metal interfaces and propagate in the metal. If they reach other interfaces, they may be transmitted by the metal. It is a phenomenon known as Extraordinary Optical Transmission that occurs in nanostructures at the optical range. Depending on the metal it is possible to tune the wavelengths and incident angles where this phenomenon occurs. Gold, silver, aluminium and copper nanolayers are analysed on top of silicon (a-Si and c-Si) considering a sweep between 250 nm and 2500 nm. Considering a novel model based on Fresnel Coefficients in absorbing media, it is possible to improve energy harvesting in the ultraviolet–visible range, mainly due to the propagation of Surface Plasmon Polaritons. Then, the role of Surface Plasmon Polaritons in Air–Metal–Silicon nanostructures is analysed. The inclusion of the metal layer may decrease the reflectance by at least 10%, reaching values higher than 60%. The presented charts allow us to analyse the materials, wavelengths and incident angles where reflectance is decreased. There, the inclusion of metal layers brings benefits to the photodetection, since more energy is available in the absorbing layer. Considering this approach, the detection of specific wavelengths may be improved by introducing metals in the detectors.

In this article, a plasmonic gold nanoantenna is proposed as a sensor to monitor refractive index variations between 1.30 and 1.35. These values are defined since they are characteristic of, for instance, water-based solutions, DNA, or haemoglobin. To simulate the device a novel model is used, which takes advantage of the wave-particle dualism and the generalised Fresnel coefficients for absorbing media. Although it is a time-domain model, in this research work the model is improved to compute steady state and frequency-domain results. The response to a Dirac excitation is obtained using that novel model. The steady state is reached for a long pulse emission. The long pulse emission is emulated by a Dirac comb and consequently, the optical response of the device for this kind of excitation is obtained considering the sum of several Dirac's responses shifted in time. Then, steady state might be reached as suggested by the presented results. Taking into account the obtained pulse responses, the refractive index sensor for the range 1.30–1.35 is proposed. The obtained results suggest that 350 nm and 450 nm are the best wavelengths to detect these analyte variations. The sensitivity reaches values up to around 110%/RIU, but sensitivities around 80%/RIU are computed within the range 250–500 nm.

Rodrigo Vilares-Morgado,1,2 Vera Correia,3 Ana Margarida Ferreira,1 Flávio Alves,1 António Benevides Melo,1,3 Sérgio Estrela-Silva,1,3 Joana Araújo,1,3 João Tavares-Ferreira,1,3 Marta Silva,1 Amândio Rocha-Sousa,1,2 Angela Carneiro,1,2 João Barbosa-Breda1,2,4 1Department of Ophthalmology, Centro Hospitalar e Universitário de São João, Porto, Portugal; 2UnIC@RISE, Department of Surgery and Physiology, Faculty of Medicine of the University of Porto, Porto, Portugal; 3Faculty of Medicine, University of Porto, Porto, Portugal; 4KULeuven, Research Group Ophthalmology, Department of Neurosciences, Leuven, BelgiumCorrespondence: Rodrigo Vilares-Morgado, Department of Ophthalmology, Centro Hospitalar e Universitário de São João, Alameda Professor Hernâni Monteiro, 4202 – 451, Porto, Portugal, Tel +351 914 471 067, Fax +351 225 512 100, Email vilaresmorgador@gmail.comPurpose: To evaluate whether repeated intravitreal injections (IVI) with an anti-vascular endothelial growth factor (anti-VEGF) agent are associated with glaucomatous progression in eyes with glaucoma spectrum diseases (GSD).Methods: Single-center, retrospective, longitudinal study of patients with bilateral and similar GSD who: (1) received ≥ 8 IVI in only one eye during the study period; (2) had ≥ 2 retinal nerve fiber layer thickness (RNFL) measurements obtained by spectral-domain optical coherence tomography (SD-OCT) at least 12 months apart. The primary outcome was the absolute RNFL thickness change, comparing injected and fellow uninjected eyes. Linear mixed effects models were constructed, including a multivariable model.Results: Sixty-eight eyes from 34 patients were included, 34 injected and 34 fellow uninjected eyes. Average baseline age was 67.68± 21.77 years with a follow-up of 3.66± 1.89 years and 25.12± 14.49 IVI. RNFL thickness decreased significantly from 80.92± 15.78 to 77.20± 17.35 μm (p< 0.001; − 1.18± 1.93 μm/year) in injected eyes and from 79.95± 17.91 to 76.61± 17.97 μm (p< 0.001; − 1.07± 0.98 μm/year) in uninjected eyes. In a multivariable linear mixed model of injected eyes, only higher baseline RNFL thickness (p < 0.001) significantly predicted higher absolute RNFL thickness loss. Neither absolute RNFL thickness variation (p=0.716) nor RNFL rate (p=0.779) was significantly different between paired injected and uninjected eyes. Absolute IOP variation was not significantly different between groups (16.62± 4.77 to 15.09± 4.34 mmHg in injected eyes and 17.68± 5.01 to 14.50± 3.39 mmHg in fellow uninjected eyes; p=0.248). The proportion of eyes receiving glaucoma medical treatment increased significantly in both groups (55.9% to 76.5% in injected eyes; p=0.039; 58.8% to 76.5% in uninjected eyes; p = 0.031). The number of glaucoma medications also increased significantly in both groups (1.03± 1.11 to 1.59± 1.18 glaucoma medications in injected eyes; p=0.003; 1.09± 1.11 to 1.56± 1.19 glaucoma medications in uninjected eyes; p=0.003).Conclusion: Repeated IVI do not seem to accelerate glaucomatous progression. Future studies with a longer follow-up are needed.Keywords: glaucoma, intravitreal injections, progression, optical coherence tomography, retinal nerve fiber layer thickness

Abstract Renewable energies are increasingly playing an important role in the world’s energy supply. Society demands new solutions to solve environmental issues caused by fossil fuels. The importance of photovoltaic technology has been increasing and consequently, the necessity to have more accurate models to characterise the performance of solar cells during their entire lifetime has rose as well. Performance problems may appear during devices’ lifetimes associated with factors, such as weather conditions or faulty installation. Cracking might occur, leading to abrupt reductions on the produced power, quite difficult and expensive to fix. The I–V curves of a defected or cracked solar cell might not have the shape imposed by the usual models as 1M5P. In this article, cracked c-Si solar cells are modelled using a novel model: d1MxP. This model is based on the discretisation of the diode’s response on models as 1M5P. Instead of imposing a shape and compute some parameters to fit it on experimental data, the proposed model connects every two points. The results suggest a better fit using the proposed model in comparison with the 1M5P, not only in the original curves, but also modelling cracked cells. As consequence of a better fitting, the computation of important figures of merit as maximum power point or fill factor, reveals to be more precise. It is concluded that the proposed model might characterise the performance of a solar cell, even cracked, which is a huge advance aiming the possibility of simulating complex problems during the cells’ operation lifetime.

Nowadays, optical systems play an important role in communications. Dual depletion PIN photodiodes are common devices that can operate in different optical bands, depending on the chosen semiconductors. However, since semiconductor properties vary with the surrounding conditions, some optical devices/systems can act as sensors. In this research work, a numerical model is implemented to analyze the frequency response of this kind of structure. It considers both transit time and capacitive effects, and can be applied to compute photodiode frequency response under nonuniform illumination. The InP-In0.53Ga0.47As photodiode is usually used to convert optical into electrical power at wavelengths around 1300 nm (O-band). This model is implemented considering an input frequency variation of up to 100 GHz. The focus of this research work was essentially the determination of the device’s bandwidth from the computed spectra. This was performed at three different temperatures: 275 K, 300 K, and 325 K. The aim of this research work was to analyze if a InP-In0.53Ga0.47As photodiode can act as a temperature sensor, to detect temperature variations. Furthermore, the device dimensions were optimized, to obtain a temperature sensor. The optimized device, for a 6 V applied voltage and an active area of 500 μm2, had a total length of 2.536 μm, in which 53.95% corresponded to the absorption region. In these conditions, if the temperature increases 25 K from the room temperature, one should expect a bandwidth increase of 8.374 GHz, and if it decreases 25 K from that reference, the bandwidth should reduce by 3.620 GHz. This temperature sensor could be incorporated in common InP photonic integrated circuits, which are commonly used in telecommunications.

Solar cell equivalent circuit modelling is usually based on continuous I-V models, with a set of data obtained by analytical expressions. This work proposes an almost discrete novel mathematical method and correspondent electrical model, based on the I-V curve adjustment at every two adjacent points. It is based on the discretisation of any diode model behaviour, such as the 1M5P (also known as 1D5P) or the 1M7P (also known as 2D7P). For this reason, the model is named d1MxP, meaning that it is a discrete (d) model (1M) with x parameters (xP). The modelling methodology validation process uses experimental data already published in the literature. According to the presented results, the proposed method shows increased accuracy when compared to the 1M5P or 1M7P equivalent models. The accuracy on the maximum power point and fill factor determination is relevant, resulting in an improvement of up to 3.34% in the maximum power, up to 5.70% in its voltage and up to 8.20% in its current, for the analysed data. Furthermore, Fill Factor values, have variation from up to 35.98%. The temperature influence on the silicon solar cell is also analysed, to validate the results. The proposed method allows highly accurate curve fitting to the (experimental) points and consequently, to obtain a more accurate model to analyse the performance of solar cells under different conditions.

Renewable energy sources are becoming more and more essential to energy production as societies evolve toward a fossil-fuel-free world. Solar energy is one of the most abundant sources of green energy. Nanoantennas can be used to improve and enhance the absorption of light into a photovoltaic cell in order to generate more current. In this study, different nanoantenna structures are analysed in tandem with a silicon solar cell in an effort to improve its output. The nanoantennas studied are metallic aperture nanoantennas made up of either silver, aluminium, gold or copper. The three geometries compared are rectangular, circular and triangular. The maximum field enhancement obtained is for an aluminium rectangular nanoantenna of 50 nm thickness. Despite this, the geometry with more improvements compared with a basic silicon cell was the circle geometry with a 100 nm radius.

Nowadays, optical systems play an important role in communications. Dual depletion PIN photodiodes are common devices that can operate in different optical bands, depending on the chosen semiconductors. However, since semiconductor properties vary with the surrounding conditions, some optical devices/systems can act as sensors. In this research work, a numerical model is implemented to analyze the frequency response of this kind of structure. It considers both transit time and capacitive effects, and can be applied to compute photodiode frequency response under nonuniform illumination. The InP-In 0.53 Ga 0.47 As photodiode is usually used to convert optical into electrical power at wavelengths around 1300 nm (O-band). This model is implemented considering an input frequency variation of up to 100 GHz. The focus of this research work was essentially the determination of the device's bandwidth from the computed spectra. This was performed at three different temperatures: 275 K, 300 K, and 325 K. The aim of this research work was to analyze if a InP-In 0.53 Ga 0.47 As photodiode can act as a temperature sensor, to detect temperature variations. Furthermore, the device dimensions were optimized, to obtain a temperature sensor. The optimized device, for a 6 V applied voltage and an active area of 500 μ m 2 , had a total length of 2.536 μ m , in which 53.95% corresponded to the absorption region. In these conditions, if the temperature increases 25 K from the room temperature, one should expect a bandwidth increase of 8.374 GHz, and if it decreases 25 K from that reference, the bandwidth should reduce by 3.620 GHz. This temperature sensor could be incorporated in common InP photonic integrated circuits, which are commonly used in telecommunications. [ABSTRACT FROM AUTHOR]

Solar cell equivalent circuit modelling is usually based on continuous I-V models, with a set of data obtained by analytical expressions. This work proposes an almost discrete novel mathematical method and correspondent electrical model, based on the I-V curve adjustment at every two adjacent points. It is based on the discretisation of any diode model behaviour, such as the 1M5P (also known as 1D5P) or the 1M7P (also known as 2D7P). For this reason, the model is named d1MxP, meaning that it is a discrete (d) model (1M) with x parameters (xP). The modelling methodology validation process uses experimental data already published in the literature. According to the presented results, the proposed method shows increased accuracy when compared to the 1M5P or 1M7P equivalent models. The accuracy on the maximum power point and fill factor determination is relevant, resulting in an improvement of up to 3.34% in the maximum power, up to 5.70% in its voltage and up to 8.20% in its current, for the analysed data. Furthermore, Fill Factor values, have variation from up to 35.98%. The temperature influence on the silicon solar cell is also analysed, to validate the results. The proposed method allows highly accurate curve fitting to the (experimental) points and consequently, to obtain a more accurate model to analyse the performance of solar cells under different conditions. [ABSTRACT FROM AUTHOR]

Renewable energy sources are becoming more and more essential to energy production as societies evolve toward a fossil-fuel-free world. Solar energy is one of the most abundant sources of green energy. Nanoantennas can be used to improve and enhance the absorption of light into a photovoltaic cell in order to generate more current. In this study, different nanoantenna structures are analysed in tandem with a silicon solar cell in an effort to improve its output. The nanoantennas studied are metallic aperture nanoantennas made up of either silver, aluminium, gold or copper. The three geometries compared are rectangular, circular and triangular. The maximum field enhancement obtained is for an aluminium rectangular nanoantenna of 50 nm thickness. Despite this, the geometry with more improvements compared with a basic silicon cell was the circle geometry with a 100 nm radius. [ABSTRACT FROM AUTHOR]

Flexible and stretchable materials are increasingly being investigated for future technological platforms, polymer based materials being the most suitable candidates for those emerging technologies. This work reports on polymer based scintillator composites based on the thermoplastic elastomer Styrene-Ethylene/Butadiene-Styrene (SEBS) and Gd 2 O 3 :Eu 3+ scintillator nanoparticles, to form a polymer-based flexible and stretchable material for X-ray indirect detectors. Further, visible light yield under X-ray irradiation was improved by the inclusion of 2,5 dipheniloxazol (PPO) and (1,4-bis (2-(5-phenioxazolil))-benzol (POPOP) within the polymer matrix. Together with high levels of stretchability, with deformations up to 100%, the films exhibit suitable performance with low mechanical hysteresis (less than 1.5 MJ/m 3 for cycles up to 100% of strain) and reproducibly such as a scintillator material for the conversion of X-ray radiation into visible radiation. The decrease of just ∼13% of the X-ray radiation into visible light upon stretching up to 100% is attributed to a reduction of the effective filler concentration and proves the suitability of the developed materials for large area and stretchable X-ray radiation detectors. [ABSTRACT FROM AUTHOR]

Abstract: Despite huge advances in wireless communications in the last few years, underwater wireless communications is still a not fully developed technology, due to the lack of efficiency of radio waves for underwater communication. This problem can be overcome by using acoustic waves instead. In order to implement high-speed acoustic communications, it is imperative to develop transducers with high performance at high frequency. In this paper, a study of both piezoelectric ceramics and polymers used as water-coupled ultrasonic transducers is presented. As the main goal is to analyze their performance for high-speed communications, the behaviour of the piezoelectric ceramic (lead zirconate titanate, PZT) and the piezoelectric polymer (poly(vynilidene fluoride),PVDF) at high frequencies in underwater environment are compared. Results show that PVDF has a better response under the same ideal conditions, mainly with increasing frequency. [ABSTRACT FROM AUTHOR]

Polymer based smart materials and, in particular, piezoresistive ones, are increasingly being used in a wide variety of applications ranging from automotive components to medical devices. This work reports on water-based piezoresistive polymer composites developed from thermoplastic poly (vinyl alcohol) (PVA) filled with carbon nanotubes (MWCNT) for the fabrication of high performance piezoresistive materials and sensors. PVA is a water-soluble synthetic polymer with suitable mechanical properties for the development of large strain sensors. MWCNT/PVA nanocomposites with good linearity between deformation and electrical resistance variation and with gauge factors up to 3 were achieved. Further, the materials were formulated in the form of inks for spray and screen printing of the sensors, which demonstrated a good performance for strain sensing both under laboratory tests conditions and when connected to a readout and communication system. Therefore, polymer based piezoresistive sensors were developed by a green approach and capable to be implemented by scalable printing technologies. [ABSTRACT FROM AUTHOR]