Bragg grating design method for the implementation of an optimised symmetric add/drop multiplexer

An efficient and simple method is proposed for the design of a novel Bragg grating based optical add/drop multiplexer. Central to this method is the existence of generic engineering curves that relate for any BG of a specific apodization profile, its penetration slope α = Lp/Lg to its reflectivity. The implemented by this method, interferometric device based on a full-cycle waveguide coupler exhibits symmetric and simultaneously optimised add/drop responses, of zero loss

Terahertz bandwidth photonic Hilbert transformers and implementations in ultra wideband single-sideband filters

Planar Bragg grating based photonic Hilbert transformers (PHTs) with THz bandwidths are proposed and practically demonstrated. An X-coupler, PHT, and a flat-top reflector are incorporated, demonstrating 2THz all-optical single-sideband filters. Devices are fabricated via a direct UV grating writing technique on a silica-on-silicon platform

Ultra-wide detuning planar Bragg grating fabrication technique based on direct UV grating writing with electro-optic phase modulation

A direct UV grating writing technique based on phase-controlled interferometry is proposed and demonstrated in a silica-on-silicon platform, with a wider wavelength detuning range than any previously reported UV writing technology. Electro-optic phase modulation of one beam in the interferometer is used to manipulate the fringe pattern and thus control the parameters of the Bragg gratings and waveguides. Various grating structures with refractive index apodization, phase shifts and index contrasts of up to 0.8×10-3 have been demonstrated. The method offers significant time/energy efficiency as well as simplified optical layout and fabrication process. We have shown Bragg gratings can be made from 1200 nm to 1900 nm exclusively under software control and the maximum peak grating reflectivity only decreases by 3dB over a 250 nm (~32THz) bandwidth

Simple planar Bragg grating devices for photonic Hilbert transform

Hilbert transformers are important devices widely used in information processing and signal analysis in the electronic domain. For example, for spectral efficiency improvement, it is used to construct the analytic signal for single sideband (SSB) modulation from a real signal. Photonic Hilbert transformers (PHTs) are proposed for a similar range of applications and would allow the direct processing of optical signals at bandwidths far beyond current electronic technologies

Adaptive epidemic dissemination as a finite-horizon optimal stopping problem

Wireless ad hoc networks are characterized by their limited capabilities and their routine deployment in unfavorable environments. This creates the strong requirement to regulate energy expenditure. We present a scheme to regulate energy cost through optimized transmission scheduling in a noisy epidemic dissemination environment. Building on the intrinsically cross-layer nature of the adaptive epidemic dissemination process, we strive to deliver an optimized mechanism, where energy cost is regulated without compromising the network infection. Improvement of data freshness and applicability in routing are also investigated. Extensive simulations are used to support our proposal

Assessing the Ecological Water Level: The Case of Four Mediterranean Lakes

Petriki, O., D. Zervas, Ch. Doulgeris, D. Bobori. 2020. Assessing the Ecological Water Level: The Case of Four Mediterranean Lakes. Water: 12, 2977. doi:10.3390/w12112977The ecological water regime in lake water bodies refers to the water levels that enable the fulfillment of the ecosystem’s multiple functions. Therefore, assessing the ecological water regime necessitates the consideration of hydrological, economic, social, and ecological factors. The present research is focused on the assessment of the ecological water level of four Mediterranean natural lake ecosystems, considering their morphological and biological features. Initially, suggestions on the ecological water regime of the studied lakes were made based on an analysis of the lakes’ morphometry. Further, the ecological and biological requirements of the present fish fauna and aquatic macrophytic vegetation were considered. For the latter, mapping was conducted by extensive sampling according to international standards, in order to assess macrophyte composition, abundance, and chorology, as well as species sensitivity to water level fluctuations. The above guided the proposals on the optimal water level regime that should be met by each lake regarding the macrophytic and fish communities’ sustainability, also taking into account the unique hydromorphological features of each lake. The di erences in the outcoming results revealed that hydromorphological and biological approaches should be combined for assessing lakes’ ecological water regime

Phase modulation technique for high modulation wide band planar Bragg grating fabrication

Direct UV Grating Writing (DGW) is effective route for fabricating high quality Bragg gratings, similar to fiber Bragg gratings, in a planar geometry. We will present a phase modulation controlled DGW method using an Electro-Optical Modulator for planar Bragg grating fabrication that offers improved performance. This new approach not only provides much greater modulation depths for stronger and shorter Bragg gratings but also offers greater fabrication speed and a higher fidelity of control than previous amplitude modulation methods

Limited Depressive and Anxiety Symptoms Late in Pregnancy Are Not Related to Neonatal Outcomes

Background: Prior studies have reported inconsistent findings regarding the link between antenatal depressive and anxiety symptomatology, with neonatal outcomes. Objectives: The aim of the present study was to assess the possible association of prenatal depressive and anxiety symptoms, in the third trimester of pregnancy, with perinatal outcomes (birth weight of the newborn, Apgar score and the newborn’s admission in neonatal intensive care unit) in a sample of pregnant women, in Greece. Patients and Methods: A total of 117 women from Athens, during the 32nd to 35th week of pregnancy, participated in the study. Demographic and obstetric history data, as well as neonatal outcomes, were recorded. Three self-administered psychometric scales (Beck depression inventory (BDI), Edinburg postnatal depression scale (EPDS) and beck anxiety inventory (BAI)) were used to evaluate in detail the prenatal depressive and anxiety symptoms. Descriptive statistics, Spearman’s Rho coefficients, Mann-Whitney U and Kruskal-Wallis testes were applied to analyze the data. Results: On the basis of BDI, 81.1% of the sample showed minimal, 15.4% mild, 2.6% moderate and 0.9% severe depressive symptoms, respectively. Furthermore, 80.3% of the participants, scored on EPDS below the cut-off point for a likely diagnosis of depression. According to BAI scale, 43.6% showed minimal, 42.7% women mild, 10.3% moderate and 3.4% severe anxiety symptoms. No statistically significant correlations were found between depressive and anxiety symptoms and neonatal outcomes (birth weight, Apgar score and admission in neonatal intensive care unit). Conclusions: Limited levels of prenatal depressive and anxiety symptoms do not seem to be associated with neonatal outcomes. In clinical practice, pregnant women, who suffer from low levels of prenatal depressive and anxiety symptoms, may be reassured, in respect of the adverse outcomes of these mood symptoms on the neonate

AI-optimised tuneable sources for bandwidth-scalable, sub-nanosecond wavelength switching

Wavelength routed optical switching promises low power and latency networking for data centres, but requires a wideband wavelength tuneable source (WTS) capable of sub-nanosecond switching at every node. We propose a hybrid WTS that uses time-interleaved tuneable lasers, each gated by a semiconductor optical amplifier, where the performance of each device is optimised using artificial intelligence. Through simulation and experiment we demonstrate record wavelength switch times below 900 ps across 6.05 THz (122×50 GHz) of continuously tuneable optical bandwidth. A method for further bandwidth scaling is evaluated and compared to alternative designs

Loyalty Programs in the Sharing Economy: Optimality and Competition

Loyalty programs are important tools for sharing platforms seeking to grow supply. Online sharing platforms use loyalty programs to heavily subsidize resource providers, encouraging participation and boosting supply. As the sharing economy has evolved and competition has increased, the design of loyalty programs has begun to play a crucial role in the pursuit of maximal revenue. In this paper, we first characterize the optimal loyalty program for a platform with homogeneous users. We then show that optimal revenue in a heterogeneous market can be achieved by a class of multi-threshold loyalty program (MTLP) which admits a simple implementation-friendly structure. We also study the performance of loyalty programs in a setting with two competing sharing platforms, showing that the degree of heterogeneity is a crucial factor for both loyalty programs and pricing strategies. Our results show that sophisticated loyalty programs that reward suppliers via stepwise linear functions outperform simple sign-up bonuses, which give them a one time reward for participating