Field-Induced Nonlinearities in Silicon Waveguides Embedded in Lateral p-n Junctions

Silicon waveguides embedded in lateral p-n junctions show field-induced optical nonlinearities. By properly polarizing the junction, these can be used to achieve electro-optic modulation through the Direct Current Kerr effect. In addition, these enable second-order nonlinear processes such as the electric-field-induced second harmonic generation (EFISHG). In this work, we study in detail electro-optic effects in integrated silicon microresonators and demonstrate experimentally a field-induced resonance wavelength shift. This process is due to both the DC Kerr effect and the plasma-dispersion effect. By means of finite element method simulations, these effects are properly modeled and their contributions are accurately disentangled. The strength of the equivalent second-order nonlinear coefficient that would have provided the same electro-optic effect is about 16 pm/V. This result is comparable with that of materials possessing an intrinsic second order nonlinearity, and is one order of magnitude stronger than the most recent measurements of strain-induced Pockels effect in silicon

Patient's adherence on pharmacological therapy for benign prostatic hyperplasia (BPH)-associated lower urinary tract symptoms (LUTS) is different: Is combination therapy better than monotherapy

Abstract BACKGROUND: Recent studies showed that the non-adherence to the pharmacological therapy of patients affected by BPH-associated LUTS increased the risk of clinical progression of BPH. We examined the patients adherence to pharmacological therapy and its clinical consequences in men with BPH-associated LUTS looking at the differences between drug classes comparing mono vs combination therapy. METHODS: A retrospective, population-based cohort study, using prescription administrative database and hospital discharge codes from a total of 1.5 million Italian men. Patients ≥ 40 years, administered alpha-blockers (AB) and 5alpha-reductase inhibitors (5ARIs), alone or in combination (CT), for BPH-associated LUTS were analyzed. The 1-year and long term adherence together with the analyses of hospitalization rates for BPH and BPH-related surgery were examined using multivariable Cox proportional hazards regression model and Pearson chi square test. RESULTS: Patients exposed to at least 6 months of therapy had a 1-year overall adherence of 29 % (monotherapy AB 35 %, monotherapy 5ARI 18 %, CT 9 %). Patient adherence progressively declined to 15 %, 8 % and 3 % for AB, 5ARI, and CT, respectively at the fifth year of follow up. Patients on CT had a higher discontinuation rate along all the follow-up compared to those under monotherapy with ABs or 5ARIs (all p < 0.0001). Moreover, CT was associated with a reduced risk of hospitalization for BPH-related surgery (HR 0.94; p < 0.0001) compared to AB monotherapy. CONCLUSIONS: Adherence to pharmacological therapy of BPH-associated LUTS is low and varies depending on drugs class. Patients under CT have a higher likelihood of discontinuing treatment for a number of reasons that should be better investigated. Our study suggests that new strategies aiming to increase patient's adherence to the prescribed treatment are necessary in order to prevent BPH progression

Second order nonlinearities in silicon photonics

In this thesis, second order optical nonlinearities in silicon waveguides are studied. At the beginning, the strained silicon platform is investigated in detail. In recent years, second order nonlinearities have been demonstrated on this platform. However, the origin of these nonlinearities was not clear. This thesis offers a clear answer to this question, demonstrating that this nonlinearity does not originate on the applied strain, but on the presence of trapped charges that induce a static electric field inside the waveguide. Based on this outcome, a way to induce larger electric fields in silicon waveguide is studied. Using lateral p-n junctions, strong electric fields are introduced in the waveguides, demonstrating both electro-optic effects and second-harmonic generation. These results, together with a detailed modeling of the system, pave the way through the demonstration of spontaneous parametric down-conversion in silicon

Automatic Initialization Methods for Photonic Components on a Silicon-Based Optical Switch

In this work we showed the optimization of the spectral response of several optical elements in a silicon-based optical switch. Integrated thermal resistors induced a local heating of the components. The temperature increase, in turn, caused a thermal shift of the optical response of the component. In this manner, we aligned interleavers and micro-ring resonators to the International Telecommunication Union (ITU) channels, by using a stochastic method named Globalized Bounded Nelder-Mead (GBNM) to determine the proper temperatures. The optimization engine relied on the optical feedback from on-chip monitor photodiodes to drive these photonic elements into the wanted functioning condition. This method is suited for restoring the spectral response of optical elements impaired by fabrication inaccuracies. In the same way, it can be applied to tune in resonance active components, whose transfer function has one or more local optima. We proved the reliability of the GBNM method for the optimization of an integrated optical switch, with more than thousand optical components, each one interfaced with a thermal resistor driven by a dedicated electronic circuit. On the one hand, the GBNM guaranteed the automatic alignment of all active components on the chip, over multiple instances. On the other hand, the method allowed for the proper working of such a complex device

La genomica in medicina: attualità e prospettive per l’assistenza infermieristica

È ormai consolidato il riconoscimento della componente genetica nella maggior parte delle patologie, non solo quelle ereditarie o di ambito oncologico, ma anche nelle malattie infettive e nelle risposte biologiche individuali alle terapie. Obiettivi. Gli attuali sviluppi della genomica impongono una riconsiderazione delle modalità di approccio alla prevenzione, diagnosi e terapia anche delle malattie più comuni, tramite l’impiego di test genetici diagnostici o predittivi e lo sviluppo di farmaci innovativi e di nuove modalità d’impostazione della terapia convenzionale, con l’obiettivo di realizzare una medicina “personalizzata”. Risultati. La possibilità che queste conoscenze apportino i benefici sperati alla pratica medica e assistenziale, è determinata dalla consapevolezza da parte degli operatori sanitari delle implicazioni cliniche, etiche, sociali ed economiche dei nuovi test e dell’efficacia nel comunicare ai pazienti e ai familiari i rischi e le opportunità derivanti dall’informazione genetica. Si presenta per gli infermieri l’opportunità di aggiornare le proprie conoscenze. L’acquisizione di nuove competenze in ambito genetico consentirà loro di poter rispondere alle nuove domande che i pazienti porranno. Questo articolo fornisce un aggiornamento sugli aspetti che più direttamente interessati dalle ricadute applicative che le conoscenze genomiche hanno oggi nella medicina con riferimento a: test genetici, determinazione del rischio genetico, farmacogenomica, terapi genica, assistenza infermieristica di consulenza genetica in centri di genetica medic

Methods for Low Crosstalk and Wavelength Tunability in Arrayed-Waveguide Grating for On-Silicon Optical Network

International audienceArrayed waveguide gratings (AWGs) are used to accomplish complex functionalities in dense wavelength division multiplexing networks, as well as in signal processing, measurement, characterization or sensing. In this work, we discuss the design and the experimental characterization of a 6 x 400 GHz channel-spaced AWG to be used as wavelength multiplexer/demultiplexer in a silicon-on-insulator based optical transport network. We adopted a whiskered-shaped star coupler design to investigate how the reduction in the reflectivity of the free propagation region boundaries affects the overall performances of the AWG. We demonstrated 2.9 dB insertionloss, which does not include fiber coupling loss, and (-24.4 +/- 0.1) dB crosstalk for a design realized with a single etching technique. Moreover, we demonstrated an efficient fine-tuning (7.5 nm/W) of the spectral position of the AWG output channels

Terminal deletion, del(1)(p36.3), detected through screening for terminal deletions in patients with unclassified malformation syndromes

We report on a 4 year-old girl with a 1p36.3-pter deletion. Clinical findings included minor anomalies of face and distal limbs, patent ductus arteriosus, the Ebstein heart anomaly, and brain atrophy with seizures. Conventional GTG-banded chromosome analysis revealed a normal (46,XX) result. Subsequent analysis by fluorescent in situ hybridization (FISH) using distal probes demonstrated a deletion of 1p36.6-pter. Molecular investigations with microsatellite markers showed hemizygosity at three loci at 1p36.3 with loss of the paternal allele. The deletion of 1p36.3 is difficult to identify by banding alone; indeed, our patient represents the third reported case with a del(1)(p36.3) that was detected only after more detailed analysis. In all three cases the deletion was detected through screening of patients with multiple congenital anomalies/mental retardation syndromes suggestive of autosomal chromosome aberrations for subtelomeric submicroscopic deletions by means of FISH or microsatellite marker analysis. On the basis of these observations we highly recommend that FISH with a subtelomeric 1p probe be routinely performed in patients with similar facial phenotype, severe mental retardation and seizures, and a heart malformation, particularly the Ebstein anomaly

From SHG to mid-infrared SPDC generation in strained silicon waveguides

The centrosymmetric crystalline structure of Silicon inhibits second order nonlinear optical processes in this material. We report here that, by breaking the silicon symmetry with a stressing silicon nitride over-layer, Second Harmonic Generation (SHG) is obtained in suitably designed waveguides where multi-modal phase-matching is achieved. The modeling of the generated signal provides an effective strain-induced second order nonlinear coefficient of χ(2) = (0.30 ± 0.02) pm/V. Our work opens also interesting perspectives on the reverse process, the Spontaneous Parametric Down Conversion (SPDC), through which it is possible to generate mid-infrared entangled photon pairs

On the origin of second harmonic generation in silicon waveguides with silicon nitride cladding

none8Strained silicon waveguides have been proposed to break the silicon centrosymmetry, which inhibits second-order nonlinearities. Even if electro-optic effect and second harmonic generation (SHG) were measured, the published results presented plenty of ambiguities due to the concurrence of different effects affecting the process. In this work, the origin of SHG in a silicon waveguide strained by a silicon nitride cladding is investigated in detail. From the measured SHG efficiencies, an effective second-order nonlinear susceptibility of ~0.5 pmV−1 is extracted. To evidence the role of strain, SHG is studied under an external mechanical load, demonstrating no significant dependence on the applied stress. On the contrary, a 254 nm ultraviolet (UV) exposure of the strained silicon waveguide suppresses completely the SHG signal. Since UV irradiation is known to passivate charged defects accumulated in the silicon nitride cladding, this measurement evidences the crucial role of charged centers. In fact, charged defects cause an electric field in the waveguide that via the third order silicon nonlinearity induces the SHG. This conclusion is supported by numerical simulations, which accurately model the experimental results.noneCastellan, Claudio; Trenti, Alessandro; Vecchi, Chiara; Marchesini, Alessandro; Mancinelli, Mattia; Ghulinyan, Mher; Pucker, Georg; Pavesi, LorenzoCastellan, Claudio; Trenti, Alessandro; Vecchi, Chiara; Marchesini, Alessandro; Mancinelli, Mattia; Ghulinyan, Mher; Pucker, Georg; Pavesi, Lorenz