Three-dimensional modelling of scattering loss in InGaAsP/InP and silica-on-silicon bent waveguides

A three-dimensional (3D) method for the estimation of scattering loss due to sidewalls roughness in bent optical waveguides is proposed and validated. The approach, based on Volume Current Method (VCM), has been pointed out to accurately calculate the scattering loss as dependent on curvature radius and wavelength. An exponential model has been employed to analytically describe the sidewalls roughness and a 3D mode solver based on mode-matching method has been used to calculate optical field distribution in the bent waveguide cross-section. Scattering loss suffered by two low index contrast waveguides has been investigated by the developed algorithm. For a buried InGaAsP/InP waveguide and a 6 μm x 6 μm Silica-on-Silicon guiding structure scattering loss dependence on bending radius, wavelength, roughness, correlation length and standard deviation has been investigated and discussed. Because of the different index contrast values, InGaAsP/InP waveguide exhibits a scattering loss which is quite six times larger than in Silica-on-Silicon. For both guiding structures, quasi-TM mode shows a larger scattering loss than quasi-TE one

Quality factor and finesse optimization in buried InGaAsP/InP ring resonators

Quality factor and finesse of buried In1-xGaxAsyP1-y / InP ring resonators have been optimized in this paper by a very general modelling technique. Limiting effect of propagation loss within the ring has been investigated using a three-dimensional (3D) highly accurate complex mode solver based on mode matching method to analyze bending loss dependence on ring radius and wavelength. Coupling between straight input/output (I/O) bus waveguides and ring resonator has been studied by 3D Beam Propagation Method (BPM), deriving coupling loss and coupling coefficient for a large range of ring radius and bus waveguides-ring distance values (for both polarizations). Ring resonator has been modelled by the transfer-matrix approach, while finesse and quality factor dependence on radius has been estimated for two resonator architectures (including one or two I/O bus waveguides) and for quasi-TE and quasi-TM modes. Guiding structure has been optimized to enhance resonator performance. The modelling approach has been validated by comparing results obtained by our algorithm with experimental data reported in literature. Influence of rejection (at resonance wavelength) at through port on quality factor and finesse has been widely discussed. A quality factor larger than 8 x 105 has been predicted for the ring resonator employing only one I/O bus waveguide and having a radius of 400 μm. This resonator exhibits a rejection of -8 dB at through port

Ultra-high Q/V hybrid cavity for strong light-matter interaction

The ability to confine light at the nanoscale continues to excite the research community, with the ratio between quality factor Q and volume V, i.e., the Q/V ratio, being the key figure of merit. In order to achieve strong light-matter interaction, however, it is important to confine a lot of energy in the resonant cavity mode. Here, we demonstrate a novel cavity design that combines a photonic crystal nanobeam cavity with a plasmonic bowtie antenna. The nanobeam cavity is optimised for a good match with the antenna and provides a Q of 1700 and a transmission of 90%. Combined with the bowtie, the hybrid photonic-plasmonic cavity achieves a Q of 800 and a transmission of 20%, both of which remarkable achievements for a hybrid cavity. The ultra-high Q/V of the hybrid cavity is of order of 106 (λ/n)−3, which is comparable to the state-of-the-art of photonic resonant cavities. Based on the high Q/V and the high transmission, we demonstrate the strong efficiency of the hybrid cavity as a nanotweezer for optical trapping. We show that a stable trapping condition can be achieved for a single 200 nm Au bead for a duration of several minutes (ttrap > 5 min) and with very low optical power (Pin = 190 μW)

Double electromagnetically induced transparency resonance in slotted metasurfaces supporting bound states in the continuum

This work proposes and theoretically demonstrates a double electromagnetic induced transparency resonance generated by a novel dielectric metasurface consisting of a periodic array of square slots. The resonances stem from symmetry-protected bound states in the continuum whose quality factor tends to infinity when the structure is symmetric. The quasi-bound states in the continuum supported by the asymmetric metasurface can be exploited to obtain double high quality factor resonances in transmission (electromagnetic induced transparency like effect) that can be modulated with the external refractive index for sensing.This work was supported by Comunidad de Madrid and FEDER Program (S2018/NMT-4326), the Ministerio de Economía y Competitividad of Spain (TEC2016-77242-C3-1-R and TEC2016-76021-C2-2-R), the FEDER/Ministerio de Ciencia, Innovación y Universidades and Agencia Estatal de Investigación (RTC2017-6321-1, PID2019-107270RB-C21 and PID2019-109072RB-C31)

Strongly resonant silicon slot metasurfaces with symmetry-protected bound states in the continuum

In this work, a novel all-dielectric metasurface made of arrayed circular slots etched in a silicon layer is proposed and theoretically investigated. The structure is designed to support both Mie-type multipolar resonances and symmetry-protected bound states in the continuum (BIC). Specifically, the metasurface consists of interrupted circular slots, following the paradigm of complementary split-ring resonators. This configuration allows both silicon-on-glass and free-standing metasurfaces and the arc length of the split-rings provides an extra tuning parameter. The nature of both BIC and non-BIC resonances supported by the metasurface is investigated by employing the Cartesian multipole decomposition technique. Thanks to the non-radiating nature of the quasi-BIC resonance, extremely high Q-factor responses are calculated, both by fitting the simulated transmittance spectra to an extended Fano model and by an eigenfrequency analysis. Furthermore, the effect of optical losses in silicon on quenching the achievable Q-factor values is discussed. The metasurface features a simple bulk geometry and sub-wavelength dimensions. This novel device, its high Q-factors, and strong energy confinement open new avenues of research on light-matter interactions in view of new applications in non-linear devices, biological sensors, and optical communications.Ministerio de Ciencia, Innovación y Universidades (PID2019-107270RB-C21, PID2019-109072RB-C31, RTC2017-6321-1); Comunidad de Madrid (S2018/NMT-4326); Ministerio de Economía y Competitividad (TEC2016-76021-C2-2-R, TEC2016-77242-C3-1-R)

Refractive index sensing by all-dielectric metasurfaces supporting quasi-bound states in the continuum

All-dielectric metasurfaces have attracted increasing attention due to their negligible losses and sharper resonances compared to their metallic counterparts. In this work, we numerically studied the optical performance of a novel alldielectric metasurface based on complementary split-ring resonators (CSRRs), in which ultrathin slots were periodically etched in a thin silicon layer. The proposed CSRR metasurface exhibits two multipolar resonances in the near-infrared (NIR) window. Moreover, a quasi-bound state in the continuum (quasi-BIC) with an ultra-high quality factor can be excited by breaking the symmetry of the structure. Taking advantage of the high-quality factor quasi-BIC mode and its sensitivity to the superstrate medium refractive index (S = [Di] res/[Dn]), we design an ultra-high figure of merit (FoM = S/FWHM) refractive index sensor for biomedical applications. By three-dimensional finite element method (3D-FEM), we evaluate the sensitivity of the sensing device to the variation of the superstrate refractive index in the range 1.31-1.33, which is typical for aqueous solutions. Our simulations reveal that a sensitivity of S ~ 155 nm RIU-1 and an extraordinary FoM ~ 387500 RIU-1 can be achieved using the ultra-narrow quasi-BIC resonance in the CSRR metasurface structure. The proposed approach opens new paths to develop flat biochemical sensors with high accuracy and real-time performance

R-CVP versus R-CHOP versus R-FM for the initial treatment of patients with advanced-stage follicular lmphoma: results of the FOLL05 trial conducted by the Fondazione Italiana Linfomi

PURPOSE Although rituximab (R) is commonly used for patients with advanced follicular lymphoma (FL) requiring treatment, the optimal associated chemotherapy regimen has yet to be clarified. PATIENTS AND METHODS We conducted an open-label, multicenter, randomized trial among adult patients with previously untreated stages II to IV FL to compare efficacy of eight doses of R associated with eight cycles of cyclophosphamide, vincristine, and prednisone (CVP) or six cycles of cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) or six cycles of fludarabine and mitoxantrone (FM). The principal end point of the study was time to treatment failure (TTF). Results There were 534 patients enrolled onto the study. Overall response rates were 88%, 93%, and 91% for R-CVP, R-CHOP, and R-FM, respectively (P=.247). After a median follow-up of 34 months, 3-year TTFs were 46%, 62%, and 59% for the respective treatment groups (R-CHOP v R-CVP, P=.003; R-FM v R-CVP, P=.006; R-FM v R-CHOP, P=.763). Three-year progression-free survival (PFS) rates were 52%, 68%, and 63% (overall P=.011), respectively, and 3-year overall survival was 95% for the whole series. R-FM resulted in higher rates of grade 3 to 4 neutropenia (64%) compared with R-CVP (28%) and R-CHOP (50%; P< .001). Overall, 23 second malignancies were registered during follow-up: four in R-CVP, five in R-CHOP, and 14 in R-FM. CONCLUSION In this study, R-CHOP and R-FM were superior to R-CVP in terms of 3-year TTF and PFS. In addition, R-CHOP had a better risk-benefit ratio compared with R-FM

Efficient Chemical Sensing by Coupled Slot SOI Waveguides

A guided-wave chemical sensor for the detection of environmental pollutants or biochemical substances has been designed. The sensor is based on an asymmetric directional coupler employing slot optical waveguides. The use of a nanometer guiding structure where optical mode is confined in a low-index region permits a very compact sensor (device area about 1200 μm2) to be realized, having the minimum detectable refractive index change as low as 10-5. Silicon-on-Insulator technology has been assumed in sensor design and a very accurate modelling procedure based on Finite Element Method and Coupled Mode Theory has been pointed out. Sensor design and optimization have allowed a very good trade-off between device length and sensitivity. Expected device sensitivity to glucose concentration change in an aqueous solution is of the order of 0.1 g/L

Metodología para el fomento de modos de transporte sostenibles en campus universitarios

RESUMEN. Como cualquier empresa grande, los campus universitarios presentan serios problemas de movilidad como consecuencia del aumento del número de viajes en vehículo privado (coche) originado por el crecimiento del nivel de vida que se ha experimentado durante los últimos 25 años. Por esta razón, el presente estudio propone una serie de políticas de movilidad de las universidades que consisten en el fomento del uso de sistemas de transportes más sostenibles y alternativas al vehículo privado. Además, se pretende el logro de una correcta planificación de la gestión de sus espacios de aparcamientos, circulaciones, peatonalizaciones, carriles bici y otras actuaciones, que doten a dichos ámbitos universitarios de la correspondiente habitabilidad y racionalización de usos del suelo. La metodología utilizada ha consistido en el diseño de Encuestas de Preferencias Declaradas (PD) en las que se plantean toda una serie de escenarios "hipotéticos" con los que se estudia la reacción de los usuarios frente a cambios en el sistema de transporte y la influencia de diferentes políticas de aparcamientos en la Universidad. A partir de los resultados obtenidos en estas encuestas, se ha conseguido modelizar el comportamiento del usuario utilizando modelos de elección discreta. Asimismo se han calculado las correspondientes disposiciones al pago al disminuir el tiempo de acceso a destino como indicativas de los posibles regímenes tarifarios del uso de bicicletas y de las plazas de aparcamiento en el interior del campus. Todo ello ha sido aplicado al Campus de las Llamas de la Universidad de Cantabria (UC), aunque cabe destacar que esta metodología es extensible a cualquier campus universitario o a cualquier gran empresa que requiera una concentración importante de personal