Compact and fault-tolerant photonic crystal add drop filter

International audienceWe propose an add-drop filter consisting of two adjacent waveguides carved into a two-dimensional photonic crystal that is etched through a standard guiding structure. This filter is based on distributed energy transfer via the frequency-selective intermediate conversion of the fundamental guided mode to a high-order low-group-velocity mode. This geometry circumvents the fabrication sensitivity on the single-hole scale of previous cavity-based designs. Combining distributed energy transfer and reduced group velocity preserves compactness. The design is analytically optimized with a coupled-mode approach

Head-to-head domain walls in one-dimensional nanostructures: an extended phase diagram ranging from strips to cylindrical wires

International audienceSo far magnetic domain walls in one-dimensional structures have been described theoretically only in the cases of flat strips, or cylindrical structures with a compact cross-section, either square or disk. Here we describe an extended phase diagram unifying the two pictures, extensively covering the (width,thickness) space. It is derived on the basis of symmetry and phase-transition arguments, and micromagnetic simulations. A simple classification of all domain walls in two varieties is proposed on the basis of their topology: either with a combined transverse/vortex character, or of the Bloch-point type. The exact arrangement of magnetization within each variety results mostly from the need to decrease dipolar energy, giving rise to asymmetric and curling structures. Numerical evaluators are introduced to quantify curling, and scaling laws are derived analytically for some of the iso-energy lines of the phase diagram

Spontaneous emission enhancement at a photonic wire miniband edge

International audienceIn a multimode photonic-crystal waveguide, we observe strong enhancement of the photoluminescence of embedded quantum dots at the edges of the so-called mini-stopband that were opened by Bragg diffraction between two guided modes. Taking into account light collection, we relate this observation to the singular photon density of states that is characteristic of a one-dimensional photon system. Furthermore, we quantify by how much the radiation losses smooth the divergence. For the first time to our knowledge, a clear account of the control of spontaneous emission in a one-dimensional system is thus demonstrated

Probing domain walls in cylindrical magnetic nanowires with electron holography

3 pages, 2 figuresInternational audienceWe probe magnetic domain walls in cylindrical soft magnetic nanowires using electron holography. We detail the modelling of expected contrast for both transverse and Bloch point domain walls and provide comparison with experimental observations performed on NiCo nanowires, involving also both magnetic and electrostatic contribution to the electron holography map. This allows the fast determination of the domain wall type without the need for uneasy and time-consuming experimental removal of the electrostatic contribution. Finally, we describe and implement a new efficient algorithm for calculating the magnetic contrast

Low-loss, compact, spot-size-converter based vertical couplers for photonic integrated circuits

Funding: (i) European Union Horizon H2020 Programme (H2020-ICT27-2015, COSMICC No. 688516). (ii) European Union Research Council (ERC) starting grant 337508.In recent years, the monolithic integration of new materials such as SiN, Ge and LiNbO3 on silicon (Si) has become important to the Si photonics community due to the possibility of combining the advantages of both material systems. However, efficient coupling between the two different layers is challenging. In this work, we present a spot size converter based on a two-tier taper structure to couple the optical mode adiabatically between Si and SiN. The fabricated devices show a coupling loss as low as 0.058 dB  ±  0.01 dB per transition at 1525 nm. The low coupling loss between the Si to SiN, and vice versa, reveals that this interlayer transition occurs adiabatically for short taper lengths (<200 µm). The high refractive index contrast between the Si and SiN is overcome by matching the optical impedance. The proposed two-tier taper structure provides a new platform for optoelectronic integration and a route towards 3D photonic integrated circuits.PostprintPeer reviewe

Respective roles of social deprivation, health literacy, and clinical factors for COVID-19: a case-control study in hospitalized patients

IntroductionTo investigate the association between social deprivation and COVID-19 among hospitalized patients in an underprivileged department of the greater Paris area.MethodsIndividuals hospitalized for COVID-19 between March 1st and October 31, 2020, were included, matched on age and sex, and compared with patients hospitalized for any other reason with negative RT-PCR for SARS-CoV-2, through a case-control study. Clinical, socio-demographic characteristics, health literacy, and social deprivation, assessed by the EPICES score, were collected. Factors associated with COVID-19 in hospitalized patients were assessed using univariate and multivariate logistic regression models.Results69 cases and 180 controls were included. Participants were mostly men (N = 148: 59.4%) aged 65 or older (N = 109: 44.1%). Median EPICES score was 43.2 (IQR 29.4–62.9). EPICES score &gt; 30.17 (precariousness threshold) was not significantly associated with COVID-19 in hospitalized patients (adjusted odds ratio (aOR) = 0.46; 95% Confidence Interval (CI) [0.21–1.01]). Advanced age, higher BMI, professional activity, home area of less than 25 m2 per person, and low health literacy, were significantly associated with COVID-19 in hospitalized patients.DiscussionThis study highlights probable risk factors for specific exposition in disadvantaged area: maintenance of professional activity, smaller home area, and low health literacy

A versatile silicon-silicon nitride photonics platform for enhanced functionalities and applications

Silicon photonics is one of the most prominent technology platforms for integrated photonics and can support a wide variety of applications. As we move towards a mature industrial core technology, we present the integration of silicon nitride (SiN) material to extend the capabilities of our silicon photonics platform. Depending on the application being targeted, we have developed several integration strategies for the incorporation of SiN. We present these processes, as well as key components for dedicated applications. In particular, we present the use of SiN for athermal multiplexing in optical transceivers for datacom applications, the nonlinear generation of frequency combs in SiN micro-resonators for ultra-high data rate transmission, spectroscopy or metrology applications and the use of SiN to realize optical phased arrays in the 800&ndash;1000 nm wavelength range for Light Detection And Ranging (LIDAR) applications. These functionalities are demonstrated using a 200 mm complementary metal-oxide-semiconductor (CMOS)-compatible pilot line, showing the versatility and scalability of the Si-SiN platform