Enhanced sensitivity subwavelength grating waveguides for silicon photonics sensing applications

OSA (Optical Society of America)In this work we will review the enormous potential of subwavelength grating waveguides for sensing applications in the near and mid-infrared bands, demonstrating the capability to engineer the mode profile to maximize the light-matter interaction.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Diseño de grating couplers de orden cero de banda ancha y alta eficiencia para el infrarrojo medio

The mode fields of optical fibers and high-index contrast photonic waveguides have different dimensions, making difficult the coupling of light from one to the other. To solve this problem, surface grating couplers are one of the most used alternatives. However, in conventional grating couplers the bandwidth is limited. To overcome this drawback, we have recently proposed zero-order grating couplers, which, making use of a high-index prism and subwavelength grating structures, substantially mitigate the wavelength dependency of conventional grating couplers. In the near-infrared (λ = 1.55 μm) it is not possible to take full benefit from the potential bandwidth enhancement of zero-order grating couplers. Thus, in this work we migrate our zero-order grating coupler design from the near-infrared wavelength range to the mid-infrared one, which is attaining increasing attention because of its sensing applications. Subdecibel coupling efficiencies and broad bandwidths up to ~680 nm are achieved at λ = 3.8 μm for silicon-on-insulator and germanium-on-silicon nitride platforms.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

GRB 021004: Tomography of a gamma-ray burst progenitor and its host galaxy

We analyse the distribution of matter around the progenitor star of gamma-ray burst GRB 021004 as well as the properties of its host galaxy with high-resolution echelle as well as near-infrared spectroscopy. Observations were taken by the 8.2m Very Large Telescope with the Ultraviolet and Visual Echelle spectrograph (UVES) and the Infrared Spectrometer And Array Camera (ISAAC) between 10 and 14 hours after the onset of the event. We report the first detection of emission lines from a GRB host galaxy in the near-infrared, detecting H-alpha and the [O III] doublet. These allow an independent measurement of the systemic redshift (z = 2.3304 +/- 0.0005) which is not contaminated by absorption as the Ly-alpha line is, and the deduction of properties of the host galaxy. From the visual echelle spectroscopy, we find several absorption line groups spanning a range of about 3,000 km/s in velocity relative to the redshift of the host galaxy. The absorption profiles are very complex with both velocity-broadened components extending over several 100 km/s and narrow lines with velocity widths of only 20 km/s. By analogy with QSO absorption line studies, the relative velocities,widths, and degrees of ionization of the lines ("line-locking", "ionization--velocity correlation") show that the progenitor had both an extremely strong radiation field and several distinct mass loss phases (winds). These results are consistent with GRB progenitors being massive stars, such as Luminous Blue Variables (LBVs) or Wolf--Rayet stars, providing a detailed picture of the spatial and velocity structure of the GRB progenitor star at the time of explosion. The host galaxy is a prolific star-forming galaxy with a SFR of about 40 solar masses per year.Comment: 11 pages, 5 figures. Accepted for publication in Astronomy and Astrophysics

Spectrophotometric analysis of GRB afterglow extinction curves with X-shooter

In this work we use gamma-ray burst (GRB) afterglow spectra observed with the VLT/X-shooter spectrograph to measure rest-frame extinction in GRB lines-of-sight by modeling the broadband near-infrared (NIR) to X-ray afterglow spectral energy distributions (SEDs). Our sample consists of nine Swift GRBs, eight of them belonging to the long-duration and one to the short-duration class. Dust is modeled using the average extinction curves of the Milky Way and the two Magellanic Clouds. We derive the rest-frame extinction of the entire sample, which fall in the range $0 \lesssim {\it A}_{\rm V} \lesssim 1.2$. Moreover, the SMC extinction curve is the preferred extinction curve template for the majority of our sample, a result which is in agreement with those commonly observed in GRB lines-of-sights. In one analysed case (GRB 120119A), the common extinction curve templates fail to reproduce the observed extinction. To illustrate the advantage of using the high-quality X-shooter afterglow SEDs over the photometric SEDs, we repeat the modeling using the broadband SEDs with the NIR-to-UV photometric measurements instead of the spectra. The main result is that the spectroscopic data, thanks to a combination of excellent resolution and coverage of the blue part of the SED, are more successful in constraining the extinction curves and therefore the dust properties in GRB hosts with respect to photometric measurements. In all cases but one the extinction curve of one template is preferred over the others. We show that the modeled values of the extinction and the spectral slope, obtained through spectroscopic and photometric SED analysis, can differ significantly for individual events. Finally we stress that, regardless of the resolution of the optical-to-NIR data, the SED modeling gives reliable results only when the fit is performed on a SED covering a broader spectral region.Comment: 17 pages, 7 figures, 4 tables, accepted for publication in Astronomy & Astrophysic

Dynamics and within-host interaction of Theileria lestoquardi and T. ovis among naive sheep in Oman

Mixed species infections of Theileria spp. are common in nature. Experimental and epidemiological data suggest that mixed species infections elicit cross-immunity that can modulate pathogenicity and disease burden at the population level. The present study examined within-host interactions, over a period of 13 months during natural infections with two Theileria spp., pathogenic (T. lestoquardi) and non-pathogenic (T. ovis), amongst a cohort of naive sheep in Oman. In the first two months after exposure to infection, a high rate of mortality was seen among sheep infected with T. lestoquardi alone. However, subsequently mixed-infections of T. lestoquardi and T. ovis prevailed, and no further death occurred. The overall densities of both parasite species were significantly higher as single infection vs mixed infection and the higher relative density of pathogenic T. lestoquardi indicated a competitive advantage over T. ovis in mixed infection. The density of both species fluctuated significantly over time, with no difference in density between the very hot (May to August) and warm season (September to April). A high degree of genotype multiplicity was seen among T. lestoquardi infections, which increased with rising parasite density. Our results illustrate a potential competitive interaction between the two ovine Theileria spp., and a substantial reduction in the risk of mortality in mixed parasite infections, indicating that T. ovis confers heterologous protection against lethal T. lestoquardi infection

Detection of an optical transient following the 13 March 2000 short/hard gamma-ray burst

We imaged the error box of a gamma-ray burst of the short (0.5 s), hard type (GRB 000313), with the BOOTES-1 experiment in southern Spain, starting 4 min after the gamma-ray event, in the I-band. A bright optical transient (OT 000313) with I = 9.4 +/- 0.1 was found in the BOOTES-1 image, close to the error box (3-sigma) provided by BATSE. Late time VRIK'-band deep observations failed to reveal an underlying host galaxy. If the OT 000313 is related to the short, hard GRB 000313, this would be the first optical counterpart ever found for this kind of events (all counterparts to date have been found for bursts of the long, soft type). The fact that only prompt optical emission has been detected (but no afterglow emission at all, as supported by theoretical models) might explain why no optical counterparts have ever been found for short, hard GRBs.This fact suggests that most short bursts might occur in a low-density medium and favours the models that relate them to binary mergers in very low-density enviroments.Comment: Revised version. Accepted for publication in Astronomy and Astrophysics Letters, 5 pages, 3 figure

Metamaterial antenna array fed by distributed Bragg deflector for beam steering on SOI platform

The capability to radiate collimated steerable beams of light is crucial for many applications, such as remote sensing and free-space optical communications. Here we experimentally demonstrate a novel 1D-antenna array architecture that exhibits a far-field Gaussian profile with an angular divergence of 1.8° × 0.2°.We acknowledge funds from National Research Council of Canada (NRC) Collaborative Science, Technology and Innovation Program (CSTIP) (HTSN 209); Ministerio de Ciencia, Innovación y Universidades (MCIU) (PID2019- 106747RB-I00); Ministerio de Universidades (FPU16/03401, FPU20/03487); Junta de Andalucía (P18-RT-1453, P18-RT- 793); FEDER Andalucía (UMA20-FEDERJA-158). Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Metamaterial antenna array fed by distributed Bragg deflector for SOI platform

We propose a distributed Bragg deflector working as a low loss (<0.3 dB) ultra compact beam expander, which generates an on chip Gaussian beam that illuminates a 1D array of 112 optical antennas with a length of 1.5 mm . The device has been fabricated on a 220 nm silicon on insulator platform using a single etch process with a minimum feature size of 80 nm. We present an antenna array with a directivity of 53 dBi , a radiation efficiency of 3.8 dB and a far field spot with an angular divergence of 1.8 × 0.2Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. High Throughput and Secure Networks Challenge Program at the National Research Council of Canada (HTSN209) Ministerio de Universidades (FPU16/03401, FPU20/03487) Junta de Andalucía (P18 RT 1453, P18 RT 793); FEDER Andalucía (UMA20 FEDERJA 158); Ministerio de Ciencia, Innovación y Universidades (MCIU) (PID2019 106747RB I00)I00)

GRB 091029: At the limit of the fireball scenario

Using high-quality, broad-band afterglow data for GRB 091029, we test the validity of the forward-shock model for gamma-ray burst afterglows. We used multi-wavelength (NIR to X-ray) follow-up observations obtained with the GROND, BOOTES-3/YA and Stardome optical ground-based telescopes, and the UVOT and the XRT onboard the Swift satellite. To explain the almost totally decoupled light curves in the X-ray and optical/NIR domains, a two-component outflow is proposed. Several models are tested, including continuous energy injection, components with different electron energy indices and components in two different stages of spectral evolution. Only the last model can explain both the decoupled light curves with asynchronous peaks and the peculiar SED evolution. However, this model has so many unknown free parameters that we are unable to reliably confirm or disprove its validity, making the afterglow of GRB 091029 difficult to explain in the framework of the simplest fireball model.Comment: Accepted to A&