Micro ring resonators in silicon-on-insulator

Silicon as a platform for photonics has recently seen a very large increase in interest because of its potential to overcome the bandwidth limitations of microprocessor interconnects and the low manufacturing cost given by the high compatibility with the already established micro-electronics industry. There has therefore been a signicant push in silicon photonics research to develop all silicon based optical components for telecoms applications. The work reported in this Thesis is con- cerned with the design, fabrication and characterisation of coupled ring resonators on silicon-on-insulator (SOI) material. The nal objective of this work is to pro- vide a robust and reliable technology for the demonstration of optical buers and delay-lines operating at signal bandwidths up to 100 GHz and in the wavelength region around 1550 nm. The core of the activity focused on the optimisation of the fabrication technology and device geometry to ensure the required device performance for the fabrication of long chains of ring resonators. The nal pro- cess has been optimised to obtain both intra-chip and chip-to-chip reproducibility with a variability of the process controlled at the nanometre scale. This was made possible by careful control of all the variables involved in the fabrication process, reduction of the fabrication complexity, close feature-size repeatability, line-edge roughness reduction, nearly vertical sidewall proles and high uniformity in the ebeam patterning. The best optical propagation losses of the realized waveguides reduced down to 1 dB=cm for 480 220 nm2 rectangular cross-section photonic wires and were consistently kept at typical values of around 1.5 dB=cm. Control of the coupling coecients between resonators had a standard deviation of less than 4 % for dierent realizations and resonance dispersion between resonators was below 50 GHz. All these gures represent the state-of-the-art in SOI photon- ics technology. Considerable eort has also been devoted to the development of ecient thermal electrodes (52 W=GHz) to obtain a recongurable behaviour of the structure and polymer inverse tapers to improve the o-chip coupling (inser- tion losses < 2 dB). Phase-preserving and error-free transmission up to 100 Gbit=s with continuously tunable optical delay up to 200 ps has been demonstrated on the nal integrated systems, proving the compatibility of these devices with advanced modulation formats and high bit-rate transmission systems

Thermoelectric cross-plane properties on p- and n-Ge/SixGe1-x superlattices

Silicon and germanium materials have demonstrated an increasing attraction for energy harvesting, due to their sustainability and integrability with complementary metal oxide semiconductor and micro-electro-mechanical-system technology. The thermoelectric efficiencies for these materials, however, are very poor at room temperature and so it is necessary to engineer them in order to compete with telluride based materials, which have demonstrated at room temperature the highest performances in literature [1]. Micro-fabricated devices consisting of mesa structures with integrated heaters, thermometers and Ohmic contacts were used to extract the cross-plane values of the Seebeck coefficient and the thermal conductivity from p- and n-Ge/SixGe1-x superlattices. A second device consisting in a modified circular transfer line method structure was used to extract the electrical conductivity of the materials. A range of p-Ge/Si0.5Ge0.5 superlattices with different doping levels was investigated in detail to determine the role of the doping density in dictating the thermoelectric properties. A second set of n-Ge/Si0.3Ge0.7 superlattices was fabricated to study the impact that quantum well thickness might have on the two thermoelectric figures of merit, and also to demonstrate a further reduction of the thermal conductivity by scattering phonons at different wavelengths. This technique has demonstrated to lower the thermal conductivity by a 25% by adding different barrier thicknesses per period

Tunable delay lines in silicon photonics: coupled resonators and photonic crystals, a comparison

In this paper, we report a direct comparison between coupled resonator optical waveguides (CROWs) and photonic crystal waveguides (PhCWs), which have both been exploited as tunable delay lines. The two structures were fabricated on the same silicon-on-insulator (SOI) technological platform, with the same fabrication facilities and evaluated under the same signal bit-rate conditions. We compare the frequency- and time-domain response of the two structures; the physical mechanism underlying the tuning of the delay; the main limits induced by loss, dispersion, and structural disorder; and the impact of CROW and PhCW tunable delay lines on the transmission of data stream intensity and phase modulated up to 100 Gb/s. The main result of this study is that, in the considered domain of applications, CROWs and PhCWs behave much more similarly than one would expect. At data rates around 100 Gb/s, CROWs and PhCWs can be placed in competition. Lower data rates, where longer absolute delays are required and propagation loss becomes a critical issue, are the preferred domain of CROWs fabricated with large ring resonators, while at data rates in the terabit range, PhCWs remain the leading technology

Microelectromechanical system gravimeters as a new tool for gravity imaging

A microelectromechanical system (MEMS) gravimeter has been manufactured with a sensitivity of 40 ppb in an integration time of 1 s. This sensor has been used to measure the Earth tides: the elastic deformation of the globe due to tidal forces. No such measurement has been demonstrated before now with a MEMS gravimeter. Since this measurement, the gravimeter has been miniaturized and tested in the field. Measurements of the free-air and Bouguer effects have been demonstrated by monitoring the change in gravitational acceleration measured while going up and down a lift shaft of 20.7 m, and up and down a local hill of 275 m. These tests demonstrate that the device has the potential to be a useful field-portable instrument. The development of an even smaller device is underway, with a total package size similar to that of a smartphone

Mid-Infrared Plasmonic Platform based on Heavily Doped Epitaxial Ge-on-Si: Retrieving the Optical Constants of Thin Ge Epilayers

The n-type Ge-on-Si epitaxial material platform enables a novel paradigm for plasmonics in the mid-infrared, prompting the future development of lab-on-a-chip and subwavelength vibrational spectroscopic sensors. In order to exploit this material, through proper electrodynamic design, it is mandatory to retrieve the dielectric constants of the thin Ge epilayers with high precision due to the difference from bulk Ge crystals. Here we discuss the procedure we have employed to extract the real and imaginary part of the dielectric constants from normal incidence reflectance measurements, by combining the standard multilayer fitting procedure based on the Drude model with Kramers-Kronig transformations of absolute reflectance data in the zero-transmission range of the thin film.Comment: Infrared, Millimeter, and Terahertz waves (IRMMW-THz), 2014 39th International Conference o

Optical activation of germanium plasmonic antennas in the mid-infrared

Impulsive interband excitation with femtosecond near-infrared pulses establishes a plasma response in intrinsic germanium structures fabricated on a silicon substrate. This direct approach activates the plasmonic resonance of the Ge structures and enables their use as optical antennas up to the mid-infrared spectral range. The optical switching lasts for hundreds of picoseconds until charge recombination redshifts the plasma frequency. The full behavior of the structures is modeled by the electrodynamic response established by an electron-hole plasma in a regular array of antennas

Group-IV midinfrared plasmonics

The use of heavily doped semiconductors to achieve plasma frequencies in the mid-IR has been recently proposed as a promising way to obtain high-quality and tunable plasmonic materials. We introduce a plasmonic platform based on epitaxial n-type Ge grown on standard Si wafers by means of low-energy plasma-enhanced chemical vapor deposition. Due to the large carrier concentration achieved with P dopants and to the compatibility with the existing CMOS technology, SiGe plasmonics hold promises for mid-IR applications in optoelectronics, IR detection, sensing, and light harvesting. As a representative example, we show simulations of mid-IR plasmonic waveguides based on the experimentally retrieved dielectric constants of the grown materials

Measurement of empathy among Argentine cardiologists: Psychometrics and differences by age, gender, and subspecialty

Background: Cardiologists are involved in the management of patients with multiple cardiovascular risk factors and chronic heart diseases, so empathy is a necessary feature to deal with them. The aim of the study was to evaluate the validity and reliability of the Spanish version of the Jefferson Scale of Physician Empathy (JSPE) among Argentine cardiologists and to explore the potential differences by age, gender, and subspecialty. Methods: Between August and September 2012, we performed a survey in a non-randomized sample of 566 Spanish-speaking cardiologists of Argentina. A Principle Component Analysis (PCA) was used to explore the link between observed variables and latent variables in order to identify the factor structure. The PCA criteria for identifying the factor structure were examined with the Kaiser-Meyer-Olkin (KMO) analysis. Results: The KMO measure of sampling adequacy was 0.86 and Bartlett’s test of sphericity was highly significant (p = 0.000), determining the suitability of the data set for factor analysis. The PCA of 20 items yielded a three factor model that accounted for 40.6% of the variance. The JSPE mean rank score for women was 307.9 vs. 275.0 for men (p = 0.017). The compa­rison of mean rank score according to age (quartiles) showed a significant relation between older age and empathy. No difference was found when the mean rank scores were compared by respondent subspecialty. Conclusions: JSPE provides a valid and reliable scale to measure Argentine cardiologists’ attitudes towards empathy. Female cardiologists seem to be more empathic than their male colleagues, and a positive relationship between age and empathy was found.

Mid-Infrared Plasmonic Platform Based on n-Doped Ge-on-Si: Molecular Sensing with Germanium Nano-Antennas on Si

CMOS-compatible, heavily-doped semiconductor films are very promising for applications in mid-infrared plasmonic devices because the real part of their dielectric function is negative and broadly tunable in this wavelength range. In this work we investigate n-type doped germanium epilayers grown on Si substrates. We design and realize Ge nanoantennas on Si substrates demonstrating the presence of localized plasmon resonances, and exploit them for molecular sensing in the mid-infrared

Factors Affecting the Quality of Bacterial Genomes Assemblies by Canu after Nanopore Sequencing

Long-read sequencing (LRS), like Oxford Nanopore Technologies, is usually associated with higher error rates compared to previous generations. Factors affecting the assembly quality are the integrity of DNA, the flowcell efficiency, and, not least all, the raw data processing. Among LRS-intended de novo assemblers, Canu is highly flexible, with its dozens of adjustable parameters. Different Canu parameters were compared for assembling reads of Salmonellaenterica ser. Bovismorbificans (genome size of 4.8 Mbp) from three runs on MinION (N50 651, 805, and 5573). Two of them, with low quality and highly fragmented DNA, were not usable alone for assembly, while they were successfully assembled when combining the reads from all experiments. The best results were obtained by modifying Canu parameters related to the error correction, such as corErrorRate (exclusion of overlaps above a set error rate, set up at 0.40), corMhapSensitivity (the coarse sensitivity level, set to “high”), corMinCoverage (set to 0 to correct all reads, regardless the overlaps length), and corOutCoverage (corrects the longest reads up to the imposed coverage, set to 100). This setting produced two contigs corresponding to the complete sequences of the chromosome and a plasmid. The overall results highlight the importance of a tailored bioinformatic analysis