Optical interconnection networks based on microring resonators

Optical microring resonators can be integrated on a chip to perform switching operations directly in the optical domain. Thus they become a building block to create switching elements in on-chip optical interconnection networks, which promise to overcome some of the limitations of current electronic networks. However, the peculiar asymmetric power losses of microring resonators impose new constraints on the design and control of on-chip optical networks. In this work, we study the design of multistage interconnection networks optimized for a particular metric that we name the degradation index, which characterizes the asymmetric behavior of microrings. We also propose a routing control algorithm to maximize the overall throughput, considering the maximum allowed degradation index as a constrain

Ring-resonator-based wavelength filters

Microring resonators (MR) represent a class of filters with characteristics very similar to those of Fabry–Perot filters. However, they offer the advantage that the injected and reflected signals are separated in individual waveguides, and in addition, their design does not require any facets or gratings and is thus particularly simple. MRs evolved from the fields of fibre optic ring resonators and micron scale droplets. Their inherently small size (with typical diameters in the range between several to tens of micrometres), their filter characteristics and their potential for being used in complex and flexible configurations make these devices particularly attractive for integrated optics or VLSI photonics applications.\ud MRs for filter applications, delay lines, as add/drop multiplexers, and modulators will be covered in detail in this chapter, while other applications such as in optical sensing, in spectroscopy or for coherent light generation (MR lasers) are outside the scope of this chapter.\ud This chapter focuses primarily on 4-port microrings, while 2-port devices will play a minor role here and are covered in more detail in Chap. 9. The present chapter starts with design considerations, the functional behaviour, and key characteristics of a single microring resonator and continues with the design of cascaded MRs allowing the implementation of higher order filters. Finally, complex devices like add-drop filters, tuneable dispersion compensators, all-optical wavelength converters, and tuneable cross-connects are treated.\u

Optical architectures for high performance switching and routing

This thesis investigates optical interconnection networks for high performance switching and routing. Two main topics are studied. The first topic regards the use of silicon microring resonators for short reach optical interconnects. Photonic technologies can help to overcome the intrinsic limitations of electronics when used in interconnects, short-distance transmissions and switching operations. This thesis considers the peculiarasymmetric losses of microring resonators since they pose unprecedented challenges for the design of the architecture and for the routing algorithms. It presents new interconnection architectures, proposes modifications on classical routing algorithms and achieves a better performance in terms of fabric complexity and scalability with respect to the state of the art. Subsequently, this thesis considers wavelength dimension capabilities of microring resonators in which wavelength reuse (i.e. crosstalk accumulation) presents impairments on the system performance. To this aim, it presents different crosstalk reduction techniques, a feasibility analysis for the design of microring resonators and a novel wavelength-agile routing matrix. The second topic regards flexible resource allocation with adaptable infrastructure for elastic optical networks. In particular, it focus on Architecture on Demand (AoD), whereby optical node architectures can be reconfigured on the fly according to traffic requirements. This thesis includes results on the first flexible-grid optical spectrum networking field trial, carried out in a collaboration with University of Essex. Finally, it addresses several challenges that present the novel concept AoD by means of modeling and simulation. This thesis proposes an algorithm to perform automatic architecture synthesis, reports AoD scalability and power consumption results working under the proposed synthesis algorithm. Such results validate AoD as a flexible node concept that provides power efficiency and high switching capacity

Electronic and spintronic devices using two-dimensional materials

179 p. El contenido del capítulo 8 está sujeto a confidencialidadEver since in 2004 atomically-thin two-dimensional van der Waals materials became available to the scientific community, at the reach of manual microexfoliation techniques, their implementation in novel device structures and concepts promised disruptive new applications and motivated research in a vast range of fields.Confined to the thinnest possible thickness, electrons in these materials exhibit a plethora of electronic properties, from semiconducting MoS2, to superconductor NbSe2, dielectric BN, and, jack-of-all trades, graphene.In this thesis, we explore fundamental and applied aspects of chemical vapor deposition (CVD) graphene, MoS2, and WSe2 using electronic device structures that use them as transporting channel, namely field-effect transistors (FETs), Hall bars, and diodes.MoS2 is a n-type semiconducting 2D vdW that complements one of the weak aspects of graphene-based transistors, which is the small ratio between the maximum current output and of the minimum current output of the transistors. Using MoS2 we identify an electron doping constraint for performing stable magnetotransport measurements, and we investigate the origins of the strong current fluctuations of the FETs. We study the low-frequency noise (LFN) of the current output of devices made with different layer thicknesses, and use the strong light-matter interactions of MoS2 to employ photodoping techniques together with the electrostatic gating to dope the channel. By converging all these conditions, we are able to discern the mechanism behind the different types of LFN noise reported in literature for MoS2, while at the same time identifying a LFN crossover driven by photodoping.With p-type semiconducting WSe2 we optimize the electron and hole transport properties of ambipolar FETs by considering BN as a top and bottom interface substrate and encapsulation layer, respectively. By doing so, we areable to address to some extent the strong hysteretic effects that adversely affect the operation of WSe2 FETs on oxide substrates, and improve the overall device performance.The versatility of CVD graphene allows us to do both applied and fundamental studies, both related to spintronics and electronics.The unique properties of graphene make it a core material in the search of full-electrical approaches to generate, transport, and detect spin currents without the use of magnetic elements. Using a Hall-bar shaped sample, non-local signals in graphene have been demonstrated to be associated with spin transport. In our case, we use the large area availability of CVD graphene to study non-local effects in an unlikely scenario for the transport of spins. We study the non-local signals of millimeter sized Hall-bars of CVD graphene, and by doing a systematic study as a function of device scale, from macro-to-microscale we identify a mechanism that cannot be connected with spin diffusion that also leads to large signals. By evaluating the microscopic details of the samples, and the different effects observed, we propose a mechanism mediated by grain boundaries to drive such effects.In a more applied manner, we use CVD graphene for two other types of devices. First, we study the use of graphene as an electrode material for lateral and vertical field-effect transistors that operate using organic channels, and determine that the low density of states of graphene allows for unscreened electric fields to reach the organic layer and enable the transistor operation in the vertical geometry.The second applied study is the large-scale fabrication of diodes using CVD graphene. Benefiting from the ultra-thin cross section of graphene, and using a lateral geometry we demonstrate the reliable fabrication of lateral metal/insulator/graphene diodes. The time constants determined from the direct-current analysis place the operation of the fabricated devices in the THz range. Additionally, the material combination considered enabled large current densities based on field-emission processes.CICnanoGUNE : nanoscience cooperative research cente

A Critical Evaluation of Remote Sensing Based Land Cover Mapping Methodologies

A novel, disaggregated approach to land cover survey is developed on the basis of land cover attributes; the parameters typically used to delineate land cover classes. The recording of land cover attributes, via objective measurement techniques, is advocated as it eliminates the requirement for surveyors to delineate and classify land cover; a process proven to be subjective and error prone. Within the North York Moors National Park, a field methodology is developed to characterise five attributes: species composition, cover, height, structure and density. The utility of land cover attributes to act as land cover ‘building blocks’ is demonstrated via classification of the field data to the Monitoring Landscape Change in the National Parks (MLCNP), National Land Use Database (NLUD) and Phase 1 Habitat Mapping (P1) schemes. Integration of the classified field data and a SPOT5 satellite image is demonstrated within per-pixel and object-orientated classification environments. Per-pixel classification produced overall accuracies of 81%, 80% and 76% at the field samples for the MLCNP, NLUD and P1 schemes, respectively. However, independent validation produced significantly lower accuracies. These decreases are demonstrated to be a function of sample fraction. Object-orientated classification, exemplified for the MLCNP schema at 3 segmentation scales, achieved accuracies approaching 75%. The aggregation of attributes to classes underutilises the potential of the remotely sensed data to describe landscape variability. Consequently, classification and geostatistical techniques capable of land cover attribute parameterisation, across the study area, are reviewed and exemplified for a sub-pixel classification. Land cover attributes provide a flexible source of field data which has been proven to support multiple land cover classification schemes and classification scales (sub-pixel, pixel and object). This multi-scaled/schemed approach enables the differential treatment of regions, within the remote sensing image, as a function of landscape characteristics and the users’ requirements providing a flexible mapping solution

Green Buildings and Ambient Intelligence: case study for N.A.S.A. Sustainability Base and future Smart Infrastructures

Con la diffusione delle smart infrastructures, espressione con cui ci si riferisce collettivamente ai concetti di smart cities e smart grid, i sistemi di building automation vedono il proprio ruolo espandersi oltre i tradizionali limiti degli ambienti isolati che sono progettati per gestire, supervisionare ed ottimizzare. Da sistemi isolati all’interno di edifici residenziali o commerciali, stanno iniziando ad ottenere un ruolo importante su scala più ampia nell’ambito di scenari più complessi a livello urbano o a livello di infrastruttura. Esempi di questa tendenza possono essere le attuali sperimentazioni in varie città del mondo per automatizzare l’illuminazione pubblica, complessi residenziali diffusi (spesso denominati smart connected comunities) e microgrid locali generate dalla federazione di varie unità residenziali a formare cosidette virtual power plants. A causa di questo processo, ci sono aspettative crescenti circa il potenziale delle reti di automazione di introdurre funzionalità sofisticate da un parte ed efficienza energetica dall’altra, ed entrambi gli aspetti su vasta scala. Sfortunatamente questi due obiettivi sono per diversi motivi in conflitto ed è dunque inevitabile individuare un ragionevole compromesso di progettazione. Questa ricerca realizza una caratterizzazione delle attuali tecnologie di automazione per identificare i termini di tale compromesso, con un’attenzione maggiormente polarizzata sugli aspetti di efficienza energetica, analizzata seguendo un approccio olistico, affrontando diversi aspetti del problema. Indubbiamente, data la complessità del vasto scenario tecnologico delle future smart infrastructures, non c’è una finalità sistematica nel lavoro. Piuttosto si intende fornire un contributo alla conoscenza, dando priorità ad alcune sfide di ricerca che sono altresì spesso sottovalutate. Il Green networking, ovvero l’efficienza energetica nel funzionamento di rete, è una di tali sfide. L’attuale infrastruttura IT globale è costruita su attrezzature che collettivamente consumano 21.4 TWh/anno (Global e-Sustainability Initiative, 2010). Questo è dovuto alla scarsa consapevolezza del fatto che le specifiche dei protocolli di comunicazione hanno varie implicazioni sull’efficienza energetica e alla generale tendenza ad una progettazione ridondante e sovra-dimensionata per il caso peggiore. Questo problema potrebbe essere riscontrato anche nelle reti di automazione, specialmente data la tendenza di cui si discuteva sopra, e in tal caso, queste potrebbero introdurre un ulteriore carbon footprint, in aggiunta a quello della rete internet. In questa ricerca si intende dimensionare tale problema e proporre approcci alternativi agli attuali modelli di hardware e protocollo tipici delle tecnologie di automazione in commercio. Spostandosi dalla rete di controllo all’ambiente fisico, altro obiettivo di questo lavoro è la caratterizzazione di sistemi di gestione automatica dei plug loads, carichi elettrici altrimenti non gestiti da alcun impianto di building automation. Per tali sistemi verranno mostrati i limiti e le potenzialità, identificando potenziali problematiche di design e proponendo un approccio integrato di tali sistemi all’interno di sistemi più ampi di gestione dell’energia. Infine, il meccanismo introdotto nella parte di green networking è potenzialmente in grado di fornire informazioni in tempo reale circa il contesto controllato. Si tratta di un potenziale sfruttabile per sviluppare soluzioni di Demand Side Management, allo scopo di effettuare previsioni di picco e di carico. Questa analisi è attualmente in corso, attraverso una partnership con Enel Distribuzione. With the advent of smart infrastructures, collective expression used here to refer to novel concepts such as smart cities and smart grid, building automation and control networks are having their role expanded beyond the traditional boundaries of the isolated environments they are designed to manage, supervise and optimize. From being confined within residential or commercial buildings as islanded, self-contained systems, they are starting to gain an important role on a wider scale for more complex scenarios at urban or infrastructure level. Example of this ongoing process are current experimental setups in cities worldwide to automate urban street lighting, diffused residential facilities (also often addressed to as smart connected communities) and local micro-grids generated by the federation of several residential units into so-called virtual power plants. Given this underlying process, expectations are dramatically increasing about the potential of control networks to introduce sophisticated features on one side and energy efficiency on the other, and both on a wide scale. Unfortunately, these two objectives are, in several ways, conflicting, and impose to settle for reasonable trade-offs. This research work performs an assessment of current control and automation technologies to identify the terms of this trade-off with a stronger focus on energy efficiency which is analyzed following a holistic approach covering several aspects of the problem. Nevertheless, given the complexity of the wide technology scenario of future smart infrastructure, there isn’t a systematic intention in the work. Rather, this research will aim at providing valuable contribution to the knowledge in the field, prioritizing challenges within the whole picture that are often neglected. Green networking, that is energy efficiency of the very network operation, is one of these challenges. The current worldwide IT infrastructure is built upon networking equipment that collectively consume 21.4 TWh/year (Global e-Sustainability Initiative, 2010). This is the result of an overall unawareness of energy efficiency implications of communication protocols specifications and a tendency toward over-provisioning and redundancy in architecture design. As automation and control networks become global, they may be subject to the same issue and introduce an additional carbon footprint along with that of the internet. This research work performs an assessment of the dimension of this problem and proposes an alternative approach to current hardware and protocol design found in commercial building automation technologies. Shifting from the control network to the physical environment, another objective of this work is related to plug load management systems, which will be characterized as to their performance and limitations, highlighting potential design pitfalls and proposing an approach toward integrating these systems into more general energy management systems. Finally, the mechanism introduced above to increase networking energy efficiency also demonstrated a potential to provide real-time awareness about the context being managed. This potential is currently under investigation for its implications in performing basic load/peak forecasting to support demand side management architectures for the smart grid, through a partnership with the Italian electric utility

Electronic and spintronic devices using two-dimensional materials

179 p. El contenido del capítulo 8 está sujeto a confidencialidadEver since in 2004 atomically-thin two-dimensional van der Waals materials became available to the scientific community, at the reach of manual microexfoliation techniques, their implementation in novel device structures and concepts promised disruptive new applications and motivated research in a vast range of fields.Confined to the thinnest possible thickness, electrons in these materials exhibit a plethora of electronic properties, from semiconducting MoS2, to superconductor NbSe2, dielectric BN, and, jack-of-all trades, graphene.In this thesis, we explore fundamental and applied aspects of chemical vapor deposition (CVD) graphene, MoS2, and WSe2 using electronic device structures that use them as transporting channel, namely field-effect transistors (FETs), Hall bars, and diodes.MoS2 is a n-type semiconducting 2D vdW that complements one of the weak aspects of graphene-based transistors, which is the small ratio between the maximum current output and of the minimum current output of the transistors. Using MoS2 we identify an electron doping constraint for performing stable magnetotransport measurements, and we investigate the origins of the strong current fluctuations of the FETs. We study the low-frequency noise (LFN) of the current output of devices made with different layer thicknesses, and use the strong light-matter interactions of MoS2 to employ photodoping techniques together with the electrostatic gating to dope the channel. By converging all these conditions, we are able to discern the mechanism behind the different types of LFN noise reported in literature for MoS2, while at the same time identifying a LFN crossover driven by photodoping.With p-type semiconducting WSe2 we optimize the electron and hole transport properties of ambipolar FETs by considering BN as a top and bottom interface substrate and encapsulation layer, respectively. By doing so, we areable to address to some extent the strong hysteretic effects that adversely affect the operation of WSe2 FETs on oxide substrates, and improve the overall device performance.The versatility of CVD graphene allows us to do both applied and fundamental studies, both related to spintronics and electronics.The unique properties of graphene make it a core material in the search of full-electrical approaches to generate, transport, and detect spin currents without the use of magnetic elements. Using a Hall-bar shaped sample, non-local signals in graphene have been demonstrated to be associated with spin transport. In our case, we use the large area availability of CVD graphene to study non-local effects in an unlikely scenario for the transport of spins. We study the non-local signals of millimeter sized Hall-bars of CVD graphene, and by doing a systematic study as a function of device scale, from macro-to-microscale we identify a mechanism that cannot be connected with spin diffusion that also leads to large signals. By evaluating the microscopic details of the samples, and the different effects observed, we propose a mechanism mediated by grain boundaries to drive such effects.In a more applied manner, we use CVD graphene for two other types of devices. First, we study the use of graphene as an electrode material for lateral and vertical field-effect transistors that operate using organic channels, and determine that the low density of states of graphene allows for unscreened electric fields to reach the organic layer and enable the transistor operation in the vertical geometry.The second applied study is the large-scale fabrication of diodes using CVD graphene. Benefiting from the ultra-thin cross section of graphene, and using a lateral geometry we demonstrate the reliable fabrication of lateral metal/insulator/graphene diodes. The time constants determined from the direct-current analysis place the operation of the fabricated devices in the THz range. Additionally, the material combination considered enabled large current densities based on field-emission processes.CICnanoGUNE : nanoscience cooperative research cente