Search

A city is an organism made of social, economic, cultural, and environmental fabrics, the interactions of which determine the form and functioning of city life. Different disciplines are then involved in analyzing the complex processes of the 21st-century city. The aim of this study was to explore the use of an analytical method that can act as a catalyst for the main players involved in the environmental urban morphology (EUM). This multidisciplinary methodology focuses on the study of public space in dense urban fabrics as a key context for understanding a city. Operationally, the work shows the potential of integrating morphological analysis, pedestrian flow analysis, and environmental analysis and applying them in dense and compact urban fabrics. The first of these analyses methods was carried out using urban survey tools and the geographic information system (GIS) in order to detect the physical forms of the city and develop a number of morphological maps. The second, using the global positioning system (GPS) and on-site detectors, maps pedestrian movement within public spaces. The latter mainly focuses on the microclimatic analysis of public spaces and outdoor comfort, carried out using environmental software such as ENVI-met (4.4 version). The ultimate goal of this study was to achieve the definition of a dynamic, multidisciplinary, and multilayer methodology for the analysis of dense urban fabrics which we believe could be very useful for addressing the regenerative processes of the contemporary city., Environmental Technology and Design

Locking of oscillators to ultra-stable external sources is of paramount importance for improving close-to-carrier phase noise in free running oscillators. In most of them, such as Micro-Electro-Mechanical-Systems or LC circuit-based oscillators, the locking frequency range is limited by the robustness of their natural frequency, which comes explicitly related with intrinsic parameters of the system. In this work we report the synchronization of an optically-driven self-pulsing limit-cycle taking place in a silicon optomechanical crystal cavity to an external harmonic signal that modulates the driving laser. Because of the extreme ductility of the natural self-pulsing frequency (several tens of MHz), the injection-locking mechanism is highly efficient and displays giant relative bandwidths exceeding 60%. The external modulation reveals itself as a knob to explore dynamical attractors that are otherwise elusive and, in particular, as a means to initialize a mechanical resonator into a state of self-sustained oscillations driven by radiation pressure forces. Moreover, we exploit the large anharmonicity of the studied limit-cycle to induce injection-locking to integer multiples and fractions of the frequency of the external reference, which can be used for frequency conversion purposes in nano-electro-opto-mechanical systems.

We report on a minor correction in our article: “High frequency mechanical excitation of a silicon nanostring with piezoelectric aluminum nitride layers”...

Nanoelectro-opto-mechanical systems enable the synergistic coexistence of electrical, mechanical, and optical signals on a chip to realize new functions. Most of the technology platforms proposed for the fabrication of these systems so far are not fully compatible with the mainstream CMOS technology, thus, hindering the mass-scale utilization. We have developed a CMOS technology platform for nanoelectro-opto-mechanical systems that includes piezoelectric interdigitated transducers for electronic driving of mechanical signals and nanocrystalline silicon nanobeams for an enhanced optomechanical interaction. Room-Temperature operation of devices at 2 GHz and with peak sensitivity down to 2.6 cavity phonons is demonstrated. Our proof-of-principle technology platform can be integrated and interfaced with silicon photonics, electronics, and MEMS devices and may enable multiple functions for coherent signal processing in the classical and quantum domains.

Altres ajuts: CERCA Programme/Generalitat de Catalunya., Spontaneous locking of the phase of a coherent phonon source to an external reference is demonstrated in a deeply sideband-unresolved optomechanical system. The high-amplitude mechanical oscillations are driven by the anharmonic modulation of the radiation pressure force that result from an absorption-mediated free-carrier/temperature limit cycle, i.e., self-pulsing. Synchronization is observed when the pump laser driving the mechanical oscillator to a self-sustained state is modulated by a radiofrequency tone. We employ a pump-probe phonon detection scheme based on an independent optical cavity to observe only the mechanical oscillator dynamics. The lock range of the oscillation frequency, i.e., the Arnold tongue, is experimentally determined over a range of external reference strengths, evidencing the possibility to tune the oscillator frequency for a range up to 350 kHz. The stability of the coherent phonon source is evaluated via its phase noise, with a maximum achieved suppression of 44 dBc/Hz at 1 kHz offset for a 100 MHz mechanical resonator. Introducing a weak modulation in the excitation laser reveals as a further knob to trigger, control and stabilize the dynamical solutions of self-pulsing based optomechanical oscillators, thus enhancing their potential as acoustic wave sources in a single-layer silicon platform.

Spontaneous locking of the phase of a coherent phonon source to an external reference is demonstrated in a deeply sideband-unresolved optomechanical system. The high-amplitude mechanical oscillations are driven by the anharmonic modulation of the radiation pressure force that result from an absorption-mediated free-carrier/temperature limit cycle, i.e., self-pulsing. Synchronization is observed when the pump laser driving the mechanical oscillator to a self-sustained state is modulated by a radiofrequency tone. We employ a pump-probe phonon detection scheme based on an independent optical cavity to observe only the mechanical oscillator dynamics. The lock range of the oscillation frequency, i.e., the Arnold tongue, is experimentally determined over a range of external reference strengths, evidencing the possibility to tune the oscillator frequency for a range up to 350 kHz. The stability of the coherent phonon source is evaluated via its phase noise, with a maximum achieved suppression of 44 dBc/Hz at 1 kHz offset for a 100 MHz mechanical resonator. Introducing a weak modulation in the excitation laser reveals as a further knob to trigger, control and stabilize the dynamical solutions of self-pulsing based optomechanical oscillators, thus enhancing their potential as acoustic wave sources in a single-layer silicon platform.

Nanowires (NWs) are ideal nanostructures for exploring the effects of low dimensionality and thermal conductivity suppression on thermoelectric behavior. However, it is challenging to accurately measure temperature gradients and heat flow in such systems. Here, using a combination of spatially resolved Raman spectroscopy and transport measurements, we determine all the thermoelectric properties of single Se-doped InSb NWs and quantify the figure of merit ZT. The measured laser-induced heating in the NWs and associated electrical response are well described by a 1D heat equation model. Our method allows the determination of the thermal contact resistances at the source and drain electrodes of the NW, which are negligible in our system. The measured thermoelectric parameters of InSb NWs agree well with those obtained based on field-effect transistor Seebeck measurements.

The complexity of contemporary cities requires new tools for the Urban Resilience: old approaches based on the "defensive control" and corrective contingency responses, are replaced by "synergy policies" addressed through preventive, adaptable and reversible actions. In this framework, the term Resili(g)ence proposes to combine "Intelligent" values (information, knowledge, anticipation, projection and adaptation) and "Resilient" valences (resistance and recycling, reaction and recovery, renovation and adaptation) in a new responsive and reactive condition, sensory, sensorized and sensitive, at time. In the context of a new Resili(g)ent approach this new sensibility must take in consideration six resilient main topics (water, earth, fire, air, land-use, eco-systems and communities) referring them to a more complex and crossed network of six possible strategic fields of investigation and prospection (Mapping/Managing – Planning/ Landing – Designing/Socializing), which, interconnected, configure also the framework of multiple innovative experiences and integrated approaches today, infra-, intra-, intro-, eco-, info-… and trans- structural and systemic at time. The 3 IN combination "information (trended) + interaction (threaded) + integration (tended)" announces new dynamics of urban planning aimed at advanced interdisciplinary research, oriented to a strategic integration of operating systems and to a holistic view of its multiple dimensions (patrimonial, sensorial, environmental, cultural and social) in new scenarios not only associated with pure informational management (Smart Cities), but also to its network systematic and to its strategic-planning projection (Intelligent Cities). All this, in the same terms of exploration that are defining a new and emerging Advanced Urbanism linked with the KA-AU Project (Knowledge Alliance for Advanced Urbanism), associated to the European Erasmus Project (2015-2018). The contribution proposes a reflection on this new Resili(g)en

Being at the base of the development of all societies, in so many different levels: food - its culture, production, diffusion, and consumption have a central role in shaping more resilient societies and habitats. This contribution, presenting the Dutch case study of the Nature Farm of Kezersrande, aims to highlight the possibility and the opportunity of exchange between different systems. The design of resilient food cycles is not limited to influencing our society and behaviour, but it also can shape our territories and our cities, in order to achieve both positive ecological results and a wider social integration. The presented project shows the possibility of exchange and integration between a resilient management of hydrogeological risk and a circular and sustainable food production system.

A strong trend for quantum-based technologies and applications follows the avenue of combining different platforms to exploit their complementary technological and functional advantages. Micro and nanomechanical devices are particularly suitable for hybrid integration due to the ease of fabrication at multiscales and their pervasive coupling with electrons and photons. Here, we report on a nanomechanical technological platform where a silicon chip is combined with an aluminum nitride layer. Exploiting the AlN piezoelectricity, surface acoustic waves (SAWs) are injected in the Si layer where the material has been locally patterned and etched to form a suspended nanostring. Characterizing the nanostring vertical displacement induced by the SAW, we find an external excitation peak efficiency in excess of 500 pm/V at 1-GHz mechanical frequency. Exploiting the long-term expertise in silicon photonic and electronic devices as well as the SAW robustness and versatility, our technological platform represents a candidate for hybrid quantum systems.

The resonant enhancement of mechanical and optical interaction in optomechanical cavities enables their use as extremely sensitive displacement and force detectors. In this Letter, we demonstrate a hybrid magnetometer that exploits the coupling between the resonant excitation of spin waves in a ferromagnetic insulator and the resonant excitation of the breathing mechanical modes of a glass microsphere deposited on top. The interaction is mediated by magnetostriction in the ferromagnetic material and the consequent mechanical driving of the microsphere. The magnetometer response thus relies on the spectral overlap between the ferromagnetic resonance and the mechanical modes of the sphere, leading to a peak sensitivity of 850pTHz−1/2 at 206 MHz when the overlap is maximized. By externally tuning the ferromagnetic resonance frequency with a static magnetic field, we demonstrate sensitivity values at resonance around a few nT Hz−1/2 up to the gigahertz range. Our results show that our hybrid system can be used to build a high-speed sensor of oscillating magnetic fields.

During the last decades, the evolution of the urban-territorial city produced a combination of issues about the City-Nature and City-Nature-Landscape relation, such as the change of perspective between the urban, physical and social dimension and the agricultural-landscape system and agricultural-environmental system in the context within which the city redefines and develops itself. This change of perspective stabilized and manifested itself with the increasing awareness that agricultural and forestry spaces must develop a plural, structural, articulate and functional role; a role within which various forms of knowledge and regulations, various norms and sections of public policies are combined. To overcoming the opposition city-country, within which the suburban areas play a vital role - producing and creating function of complex value - a new model of integrated approach towards territorial policies and the geo-urban project is needed; a model able to adequately represents the different applications within the territory, specially in the middle or proto-metropolitan cities on the Mediterranean (Med-Net AgroCities) where the combination Heritage-Tourism-Agriculture-Environment is absolutely crucial but not always well developed in the sense of integrated systems or holistic gazes. This kind of approach focus on a matter that, from the planning point of view appears unavoidable and that refers to the need of integration between territorial and political planning and rural development plans that combine primary/tertiary activities and agricultural production. In this framework, the contribution wants to explore and to analyse the Med-Net AgroCities, with a transdisciplinary, transversal and integrated approach, presenting the theme through the theoretical and active experiences of the GicLab team.

The synchronization of coupled oscillators is a phenomenon found throughout nature. Mechanical oscillators are paradigmatic examples, but synchronizing their nanoscaled versions is challenging. We report synchronization of the mechanical dynamics of a pair of optomechanical crystal cavities that, in contrast to previous works performed in similar objects, are intercoupled with a mechanical link and support independent optical modes. In this regime they oscillate in antiphase, which is in agreement with the predictions of our numerical model that considers reactive coupling. We also show how to temporarily disable synchronization of the coupled system by actuating one of the cavities with a heating laser, so that both cavities oscillate independently. Our results can be upscaled to more than two cavities and pave the way towards realizing integrated networks of synchronized mechanical oscillators.

This contribution explores the role of information technology, relating to the representation and processing of data in open source and crowd-sourced format, for the purpose of urban planning and design process. In the research field, an experimental analysis is carried out within the Genoese neighborhood of Molassana by comparing and processing, in a single system, the traditional cartography provided by the online portals of the public administration and the data shared by users on social networks and open source platforms. The complexity of the information obtained grows a synthetic multi-layer territorial strategy, strongly linked to the local and social context., Il contributo indaga l’apporto fornito dalla tecnologia dell’informazione, relativamente alla rappresentazione ed elaborazione di dati in formato open source, e crowd-sourced, ai fini del processo di pianificazione e progettazione urbana. Nell’ambito di ricerca si svolge un’analisi sperimentale all’interno della frazione genovese di Molassana comparando ed elaborando, in un unico sistema, la cartografia tradizionale fornita dai portali online della pubblica amministrazione e i dati condivisi dagli utenti sui social network e sulle piattaforme open source. Dalla complessità delle informazioni ottenute nasce una strategia territoriale sintetica multilivello, fortemente legata al contesto sia territoriale sia sociale.

This contribution explores the role of information technology, relating to the representation and processing of data in open source and crowd-sourced format, for the purpose of urban planning and design process. In the research field, an experimental analysis is carried out within the Genoese neighborhood of Molassana by comparing and processing, in a single system, the traditional cartography provided by the online portals of the public administration and the data shared by users on social networks and open source platforms. The complexity of the information obtained grows a synthetic multi-layer territorial strategy, strongly linked to the local and social context., Il contributo indaga l’apporto fornito dalla tecnologia dell’informazione, relativamente alla rappresentazione ed elaborazione di dati in formato open source, e crowd-sourced, ai fini del processo di pianificazione e progettazione urbana. Nell’ambito di ricerca si svolge un’analisi sperimentale all’interno della frazione genovese di Molassana comparando ed elaborando, in un unico sistema, la cartografia tradizionale fornita dai portali online della pubblica amministrazione e i dati condivisi dagli utenti sui social network e sulle piattaforme open source. Dalla complessità delle informazioni ottenute nasce una strategia territoriale sintetica multilivello, fortemente legata al contesto sia territoriale sia sociale.

[EN] The information revolution is radically transforming the very foundation of the ‘fossil city’. A ‘virtual’ macro-urbanism will intersect with an ‘actual’ micro-urbanism, physical and concrete, determining the form of the new urban environment. Within the binomial of macro- and micro- urbanism, urban morphology identifies an interesting socio-building scale that can serve as the basic strategy for sustainable city planning in the twenty-first century. Morphology thus becomes the necessary ‘plug-in’ for registering the different ‘networks’ that characterize the contemporary city – from IT and ‘smart’ devices to energy and environmental systems - translating these networks into building practices, into ‘fabrics’, for the physical city. At this purpose an Urban Design methodology has been developed in order to combine the Urban Morphology tools with those of Sustainability giving particular attention to the topics of the comfort outdoor and the passive environmental control systems. The methodology has then been applied in the Sant Adrià De Besos Waterfront Regeneration Project in Barcelona. Neighbourhood’s size, complexity and localisation, between the sea and a large area of brown fields at the northern gateway of the Catalan capital, has set up an interesting testing bench. A sequence of consecutive steps characterizes the methodology in which morphology, architecture and sustainability intersect one another within a single design process.

[EN] The information revolution is radically transforming the very foundation of the ‘fossil city’. A ‘virtual’ macro-urbanism will intersect with an ‘actual’ micro-urbanism, physical and concrete, determining the form of the new urban environment. Within the binomial of macro- and micro- urbanism, urban morphology identifies an interesting socio-building scale that can serve as the basic strategy for sustainable city planning in the twenty-first century. Morphology thus becomes the necessary ‘plug-in’ for registering the different ‘networks’ that characterize the contemporary city – from IT and ‘smart’ devices to energy and environmental systems - translating these networks into building practices, into ‘fabrics’, for the physical city. At this purpose an Urban Design methodology has been developed in order to combine the Urban Morphology tools with those of Sustainability giving particular attention to the topics of the comfort outdoor and the passive environmental control systems. The methodology has then been applied in the Sant Adrià De Besos Waterfront Regeneration Project in Barcelona. Neighbourhood’s size, complexity and localisation, between the sea and a large area of brown fields at the northern gateway of the Catalan capital, has set up an interesting testing bench. A sequence of consecutive steps characterizes the methodology in which morphology, architecture and sustainability intersect one another within a single design process.

[EN] The information revolution is radically transforming the very foundation of the ‘fossil city’. A ‘virtual’ macro-urbanism will intersect with an ‘actual’ micro-urbanism, physical and concrete, determining the form of the new urban environment. Within the binomial of macro- and micro- urbanism, urban morphology identifies an interesting socio-building scale that can serve as the basic strategy for sustainable city planning in the twenty-first century. Morphology thus becomes the necessary ‘plug-in’ for registering the different ‘networks’ that characterize the contemporary city – from IT and ‘smart’ devices to energy and environmental systems - translating these networks into building practices, into ‘fabrics’, for the physical city. At this purpose an Urban Design methodology has been developed in order to combine the Urban Morphology tools with those of Sustainability giving particular attention to the topics of the comfort outdoor and the passive environmental control systems. The methodology has then been applied in the Sant Adrià De Besos Waterfront Regeneration Project in Barcelona. Neighbourhood’s size, complexity and localisation, between the sea and a large area of brown fields at the northern gateway of the Catalan capital, has set up an interesting testing bench. A sequence of consecutive steps characterizes the methodology in which morphology, architecture and sustainability intersect one another within a single design process.

[EN] The information revolution is radically transforming the very foundation of the ‘fossil city’. A ‘virtual’ macro-urbanism will intersect with an ‘actual’ micro-urbanism, physical and concrete, determining the form of the new urban environment. Within the binomial of macro- and micro- urbanism, urban morphology identifies an interesting socio-building scale that can serve as the basic strategy for sustainable city planning in the twenty-first century. Morphology thus becomes the necessary ‘plug-in’ for registering the different ‘networks’ that characterize the contemporary city – from IT and ‘smart’ devices to energy and environmental systems - translating these networks into building practices, into ‘fabrics’, for the physical city. At this purpose an Urban Design methodology has been developed in order to combine the Urban Morphology tools with those of Sustainability giving particular attention to the topics of the comfort outdoor and the passive environmental control systems. The methodology has then been applied in the Sant Adrià De Besos Waterfront Regeneration Project in Barcelona. Neighbourhood’s size, complexity and localisation, between the sea and a large area of brown fields at the northern gateway of the Catalan capital, has set up an interesting testing bench. A sequence of consecutive steps characterizes the methodology in which morphology, architecture and sustainability intersect one another within a single design process.

[EN] The information revolution is radically transforming the very foundation of the ‘fossil city’. A ‘virtual’ macro-urbanism will intersect with an ‘actual’ micro-urbanism, physical and concrete, determining the form of the new urban environment. Within the binomial of macro- and micro- urbanism, urban morphology identifies an interesting socio-building scale that can serve as the basic strategy for sustainable city planning in the twenty-first century. Morphology thus becomes the necessary ‘plug-in’ for registering the different ‘networks’ that characterize the contemporary city – from IT and ‘smart’ devices to energy and environmental systems - translating these networks into building practices, into ‘fabrics’, for the physical city. At this purpose an Urban Design methodology has been developed in order to combine the Urban Morphology tools with those of Sustainability giving particular attention to the topics of the comfort outdoor and the passive environmental control systems. The methodology has then been applied in the Sant Adrià De Besos Waterfront Regeneration Project in Barcelona. Neighbourhood’s size, complexity and localisation, between the sea and a large area of brown fields at the northern gateway of the Catalan capital, has set up an interesting testing bench. A sequence of consecutive steps characterizes the methodology in which morphology, architecture and sustainability intersect one another within a single design process.

[EN] The information revolution is radically transforming the very foundation of the ‘fossil city’. A ‘virtual’ macro-urbanism will intersect with an ‘actual’ micro-urbanism, physical and concrete, determining the form of the new urban environment. Within the binomial of macro- and micro- urbanism, urban morphology identifies an interesting socio-building scale that can serve as the basic strategy for sustainable city planning in the twenty-first century. Morphology thus becomes the necessary ‘plug-in’ for registering the different ‘networks’ that characterize the contemporary city – from IT and ‘smart’ devices to energy and environmental systems - translating these networks into building practices, into ‘fabrics’, for the physical city. At this purpose an Urban Design methodology has been developed in order to combine the Urban Morphology tools with those of Sustainability giving particular attention to the topics of the comfort outdoor and the passive environmental control systems. The methodology has then been applied in the Sant Adrià De Besos Waterfront Regeneration Project in Barcelona. Neighbourhood’s size, complexity and localisation, between the sea and a large area of brown fields at the northern gateway of the Catalan capital, has set up an interesting testing bench. A sequence of consecutive steps characterizes the methodology in which morphology, architecture and sustainability intersect one another within a single design process.

In this work we show how a continuous wave, low threshold and well collimated terahertz laser source can be obtained by coupling two sub-wavelength whispering galleries quantum cascade optical resonators with a suspended metallic bridge.

In this work we show how a continuous wave, low threshold and well collimated terahertz laser source can be obtained by coupling two sub-wavelength whispering galleries quantum cascade optical resonators with a suspended metallic bridge.

We demonstrate the use of a compound optical cavity as linear displacement detector, by measuring the thermal motion of a silicon nitride suspended membrane acting as the external mirror of a near-infrared Littrow laser diode. Fluctuations in the laser optical power induced by the membrane vibrations are collected by a photodiode integrated within the laser, and then measured with a spectrum analyzer. The dynamics of the membrane driven by a piezoelectric actuator is investigated as a function of air pressure and actuator displacement in a homodyne configuration. The high Q-factor (~3.4 · 10 4 at 8.3 · 10 −3 mbar) of the fundamental mechanical mode at ~73 kHz guarantees a detection sensitivity high enough for direct measurement of thermal motion at room temperature (~87 pm RMS). The compound cavity system here introduced can be employed as a table-top, cost-effective linear displacement detector for cavity optomechanics. Furthermore, thanks to the strong optical nonlinearities of the laser compound cavity, these systems open new perspectives in the study of non-Markovian quantum properties at the mesoscale.

In this paper we investigate the effect of a static magnetic field and of optical pumping on the transmittance of a hybrid graphene-split ring resonator metasurface. A significant modulation of the transmitted spectra is obtained, both by optical pumping, and by a combination of optical pumping and magnetostatic biasing. The transmittance modulation features spectral fingerprints that are characteristic of a non-Trivial interplay between the bare graphene response and the split ring resonance.

Laser cavities have been realized in various different photonic systems. One of the forefront research fields regards the investigation of the physics of amplifying random optical media. The random laser is a fascinating concept because, further to the fundamental research investigating light transport into complex media, it allows us to obtain non-conventional spectral distribution and angular beam emission patterns not achievable with conventional approaches. Even more intriguing is the possibility to engineer a priori the optical properties of a disordered distribution in an amplifying medium. We demonstrate here the realization of a terahertz quantum cascade laser in an isotropic hyperuniform disordered distribution exhibiting unique features, such as the presence of a photonic band gap, low threshold current density, unconventional angular emission and optical bistability.

Laser cavities have been realized in various different photonic systems. One of the forefront research fields regards the investigation of the physics of amplifying random optical media. The random laser is a fascinating concept because, further to the fundamental research investigating light transport into complex media, it allows us to obtain non-conventional spectral distribution and angular beam emission patterns not achievable with conventional approaches. Even more intriguing is the possibility to engineer a priori the optical properties of a disordered distribution in an amplifying medium. We demonstrate here the realization of a terahertz quantum cascade laser in an isotropic hyperuniform disordered distribution exhibiting unique features, such as the presence of a photonic band gap, low threshold current density, unconventional angular emission and optical bistability.

[EN] We report a novel injection scheme that allows for phonon lasing in a one-dimensional optomechanical photonic crystal, in a sideband unresolved regime and with cooperativity values as low as 10-2. It extracts energy from a cw infrared laser source and is based on the triggering of a thermooptical/free-carrier-dispersion self-pulsing limit-cycle, which anharmonically modulates the radiation pressure force. The large amplitude of the coherent mechanical motion acts as a feedback that stabilizes and entrains the self-pulsing oscillations to simple fractions of the mechanical frequency. A manifold of frequency-entrained regions with two different mechanical modes (at 54 and 122 MHz) are observed as a result of the wide tuneability of the natural frequency of the self-pulsing. The system operates at ambient conditions of pressure and temperature in a silicon platform, which enables its exploitation in sensing, intra-chip metrology or time-keeping applications.

[EN] We report a novel injection scheme that allows for phonon lasing in a one-dimensional optomechanical photonic crystal, in a sideband unresolved regime and with cooperativity values as low as 10-2. It extracts energy from a cw infrared laser source and is based on the triggering of a thermooptical/free-carrier-dispersion self-pulsing limit-cycle, which anharmonically modulates the radiation pressure force. The large amplitude of the coherent mechanical motion acts as a feedback that stabilizes and entrains the self-pulsing oscillations to simple fractions of the mechanical frequency. A manifold of frequency-entrained regions with two different mechanical modes (at 54 and 122 MHz) are observed as a result of the wide tuneability of the natural frequency of the self-pulsing. The system operates at ambient conditions of pressure and temperature in a silicon platform, which enables its exploitation in sensing, intra-chip metrology or time-keeping applications.

A terahertz quantum cascade laser has been realized from an isotropic disordered hyperuniform design. Such a system presents a photonic band-gap although it is characterized by an efficient depletion of the long range order. Hyperuniform patterns allow greater versatility in engineering band gaps in comparison to standard photonic-crystal materials. Bidimensional hyperuniform patterns were simulated for hexagonal tiles composed of high refractive index disks merged in a low dielectric constant polymeric matrix. Based on this design, quantum cascade lasers were fabricated by standard photolithography, metal evaporation, lift-off and dry-etching techniques in a half-stack bound to continuum active region emitting around 2.9 THz.

By placing a material in close vicinity of a resonant optical element, its intrinsic optical response can be tuned, possibly to a wide extent. Here, we show that a graphene monolayer, spaced a few tenths of nanometers from a split ring resonator metasurface, exhibits a magneto-optical response which is strongly influenced by the presence of the metasurface itself. This hybrid system holds promises in view of thin optical modulators, polarization rotators, and nonreciprocal devices, in the technologically relevant terahertz spectral range. Moreover, it could be chosen as the playground for investigating the cavity electrodynamics of Dirac fermions in the quantum regime.

A terahertz quantum cascade laser has been realized from an isotropic disordered hyperuniform design. Such a system presents a photonic band-gap although it is characterized by an efficient depletion of the long range order. Hyperuniform patterns allow greater versatility in engineering band gaps in comparison to standard photonic-crystal materials. Bidimensional hyperuniform patterns were simulated for hexagonal tiles composed of high refractive index disks merged in a low dielectric constant polymeric matrix. Based on this design, quantum cascade lasers were fabricated by standard photolithography, metal evaporation, lift-off and dry-etching techniques in a half-stack bound to continuum active region emitting around 2.9 THz.

[EN] We report on the optomechanical properties of a breathing mechanical mode oscillating at 5.5 GHz in a 1D corrugated Si nanobeam. This mode has an experimental single-particle optomechanical coupling rate of vertical bar g(o, OM)vertical bar= 1.8 MHz (vertical bar g(o, OM)vertical bar/2 pi=0.3 MHz) and shows strong dynamical back-action effects at room temperature. The geometrical flexibility of the unit-cell would lend itself to further engineering of the cavity region to localize the mode within the full phononic band-gap present at 4 GHz while keeping high go, OM values. This would lead to longer lifetimes at cryogenic temperatures, due to the suppression of acoustic leakage.

[EN] We report on the optomechanical properties of a breathing mechanical mode oscillating at 5.5 GHz in a 1D corrugated Si nanobeam. This mode has an experimental single-particle optomechanical coupling rate of vertical bar g(o, OM)vertical bar= 1.8 MHz (vertical bar g(o, OM)vertical bar/2 pi=0.3 MHz) and shows strong dynamical back-action effects at room temperature. The geometrical flexibility of the unit-cell would lend itself to further engineering of the cavity region to localize the mode within the full phononic band-gap present at 4 GHz while keeping high go, OM values. This would lead to longer lifetimes at cryogenic temperatures, due to the suppression of acoustic leakage.

We fabricate and characterize a microscale silicon electro-opto-mechanical system whose mechanical motion is coupled capacitively to an electrical circuit and optically via radiation pressure to a photonic crystal cavity. To achieve large electromechanical interaction strength, we implement an inverse shadow mask fabrication scheme which obtains capacitor gaps as small as 30 nm while maintaining a silicon surface quality necessary for minimizing optical loss. Using the sensitive optical read-out of the photonic crystal cavity, we characterize the linear and nonlinear capacitive coupling to the fundamental 63 MHz in-plane flexural motion of the structure, showing that the large electromechanical coupling in such devices may be suitable for realizing efficient microwave-to-optical signal conversion.

We fabricate and characterize a microscale silicon electro-opto-mechanical system whose mechanical motion is coupled capacitively to an electrical circuit and optically via radiation pressure to a photonic crystal cavity. To achieve large electromechanical interaction strength, we implement an inverse shadow mask fabrication scheme which obtains capacitor gaps as small as 30 nm while maintaining a silicon surface quality necessary for minimizing optical loss. Using the sensitive optical read-out of the photonic crystal cavity, we characterize the linear and nonlinear capacitive coupling to the fundamental 63 MHz in-plane flexural motion of the structure, showing that the large electromechanical coupling in such devices may be suitable for realizing efficient microwave-to-optical signal conversion.

We report a spectroscopic study about the energy transfer mechanism among silicon nanoparticles (Si-np), both amorphous and crystalline, and Er ions in a silicon dioxide matrix. From infrared spectroscopic analysis, we have determined that the physics of the transfer mechanism does not depend on the Si-np nature, finding a fast (< 200 ns) energy transfer in both cases, while the amorphous nanoclusters reveal a larger transfer efficiency than the nanocrystals. Moreover, the detailed spectroscopic results in the visible range here reported are essential to understand the physics behind the sensitization effect, whose knowledge assumes a crucial role to enhance the transfer rate and possibly employing the material in optical amplifier devices. Joining the experimental data, performed with pulsed and continuous-wave excitation, we develop a model in which the internal intraband recombination within Si-np is competitive with the transfer process via an Auger electron"recycling" effect. Posing a different light on some detrimental mechanism such as Auger processes, our findings clearly recast the role of Si-np in the sensitization scheme, where they are able to excite very efficiently ions in close proximity to their surface. (C) 2010 American Institute of Physics.

Nanowires (NWs) are ideal nanostructures for exploring the effects of low dimensionality and thermal conductivity suppression on thermoelectric behavior. However, it is challenging to accurately measure temperature gradients and heat flow in such systems. Here, using a combination of spatially resolved Raman spectroscopy and transport measurements, we determine all the thermoelectric properties of single Se-doped InSb NWs and quantify the figure of merit ZT. The measured laser-induced heating in the NWs and associated electrical response are well described by a 1D heat equation model. Our method allows the determination of the thermal contact resistances at the source and drain electrodes of the NW, which are negligible in our system. The measured thermoelectric parameters of InSb NWs agree well with those obtained based on field-effect transistor Seebeck measurements.