Optomechanical coupling in the Anderson-localization regime

Optomechanical crystals, purposely designed and fabricated semiconductor nanostructures, are used to enhance the coupling between the electromagnetic field and the mechanical vibrations of matter at the nanoscale. However, in real optomechanical crystals, imperfections open extra channels where the transfer of energy is lost, reducing the optomechanical coupling efficiency. Here, we quantify the role of disorder in a paradigmatic one-dimensional optomechanical crystal with full phononic and photonic band gaps. We show how disorder can be exploited as a resource to enhance the optomechanical coupling beyond engineered structures, thus providing a new tool set for optomechanics

Synchronization of Optomechanical Nanobeams by Mechanical Interaction

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

Impact of distributed generation on voltage in LV networks

Cílem této práce je popsat problematiku připojování a provozu rozptýlených zdrojů elektřiny vzhledem k distribuční síti z pohledu provozovatele distribuční soustavy ? konkrétně pak napěťové poměry na přípojném místě daných výroben s ohledem na dopady na distribuční síť nn. Jako hlavní zástupce obnovitelných zdrojů elektrické energie (OZE) jsou v této práci diskutovány především fotovoltaické elektrárny (FVE) a větrné elektrárny (VTE), které společně tvoří výraznou většinu instalovaného výkonu rozptýlených obnovitelných zdrojů energie připojených do sítí nízkého napětí distribuční soustavy (DS) České republiky. Teoretická část práce shrnuje současný stav na poli s obnovitelnými zdroji energie v České republice i ve světě a kompiluje dosavadní zkušenosti z provozu OZE s teoretickými rozbory provedenými různými pracovními skupinami. Určitá pasáž je rovněž věnována výtahu nejpodstatnějších částí pravidel provozování distribuční soustavy týkající se připojování rozptýlených výroben do distribuční sítě. Výsledky práce vycházejí z detailní analýzy rozsáhlé kampaně měření sítí s instalovanou rozptýlenou výrobou v DS provedené společností E.ON Distribuce, a.s. a jejich výstupem je zhodnocení stávající situace na reprezentativním vzorku sítí a dále návrhy na nápravu případných vyskytujících se problémů s ohledem na dodržení garantovaných standardů kvality napětí v DS dle požadavků normy ČSN EN 50160.Katedra elektroenergetiky a ekologieObhájenoThe aim of this work is to describe the problems of connection and operation of distributed power resources from the perspective of the distribution network operator ? namely the voltage conditions at the point of common coupling of the particular generators with regard to the impacts on low-voltage distribution network. As the main representative of renewable energy sources (RES) the photovoltaic power plants (PVP) and the wind power plants (WPP), which form together the large majority of the installed capacity of the distributed renewable energy sources connected to the low voltage network of the distribution network (DN) of the Czech Republic, are discussed in this work. The theoretical part of the thesis summarizes the current state in the field of renewable energy in the Czech Republic and in the world and compiles experience from the operation of RES with the theoretical analysis carried out by different working groups. A certain passage is also given to the digest of the most important parts of the distribution networks operating rules related to the connection of distributed power plants. The results of this work proceeds from detailed analysis of extensive measurement campaign carried out in networks with installed distributed generation made by E.ON Distribution, a.s. company and their output is the assessment of the current situation in a sample of representative networks and the proposals to remedy any problems encountered with regard to compliance with the guaranteed voltage quality standards in the DN according to ČSN EN 50160

Optical modulation of coherent phonon emission in optomechanical cavities

Optomechanical (OM) structures are well suited to study photon-phonon interactions, and they also turn out to be potential building blocks for phononic circuits and quantum computing. In phononic circuits, in which information is carried and processed by phonons, OM structures could be used as interfaces to photons and electrons thanks to their excellent coupling efficiency. Among the components required for phononic circuits, such structures could be used to create coherent phonon sources and detectors, but more complex functions remain challenging. Here, we propose and demonstrate a way to modulate the coherent phonon emission from OM crystals by a photothermal effect induced by an external laser, effectively creating a phonon switch working at ambient conditions of pressure and temperature and the working speed of which is only limited by the build-up time of the mechanical motion of the OM structure. We additionally demonstrate two other modulation schemes: modulation of harmonics in which the mechanical mode remains active but different harmonics of the optical force are used, and modulation to and from a chaotic regime. Furthermore, due to the local nature of the photothermal effect used here, we expect this method to allow us to selectively modulate the emission of any single cavity on a chip without affecting its surroundings in the absence of mechanical coupling between the structures, which is an important step toward freely controllable networks of OM phonon emitters

Nonlinear dynamics and chaos in an optomechanical beam

Altres ajuts: Beatriu de Pinos postdoctoral fellowship (BP-DGR 2015)Optical nonlinearities, such as thermo-optic mechanisms and free-carrier dispersion, are often considered unwelcome effects in silicon-based resonators and, more specifically, optomechanical cavities, since they affect, for instance, the relative detuning between an optical resonance and the excitation laser. Here, we exploit these nonlinearities and their intercoupling with the mechanical degrees of freedom of a silicon optomechanical nanobeam to unveil a rich set of fundamentally different complex dynamics. By smoothly changing the parameters of the excitation laser we demonstrate accurate control to activate two- A nd four-dimensional limit cycles, a period-doubling route and a six-dimensional chaos. In addition, by scanning the laser parameters in opposite senses we demonstrate bistability and hysteresis between two- A nd four-dimensional limit cycles, between different coherent mechanical states and between four-dimensional limit cycles and chaos. Our findings open new routes towards exploiting silicon-based optomechanical photonic crystals as a versatile building block to be used in neurocomputational networks and for chaos-based applications

Optomechanical coupling in the Anderson-localization regime

Optomechanical crystals, purposely designed and fabricated semiconductor nanostructures, are used to enhance the coupling between the electromagnetic field and the mechanical vibrations of matter at the nanoscale. However, in real optomechanical crystals, imperfections open extra channels where the transfer of energy is lost, reducing the optomechanical coupling efficiency. Here, we quantify the role of disorder in a paradigmatic one-dimensional optomechanical crystal with full phononic and photonic band gaps. We show how disorder can be exploited as a resource to enhance the optomechanical coupling beyond engineered structures, thus providing a new tool set for optomechanics

Nanocrystalline silicon optomechanical cavities

Silicon on insulator photonics has offered a versatile platform for the recent development of integrated optomechanical circuits. However, there are some constraints such as the high cost of the wafers and limitation to a single physical device level. In the present work we investigate nanocrystalline silicon as an alternative material for optomechanical devices. In particular, we demonstrate that optomechanical crystal cavities fabricated of nanocrystalline silicon have optical and mechanical properties enabling non-linear dynamical behaviour and effects such as thermo-optic/free-carrier-dispersion self-pulsing, phonon lasing and chaos, all at low input laser power and with typical frequencies as high as 0.3 GHz

Synchronization of Optomechanical Nanobeams by Mechanical Interaction

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