125 research outputs found
Electromechanical tuning of photonic crystal cavities
Get PDFPhotonic crystal cavities (PCCs) are electromagnetic resonators obtained introducing defects in periodic dielectric structures. They have been widely used in semiconductor nanophotonics devices to realize low-threshold lasers, filters and switches operating at telecommunication wavelengths. Moreover, when coupled to quantum emitters such as quantum dots, PCC are used to enhance their spontaneous emission rate according to Fermi’s golden rule. Such a coupled cavitydot system provides a small-scale integrated implementation of a single photon source, a device which plays a fundamental role for quantum information processing. However, fabrication imperfections and ageing make the resonant wavelength of PCCs non-reproducible and tuning methods are needed to compensate the spectral mismatch between a cavity and a quantum dot during experiments. Moreover, for quantum information processing it is important to electrically tune many cavities independently over a range of several nanometers at low temperatures. In this thesis work I explored novel devices for the spectral control and reconfiguration of PCCs using nano electromechanical systems (NEMS). The fundamental idea, described in the first chapter, consists in fabricating the photonic crystal on two, closely spaced, parallel slabs to form a coupled system and modifying their distance electro-mechanically to alter the coupling strength. The displacement is obtained using doped layers to form a p-i-n junction across the air gap between the membranes and operating it under reverse bias to exert an attractive electrostatic pressure on each slab. A simple model to describe the coupled cavity system and the electrostatic actuator is proposed. This model forms the basis for the device design and the estimation of the tuning range. The latter is limited only by pull-in, an electrostatic instability which occurs whenever the membranes are displaced more than one third of the distance at rest. In chapter 1, an introduction to the physics of photonic crystals, quantum dots and cavity quantum electrodynamics is also provided along with a detailed review of the cavity tuning methods which have been already proposed in the literature. The second chapter discusses the fabrication of double-slab photonic crystals and their integration with the electrostatic actuator. The chapter addresses the problem of stiction (or static friction) between the membranes due to the strong capillary forces involved during the sample drying. A novel fabrication procedure which reduces stiction by increasing the total stiffness of the system with a dielectric layer is described. Chapter 2 also includes an overview of the experimental setups used for the electro-optical characterization of PCCs and quantum dots. The chapter ends with a discussion on the device design based on the model from chapter 1 and the practical fabrication limits due to capillary forces. In the third chapter, the experimental results on the electromechanical tuning of InGaAsP at room temperature are reported. The simultaneous blue- and redshift of the coupled normal modes is observed. A maximum tuning of 10 nm has been measured with a reverse bias of 5.8 V beyond which, the pull-in phenomenon occurs. Using a periodic signal as a driving force and measuring the spectral response, the signature of mechanical resonances has been observed and the corresponding frequencies have been compared to simulations. All these results provide a conclusive demonstration of the mechanical origin of the tuning. The fourth chapter describes the tuning of GaAs devices at low temperatures for the spectral alignment of cavity modes to single quantum dots. A PCC resonance has been shifted over 13 nm to match the emission of a far-detuned excitonic line. The enhancement of spontaneous emission rate has been confirmed with timeresolved photoluminescence measurements, a technique which allows measuring the emitter’s lifetime. A four-fold enhancement has been obtained between the dot on-resonance and the dots in the homogeneous (or bulk) medium, indicating that PCC can be used to enhance the rate of single photon emission from single quantum dots. The fifth chapter describes a slightly different tunable photonic crystal based on two, vertically-coupled, nanobeams. The device, realized on GaAs, is realized with an original fabrication method which prevents adhesion of these nanostructures under capillary forces. A new design is also introduced to mount the nanobeams on flexible frames to enhance the tunability. A tuning range of 15.6 nm has been measured, which is the current record for electromechanical tuning on doublemembrane NEMS. The sixth chapter contains several new ideas and perspectives on the integration of double membranes in photonic circuits and on the extension of the tuning range. The coupling to composite ridge waveguides and an original method to fabricate them on double slabs is discussed. The first experimental results have shown the possibility to observe Fabry-Pérot modes in a photonic crystal waveguide from the cleaved facet of a ridge waveguide, located 1 mm away from the source. The overall transmission, however, still requires optimization. The double membrane can also be integrated with the wavelength tuning of quantum dots (via Stark effect) using a third contact layer, opening up new perspectives on the generation of indistinguishable photons. The chapter ends with a proposed structure to realize a pull-in free device, thereby extending the total tuning range beyond the current record values. Finally, the last chapter summarizes the most relevant results of this thesis work and the open issues which set the basis for future research activities
Active routing of single photons from quantum dots in GaAs photonic integrated circuits (Conference Presentation)
No full textTrapianto di midollo osseo nelle aplasie midollari.
No full textDopo un breve cenno sulla etico-patogenesi delle aplasie midollari, gli AA. riferiscono i dati più salienti della letteratura sul trapianto di midolo osseo allogenico ed isogenico in tali emopatie.Vengono riferiti i risultati a distanza osservati dagli AA. nel primo caso di aplasia midollare globale trattato in Italia con mielotrapianto isogenico.Gli AA. schematizzano infine le indicazioni al mielotrapianto nelle aplasie midollari, senza minimizzare i pericoli che tuttora comporta tale trattamento e gli insuccessi cui si può incorrere
Quantum-information processing with integrated photonic circuits Nanolight 16 conference, Benasque, Spain, March 7-11
No full textNano-Opto-Electro-Mechanical Systems for Integrated Quantum Photonics
No full textThis chapter covers the topic of nano-opto-electro-mechanical systems (NOEMS) and their application in quantum photonic integrated circuits. When reducing the size of optical devices down to the nano-scale, as in nanophotonics and plasmonics, the properties of confined optical waves become increasingly affected by small geometrical variations of the materials. These variations produce a wide range of electro- and opto-mechanical interactions that do not depend on any intrinsic material property and therefore can be operated at cryogenic temperatures and seamlessly integrated in quantum photonic circuits with embedded quantum emitters and single-photon detectors. We discuss the basic principles of operation of NOEMS, the techniques involved in their fabrication, and the functionalities that such devices can provide toward the realization of scalable quantum photonic integrated technologies.</p
Design and optical properties of electromechanical double-membrane photonic crystal cavities
Get PDFWe discuss relevant design considerations for the fabrication of electromechanically tunable photonic crystal cavities based on double semiconductor slabs. A simple optical and
electromechanical model of the device based on coupled-mode theory and electrostatics is discussed and used jointly with 3-D finite-element calculations of optical cavity modes to extract the
tuning-range dependence on geometrical parameters. A design rule, which avoids the sticking of membranes due to capillary forces and keeps a large tunability, is defined. The details of
the fabrication process and a summary of the experimental results on GaAs and InGaAsP/InP material systems are given. We also address the problem of nonsymmetric devices, where the
thicknesses of the membranes are not exactly the same, resulting in an imbalanced power emission of coupled modes
Helicobacter pylori infection : bacterial killing in-vitro, serologic detection and detection of antimicrobial resistance
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Nano-opto-electro-mechanical systems
Get PDFA new class of hybrid systems that couple optical, electrical and mechanical degrees of freedom in nanoscale devices is under development in laboratories worldwide. These nano-opto-electro-mechanical systems (NOEMS) offer unprecedented opportunities to control the flow of light in nanophotonic structures, at high speed and low power consumption. Drawing on conceptual and technological advances from the field of optomechanics, they also bear the potential for highly efficient, low-noise transducers between microwave and optical signals, in both the classical and the quantum domains. This Perspective discusses the fundamental physical limits of NOEMS, reviews the recent progress in their implementation and suggests potential avenues for further developments in this field
In-plane resonant excitation of quantum dots in a dual-mode photonic-crystal waveguide with high beta-factor
No full textA high-quality quantum dot (QD) single-photon source is a key resource for quantum information processing. Exciting a QD emitter resonantly can greatly suppress decoherence processes and lead to highly indistinguishable single-photon generation. It has, however, remained a challenge to implement strict resonant excitation in a stable and scalable way, without compromising any of the key specs of the source (efficiency, purity, and indistinguishability). In this work, we propose a novel dual-mode photonic-crystal waveguide that realizes direct in-plane resonant excitation of the embedded QDs. The device relies on a two-mode waveguide design, which allows exploiting one mode for excitation of the QD and the other mode for collecting the emitted single photons with high efficiency. By proper engineering of the photonic bandstructure, we propose a design with single-photon collection efficiency of beta > 0.95 together with a single-photon impurity of epsilon < 5 x 10(-3) over a broad spectral and spatial range. The device has a compact footprint of similar to 50 mu m(2) and would enable stable and scalable excitation of multiple emitters for multi-photon quantum applications.</p
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