Near to short wave infrared light generation through AlGaAs-on-insulator nanoantennas

AlGaAs-on-insulator (AlGaAs-OI) has recently emerged as a promising platform for nonlinear optics at the nanoscale. Among the most remarkable outcomes, second-harmonic generation (SHG) in the visible/near infrared spectral region has been demonstrated in AlGaAs-OI nanoantennas (NAs). In order to extend the nonlinear frequency generation towards the short wave infrared window, in this work we propose and demonstrate via numerical simulations difference frequency generation (DFG) in AlGaAs-OI NAs. The NA geometry is finely adjusted in order to obtain simultaneous optical resonances at the pump, signal and idler wavelengths, which results in an efficient DFG with conversion efficiencies up to 0.01%. Our investigation includes the study of the robustness against random variations of the NA geometry that may occur at fabrication stage. Overall, these outcomes identify what we believe to be a new potential and yet unexplored application of AlGaAs-OI NAs as compact devices for the generation and control of the radiation pattern in the near to short infrared spectral region

Near to short wave infrared light generation through AlGaAs-on-insulator nanoantennas

AlGaAs-on-insulator (AlGaAs-OI) has recently emerged as a novel promising platform for nonlinear optics at the nanoscale. Among the most remarkable outcomes, second harmonic generation (SHG) in the visible/near infrared spectral region has been demonstrated in AlGaAs-OI nanoantennas (NA). In order to extend the nonlinear frequency generation towards the short wave infrared window, in this work we propose and demonstrate via numerical simulations difference frequency generation (DFG) in AlGaAs-OI NAs. The NA geometry is finely adjusted in order to obtain simultaneous optical resonances at the pump, signal and idler wavelengths, which results in an efficient DFG with conversion efficiencies up to 0.01%. Our investigation includes the study of the robustness against random variations of the NA geometry that may occur at fabrication stage. Overall, these outcomes identify a new potential and yet unexplored application of AlGaAs-OI NAs as compact devices for the generation and control of the radiation pattern in the near to short infrared spectral region

Contributions to nanophotonics: linear, nonlinear and quantum phenomena

(English) Nanophotonics can be defined as the science and technology studying the control optical fields at the nanoscale and their interaction with matter. In order to spatially control such fields we would need structures with characteristic dimensions of the order of the wavelength, bringing us to the nanoscale. A way to control optical fields at this scale is the use of nanoantennas, optical equivalent of radio-antennas. They provide efficient interfaces between near-fields generated by light sources and radiative channels. After a brief Introduction, Chapter 2 describes interaction between single photon emitters and nanoantennas. We start the chapter introducing a method to numerically simulate the interaction. A key concept to solving Maxwell equations is that of the Green function. I show how this function relates to the emission rate of optical emitters in a nanophotonic environment. I then describe an our efforts to build a lifetime-imaging near-field scanning optical microscope. Using this rig we are able to measure changes changes in the emission rate of single emitters that interact with resonant optical antennas. A complementary way to control optical field in the nanoscale is using dielectric confinement. Chapter 3 introduces hybrid structures combining nanoantennas and dielectric waveguides. I generalize the Green function formalism introduced in Chapter 2, and show how this is related to the energy transfer rate between a donor and an acceptor. I use this numerical method to calculate the energy transfer rate in a hybrid structure. An increase of orders of magnitude is found at distances of the order of the wavelengths of the transferred photons. This chapter finishes by discussing the role that the local density of optical states has on the energy transfer efficiency. Nanoantennas increase near-field by orders of magnitude. In these conditions, nonlinear optical effects start to play a role. Chapter 4 is devoted to these nonlinear interactions mediated by nanoantennas. I explore nonlinear interactions in resonant nanoantennas, in particular SHG. First I introduce a method to numerically compute the contributions to SHG generated by the metal in nanoantennas. Both surface and bulk contributions to SHG are considered. I use the numerical method to show that narrowings within the antenna shape are sources of increased SHG. The increase in SHG is attributed to increase of the local field gradients, that increase to the bulk contribution to SHG. We numerically validate our results by performing SHG measurements at the single resonant antenna level. Optical fields are functions of space, but also of time. The development of broadband femtosecond lasers and pulse shaping techniques allows control of optical field down to the femtosecond timescale. Chapter 5 explores the control of optical fields in time. Using phase shaping methods we optimize the two-photon absorption process in single QDs. I introduce a new optimization algorithm, that allows us to perform the optimization using as feedback signal the luminesce from single QDs. We then compare our results with standard phase shaping techniques. Based on their success to effectively control all kinds of optical fields, plasmon supporting nanoantennas are being actively researched in the field of quantum optics. In Chapter 6 I describe a quantum eraser experiment mediated by structures supporting surface plasmon resonances. I first explain the details and subtleties of a quantum eraser experiment. I then detail our efforts to reproduce previously reported results about how to fabricate elliptical bullseye antennas behaving as quarter waveplates. Quarter waveplates are a required part for the quantum eraser effect to take place. An additional key component of our experiment is a bright, state-of-the-art entangle polarization entangle photon source that is described at length. We then perform a quantum eraser experiment mediated by plasmons.(Español) La nanofotónica es el conjunto de ciencia y tecnologías que estudian el control de campos ópticos en la nanoescala y la interacción de estos con la materia. Para controlar estos campos, necesitamos estructuras con dimensiones características del orden la su longitud de onda, lo que nos lleva a la nanoescala. Una forma de controlar campos ópticos a estas escalas es mediante el uso de nanoantenas, los equivalentes a frecuencias ópticas de las antenas de radio. Las nanoantenas proporcionan interfaces entre los campos cercanos generados por emisores ópticos y modos de radiación. Tras una breve introducción, el capítulo 2 describe la interacción entre emisores de fotones individuales y nanoantennas. El capitulo comienza introduciendo un método numérico de simulación que nos permite calcular la función de Green y su relación con la tasa de emisión de fotones de emisores ópticos en entornos nanofotónicos. Describo a continuación la construcción de un microscopio óptico de campo cercano capaz de medir el tiempo de vida de las tasas de emisión de emisores de fotones individuales que interactúan con nanoantenas. Un método complementario para controlar campos ópticos es la utilización del confinamiento dialéctico. El capítulo 3 introduce estructuras híbridas que combinan nanoantenas y guías de onda. Generalizo el formalismo de las funciones de Green del capitulo 1, y muestro como las nuevas funciones están relacionadas con la transferencia de energía entre un donor y un aceptor. Seguidamente, calculo la tasa de transferencia de fotones mediada por la estructura híbrida. Observamos un incremento de ordenes de magnitud en la tasa de transferencia a distancias comparables con las longitudes de onda de los fotones transmitidos. El capitulo finaliza discutiendo el papel que la densidad local de estado ópticos juega en la eficiencia de la transferencia de energía. Las nanoantenas incrementan el campo cercano órdernes de magnitud. En estas condiciones los efectos no-linearles comienzan a entrar en juego. El capitulo 4 está dedicado a estas interacciones no lineales mediadas por nanoantenas, en particular la generación de segundo armónico (SHG). Primeramente, introduzco un método numérico para calcular las contribuciones superficiales y volumétricas a SHG. Estrecheces introducidas a lo largo de las nanoantenas incrementan las emisiones de SHG. Este incremento es atribuido al incremento de gradientes de campo, que contribuyen mayoritariamente a un incremento de la parte volumétrica. Finalmente validamos nuestros resultados numérico experimentalmente. Los campos ópticos son funciones del espacio, pero también del tiempo. El desarrollo de láseres de femtosegundo de banda ancha, unido a las técnicas de formación de pulsos permiten el control de la luz a escalada de femtosegundos. El capítulo 5 explora este control de los campos en el tiempo. Utilizando técnicas de formación de pulsos optimizamos los procesos de absorción de dos fotones en puntos cuánticos de semiconductores. Introduzco un nuevo algoritmo de optimización que nos permite utilizar como señal de retroalimentación la señal de luminiscencia de puntos cuánticos individuales. Debido al éxito en el control de todo tipo de campos ópticos, las nanoantenas basadas en resonancias de plasmones están siendo activamente investigadas en el campo de la óptica cuántica. En el capitulo 6 describo un experimento de borrado cuántico mediado por estructuras basadas en resonancias plasmónicas. Primeramente describo los detalles y sutilezas de este tipo de experimentos. Seguidamente detallo nuestros esfuerzos para reproducir resultados previos acerca de la fabricación antenas elípticas de diana que se comportan como retardados de cuarto de onda. Estos retardadores de cuarto de onda son necesarios para que el efecto de borrado cuántico pueda darse. Otro ingrediente clave de nuestro experimento es una fuente brillante de fotones ...Postprint (published version

A nested hybridizable discontinuous Galerkin method for computing second-harmonic generation in three-dimensional metallic nanostructures

In this paper, we develop a nested hybridizable discontinuous Galerkin (HDG) method to numerically solve the Maxwell's equations coupled with the hydrodynamic model for the conduction-band electrons in metals. By means of a static condensation to eliminate the degrees of freedom of the approximate solution defined in the elements, the HDG method yields a linear system in terms of the degrees of freedom of the approximate trace defined on the element boundaries. Furthermore, we propose to reorder these degrees of freedom so that the linear system accommodates a second static condensation to eliminate a large portion of the degrees of freedom of the approximate trace, thereby yielding a much smaller linear system. For the particular metallic structures considered in this paper, the resulting linear system obtained by means of nested static condensations is a block tridiagonal system, which can be solved efficiently. We apply the nested HDG method to compute the second harmonic generation (SHG) on a triangular coaxial periodic nanogap structure. This nonlinear optics phenomenon features rapid field variations and extreme boundary-layer structures that span multiple length scales. Numerical results show that the ability to identify structures which exhibit resonances at $\omega$ and $2\omega$ is paramount to excite the second harmonic response.Comment: 31 pages, 7 figure

Riesz-projection-based methods for the numerical simulation of resonance phenomena in nanophotonics

Resonance effects are ubiquitous in physics and essential for understanding wave propagation and interference. In the field of nanophotonics, devices are often based on the strong confinement of light by resonances. The numerical simulation of resonances plays a crucial role for the design and optimization of the devices. The resonances are electromagnetic field solutions to the time-harmonic source-free Maxwell's equations with loss mechanisms. The corresponding eigenproblems are non-Hermitian due to the losses leading to complex-valued eigenvalues. The material dispersion, which is typically significant in nanophotonics, results in nonlinear eigenproblems. In this thesis, we develop an approach based on Riesz projections for the expansion of electromagnetic fields caused by light sources into resonances. The Riesz projection expansion is computed by contour integration in the complex frequency plane. The numerical realization essentially relies on solving Maxwell's equations with a source term, meaning solving linear systems of equations. For this, Maxwell's equations are directly evaluated at the given frequencies on the integration contours, which implies that linearization of the corresponding nonlinear eigenproblems is not required. This makes Riesz-projection-based approaches a natural choice for dealing with eigenproblems from the field of nanophotonics. We further extend the Riesz projection expansion approach to optical far-field quantities, which is not straightforward due to the spatial divergence of the resonances with increasing distance from the underlying resonators. Based on the ideas of the Riesz projection expansion, we introduce approaches for the calculation of physically relevant eigenvalues and for computing eigenvalue sensitivities. Physically relevant means that the eigenvalues are significant with respect to the resonance expansion of the physical observable of interest. By using physical solutions to Maxwell's equations for the contour integration, the developed numerical methods have a strong relation to physics. The methods can be applied to any material system and to any measurable physical quantity that can be derived from the electric field. We apply the numerical methods to several recent nanophotonic applications, for example, single-photon sources from the field of quantum technology, plasmonic nanostructures characterized by nonlocal material properties, and nanoantennas based on bound states in the continuum. The approaches introduced in this thesis are developed for nanophotonic systems, but can be applied to any resonance problem.Resonanzeffekte treten in allen physikalischen Systemen auf, die durch Wellen beschrieben werden, und sie sind für die Beschreibung von Wellenausbreitung und Interferenz unerlässlich. Auf dem Gebiet der Nanophotonik basieren viele Geräte auf den durch Lichtquellen angeregten Resonanzen mit ihren stark erhöhten elektromagnetischen Feldern. Die numerische Simulation von Resonanzen ist ein wichtiges Hilfsmittel für die Entwicklung und Optimierung der Geräte. Die Resonanzen sind die Lösungen der zeitharmonischen quellenfreien Maxwell-Gleichungen mit Verlustmechanismen. Die entsprechenden Eigenwertprobleme sind aufgrund der Verluste nicht-Hermitesch, was zu komplexwertigen Eigenwerten führt. Die Materialdispersion, die in der Nanophotonik typischerweise signifikant ist, führt zu nichtlinearen Eigenwertproblemen. In dieser Dissertation entwickeln wir einen auf der Riesz-Projektion basierenden Ansatz für die Expansion von elektromagnetischen Feldern, die von Lichtquellen erzeugt werden, in Resonanzen. Wir berechnen die Riesz-Projektionen durch Konturintegration in der komplexen Frequenzebene. Die numerische Realisierung basiert im Wesentlichen auf der Lösung der Maxwell-Gleichungen mit einem Quellterm, das heißt der Lösung von linearen Gleichungssystemen. Dabei werden die Maxwell-Gleichungen direkt bei den gegebenen Frequenzen auf den Integrationskonturen ausgewertet, sodass eine Linearisierung der entsprechenden nichtlinearen Eigenwertprobleme nicht erforderlich ist. Das macht die auf der Riesz-Projektion basierenden Methoden zu einer natürlichen Wahl für die Behandlung von Eigenwertproblemen aus dem Bereich der Nanophotonik. Wir erweitern den Ansatz der Riesz-Projektions-Expansion auf optische Größen im Fernfeld, was aufgrund der räumlichen Divergenz der Resonanzen mit zunehmender Entfernung von den zugrunde liegenden Resonatoren problematisch ist. Basierend auf den Ideen der Riesz-Projektions-Expansion entwickeln wir außerdem Methoden zur Berechnung physikalisch relevanter Eigenwerte und zur Berechnung von Sensitivitäten von Eigenwerten. Physikalisch relevant bedeutet, dass die Eigenwerte in Bezug auf die Resonanzexpansion der interessierenden physikalischen Größe signifikant sind. Durch die Verwendung physikalischer Lösungen der Maxwell-Gleichungen für die Konturintegration haben die entwickelten numerischen Methoden einen starken Bezug zur zugrunde liegenden Physik. Die Methoden können auf jedes Materialsystem und auf jede messbare physikalische Größe angewendet werden, die sich aus dem elektrischen Feld herleiten lässt. Wir wenden die numerischen Methoden auf mehrere aktuelle nanophotonische Strukturen an, wie zum Beispiel Einzelphotonenquellen aus dem Bereich der Quantentechnologie, plasmonische Nanostrukturen, die sich durch nichtlokale Materialeigenschaften auszeichnen, und Nanoantennen, die auf gebundenen Zuständen im Kontinuum basieren. Die in dieser Dissertation vorgestellten Ansätze werden für nanophotonische Systeme entwickelt, lassen sich aber auf jedes Resonanzproblem anwenden

Engineering aperiodic spiral order for photonic-plasmonic device applications

Thesis (Ph.D.)--Boston UniversityDeterministic arrays of metal (i.e., Au) nanoparticles and dielectric nanopillars (i.e., Si and SiN) arranged in aperiodic spiral geometries (Vogel's spirals) are proposed as a novel platform for engineering enhanced photonic-plasmonic coupling and increased light-matter interaction over broad frequency and angular spectra for planar optical devices. Vogel's spirals lack both translational and orientational symmetry in real space, while displaying continuous circular symmetry (i.e., rotational symmetry of infinite order) in reciprocal Fourier space. The novel regime of "circular multiple light scattering" in finite-size deterministic structures will be investigated. The distinctive geometrical structure of Vogel spirals will be studied by a multifractal analysis, Fourier-Bessel decomposition, and Delaunay tessellation methods, leading to spiral structure optimization for novel localized optical states with broadband fluctuations in their photonic mode density. Experimentally, a number of designed passive and active spiral structures will be fabricated and characterized using dark-field optical spectroscopy, ellipsometry, and Fourier space imaging. Polarization-insensitive planar omnidirectional diffraction will be demonstrated and engineered over a large and controllable range of frequencies. Device applications to enhanced LEDs, novel lasers, and thin-film solar cells with enhanced absorption will be specifically targeted. Additionally, using Vogel spirals we investigate the direct (i.e. free space) generation of optical vortices, with well-defined and controllable values of orbital angular momentum, paving the way to the engineering and control of novel types of phase discontinuities (i.e., phase dislocation loops) in compact, chip-scale optical devices. Finally, we report on the design, modeling, and experimental demonstration of array-enhanced nanoantennas for polarization-controlled multispectral nanofocusing, nanoantennas for resonant near-field optical concentration of radiation to individual nanowires, and aperiodic double resonance surface enhanced Raman scattering substrates