This thesis focuses on the physics of nanoplasmonic systems for dispersive and lossy media. Gold nanoparticles in P3HT (poly(3-hexylthiophene)) and PMMA (poly(methyl methacrylate)) are analyzed both theoretically and experimentally. It is found in both cases that the presence of P3HT narrows the linewidth of the gold plasmon peak. This is a counter-intuitive result, and this narrowing of the linewidth by a lossy material is analyzed in detail. It is found that dispersion in both the real and imaginary parts of the permittivity of the surrounding medium can significantly affect the linewidth. Another plasmonic phenomena was also researched. An atomic energy level model of erbium was constructed and used to solve a rate equation to calculate the far-field emission enhancement from an erbium atom nearby a gold nanorod when the dark mode is excited. Normally a small emission enhancement is expected in the far field since dark modes do not couple strongly to radiation, but in experiments this dark field emission enhancement was seen to be significant. The results of the calculation were compared to this previous experimental result. Although the incident power dependence of the calculated 980 nm emission line agreed with experiments, the 650 nm emission line power dependence and the calculated emission enhancement did not, and so more work needs to be done with this model to explain the experimental results. / Graduate

<p>In the realm of tunable optical devices, 3D nanostructures with metals and dielectrics have been utilized in a wide variety of practical applications ranging from optical switching to beam-steering devices. 2D materials, on the other hand, have enabled the exploration of truly new physics unattainable with 3D systems due to quantum confinement leading to unique optical properties and enhanced light-matter interactions. Transdimensional materials (TDMs) – atomically thin films of metals – can couple the robustness of 3D nanostructures with the new physics enabled by 2D features. However, the evolution of the optical properties in the transdimensional regime between 3D and 2D is still underexplored. The optical properties of metallic TDMs are expected to show unprecedented tailorability, including strong dependences on the film thickness, composition, strain, and surface termination. They also have an increased sensitivity to external optical and electrical perturbations, owing to their extraordinary light-confinement. Additionally, the small atomic thicknesses may lead to strongly confined surface plasmons and quantum and nonlocal phenomena. The strong tunability and light-confinement offered by TDMs have resulted in a search for atomically thin plasmonic material platforms that facilitate active metasurfaces with novel functionalities in the visible and near infrared (NIR) range. In this research, we explore the plasmonic properties and tailorability of atomically thin titanium nitride (TiN). We experimentally and theoretically study the thickness-dependent optical properties of epitaxial TiN films with thicknesses down to 1 nm to demonstrate confinement induced optical properties. Overall, this research demonstrates the potential of TDMs for unlocking novel optical phenomena at visible and NIR wavelengths and realizing a new generation of atomically thin tunable nanophotonic devices. </p>

Malgré les remarquables performances démontrées par les photo-détecteurs quantiques pour l'infrarouge, les progrès dans cette filière stagnent. La principale limitation est due au bruit lié à leur courant d'obscurité, qui impose, aux plus grandes longueurs d'onde, un fonctionnement à des températures cryogéniques. Ce travail de thèse a pour principal objectif de dépasser cette limite intrinsèque en combinant des structures photo-détectrices innovantes et des nano-résonateurs optiques. La réduction par plus d'un ordre de grandeur de l'épaisseur de la zone absorbante, modifie considérablement les propriétés optiques et électroniques de la structure, imposant de revisiter entièrement ses modes de fonctionnement. Dans ce contexte, ce travail de thèse vise à valider expérimentalement l'apport de la nano-photonique à l'amélioration des performances des photodiodes InGaAs.La première partie est dédiée à l'étude de photodiodes InGaAs à double hétérojonction dans le but de réduire à la fois le courant d'obscurité et l'épaisseur de la structure pour la rendre compatible à celle des nano-résonateurs optiques. La seconde partie est dévolue à la conception, la fabrication et la caractérisation de photo-détecteurs InGaAs nano-structurés de type résonateurs de mode guidé. Dans la troisième partie, les remarquables propriétés de ces photo-détecteurs sont étudiées dans un contexte de mini-matrices, premier pas vers la réalisation de caméras.Les concepts développés durant cette thèse et les résultats expérimentaux obtenus, ouvrent la voie vers une nouvelle génération de photo-détecteurs pour l'imagerie infrarouge. / Despite the outstanding performances reached by today's infrared quantum photo-detectors, progresses have been stagnating for years. The main limitation is due to the noise generated by the dark current, which requires, cooling down the devices at a cryogenic temperature for the largest wavelengths. The main objective of this thesis is to propose new concepts for overcoming these fundamental limits. By combining innovative photo-detector structures and optical nano-resonators, new structures are proposed. By reducing by more than order of magnitude the thickness of the absorbing layer, optical and electrical properties of the structure are deeply modified. As a result operating modes have to be entirely revisited. In this context, the purpose of this thesis is to characterize the behaviors, to find new compromise and to experimentally validate the nano-photonics potential to improve the performances of InGaAs photodiodes.The first part is dedicated to the study of double heterojunction InGaAs photodiodes in order to reduce both the dark current and the thickness of the structure to make it compatible with that of optical nano-resonators. The second part is devoted to the design, the fabrication and the characterization of guided mode resonant nanostructured InGaAs photo-detectors. In the third part, the remarkable properties of these photo-detectors are studied in the context of mini-arrays, the first step towards cameras realization.The concepts developed during this thesis and experimental results, pave the way to a new generation of infrared photodetector.

<p>Thermal radiation, an omnipresent phenomenon characterized by electromagnetic wave emission from objects above absolute zero, has consistently intrigued scientific exploration throughout history and profoundly influences various technological applications. Traditionally, the primary utilization of thermal radiation has been limited to fields such as lighting, cooling, and energy harvesting. However, the true potential of thermal radiation extends far beyond these energy-oriented applications. Every object imprints a unique signature within its emitted thermal radiation. These signatures, distinguished by their wide-ranging spectral and polarimetric characteristics, represent a rich information source about the emitting objects. The goal of this dissertation is to offer novel prospective and platforms to expand our perception and utilization of the spectral and polarimetric attributes of thermal radiation. It seeks to augment the conventional understanding of thermal radiation as merely an energy source, underlining its immense potential as an information carrier.</p> <p>This dissertation explores the spectral and polarimetric features left within the thermal radiation and how these features can be manipulated. The research uncovers that the macroscopic spectral, spatial, and particularly spin properties of thermal radiation are intimately connected to the underlying symmetry of the microscopic emitters within a nanophotonic system. This close relationship between symmetry and thermal radiation introduces a universal strategy to gain thorough control over the spectral-polarimetric properties of thermal radiation. The control of these properties may spur pioneering developments in encoding information within thermal radiation.</p> <p>Furthermore, platforms to decode these spectral and polarimetric properties in thermal radiation are as pivotal as the encoding platforms. These decoding platforms allow us to uncover hidden messages within this invisible light and enable us to push the boundaries of fully passive and physics-aware machine perception. Nevertheless, contemporary methods for spectrum and polarization resolved detection of thermal radiation, especially in imaging form, are cumbersome, lacking robustness, and prohibitively expensive. Hence, this dissertation explores two fundamentally innovative spectral separation schemes: the nonlocal super-dispersion enabled by optically active crystals and the dispersive dichroism in 2D infrared metasurfaces. These methods present compact, cost-effective, and high-performance solutions for spectral-polarimetric thermal imaging, thereby enhancing its efficacy in diverse applications.</p>

In this thesis, I develop a novel time-domain approach for nonlinear scattering theory (NLST), a previously frequency domain method for estimating the nonlinear generation from a nanostructure. Due to a gap in literature, I then perform a full comparison of this novel time domain approach to the existing one in the frequency domain. Using the example scenario of third harmonic generation from various media in 1D and 3D, I compare - quantitatively - the NLST estimated nonlinear spectra to two types of direct nonlinear simulations: one using an experimental value for the nonlinear optical susceptibility, and, for plasmonic systems, another using a hydrodynamics model for the nonlinear plasmonic response. Through testing differing NLST approaches on these systems, I demonstrate the effectiveness of the novel time-domain NLST and assess the use cases for this method as well as the pre-existing ones. Lastly, I discuss the applicability of NLST in future works involving the inverse design process, and high-order harmonic generation.

Nanophotonics is the study and technological application of the interaction of electromagnetic waves (light) and matter at the nanometer scale. The field's extensive research focuses on generating, detecting, and controlling light using nanoscale features such as nanoparticles, waveguides, resonators, nanoantennas, and more. Exploration in the field is highly dependent on computational methods, which simulate how light will interact with matter in specific situations. However, as nanophotonics advances, so must the computational techniques. In this thesis, I present my work in various numerical studies in nanophotonics, sorted into three categories; plasmonics, inverse design, and deep learning. In plasmonics, I have developed methods for solving advanced material models (including nonlinearities) for small metallic and epsilon-near-zero features and validated them with other theoretical and experimental results. For inverse design, I introduce new methods for designing optical pulse shapes and metalenses for focusing high-harmonic generation. Finally, I used deep learning to model plasmonic colour generation from structured metal surfaces and to predict plasmonic nanoparticle multipolar responses.

This thesis describes the development of a minimally invasive integrated platform for all-optical neural stimulation and measurement (OptoSAM). The OptoSAM platform is a single mixed-signal complementary metal-oxide semiconductor (CMOS) chip. After design, the chip is postprocessed to contain the necessary optical filters and emitters to enable both fluorescent detection and neural stimulation. Finally, the chip is packaged in a probe form factor for minimally-invasive implantation into neural tissue. The thesis describes how the OptoSAM is engineered for two applications: optical fluorescent imaging on one hand and optogenetic stimulation on the other. For either application, constraints and tradeoffs are described that guide design specifications. For fluorescent neural detection, this thesis focuses on improvements made in lens-less image reconstruction and optical filtering. It describes circuit design for the lens-less, filter-less fluorescent imaging subsystem and characterizes the resulting imaging performance. The lack of on-chip filters precludes reliable imaging of fluorescent targets both in-vivo and ex-vivo. To address these limitations, the metal-insulator-metal angle sensitive pixel (MIMASP) is introduced, a novel nanophotonic structure that integrates lens-less imaging and optical filtering in an ultrathin (<5μm) frontend. The MIMASP offers three advantages over previously published angle sensitive pixels. First, it orthogonally modulates the detection light field for two arbitrary wavelengths, enabling the separation and detection of colors in the image. Secondly, each layer is constructed from optical long-pass filters, rejecting the blue excitation light. Third, an analytical framework is created that allows to optimize the ensemble image reconstruction resolution as a function of the available per-pixel geometries. The angle sensitive pixels are a promising lens-less imaging method for situations where both the number of pixels and the permitted device dimensions are extremely constrained. Equipped with the MIMASP frontend, the imager is demonstrated in scattering media to successfully separate fluorescent targets based on color, fluorescent lifetime and even environmental pH. The experiments are extended to fluorescent detection in ex-vivo acute brain slices. For optogenetic stimulation, we equip the OptoSAM platform with organic light emitting diodes (OLEDs) as thin-film emitters. In-vivo results show how the OLED probe can evoke neural activity in a fully scalable fashion. Using synchronized groups of OLEDs, large neural populations can be synchronously activated. Simultaneously, single neurons can be manipulated by emission from single OLEDs at a 25μm pitch. We demonstrate single-unit manipulation and separation of both pyramidal and interneurons. A custom flexible, transparent multi-electrode array (MEA) provides the electrophysiological recording for cross-validation in the deep-brain. Measurements show how local field potentials (LFPs) are evoked at both 300μm and 1.2mm deep, and how the LFP magnitude roll-off proves locality of the induced activity. Compared to previously published stateof- the-art, the OLED-on-CMOS approach provides a two orders of magnitude larger field of view (FoV) while improving resolution by 3×. Pixel pitch and count can be fully scaled to provide arbitrary fields of view and resolution. The OptoSAM platform proves a pathway towards behavioral studies in awake mice. These studies could address multiple brain regions independently with a single device insertion. This provides neuroscientists with the tools to study relationship between distant regions with single-neuron resolution. While the detection and stimulation are separately optimized and validated, the chip is a promising platform for future integration of both modalities. To this end, it proposes three future chip designs, each with their respective strengths. The proposals also provide potential solutions to the challenges associated with the design and fabrication. The thesis concludes with recommendations for future experiments, both for the OptoSAM platform and for future designs.

<p>Metasurfaces are broadly defined as artificially engineered material interfaces that have the ability to determinately control the amplitude and phase signatures of an incident electromagnetic wave. Subwavelength sized optical scatterers employed at the planar interface of two media, introduce abrupt modifications to impinged light characteristics. Arbitrary engineering of the optical interactions and the arrangement of the scatterers on plane, enable ultra-compact, miniaturized optical systems with a wide array of applications (e.g. nanoscale and nonlinear optics, sensing, detection, energy harvesting, information processing and so on) realizable by the metasurfaces. However, maturation from the laboratory to industry scale realistic systems remain largely elusive despite the expanding reach and vast domains of functionalities demonstrated by researchers. A large part of this multi-faceted problem stems from the practical constraints posed by the commonly used plasmonic materials that limit their applicability in devices requiring high temperature stability, robustness in varying ambient, mechanical durability, stable growth into nanoscale films, CMOS process compatibility, stable bio-compatibility, and so on. </p> <p>Aiming to create a whole-some solution, my research has focused on developing novel, high-performance, functional plasmonic metasurface devices that utilize the inherent benefits of various emerging and alternative material platforms. Among these, the two-dimensional MXenes and the refractory transition metal nitrides are of particular importance. By exploiting the plasmonic response of thin films of the titanium carbide MXene (Ti₃C₂T_x) in the near infrared spectral window, a highly broadband metamaterial absorber has been designed, fabricated and experimentally demonstrated. In another work, high efficiency photonic spin Hall Effect has been experimentally realized in robust phase gradient metasurface devices based on two different refractory transition metal nitrides –titanium nitride (TiN) and zirconium nitride (ZrN). Further, taking advantage of the refractory nature of these plasmonic nitrides, a metasurface based temperature sensor has been developed that is capable of remote, optical sensing of very high temperatures ranging up to 1200^oC.</p>

The two main themes in this thesis are the implementation of interference methods with optically trapped particles for measurements of position and optical phase (optical interferometric metrology) and the optical manipulation of nanoparticles for studies in the assembly of nanostructures, nanoscale heating and nonlinear optics (nanophotonics). The first part of the thesis (chapter 1, 2) provides an introductory overview to optical trapping and describes the basic experimental instrument used in the thesis respectively. The second part of the thesis (chapters 3 to 5) investigates the use of optical interferometric patterns of the diffracting light fields from optically trapped microparticles for three types of measurements: calibrating particle positions in an optical trap, determining the stiffness of an optical trap and measuring the change in phase or coherence of a given light field. The third part of the thesis (chapters 6 to 8) studies the interactions between optical traps and nanoparticles in three separate experiments: the optical manipulation of dielectric enhanced semiconductor nanoparticles, heating of optically trapped gold nanoparticles and collective optical response from an ensemble of optically trapped dielectric nanoparticles.

<p>Developing a hybrid platform that combines nanophotonic circuits and atomic physic may provide new chip-scale devices for quantum application or versatile tools for exploring photon-mediated long-range quantum systems. However, this challenging project demands the excellent integration of cold atom trapping and manipulation technology with cutting-edge nanophotonics circuit design and fabrication. In this thesis project, we aim to develop a novel suspended membrane platform that serves as a quantum interface between laser-cooled, trapped atoms in an ultrahigh vacuum and the photons guided in the nanophotonic circuits based on high-quality silicon nitride microring resonators fabricated on a transparent membrane substrate. </p> <p><br></p> <p>The proposed platform meets the stringent performance requirements imposed by nanofabrication and optical physics in an ultra-high vacuum. These include a high yield rate for mm-scale suspended dielectric photonic devices, minimization of the surface roughness to achieve ultrahigh-optical quality, complete control of optical loss/in-coupling rate to achieve critical photon coupling to a microring resonator, and high-efficiency waveguide optical input/output coupler in an ultrahigh vacuum environment. This platform is compatible with laser-cooled and trapped cold atoms. The experimental demonstration of trapping and imaging single atoms on a photonic resonator circuit using optical tweezers has been demonstrated. Our circuit design can potentially reach a record-high cooperativity parameter C$>$500 for single atom-photon coupling, which is of high importance in realizing a coherent quantum nonlinear optical platform and holds great promise as an on-chip atom-cavity QED platform.</p>