The Investigation of Surplus of Energy and Signal Propagation at Time-Domain Waveguide Modes

Classical waveguide theory has been developed bearing on Bernoulli’s product method which results in separation of space and time variables in Maxwell’s equations. The time-harmonic waveguide modes have been stated mathematically for transmitting signals along the waveguides. As a starting point, present studies on transverse-electric (TE) and transverse-magnetic (TM) waveguide modes with previous results are taken and exhibited in an advanced form. They have been obtained within the framework of an evolutionary approach to solve Maxwell’s equations with time derivative. As a result every modal field is obtained in the form of a product of vector functions of transverse coordinates and modal amplitudes. The modal amplitudes which are the functions of axial coordinate z and time t are the central matter of this study. The amplitudes are generated by a potential which is governing by Klein-Gordon equation (KGE). The KGE has remarkable properties of symmetry which has great importance in our analytical studies of the transient modes. Ultimately, in this study, a time-domain waveguide problem is solved analytically in accordance with the causality principle. Moreover, the graphical results are shown for the case when the energy and surplus of the energy for the time-domain waveguide modes are represented via Airy functions

Phase-driven optomechanics in exotic photonic media

Integrated photonics provide unique advantages in tailoring and enhancing optical forces. Recent advancements in integrated photonics have introduced many novel phenomena and exotic photonic media, such as photonic topological insulator, negative index material, photonic crystals, 2D material, and strongly-modulated time-dynamic systems. In my dissertation, I theoretically and numerically explore the novel properties and applications of optical forces in these systems. We propose guided-wave photonic pulling forces in photonic crystal waveguides. Photonic crystal waveguides offer great capability to define the mode properties, and can incorporate complex trajectories, leading to unprecedented flexibility and robustness compared to previous works in free space or in longitudinally uniform waveguides. With response theory, a virtual work approach, we establish general rules to tailor optical forces in periodic structures involved with photonic crystals: pulling forces arise from negative gradients in the phase responses of the outgoing modes, which corresponds to forward scattering on the Bloch band diagram with unit cell function corrections. We devise robust forward scattering, first, using topologically protected nonreciprocal chiral edge states, second, using backward (i.e. negative index) waves in a reciprocal system. The structures are tailored to accommodate only the necessary modes, which largely benefits the robustness. With these, we numerically demonstrate long range pulling forces on arbitrary particles through sharp corners. Our work paves the way towards sophisticated optical manipulation with single laser beam. We next explore the implication and applicability of momentum conservation in periodic media, which has been unclear due to the inhomogeneity and strong near field. We first quantify the linear momentum flux of Bloch modes under discrete translational symmetry, which is further understood from their plane wave composition. We then demonstrate through varies examples that the change in momentum flux predicts a total force distributed to both the scatterer and the media. However, one still need response theory to predict the forces on individual objects. Using response theory, we can predict more general forms of optical forces. We numerically demonstrate optical motoring effect due to singularity in the phase responses, and strong optical forces between graphene sheets due to large gradients in the phase responses. In particular, by combining the strong forces in graphene guided-wave system and the exceptional elastic properties of graphene, we can get an SBS gain that is four orders of magnitude stronger than in a silicon step-index waveguide, which may lead to smaller devices for RF signal processing.Physic

Cross-Junction Based Metasurfaces: A Roadmap to Fano Resonances

The first part of the thesis presents a summary of the classification of materials, followed by the development of metamaterials and their salient role. Then, a study of metamaterials and the evolution of these 3D structures to 2D, known as metasurfaces, have been discussed. Moreover, the physics and practical interest behind Fano resonance have been discussed. Furthermore, the physical fundamentals guiding the performance of both the metamaterials and metasurfaces, including the temporal coupled-mode theory and the generalized laws of reflection and refraction, have been intensely investigated, along with some of the outstanding properties of the metamaterials. Then, a comparison between metamaterials and photonic/electronic bandgap materials, in addition to a comparison between metasurfaces and frequency-selective surfaces, has been shown. Finally, a literature review for previous work on the application of metasurfaces in different fields and the progress of Fano resonance in numerous applications are stated. The second part of the thesis presents the research work that has been done, in which a design for an electromagnetic metasurface in the microwave regime has been proposed. Breaking the structural symmetry of the unit cell constituting the metasurface is shown to introduce a route for inducing high-quality factor (Q) Fano resonance (FR). The total thickness of the structure is deeply subwavelength, with the metasurface’s thickness equal to 0.08 of the wavelength. The design has been fabricated and characterized inside an anechoic chamber. Both numerical and measured data show to be in perfect agreement. This work paves the way for numerous applications, including but not limited to sensing and polarization rotation

Enhanced transmission of slit arrays in an extremely thin metallic film

Horizontal resonances of slit arrays are studied. They can lead to an enhanced transmission that cannot be explained using the single-mode approximation. A new type of cavity resonance is found when the slits are narrow for a wavelength very close to the period. It can be excited for very low thicknesses. Optimization shows these structures could constitute interesting monochromatic filters

Laterally modified microcavity systems containing organic emitters

The scope of this work is an in-depth investigation of dielectric mirror microcavities with central organic dye layers, which are preferably modified in at least one lateral dimension. The large quality factor of the planar resonator in conjunction with comparatively stable and spectrally broad emitting molecules allows for a detailed analysis of several aspects of microresonator systems. Their optical properties are analyzed both with transmission and luminescence measurements as well as in the lasing regime. The first part presents the resonant mode properties of planar and laterally structured microcavities. With the help of a high-resolution imaging micro-photoluminescence setup, working either in the spatial (near field) or vectorial (far field) regime, the polarization splitting is studied in a detuned microcavity, containing the dye 4,4'-bis[(N-carbazole)styryl]biphenyl (BSB-Cz) in a matrix of 4,4'-di(N-carbazolyl)- biphenyl (CBP). With the help of a thickness gradient, a relation between the large spectral distance of the cross-polarized states and the mode position within the stop band is investigated. In shadow-mask prepared, laterally restricted devices (5x5 µm2 square boxes), the three-dimensional confinement introduces sets of discrete modes, which experience a similar polarization splitting. The origin in this case is a different phase shift of electromagnetic waves during internal total reflection at a boundary. By using a concentration gradient planar microcavity sample of the dye 4-(dicyanomethylene)-2-methyl-6-(4-(dimethylamino)styryl)-4H-pyran (DCM) in a tris-(8-hydroxyquinoline)aluminum (Alq3) matrix, the influence of the number of emitters on the lasing characteristics is subsequently analyzed. Depending on the pumping conditions, and thus the involvement of the Förster resonant energy transfer, an optimal composition is identified. After a qualitative evaluation of the long-term stability upon various excitation energies, the attention is focussed to the modification of the stimulated emission properties of photonic boxes. The stronger field concentration and altered density of states leads to a significant improvement of the values for the coupling factor fi and the threshold levels. Furthermore, new properties arise, namely simultaneous multimode and off-axis laser emission. With an inhomogeneous excitation of the box, it is possible to selectively excite single modes above the threshold. The work ends with experimental results of metal structures as additional optical element in the organic microcavity layer. Here, the aim is is to understand the passive influence of these possible contact- devices on the lasing performance. For this purpose, the lasing is studied at an interface of an areal thin metal layer, which is incorporated in the organic layer.:List of publication Introduction Optical properties of dielectric microresonator systems Sample fabrication and characterization Resonant mode properties of dielectric mirror microcavities Lasing from laterally modified organic cavity systems Conclusion and outlook Bibliograph

EM Wave Interaction with a Bounded Plasma Column Supporting an Electron Beam

In this thesis, the disruption of an incoming external transverse electromagnetic wave by an inhomogeneous plasma with energetic electron beam is examined. The plasma-beam characteristics are motivated by theory and experiment. Wave-plasma interactions and wave propagation and reflection in and from a plasma medium is studied. Physical sources such as the plate current density are considered. The inhomogeneity of the plasma slab supporting the energetic electron beam is partially built into the supported fields. The wave-plasma-beam interaction is examined over a wide parameter space. Absorption or reflection of electromagnetic waves can be achieved by changing the plasma number density, collision frequency, beam number density, and the Gaussian nature of the beam and slab thickness. Under appropriate condition in the presence of an energetic electron beam supported by the plasma slab, the externally generated wave incident on and exciting the slab can resonate with the beam. Although insignificant for the parameters studied, this becomes apparent when the operation frequency (both the wave and the beam) approaches the electron plasma frequency. Initial studies conducted have not exhausted all possible parameter space scenarios and physics mechanisms. Based on the results obtained, more involved investigations are warranted

Application of porous silicon in terahertz technology

In this thesis, we discuss our efforts in developing porous silicon based devices for terahertz signal processing. In the first stage of our research, we demonstrate that porous silicon samples fabricated from highly doped p-type silicon can have adjustable refractive indices ranging from 1.5-2.1 and can exhibit a resistivity that is four orders of magnitude higher than that of the silicon wafer from which they were made. We show that the porous silicon becomes stable and relatively lossless after thermal oxidation. The partially oxidized porous silicon is shown to exhibit a smooth absorption spectrum, with low absorption loss of <10 cm^-1 over the entire terahertz spectrum. As a proof of concept, we fabricated, for the first time, a porous silicon based multilayered Bragg filter with reflectance of 93% and full-width at half-maximum bandwidth of 0.26 THz. Compared with other multilayered filtering techniques, porous silicon has the advantage that it can be easily fabricated, and offers the possibility of forming multilayer and graded index structures for more advanced filters. The large surface area of nanoporous silicon makes it an especially attractive platform for applications in biochemical detection and diagnostics As part of our effort in developing terahertz waveguide for biosensing, we reported the world's first porous silicon based terahertz waveguide using the principle of surface plasmon polaritons. The effect of porous silicon film thickness on the propagation of surface plasmons is explained theoretically in this thesis and is found to be in good agreement with experimental results

Functional colloidal surface assemblies: Classical optics meets template-assisted self-assembly

Abstract: When noble metals particles are synthesized with progressively smaller dimensions, strikingly novel optical properties arise. For nanoscale particles, collective disturbances of the electron density known as localized surface plasmons resonances can arise, and these resonances are utilized in a variety of applications ranging from surface-enhanced molecular spectroscopy and sensing to photothermal cancer therapy to plasmon-driven photochemistry. Central to all of these studies is the plasmon’s remarkable ability to process light, capturing and converting it into intense near fields, heat, and even energetic carriers at the nanoscale. In the past decade, we have witnessed major advances in plasmonics which is directly linked with the much broader field of (colloidal) nanotechnology. These breakthroughs span from plasmon lasing and waveguides, plasmonic photochemistry and solar cells to active plasmonics, plasmonics nanocomposites and semiconductor plasmons. All the above-mentioned phenomena rely on precise spatial placement and distinct control over the dimensions and orientation of the individual plasmonic building blocks within complex one-, two- or three-dimensional complex arrangements. For the nanofabrication of metal nanostructures at surfaces, most often lithographic approaches, e.g. e-beam lithography or ion-beam milling are generally applied, due to their versatility and precision. However, these techniques come along with several drawbacks such as limited scalability, limited resolution, limited compatibility with silicon manufacturing techniques, damping effects due to the polycrystalline nature of the metal nanostructures and low sample throughput. Thus, there is a great demand for alternative approaches for the fabrication of metal nanostructures to overcome the above-mentioned limitations. But why colloids? True three-dimensionality, lower damping, high quality modes due to mono-dispersity, and the absence of grain boundaries make the colloidal assembly an especially competitive method for high quality large-scale fabrication. On top of that, colloids provide a versatile platform in terms of size, shape, composition and surface modification and dispersion media. 540The combination of directed self-assembly and laser interference lithography is a versatile admixture of bottom-up and top-down approaches that represents a compelling alternative to commonly used nanofabrication methods. The objective of this thesis is to focus on large area fabrication of emergent spectroscopic properties with high structural and optical quality via colloidal self-assembly. We focus on synergy between optical and plasmonic effects such as: (i) coupling between localized surface plasmon resonance and Bragg diffraction leading to surface lattice resonance; (ii) strong light matter interaction between guided mode resonance and collective plasmonic chain modes leading to hybrid guided plasmon modes, which can further be used to boost the hot-electron efficiency in a semiconducting material; (iii) similarly, bilayer nanoparticle chains leading to chiro-optical effects. Following this scope, this thesis introduces a real-time tuning of such exclusive plasmonic-photonic (hybrid) modes via flexible template fabrication. Mechanical stimuli such as tensile strain facilitate the dynamic tuning of surface lattice resonance and chiro-optical effects respectively. This expands the scope to curb the rigidity in optical systems and ease the integration of such systems with flexible electronics or circuits.:Contents Abstract Kurzfassung Abbreviations 1. Introduction and scope of the thesis 1.1. Introduction 1.1.1. Classical optics concepts 1.1.2. Top down fabrication methods and their challenges 1.1.3. Template-assisted self-assembly 1.1.4. Functional colloidal surface assemblies 1.2. Scope of the thesis 2. Results and Discussion 2.1. Mechanotunable Surface Lattice Resonances in the Visible Optical Range by Soft Lithography Templates and Directed Self-Assembly 2.1.1. Fabrication of flexible 2D plasmonic lattice 2.1.2. Investigation of the influence of particle size distribution on SLR quality 2.1.3. Band diagram analysis of 2D plasmonic lattice 2.1.4. Strain induced tuning of SLR 2.1.5. SEM and force transfer analysis in 2D plasmonic lattice under various strain 2.2. Hybridized Guided-Mode Resonances via Colloidal Plasmonic Self-Assembled Grating 2.2.1. Fabrication of hybrid opto-plasmonic structure via template assisted self-assembly 2.2.2. Comparison of optical band diagram of three (plasmonic, photonic and hybrid) different structures in TE and TM modes 2.2.3. Simulative comparison of optical properties of hybrid opto-plasmonic NP chains with a grating of metallic gold bars 2.2.4. Effect of cover index variation with water as a cover medium 2.3. Hot electron generation via guided hybrid modes 2.3.1. Fabrication of the hybrid GMR structure via LIL and lift-off process 2.3.2. Spectroscopic and simulative analysis of hybrid opto-plasmonic structures of different periodicities 2.3.3. Comparative study of photocurrent generation in different plasmonic structures 2.3.4. Polarization dependent response at higher wavelength 2.3.5. Directed self-assembly of gold nanoparticles within grating channels of a dielectric GMR structure supported by titanium dioxide film 2.4. Active Chiral Plasmonics Based on Geometrical Reconfiguration 2.4.1. Chiral 3D assemblies by macroscopic stacking of achiral chain substrates 3. Conclusion 4. Zusammenfassung 5. Bibliography 6. Appendix 6.1. laser interference lithography 6.2. Soft molding 6.3. Determine fill factor of plasmonic lattice 6.4. 2D plasmonic lattice of Au_BSA under strain 6.5. Characterizing order inside a 2D lattice 6.6. Template-assisted colloidal self-assembly 6.7. Out of plane lattice resonance in 1D and 2D lattices 6.8. E-Field distribution at out of plane SLR mode for 1D lattices of various periodicity with AOI 20° 6.9. Refractive index of PDMS and UV-PDMS 6.10. Refractive index measurement for sensing 6.11. Optical constants of TiO2, ma-N 405 photoresist and glass substrate measured from spectroscopic ellipsometry Acknowledgement/ Danksagung Erklärung & Versicherung List of Publication

Femtosecond Self-Reconfiguration of Laser-Induced Plasma Patterns in Dielectrics

Laser-induced modification of transparent solids by intense femtosecond laser pulses allows fast integration of nanophotonic and nanofluidic devices with controlled optical properties. So far, the local and dynamic nature of the interactions between plasma and light needed to correctly explain nanograting fabrication on dielectric surfaces has been missing in the theoretical models. With our numerical approach, we show that a self-consistent dynamic treatment of the plasma formation and its interaction with light triggers an ultrafast reconfiguration of the periodic plasma patterns on a field-cycle time scale. Within this framework, a simple stability analysis of the local interactions explains how the laser-induced plasma patterns change their orientation with respect to the incident light polarization, when a certain energy density threshold is reached. Moreover, the reconfigured sub-wavelength plasma structures grow into the bulk of the sample and agree with the experimental findings of self-organized volume nanogratings. Mode coupling of the incident and transversally scattered light with the periodic plasma structures is sufficient to initiate the growth and the self-organization of the characteristic pattern with a periodicity of a half-wavelength in the medium.Comment: 8 pages, 7 figure