Surface Plasmon Polaritonic Crystals for Applications in Optical communications

The integration and reduction in the photonic device sizes are essential for the development of applications in short-range interconnects and optical signal processing. Surface plasmon polaritonic crystals (SPPCs) can allow the manipulation of optical information in the microscale level, by coupling photons with collective electron oscillations at a metal–dielectric interface. This thesis investigates, both numerically and experimentally, the excitation and propagation of the surface plasmon polaritonic (SPP) modes on finite-size SPPCs, their dependence on the nanostructured geometry and the potential applications in implementing different device functions including SPP-beam shaping, such as focusing and splitting, and wavelength/polarisation demultiplexing. By controlling the SPPC geometry and the excitation beam parameters, directional control of propagating plasmonic modes properties, such as the beam direction, focusing power and beam width, can be achieved. The wavelength-dependent SPP signal spatial separation, due to coupling to the several eigenmodes, and the reduction of the cross-talk by combining polarisation and wavelength modulation have also been shown. In addition, a compact 4-level polarisation discriminator based on a planar, microscale-scale SPPC was developed as part of the research. Its capability to spatially separate linearly polarised signals with azimuth angles 0o , 45o , 90o and 135o , and define the S1 and S2 stokes parameters of any elliptical polarisation state was demonstrated and experimentally tested. The concept was extended to propose a fibre-coupled polarimeter, able to identify the three Stokes vectors parameters, based on the combination of the SPPC with a high -birefringence fibre. The use of SPPCs for the implementation and miniaturisation of key optical communication functionalities, in-plane plasmonic beam manipulation and polarisation/wavelength dependent SPP beam propagation, demonstrated in this work can be important for the development of novel integrated nanophotonic functionalities for subwavelength management of optical signals and the design of a new family of compact devices for optical communication applications

Engineering Plasmonic Nanostructures for Light Management and Sensing

The two major global problems are to provide health safety and to meet energy demands for ever growing population on a large scale. The study of light interaction with nanostructures has shown a promising solution in improving the fields of bio-sensor and solar energy devices which addresses above mentioned two major global problems. Nanostructures have tunable physicochemical properties such as light absorption, electrical and thermal properties unlike bulk materials, which gives an advantage in applications like bio-sensing and energy harvesting devices. The development of nanofabrication techniques along with the discovery of Surface Enhanced Raman Scattering (SERS) and Plasmon Enhanced Fluorescence (PEF), led to the development of Point of Care (POC) sensing devices. The fundamental understanding of light path in a nanostructured material led to the improvement in solar energy harvesting performance. For both of these applications, engineering nanostructures is the key to improving performance. In this work, different plasmonic nanostructures were designed, fabricated and analyzed for biosensor and light management applications. A new fabrication route, which combines nanosphere lithography with silicon-based clean-room microfabrication processes, has been developed to produce large-area long-range ordered gold nanoring array patterns in a controllable fashion. The developed nanoring structure has SERS enhancement of 2*109 and is used for miRNA detection. A novel pyramid array on gold film 3D plasmonic nanostructure is designed to convert plasmonic light scattering to confined light absorption. This structure generates a cavity mode by hybridization of fundamental modes, which creates a strong electric and magnetic field with a large mode volume. Due to its unique properties pyramids coupled film structure is used for both solar light management device and in Metal Enhanced Fluorescence (MEF). The fabricated structure is used to demonstrate plexiton (plasmon – exciton coupling) generation and is very effective in light trapping in the gap mode. In MEF, the sandwich nanostructure is used for Metal Organic Framework (MOF) fluorescence enhancement and the enhancement factor is around 5*102. With the plasmonic metal nanostructure optimization, the performance of a specific application is improved. However, the metals used for plasmonic applications are noble metals like gold and silver to support strong localized surface plasmon resonance (LSPR), which are expensive. Two-dimensional semiconductor materials have shown plasmon resonance in the visible region, having a lot of applications in sensing and photonics. Heavily doped semiconductors could replace expensive metals without compromising the performance. LSPR in metals is tuned by shape, size and refractive index of surroundings. This restricts plasmon resonance tuning over a narrow wavelength range and need to choose a different metal to exceed the rage of application. In contrast, LSPR in plasmonic semiconductors can be tuned with parameters like carrier density, annealing temperature and doping. This gives an advantage of tuning the plasmon peak over a broad range including visible, Near Infrared (NIR) and Infrared(IR) regions. This is because, for semiconductor materials, the carrier concentration can be varied over a large range. Herein, the molybdenum oxide thin films were directly deposited and nitrogen annealed which showed a tunable localized surface plasmon resonance (LSPR). A chip based 2D semiconductor material is fabricated to study the structural and size dependent plasmon resonance. This work establishes a way to fabricate chip based ordered semiconductor nanostructures, which helps in a systematic study of plasmon properties on nanostructures

Towards efficient three-dimensional wide-angle beam propagation methods and theoretical study of nanostructures for enhanced performance of photonic devices

In this dissertation, we have proposed a novel class of approximants, the so-called modified Padé approximant operators for the wide-angle beam propagation method (WA-BPM). Such new operators not only allow a more accurate approximation to the true Helmholtz equation than the conventional operators, but also give evanescent modes the desired damping. We have also demonstrated the usefulness of these new operators for the solution of time-domain beam propagation problems. We have shown this both for a wideband method, which can take reflections into account, and for a split-step method for the modeling of ultrashort unidirectional pulses. The resulting approaches achieve high-order accuracy not only in space but also in time. In addition, we have proposed an adaptation of the recently introduced complex Jacobi iterative (CJI) method for the solution of wide-angle beam propagation problems. The resulting CJI-WA-BPM is very competitive for demanding problems. For large 3D waveguide problems with refractive index profiles varying in the propagation direction, the CJI method can speed-up beam propagation up to 4 times compared to other state-of-the-art methods. For practical problems, the CJI-WA-BPM is found to be very useful to simulate a big component such as an arrayed waveguide grating (AWG) in the silicon-on-insulator platform, which our group is looking at. Apart from WA beam propagation problems for uniform waveguide structures, we have developed novel Padé approximate solutions for wave propagation in graded-index metamaterials. The resulting method offers a very promising tool for such demanding problems. On the other hand, we have carried out the study of improved performance of optical devices such as label-free optical biosensors, light-emitting diodes and solar cells by means of numerical and analytical methods. We have proposed a solution for enhanced sensitivity of a silicon-on-insulator surface plasmon interference biosensor which had been previously proposed in our group. The resulting sensitivity has been enhanced up to 5 times. Furthermore, we have developed an improved model to investigate the influence of isolated metallic nanoparticles on light emission properties of light-emitting diodes. The resulting model compares very well to experimental results. Finally, we have proposed the usefulness of core-shell nanostructures as nanoantennas to enhance light absorption of thin-film amorphous silicon solar cells. An increased absorption up to 33 % has theoretically been demonstrated

Metal nanoparticles for microscopy and spectroscopy

Metal nanoparticles interact strongly with light due to a resonant response of their free electrons. These ‘plasmon’ resonances appear as very strong extinction and scattering for particular wavelengths, and result in high enhancements of the local field compared to the incident electric field. In this chapter we introduce the reader to the optical properties of single plasmon particles as well as finite clusters and periodic lattices, and discuss several applications

Intertwine magnetooptical and plasmonic properties in metal and metal/dielectric magnetoplasmonic multilayers

This thesis deals with metal and metal-dielectric magnetoplasmonic (MP) multilayers, which combine noble metals and ferromagnetic ones and exhibit interrelated effects between the excitation of Surface Plasmon-Polaritons (SPPs) and their magnetooptical (MO) activity. Moreover, these MP systems have been used as transducers in sensing applications

Optical Sensors

This book is a compilation of works presenting recent developments and practical applications in optical sensor technology. It contains 10 chapters that encompass contributions from various individuals and research groups working in the area of optical sensing. It provides the reader with a broad overview and sampling of the innovative research on optical sensors in the world

Magneto-optical effects in hybrid plasmonic nanostructures

This thesis focuses on magneto-optical effects and their enhancement at optical resonances in hybrid plasmonic nanostructures. One of the main goals is to gain a better understanding of the transverse magnetic routing of light emission (TMRLE) regarding both components of the hybrid plasmonic-semiconductor model system used to investigate this novel effect. Here, the TMRLE describes the routing of light emitted from excitons in a diluted magnetic semiconductor (DMS) quantum well (QW), where the selection rules of the exciton optical transitions are modified by an external magnetic field to have a non-zero transverse spin along the magnetic field direction. By placing the light source near a surface, it can couple to subwavelength evanescent optical fields, such as surface plasmon polaritons (SPPs), which possess a strong transverse spin and spin-momentum locking. This translates the spin of the emitter into a routed wave along the surface and directional emission into the far-field. Firstly, the temperature dependence of the routing from the DMS QW, used as strongly polarizable light source, is investigated. The findings reveal a significant decline in the achievable emission routing for increasing temperatures, but also the emergence of the light-hole emission, which is routed in the opposite direction to the main heavy-hole emission. Additionally, alternative non-DMS-based QW structures are explored as potential candidates for achieving temperature-independent emission routing. Secondly, the influence of the plasmonic nanograting, the other constituent of the hybrid structure, on the enhanced routing is demonstrated. The emission directionality is investigated for various grating periods and slit widths, which also reveals the usually hard-to-detect weak coupling between the QW excitons and the SPPs as a large contributor to the emission directionality spectrum. Lastly, the thesis explores the transverse magneto-optical Kerr effect (TMOKE) for light reflected from or transmitted through a magnetite-based plasmonic waveguide structure. Here, the hybridization of the plasmonic and magnetic waveguide modes leads to a wide-band enhancement of the TMOKE signal in transmission.Der Fokus dieser Arbeit liegt auf magneto-optischen Effekten und deren Verstärkung an optischen Resonanzen in hybriden plasmonischen Nanostrukturen. Eines der Hauptziele ist das bessere Verständnis der transversalen magnetischen Lenkung der Lichtemission (TMRLE) bezüglich beider Komponenten des hybriden plasmonischen Halbleiter-Modellsystems, an dem dieser neuartige Effekt untersucht wird. Hier beschreibt der TMRLE die direktionale Lenkung der Lichtemission von Exzitonen aus einem semimagnetischen Halbleiter (DMS) Quantentopf (QW), wobei die Auswahlregeln der optischen Exzitonen-Übergänge von einem externen Magnetfeld so modifiziert werden, dass sie einen transversalen Spin entlang des Magnetfeldes haben. Wird diese Lichtquelle nahe einer Oberfläche platziert, so kann sie an evaneszente optische Felder mit starkem transversalem Spin und einer Kopplung von Spin und Ausbreitungsrichtung, wie Oberflächenplasmonpolaritonen (SPPs), koppeln. Dadurch wird der Emitterspin in eine direktionale Welle entlang der Oberfläche übersetzt, die dann direktional in das Fernfeld emittieren kann. Zunächst wird die Temperaturabhängigkeit der Emissionslenkung aus dem DMS QW untersucht, welcher als stark polarisierbare Lichtquelle fungiert. Dabei zeigt sich eine starke Abnahme der erreichbaren Emissionslenkung bei steigenden Temperaturen, aber auch der aufkommende Beitrag der Leichtloch-Emission, welche in die entgegengesetzte Richtung der primären Schwerloch-Emission gelenkt wird. Außerdem werden alternative nicht-DMS-basierte QW Strukturen als Kandidaten für eine temperaturunabhängige Emissionslenkung untersucht. Zweitens wird der Einfluss des plasmonischen Nanogitters als weiterer Bestandteil der Hybridstruktur auf die verstärkte Emissionslenkung gezeigt. Dafür wird die Emissionsdirektionalität für verschiedene Gitterperioden und -spaltbreiten untersucht, wobei auch die sonst schwer zu detektierende schwache Kopplung der QW-Exzitonen und SPPs als großer Beitrag zum Direktionalitätsspektrum aufgedeckt wird. Zuletzt wird noch der transversale magneto-optische Kerr-Effekt (TMOKE) für reflektiertes und transmittiertes Licht von einer Magnetit-basierten plasmonischen Nanostruktur untersucht. Hier führt die Hybridisierung der plasmonischen und der magnetischen Wellenleitermoden zu einer breitbandigen Verstärkung des TMOKE Signals in Transmission

Plasmonics and its Applications

Plasmonics is a rapidly developing field that combines fundamental research and applications ranging from areas such as physics to engineering, chemistry, biology, medicine, food sciences, and the environmental sciences. Plasmonics appeared in the 1950s with the discovery of surface plasmon polaritons. Plasmonics then went through a novel propulsion in the mid-1970s, when surface-enhanced Raman scattering was discovered. Nevertheless, it is in this last decade that a very significant explosion of plasmonics and its applications has occurred. Thus, this book provides a snapshot of the current advances in these various areas of plasmonics and its applications, such as engineering, sensing, surface-enhanced fluorescence, catalysis, and photovoltaic devices

NOVEL OPTICAL MICRORESONATORS FOR SENSING APPLICATIONS

Optical microresonators have been proven as an effective means for sensing applications. The high quality (Q) optical whispering gallery modes (WGMs) circulating around the rotationally symmetric structures can interact with the local environment through the evanescent field. The high sensitivity in detection was achieved by the long photon lifetime of the high-Q resonator (thus the long light-environment interaction path). The environmental variation near the resonator surface leads to the effective refractive index change and thus a shift at the resonance wavelength. In this Dissertation, we present our recent research on the development of new optical microresonators for sensing applications. Different structures and materials are used to develop optical resonator for broad sensing applications. Specifically, a new coupling method is designed and demonstrated for efficient excitation of microsphere resonators. The new coupler is made by fusion splicing an optical fiber with a capillary tube and consequently etching the capillary wall to a thickness of a few microns. Light is coupled through the peripheral contact between inserted microsphere and the etched capillary wall. Operating in the reflection mode and providing a robust mechanical support to the microresonator, the integrated structure has been experimentally proven as a convenient probe for sensing applications. Microspheres made of different materials (e.g., PMMA, porous glass, hollow core porous, and glass solid borosilicate glass) were successfully demonstrated for different sensing purposes, including temperature, chemical vapor concentration, and glucose concentration in aqueous solutions. In addition, the alignment free, integrated microresonator structure may also find other applications such as optical filters and microcavity lasers