In this paper, the performance simulations of a novel ultra-compact balanced coherent photodetector for operation at a wavelength of 1.5 mu m are presented and design proposals for future fabrication processes are provided. It consists of a compact 2x2 MMI that is evanescently coupled into a germanium MSM photodetection layer. The simulations demonstrate dark current less than 10 nA, capacitance less than 20 fF, and optical bandwidth in the 10-30 GHz range. We propose utilizing the simplicity of direct wafer bonding to bond the detection layer to the output waveguides to avoid complicated epitaxial growth issues. This ultra-compact device shows promise as a high-speed, low-cost integrated silicon photonics solution for the telecommunications infrastructure.

This thesis presents the development of integrated silicon photonic devices. These devices are compatible with the present and near future CMOS technology. High-khorizontal grating couplers and waveguides are proposed. This work consists of simulations and device design, as well as the layout for the fabrication process, device fabrication, process development, characterization instrument development and electro-optical characterizations. The work demonstrates an alternative solution to costly silicon-on-insulator photonics. The proposed solution uses bulk silicon wafers and thin film deposited waveguides. Back-end deposited horizontal slot grating couplers and waveguides are realized by multi-layers of amorphous silicon and high-k materials. The achievements of this work include: A theoretical study of fully etched slot grating couplers with Al2O3, HfO2 and AIN, an optical study of the high-k films with spectroscopic ellipsometry, an experimental demonstration of fully etched SiO2 single slot grating couplers and double slot Al2O3 grating couplers, a practical demonstration of horizontal double slot high-k waveguides, partially etched Al2O3 single slot grating couplers, a study of a scheme for integration of the double slot Al2O3  waveguides with selectively grown germanium PIN photodetectors, realization of test chips for the integrated germanium photodetectors, and study of integration with graphene photodetectors through embedding the graphene into a high-k slot layer. From an application point of view, these high-k slot waveguides add more functionality to the current silicon photonics. The presented devices can be used for low cost photonics applications. Also alternative optical materials can be used in the context of this photonics platform. With the robust design, the grating couplers result in improved yield and a more cost effective solution is realized for integration of the waveguides with the germanium and graphene photodetectors. / <p>QC 20141114</p>

Les travaux de cette thèse apportent une contribution théorique et expérimentale aux études portant sur les cristaux photoniques planaires à fente pour l'exaltation locale du champ électromagnétique. Nous avons étudié la propagation de lumière lente dans des cristaux photoniques à fente en réalisant une ingénierie de dispersion et le confinement de la lumière dans des micro-cavités à fente structurée. Nous avons pour cela effectué des calculs 3D pour optimiser les propriétés de dispersion des cristaux photoniques en structurant la fente elle-même. Cette optimisation a permis d'observer un renforcement de la localisation du champ électromagnétique dans la fente en vue d'un remplissage par des matériaux fortement non linéaires. Nous avons développé un procédé de fabrication pour les cristaux photoniques dans des structures en silicium sur isolant basé sur la lithographie électronique et la gravure plasma. Le régime de lumière lente a été caractérisé expérimentalement et nous a permis de valider la méthode d'optimisation choisie. Des facteurs de ralentissement supérieurs à 10 ont été mesurés dans des dispositifs allant jusqu'à 1 mm de long. Des micro-cavités à fente avec des facteurs de qualité supérieurs à 20000 sur substrat SOI ont été réalisées. Nous avons effectué des mesures d'optique non linéaire dans des guides à cristaux photoniques à fente et avons montré que les effets non linéaires du silicium sont réduits malgré l'exaltation du champ électromagnétique comparés à ceux présents dans des guides à cristaux photoniques standards. Nous avons enfin étudié les pertes le désordre dans ce type de structure par mesures de réflectométrie optique à faible cohérence. / Abstract : The work described in this PhD thesis brings theoretical and experimental contributions to the study of planar slot photonic crystals for a local exaltation of the electromagnetic field. The propagation of slow light in slot photonic crystal waveguides is investigated by achieving dispersion engineering and confinement of light in slotted microcavities. We have performed 3D calculations to optimize the dispersion properties of the photonic crystals by tailoring the slot itself. This allowed the observation of an enhancement of the field localization aiming at the infiltration of the slot by highly nonlinear materials. We achieved a fabrication process of slot photonic crystal waveguides in silicon on insulator (SOI) structures based on electron bearn lithography and plasma et­ ching. Slow light measurements are reported and validate the optimization method. Group indices higher than 20 have been measured in 1 mm long deviees. Slot photonic crystal microcavities with quality factors higher than 20,000 have been achieved on SOI. We have performed nonlinear optical measurements and revealed that silicon nonlinear effects in slot photonic crystal waveguides are reduced compare to standard waveguides, despite the increase of the exaltation of the electromagnetic field. Finally, we have investigated disorder-induced losses in this type of waveguides by opticallow coherence reflectrometry.

La photonique silicium est un domaine de recherche en pleine expansion depuis quelques années. Elle est envisagée comme une solution prometteuse pour le remplacement des interconnexions électriques par des liens optiques. A terme, l’intégration de l’optique et de l’électronique sur les mêmes puces doit permettre une augmentation des performances des circuits intégrés, et ainsi proposer des composants à hautes performances et à bas coût. Dans ce contexte, les travaux menés durant ma thèse ont porté plus spécifiquement sur l’étude de la modulation optique autour de la bande interdite directe et à température ambiante des structures à puits quantiques Ge/SiGe, par effet Stark confiné quantiquement (ESCQ). Des simulations électriques et optiques ont été menées pour concevoir un modulateur fonctionnant à la longueur d’onde de 1.3μm. La fabrication et la caractérisation de ce dispositif a permis de démontrer une modulation efficace autour de 1.3μm avec des taux de modulation atteignant 6 dB avec un dispositif de 50 µm de long. Le second objectif de mon travail a été de concevoir un modulateur intégré sur une plateforme SOI, bénéficiant de structures passives performantes et compactes. La démonstration de l’ESCQ sur une structure à puits quantique Ge/SiGe épitaxiée sur un substrat homogène de 360 nm a ouvert la voie à cette intégration. Des simulations ont été menées pour démontrer la possibilité de réaliser un couplage vertical évanescent entre un guide optique SOI et la structure Ge/SiGe, et pour évaluer les performances de ce dispositif. Un procédé technologique de fabrication a ensuite été défini et toutes les étapes ont été optimisées pour la réalisation du modulateur intégré avec les guides d’onde. Principalement six étapes de lithographies électroniques, et quatre étapes de gravure sont nécessaires. Les résultats préliminaires obtenus avec ces dispositifs sont présentés. Les perspectives de ce travail de thèse concernent la réalisation de circuits intégrés photoniques complexes, intégrant modulateurs, photodétecteurs et structures passives sur le même circuit. / Silicon photonics has generated a great interest for several years, for applications from long-haul optical telecommunication to intra-chip interconnects. The ultimate integration of optics and electronics on the same chip would allow an increase of the integrated circuit performances at low cost. In this context, the work done during my Ph.D is focused on the study of optical modulation around the direct bandgap of Ge/SiGe quantum well structures, at room temperature, by Quantum Confined Stark effect (QCSE). Electrical and optical simulations have been used to design a modulator operating at 1.3μm. Such device has been fabricated and characterized, demonstrating an extinction ratio up to 6 dB using a 50 µm-long structure. The second objective of my work was to design and demonstrate a modulator integrated on SOI waveguide. The demonstration of an efficient QCSE in Ge/SiGe quantum wells grown on the top of a 360nm homogeneous virtual substrate has paved the way for such integration. Simulations were conducted to demonstrate the feasibility of an evanescent vertical coupling between an SOI optical waveguide and a Ge/SiGe active region and to evaluate the performance of this device. A technological process has then been proposed to fabricate the devices. All steps have been optimized for the fabrication of the modulator integrated with the waveguides. Mainly six electronic beam lithography and four etching steps were used. Preliminary experimental results obtained with such component are presented. This work paves the way to the demonstration of complex photonic integrated circuits, including modulators, photodetectors and passive structures on the same chip.

Processing of high-speed data using optical signals is a promising approach for tackling the bandwidth and speed challenges of today's electronics. Realization of complex optical signal processing functionalities seems more possible than any time before, thanks to the recent achievements in silicon photonics towards large-scale photonic integration. In this Ph.D. work, a novel thermal reconfiguration technology is proposed and experimentally demonstrated for silicon photonics that is compact, low-loss, low-power, fast, with a large tuning-range. These properties are all required for large-scale optical signal processing and had not been simultaneously achieved in a single device technology prior to this work. This device technology is applied to a new class of resonator-based devices for reconfigurable nonlinear optical signal processing. For the first time, we have demonstrated the possibility of resonance wavelength tuning of individual resonances and their coupling coefficients. Using this new device concept, we have demonstrated tunable wavelength-conversion through four-wave mixing in a resonator-based silicon device for the first time.

Silicon is the dominant material in Microelectronics. Building photonic devices out of silicon can leverage the mature processing technologies developed in silicon CMOS. Silicon is also a very good waveguide material. It is highly transparent at 1550nm, and it has very high refractive index of 3.46. High refractive index enables building high index contrast waveguides with dimensions close to the diffraction limit. This provides the opportunity to build highly integrated photonic integrated circuit that can perform multiple functions on the same silicon chip, an optical parallel of the electronic integrated circuit. However, silicon does not have some of the necessary properties to build active optical devices such as lasers and modulators. For Example, silicon is an indirect band gap material that can’t be used to make lasers. The centro-symmetric crystal structure in silicon presents no electro-optic effect. By contrast, electro-optic polymer can be engineered to show very strong electro-optic effect up to 300pm/V. In this research we have demonstrated highly compact and efficient devices that utilize the strong optical confinement ability in silicon and strong electro-optic effect in polymer. We have performed detailed investigations on the optical coupling to a slow light waveguide and developed solutions to improve the coupling efficiency to a slow light photonic crystal waveguides (PCW). These studies have lead to the demonstration of the most hybrid silicon modulator demonstrate to date and a compact chip scale true time delay module that can be implemented in future phased array antenna systems. In the future, people may be able to realize a photonic integrated circuit for optical communication or sensor systems using the devices we developed in our research. / text

Manipulation of light at the nanoscale has the promise to enable numerous technological advances in biomedical sensing, optical communications, nano-mechanics and quantum optics. As photons have vanishingly small interaction cross sections, their interactions have to be mitigated by matters (i.e. quantum emitters, molecules, electrons etc.). Waveguides and cavities are the fundamental building blocks of the optical circuits, which control or confine light to specific matters of interest. The first half of the thesis (Chapters 2 & 3) focuses on how to design various photonic nanostructures to manipulate light on nano- to micro- scale, especially to modify the light-matter interaction properties. Chapter 2 discusses how nano-slot waveguides and photonic crystal nanobeam waveguides are able to modify the emission of quantum emitters, in a different way that normal ridge waveguides are not able to. Chapter 3 focuses on a more complicated and powerful structure: the photonic crystal nanobeam cavity. The design, fabrication and characterization of the photonic crystal nanobeam cavities are described and demonstrated in detail, which lays out the foundation of the biomedical sensing applications in the second half of the thesis. The second half of the thesis (Chapters 4 & 5) focuses on the application of photonic crystal nanobeam cavities in the label-free sensing of biomedical substances. Chapter 4 demonstrates detection of solutions with different refractive index (aceton, methanol, IPA etc.), glucose concentration, single polystyrene nanoparticles and single streptavidin bio-molecules. Chapter 4 proposes a novel nonlinear optical method to further enhance the sensitivity. Chapter 4 also demonstrates high quality nanobeam cavities fabricated in polymers, that open up a new route to decrease the cost, as well as to achieve novel applications with functional polymers. The broader impact of this technology lies in its potential of commercialization of a new generation of biosensors with high sensitivity and high integration. Chapter 5 discusses progresses towards instrumentation of the nanobeam cavity sensing technology for research & development apparatus, as well as point-of-care diagnostic tools. / Engineering and Applied Sciences

The goal of the research reported in this thesis is to establish the feasibility of a novel optical architecture for an optical route & select circuit switch suitable for implementation as a photonic integrated circuit. The proposed architecture combines Optical Phased Array (OPA) switch elements implemented as multimode interference coupler based Generalised Mach-Zehnder Interferometers (GMZI) with a planar Lüneburg lens-based optical transpose interconnection network implemented using graded metamaterial waveguide slabs. The proposed switch is transparent to signal format and, in principle, can have zero excess insertion loss and scale to large port counts. These switches will enable the low-energy consumption high capacity communications network infrastructure needed to provide environmentally-friendly broadband access to all. The thesis first explains the importance of switch structures in optical communications networks and the difficulties of scaling to a large number of switch ports. The thesis then introduces the Talbot effect, i.e. the self-imaging of periodic field distributions in free space. It elaborates on a new approach to finding the phase relations between pairs of Talbot image planes at carefully selected positions. The free space Talbot effect is mapped to the waveguide Talbot effect which is fundamental to the operation of multimode interference couplers (MMI). Knowledge of the phase relation between the MMI ports is necessary to achieve correct operation of the GMZI OPA switch elements. An outline of the design procedures is given that can be applied to optimise the performance of MMI couplers and, as a consequence, the GMZI OPA switch elements. The Lüneburg Optical Transpose Interconnection System (LOTIS) is introduced as a potential solution to the problem of excessive insertion loss and cross-talk caused by the large number of crossovers in a switch fabric. Finally, the thesis explains how a Lüneburg lens may be implemented in a graded ‘metamaterial’, i.e. a composite material consisting of ‘atoms’ arranged on a regular lattice suspended in a host by nano-structuring of silicon waveguide slabs using a single etch-step. Furthermore, the propagation of light in graded almost-periodic structures is discussed. Detailed consideration is given to the calibration of the local homogenised effective index; in terms of the local parameters of the metamaterial microstructure in the plane and the corrections necessary to accommodate slab waveguide confinement in the normal to the plane. The concept and designs were verified by FDTD simulation. A 4×4 LOTIS structure showed correct routing of light with a low insertion loss of -0.25 dB and crosstalk of -24.12 dB. An -0.45 dB excess loss for 2D analysis and an -0.83 dB insertion excess loss for 3D analysis of two side by side metamaterial Lüneburg lenses with diameter of 15 μm was measured, which suggests that the metamaterial implementation produces minimal additional impairments to the switch.

Research in the field of Photonics is in part, directed at the application of light-emitting materials based on silicon platforms. In this work silicon wafers are modified by carbon ion implantation to incorporate silicon carbide, a known light-emitting material. Ion beam synthesis treatments are applied with implant energy of 20 keV, and ion fluences of 3, 5 and 10 × 1016 ions/cm2 at both ambient temperature and high temperature (400 °C). The samples are annealed at 1000 °C, after implantation. The carbon ion implanted silicon is characterized using Raman and Fourier transform infrared spectroscopic techniques, grazing-incidence X-ray diffraction, transmission electron microscopy and electron energy loss spectroscopy. The materials are observed to have a multilayer structure, where the ambient temperature implanted materials have an amorphous silicon layer, and an amorphous silicon layer with carbon-rich, nanoscale inclusions. The high temperature implanted materials have the same layers, with an additional polycrystalline Si layer at the interface between the implanted layer and the target substrate and the amorphous Si layer with SiC inclusions is reduced in thickness compared to the ambient temperature samples. The carbon-rich inclusions are confirmed to be SiC, with no evidence of carbon clusters in the materials observed using Raman spectroscopy. The carbon ion-implanted material is used to fabricate Schottky diodes having a semitransparent gold contact at the implanted surface, and an aluminum contact on the opposite side. The diodes are tested using current-voltage measurements between -12 and +15 V. No reverse breakdown is observed for any of the diodes. The turn-on voltages for the ambient temperature implanted samples are 2.6±0.1 V, 2.8±0.6 V and 3.9±0.1 V for the 3, 5 and 10 × 1016 ions/cm2 samples, respectively. For the high temperature implanted samples, the turn-on voltages are 3.2±0.1 V, 2.7±0.1 V, and 2.9±0.4 V for the implanted samples with same fluences. The diode curves are modeled using the Shockley equation, and estimates are made of the ideality factor of the diodes. These are 188±16, 224.5±5.8, and 185.4±9.2 for the ambient temperature samples, and 163.6±6.3, 124.3±5.3, and 333±12 for the high temperature samples. The high ideality factor is associated with the native oxide layer on the silicon substrate and with the non-uniform, defect-rich implanted region of the carbon ion implanted silicon. Red-orange visible light emission from the diodes is observed with voltage greater than the turn-on voltage applied across the diodes. The luminescence for the ambient temperature samples is attributed to porous silicon, and amorphous silicon. The high temperature implanted samples show luminescence associated with porous silicon, nanocrystalline silicon carbide, and defects in silicon related to ion implantation. The luminescent intensity observed for the ambient temperature samples is higher than for the high temperature samples. The dominant luminescence feature in the carbon ion-implanted silicon material is porous silicon, which is described by quantum confinement of excitons in silicon.

In recent years, Silicon Photonics has emerged as a promising technology for cost-effective fabrication of photonic components and integrated circuits, the application of which is recently expanding in technological fields beyond tele- and data-communications, such as sensing and biophotonics. Compact, energy-efficient laser sources with precise wavelength control are crucial for the aforementioned applications. However, practical, efficient, electrically-pumped lasers on Silicon or other group IV elements are still absent, owing to the indirect bandgap of those materials. Consequently, the integration of III-V compounds on Silicon currently appears to be the most viable route to the realization of such lasers. In this thesis, I present and explore the potential of an External Cavity (EC) hybrid III-V/Silicon laser design, comprising a III-V-based Reflective Semiconductor Optical Amplifier (RSOA) and a Silicon reflector chip, based on a two-dimensional Photonic Crystal (PhC) cavity vertically coupled to a low-refractive-index dielectric waveguide. The vertically coupled system functions as a wavelength-selective reflector, determining the lasing wavelength. Based on this architecture mW-level continuous-wave (CW) lasing at room temperature was shown both in a fiber-based long cavity scheme and die-based short cavity scheme, with SMSR of > 25 dB and > 40 dB, respectively. Furthermore, by electrically modulating the refractive index of the PhC cavity in the reflector chip, tuning of the emitted wavelength was achieved in the die-based short cavity EC laser configuration. In this way, I demonstrated the suitability of the examined EC configuration for direct frequency modulation. The proposed scheme eliminates the need for wavelength matching between the laser source and a resonant modulator, and reveals the potential of employing low-power-consumption resonant modulation in practical Silicon Photonics applications.