This thesis delves into innovative active photonic integrated devices and circuits on the thin-film lithium niobate (TFLN) platform, focusing on their applications and potential future advancements. We introduce a new family of electrooptic modulators (EOMs), the Four-Phase Electrooptic Modulators (FEOMs), which are fabricated using the TFLN platform. These devices effectively mitigate bandwidth and dynamic-range constraints in optical communication systems by reducing dispersion penalties and common-mode noises. Their functionality is demonstrated in a photonic time-stretch system. A dual-polarization variant further exemplifies the mitigation of both dispersion penalties and common-mode noises in long-haul communication links, marking significant strides towards the practical implementation of coherent optical communication. We also engineer dual-channel, tunable ultra-narrow linewidth filters using phase-shifted Bragg grating structures on the TFLN platform. These filters act as key components for optical communication, sensing systems, and emerging quantum photonic applications. The device boasts a high extinction ratio, closely spaced channels with narrow linewidths, and efficient central wavelength tuning via the electrooptic effect. This makes it beneficial for finely adjusting high-precision photonic integrated circuits (PICs). The experimental results align well with the design and simulations, indicating promising potential for integration into advanced PICs for future quantum photonic applications and the development of multiple-channel ultra-narrowband filters with active tuning capabilities. Additionally, the thesis includes the design and simulation of a fully packaged TFLN EOM, catering to the rising demand for high-performance optical modulators in telecom and RF photonics applications. Lastly, we delve into a pioneering micro-electromechanical systems (MEMS) photonic switch that uses TFLN, harnessing LN's piezoelectric properties and outstanding operational bandwidth. These features have the potential to propel significant advancements in optical communication systems and other fields that necessitate precise light signal control.

The potential of high-energy sources within the mid-infrared region (3-8 μm) has garnered significant attention for diverse research and industrial applications. Millijoule pulses extending beyond 3 μm can facilitate the production of x-rays with photon energies in the keV range through high harmonic generation (HHG). These high-energy x-ray pulses enable the characterization of electron dynamics within molecules and condensed matter materials. Additionally, the atmospheric transmission window between 3-5 μm allows lasers within this spectral range to deliver energy efficiently to distant targets via optical filaments without divergence, highlighting promising prospects for defense applications. In contrast to laser amplifiers, which are restricted to several wavelengths within the mid-infrared spectral region, nonlinear optical effects allows the generation of pulses of similar energy but with a more adjustable spectrum. This flexibility makes amplification schemes, such as the Optical Parametric Chirped Pulse Amplifier (OPCPA), especially fitting for mid-Infrared applications. However, the efficiency of most existing systems operating above 3 μm is comparatively low due to the reliance on a near-infrared pump (0.75-1.4 μm). This thesis describes a novel tabletop OPCPA system, using ZnGeP2 pumped by a Ho:YLF chirped pulse amplifier (CPA) operating at 2 µm and seeded by intra-pulse difference frequency generation. The output energy and beam quality from the Ho:YLF laser are optimized by advancing the cooling system to reach lower operational temperatures, ensuring the quality of the OPCPA. Through the optimization of the ZGP's phase-matching bandwidth via a non-collinear configuration, and the enhancement of conversion efficiency with the aid of the top-hat pump, the OPCPA system can deliver 4-mJ, 50-fs pulses at a 1 kHz frequency. This system attains an unprecedented overall efficiency of 15% at this wavelength. The detection of harmonics up to the seventh order upon focusing the output in air substantiates the system's competence in conducting strong field experiments.

Silicon photonics is nowadays a mature technology and is on the verge of becoming a blossoming industry. Silicon photonics has also been pursued as a platform for integrated nonlinear optics based on Raman and Kerr effects. In recent years, more futuristic directions have been pursued by various groups. For instance, the realm of silicon photonics has been expanded beyond the well-established near-infrared wavelengths and into the mid-infrared (3 - 5 µm). In this wavelength range, the omnipresent hurdle of nonlinear silicon photonics in the telecommunication band, i.e., nonlinear losses due to two-photon absorption, is inherently nonexistent. With the lack of efficient light-emission capability and second-order optical nonlinearity in silicon, heterogeneous integration with other material systems has been another direction pursued. Finally, several approaches have been proposed and demonstrated to address the energy efficiency of silicon photonic devices in the near-infrared wavelength range. In this dissertation, theoretical and experimental works are conducted to extend applications of integrated photonics into mid-infrared wavelengths based on silicon, demonstrate heterogeneous integration of tantalum pentoxide and lithium niobate photonics on silicon substrates, and study two-photon photovoltaic effect in gallium arsenide and plasmonic-enhanced structures. Specifically, performance and noise properties of nonlinear silicon photonic devices, such as Raman lasers and optical parametric amplifiers, based on novel and reliable waveguide technologies are studied. Both near-infrared and mid-infrared nonlinear silicon devices have been studied for comparison. Novel tantalum-pentoxide- and lithium-niobate-on-silicon platforms are developed for compact microring resonators and Mach-Zehnder modulators. Third- and second-harmonic generations are theoretical studied based on these two platforms, respectively. Also, the two-photon photovoltaic effect is studied in gallium arsenide waveguides for the first time. The effect, which was first demonstrated in silicon, is the nonlinear equivalent of the photovoltaic effect of solar cells and offers a viable solution for achieving energy-efficient photonic devices. The measured power efficiency achieved in gallium arsenide is higher than that in silicon and even higher efficiency is theoretically predicted with optimized designs. Finally, plasmonic-enhanced photovoltaic power converters, based on the two-photon photovoltaic effect in silicon using subwavelength apertures in metallic films, are proposed and theoretically studied.

<p dir="ltr">Quantum photonics is one of the leading platforms to realize quantum information technologies. Quantum emitters embedded in host materials which can readily form photonic circuitry elements have received significant research interest in recent years for on-chip quantum information processing applications. In this work, we report on the discovery of bright, stable, and linearly polarized quantum emitters in SiN films with room temperature single photon generation. We suggest that the emission originates from a specific defect center in SiN because of the narrow wavelength distribution of the observed luminescence peak.</p><p dir="ltr">We further probe these emitters’ fundamental photophysical properties through measurements of optical transition wavelengths, linewidths, and photon antibunching as a function of temperature. Important insight into the potential for lifetime-limited linewidths is provided through measurements of inhomogeneous and temperature-dependent broadening of the zero-phonon lines. At 4.2K, spectral diffusion was found to be the main broadening mechanism, while spectroscopy time series revealed zero-phonon lines with instrument-limited linewidths.</p><p dir="ltr">Along with the optical properties of the quantum emitters, we study their formation mechanisms by investigating the effects of sample composition and thermal annealing parameters. From these measurements, we gain critical insight into the fundamental nature of the quantum emitters in SiN, as well as the dependence of their photophysical properties on the changes in the host material. Additionally, we explore alternative SiN fabrication approaches and the optical properties of the SiN films developed with these techniques. We then investigate quantum emitter formation and hypothesize why the optical properties of the defects in each type of film differ.</p><p dir="ltr">Finally, we begin preliminary investigations into the possible existence of near-infrared (NIR) emitting defects in SiN, as well as single-photon electroluminescence from thin SiN-on-silica films embedded in p-n heterojunctions.</p><p dir="ltr">The single-photon emitters in SiN we have studied extensively in this work have the potential to enable scalable and low-loss integration of quantum light sources with a mature on-chip photonics platform.</p>

如何在納米結構中控制的光的傳播，一直是物理和應用技術方面被廣泛研究的其中一個課題。在這篇論文中，我們從理論上探討在納米結構中表面等離子體激元(Surface plasmon polariton) 的特性以及其雜化。我們研究的納米結構包括金屬電介質金屬平板導波(chirped metaldielectric wave-guides) ，慘入納米金屬球的金屬電介質平板導波(metal dielectric waveguides with metallic narnoparticle doped)與光子晶體(photoniccrystals) 。 / 金屬-電介質-金屬平板導波由三層的金屬及電介質平板所組成，原本各自獨立存在於兩層金屬-介電介面的表面等離子體激元在兩層介面相距足夠近的情況下，會產生稱合作用而導致雜化表面等離子體激元(Hybridizedsurface plasmon polariton) 的產生，並且能在色散關係中被一條接近平坦、位於中頻附近的帶所表示。 / 同樣地，透過在金屬介電介面附近的電介質平板部份中加入納米金屬球，我們也能引起納米金屬球上的表面等離子體與平面金屬-介電介面上的表面等離子體激元之間的耦合作用，從而在色散關係產生另一條分支帶。 / 這些由雜化作用所導致的平坦的分支帶，其特性很容易透過操縱模型參數所改變。因此，我們可以在模型中引入一個介電常數(或厚度)的漸變梯度，從而達成表面等離子體激元的定域化，或多頻率表面等離子體激元(SPP rainbow) 的誘捕。 / 另外，透過轉移距列(transfer matrix)及哈密頓光學(Hamiltonian opticsapproach) 的應用，我們同時研究了表面等離子波在一維二元光子晶體中的斜入射色散關係及其傳播。結果證明，它可以用來引起波長尺度級別的表面等離子波的軌跡彎曲。 / Controlling the light propagation in nanostructures is one of the extensively studied topics in physics and technology. In this thesis, we theoretically investigate the behaviours of surface plasmon polariton (SPP) and the hybridized nanostructures, which include chirped metal-dielectric waveguides, metal-dielectric waveguides with metallic nanoparticle doped and photonic crystals. / In the system of chirped metal-dielectric waveguides which compose of metal-dielectric-metal multilayers, the evanescent coupling of the SPP waves at the two interfaces in the dielectric layer lead to a new hybridized surface plasmon polariton (HSPP) branch with a nearly flat dispersion at intermediate frequencies. / Similarly, by adding metallic nano-particles into the dielectric media, we can also achieve another HSPP branch which is caused by the coupling between the surface plasmon (SP) on the nanoparticles and SPP at the waveguide interface. Moreover, the nearly flat branch is tunable through changing the system parameters. Therefore by imposing a gradual variation of per-mittivity (or thickness), it is possible to achieve a localization of SPP wave, which is useful for achieving trapped SPP rainbow. / We also study at oblique incidence the dispersion relation and the propagation of SP in one dimension binary photonic crystals by using methods of transfer matrix and Hamiltonian optics approach. The result shows that it can be used to achieve a superbending of SP waves in wavelength scales. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Chau, Cheung Wai = 表面等離子光學及納米光學中的雜交化電磁極化子 / 鄒長威. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references (leaves 84-86). / Abstracts also in Chinese. / Chau, Cheung Wai = Biao mian deng li zi guang xue ji na mi guang xue zhong de za jiao hua dian ci ji hua zi / Zou Changwei. / Abstract --- p.i / 概要 --- p.iii / Acknowledgements --- p.v / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Plasmonics and nanophotonics --- p.1 / Chapter 1.2 --- Surface plasmon polaritons --- p.2 / Chapter 1.2.1 --- History of SPP --- p.2 / Chapter 1.2.2 --- Investigations and applications of SPPs --- p.3 / Chapter 1.3 --- Objective of thesis --- p.3 / Chapter 2 --- Basic principles --- p.5 / Chapter 2.1 --- Drude model --- p.5 / Chapter 2.2 --- SPP formalism --- p.7 / Chapter 2.2.1 --- SPP excitation --- p.9 / Chapter 2.3 --- Level repulsion phenomenon --- p.10 / Chapter 2.3.1 --- Simple coupled oscillator --- p.10 / Chapter 2.3.2 --- Diatomic elastic chain --- p.12 / Chapter 2.3.3 --- Summary --- p.13 / Chapter 2.4 --- Transfer matrix method --- p.14 / Chapter 2.5 --- Hamiltonian optics approach --- p.16 / Chapter 2.6 --- Maxwell Garnett approximation --- p.17 / Chapter 3 --- Thomson plasmonics --- p.20 / Chapter 3.1 --- Introduction --- p.21 / Chapter 3.2 --- Model and scheme --- p.21 / Chapter 3.3 --- HSPP formalism --- p.22 / Chapter 3.4 --- HSPP bands with varying inclusions of metallic nanospheres --- p.23 / Chapter 3.5 --- Confinement scheme --- p.25 / Chapter 3.6 --- HO simulation and localization --- p.26 / Chapter 3.6.1 --- Center excitation --- p.28 / Chapter 3.6.2 --- Off center excitation --- p.30 / Chapter 3.7 --- Tunability and fabrication --- p.31 / Chapter 3.8 --- Complications and loss --- p.33 / Chapter 3.9 --- Summary --- p.33 / Chapter 4 --- Chirped metal-dielectric waveguides --- p.41 / Chapter 4.1 --- Introduction --- p.42 / Chapter 4.2 --- Model and scheme --- p.42 / Chapter 4.3 --- SPP formalism --- p.43 / Chapter 4.4 --- HSPP bands with varying permittivity and thickness --- p.45 / Chapter 4.5 --- Confinement scheme --- p.46 / Chapter 4.5.1 --- Varying permittivity --- p.47 / Chapter 4.5.2 --- Varying thickness --- p.47 / Chapter 4.6 --- Ho simulation and localization --- p.48 / Chapter 4.6.1 --- Varying permittivity --- p.49 / Chapter 4.6.2 --- Varying thickness --- p.51 / Chapter 4.7 --- Summary --- p.53 / Chapter 5 --- Dispersion and mirage of surface plasmon waves in metallic photonic crystals --- p.60 / Chapter 5.1 --- Photonic crystal --- p.60 / Chapter 5.2 --- Introduction --- p.61 / Chapter 5.3 --- Dispersion relation formalism --- p.61 / Chapter 5.4 --- Graded material --- p.64 / Chapter 5.5 --- Ho simulation --- p.65 / Chapter 5.6 --- Results --- p.66 / Chapter 5.6.1 --- Lowest band excitation --- p.66 / Chapter 5.6.2 --- Second lowest band excitation --- p.69 / Chapter 5.6.3 --- Multiangle incidence --- p.71 / Chapter 5.7 --- Summary --- p.72 / Chapter 6 --- Conclusion --- p.82 / Bibliography --- p.84

Quantum systems’ integration in chip-scale photonic circuits is the most promising way to succeed in scaling up complex systems for applications ranging from quantum computation to secure communications. Large systems with many components, especially for scaled all-optical quantum or classical processors, will require improved building blocks with greatly reduced loss, and enhanced bandwidth and robustness to fabrication uncertainties, temperature, etc. In this work, we introduce the concept of rapid adiabatic mode evolution that is the basis of a new family of passive devices with fundamentally improved performance, that we refer to as rapid adiabatic devices. In conventional adiabatic devices, a concept well known in photonics, the waveguide cross-section slowly evolves along the propagation direction, with no particular attention paid to transverse positioning of the cross-section. In contrast, in rapid adiabatic devices, we control the transverse position evolution (taking a tailored off-axis path while advancing along the direction of propagation). This has a major impact on the dominant crosstalk mechanism, the limiting factor to all performance metrics. By judicious synthesis and design, the dominant crosstalk coupling mechanism can be minimized or even set to zero everywhere along the structure. This concept brings a new paradigm to photonic passives that we stand the test of time as an important tool in the integrated photonics tool-box. We experimentally demonstrate a new integrated 2×2 beam splitter design we call a Rapid Adiabatic Coupler (RAC) in different fabrication platforms. The design is implemented in state-of-the art, field-leading CMOS photonics platforms pioneered in our group, taking into account foundry-imposed limitations on design. It nevertheless shows field-leading, very low-loss and extremely broadband 50:50 splitting ratio over hundreds of nanometers of optical bandwidth. In addition, we also demonstrate other photonic passives based on the concept – Rapid Adiabatic Crossings (RAX), a Rapid Adiabatic Mode Splitter (RAMS) as well as a Polarization Splitter Rotator based on the RAMS. These new high performance, compact components will enable larger-scale systems on chip with a higher number of components, not only for quantum photonics applications but also for other types of systems for sensing, optical AI accelerators, optical “FPGAs”, optical switches and routers, optical communication links and others. Another key building block for quantum photonic systems is integrated single photon sources. Following the first demonstration of a pair source integrated with pump filters by our group, here we demonstrate a monolithically integrated tunable photon pair source and pump filter on chip in a commercial, advanced 45nm CMOS microelectronics process. Next, we propose electronic-photonic quantum systems on chip, that contain monolithically integrated electronics and photonic components, as a platform to further scale up complexity in, and modularize, quantum systems on chip. As a first demonstration concept, we propose and demonstrate the first experimental step toward a “wall-plug” photon pair source implemented as an electronic-photonic monolithic chiplet. The idea is a CMOS die (or electronic-photonic block on the chip) that takes only electrical DC power, optical CW laser “DC power”, and control signals, and generates high quality photon pairs. The system contains a thermally tunable second-order filter with heater drivers integrated in the chiplet electronics to clean the input pump laser, a self-locking source ring with integrated electronic circuits that allow the ring resonance to automatically align to the pump laser and low-loss, high extinction, high-order thermally tunable filters. These results taken together show that monolithic integration in CMOS micro-electronics processes does allow high performance photonics, while also supporting scalable complex circuits with electronic control to account for the extreme sensitivity of photonic components and impart reconfigurability and tunability; showing it as a viable approach to build large-scale electronic-photonic systems with a realistic path to commercial technologies. This work was supported in part by the NSF RAISE-EQuIP program (Award 1842692) and by the Packard Foundation (Award 2012-38222). / 2023-05-23T00:00:00Z

<p>New types of laser using the basic structure of FP cavity are designed and modeled, to achieve high SMSR single-mode lasing that can be immune to high level of optical feedbacks for optical network communication applications.</p> <p>The work includes design of asymmetric Bragg reflection waveguide laser that employs wavelength selective Bragg reflectors as the claddings to confine and filter desired FP longitudinal modes for amplification and lasing. Si-rich SiO₂ single-mode laser based on this structure is also proposed and analyzed.</p> <p>To optimize a recent design of discrete mode laser that is re-growth free and feedback-perturbation insensitive, a comprehensive implementation of the time domain transfer matrix method, including temperature and feedback effects, is carried out. The model helps to obtain a optimized DM structure that is balanced between high SMSR and low feedback sensitivity.</p> / Doctor of Science (PhD)

This thesis considers two broad categories of shape-preserving transformations: physical transformations, in which the chemistry of the as-grown material remains constant but some structural change is introduced (i.e., conversion of dense silicon nanowires into porous silicon nanowires); and chemical transformations, in which the physical structure of the as-grown material remains constant but the chemical composition is changed (i.e., conversion of SiO2 photonic crystal fibers into MgF¬2 photonic crystal fibers). Part I of this thesis focuses on the development of a process which allows for the introduction of porosity into dense silicon nano- and microstructures (a shape preserving net physical transformation, albeit by chemical means), while Part II focuses on conversion of SiO2-based photonic structures, including three dimensional photonic crystals and hollow-core photonic crystal fibers into Mg2Si or MgF2 replicas with more desirable chemical compositions (a shape preserving net chemical transformation) possessing enhanced optical characteristics.

A theoretical and experimental investigation of scatter from surface roughness and core refractive index fluctuations in planar waveguides was performed, with an emphasis placed on applications in solution-deposited SiO₂-TiO₂ (silica titania) planar waveguiding systems. A perturbation theory was used to model TE₀ mode scattering from surface and volume microstructure, and to predict attenuation when provided with the necessary waveguide and scattering parameters. Final forms for the equations predicting surface and volume scatter losses into the cover and substrate regions of the waveguides were provided. The rather complex perturbation theory model of surface scatter was compared to a very simple, intuitive model based on the Rayleigh criterion. The two models were shown to predict surface induced attenuation values which were in very close agreement when the guided mode propagation angle approached 90°. Thus, the simple model was shown to be adequate for predicting TE₀ mode surface scattering losses for waveguides which were very thick, and/or possessed a low refractive index. Considerable emphasis was placed on providing a simple, physical picture of guided mode scattering, utilizing rays to represent the scattered light. Following the development of this technique, it was utilized to explain the origins of interference peaks in surface scattered radiation at certain values of film thickness. Solution chemistry and processing methodologies for 50:50 mol% and 35:65 mol% SiO₂-TiO₂ sol-gel films, yielding high quality, amorphous, glass waveguides, were discussed. Attenuation in the 50:50 mol% films was 1-2 dB/cm, while attenuation in the 35:65 mol% films was 0.3-0.5 dB/cm, at λ = 0.6328 μm. Absorption in these films was negligible. Waveguide losses were measured by transferring the scattered streak to a remote image plane (using a coherent fiber bundle) and scanning it using an automated, stepper-motor controlled, apertured photomultiplier tube. Testing and calibration techniques were described in detail. We found that surface-induced scattering was the dominant loss mechanism in the 35:65 mol% SiO₂-TiO₂ films. Surface roughnesses of the sol-gel films, measured using Atomic Force Microscopy, ranged from about 2-5 A rms, with correlation lengths from about 0.05-0.75 μm.

This thesis encompasses a theoretical analysis, the fabrication, and optical characterization of a novel compact Bragg Slot Waveguide with a Cavity (BSWC). Strong light confinement in the low refractive index slot region formed by two silicon slabs on a silicon dioxide substrate [1] makes this structure useful for optofluidic, sensing, and optical trapping applications. The transmission spectrum of the BSWC can be engineered through the dimensional variations of the waveguide and through the refractive index change of the surrounding medium. BSWC is compact and can be integrated with various components on a chip for increased functionality. The results in this thesis show a good agreement between analytical and experimental results, while emphasizing the increasing importance of atomic-scale imperfections as a result of fabrication on the nano-scale. The impact of the slot width, slab width, and the cavity length on the waveguide transmission spectrum is investigated.