Semiconductor quantum dots are promising candidates as bright, indistinguishable, single-photon sources---making them desirable for applications in quantum computing and quantum cryptography protocols. By embedding the quantum dots in III-V nanowires, the collection efficiency from the quantum dot is greatly increased. Our goal is to develop a platform that allows for the stable and efficient generation of single-photons on chip. This on-chip design offers an enhanced degree of stability and miniaturization, important in many applications involving the processing of quantum information. In this thesis, we demonstrate the efficient coupling of quantum light generated in a III-V photonic nanowire to a silicon-based photonic integrated circuit. We use high quality SiN waveguide devices fabricated by a foundry (LIGENTEC) to minimize coupling and propagation losses through the waveguide. A hybrid integration of these single-photon sources with a photonic integrated circuit is developed by employing a "pick & place" method which uses a nanomanipulator in a scanning electron microscope setup. By tailoring the nanowire geometry, we are able to maximize the efficient coupling between the optical mode of the photonic nanowire and an accompanying SiN waveguide through evanescent coupling. To determine the effectiveness of our integration method, we compare our hybrid devices with free-standing nanowires on their growth substrate. For each set, we measured the optical properties (brightness, spectral purity, lifetime, and single-photon purity) and efficiencies of the devices. We have shown that using tapered nanowires with embedded quantum dots coupled to on-chip photonic structures is a viable route for the fabrication of stable, high-efficiency, single-photon sources. Although the measured collection efficiencies from device to device were substantially different 9.6%~93%, we have found that the optical properties of the hybrid devices were hardly impacted from the transfer process. In fact, from the same nanowire that achieved 93% coupling efficiency, we were able to measure a single photon purity of 97%. By comparing the amount of emitted light collected from both ends of the nanowire (taper and base), we confirmed that the coupling efficiency of the devices have a strong dependence on the geometry of the nanowire as collection from the taper yielded count rates at least 10x greater than from the base. From our promising results, we can envision integrating the nanowire devices with different types of photonic structures such as ring resonators.

The rapid growth in data communication technologies is at the heart of enriching the digital experiences for people around the world. Encoding high bandwidth data to the optical domain has drastically changed the bandwidth-distance trade-off imposed by electrical media. Silicon photonics, sharing the technological maturity of the semiconductor industry, is a platform poised to make optical interconnect components more robust, manufacturable, and ubiquitous. One of the most prominent device classes enabled by the silicon photonics platform is photonic switching, which describes the direct routing of optical signal carriers without the optical-electrical-optical conversions. While theoretical designs and prototypes of monolithic silicon photonic switch devices have been studied, realizing high-performance and feasible switch systems requires explorations of all design aspects from basic building blocks to control systems. This thesis provides a holistic collection of studies on silicon photonic switching in topics of novel switching element designs, multi-stage switch architectures, device calibration, topology scalability, smart routing strategies, and performance-aware control plane. First, component designs for assembling a silicon photonic switch device are presented. Structures that perform 2×2 optical switching functions are introduced. To realize switching granularities in both spatial and spectral domains, a resonator-assisted Mach-Zehnder interferometer design is demonstrated with high performance and design robustness. Next, multi-stage monolithic switching devices with microring resonator-based switching elements are investigated. An 8×8 switch device with dual-microring switching elements is presented with a well-balanced set of performance metrics in extinction ratio, crosstalk suppression, and optical bandwidth. Continued scaling in the switch port count requires both an economic increase in the number of switching elements integrated in a device and the preservation of signal quality through the switch fabric. A highly scalable switch architecture based on Clos network with microring switch-and-select sub-switches is presented as a solution to reach high switch radices while addressing key factors of insertion loss, crosstalk, and optical passband to ensure end-to-end switching performance. The thesis then explores calibration techniques to acquire and optimize system-wide control points for integrated silicon switch devices. Applicable to common rearrangeably non-blocking switch topologies, automated procedures are developed to calibrate entire switch devices without the need for built-in power monitors. Using Mach-Zehnder interferometer-based switching elements as a demonstration, calibration techniques for optimal control points are introduced to achieve balanced push-pull drive scheme and reduced crosstalk in switching operations. Furthermore, smart routing strategies are developed based on optical penalty estimations enabled by expedited lightpath characterization procedures. Leveraging configuration redundancies in the switch fabric, the routing strategies are capable of avoiding the worst penalty optical paths and effectively elevate the bottom-line performance of the switch device. Additional works are also presented on enhancing optical system control planes with machine learning techniques to accurately characterize complex systems and identify critical control parameters. Using flexgrid networks as a case study, light-weight machine learning workflows are tailored to devise control strategies for improving spectral power stability during wavelength assignment and defragmentation. This work affirms the efficacy of intelligent control planes to predict system dynamics and drive performance optimizations for optical interconnect systems.

Electro-optic phase modulators play a vital role in various large-scale photonic systems including Light Detection and Ranging (LIDAR), quantum circuits, optical neural networks and optical communication links. The key requirement of these modulators include strong phase change with low modulation induced optical loss, low electrical power consumption, small device footprint and low fabrication complexity. Conventional silicon phase modulators have either high power consumption (thermo-optic effect) or high optical loss (plasma-dispersion effect). On the other hand, low-loss phase modulation can be achieved using electro-optic 𝑋² effect such as LiNbO₃ which has a large device footprint (in mm's) and requires complex fabrication. The need of the hour is a material or a device that is strongly tunable with low optical loss and capable of picosecond switching speed. Transition metal dichalcogenides (TMDs) have been widely studied for optoelectronic applications due to their strong and tunable excitonic response. In fact, TMDs have been shown to experience massive changes of upto 20 % in their refractive index with doping, but this modulation is accompanied with large absorption change (60 %), which greatly limits their utility in photonic applications. In contrast, very litte is known about the effect of doping on the electro-optic response of TMDs at energies far below the exciton resonances, where the material is transparent and therefore could be used for photonic circuits. In this work, we first probe the electro-optic properties of TMDs in the near-infrared using a dielectric SiN microring resonator platform. We measure a strong doping induced change in the refractive index (Δn) of 0.52 in WS2 with minimal induced absorption (Δk) of 0.004. The |Δn/Δk| of 125, is an order of magnitude higher than the measured |Δn/Δk| for 2D materials including graphene and TMD monolayer at excitonic resonances, and for bulk electro-refractive materials commonly employed in silicon photonics. We next utilize this strong electro-refractive response to demonstrate low power, lossless optical phase modulation based on a composite SiN-TMD platform. The WS₂ based photonic modulator achieves a modulation efficiency (V_π⋅L) of 0.8 V ⋅ cm with a RC limited bandwidth of 0.3 GHz and DC electrical power consumption of 0.64 nW. The measured index change in monolayer TMDs (∼ 15%) in TMDs is unprecedented, considering the change in index of bulk (LiNbO₃) - the 'gold standard' for photonics - is typically 0.04 %. Despite the observed strong electro-refractive effect in TMDs and the enhanced light-matter interaction, the change in effective index of the propagating mode is 6.5 × 10⁻⁴ RIU, thereby requiring WS₂ phase modulators that are 1.3 mm long. This is due to the low optical mode overlap of 0.03 % with the monolayer that necessitates long phase shifter length. There is an urgent need for a compact, low-loss and high-speed optical phase shifter. Conventional phase modulators with low optical loss require long lengths to achieve strong phase change. On the contrary, traditional intensity modulators leverage compact high-finesse ring resonators to modulate output intensity. However, such cavities with conventional electro-refractive materials such as silicon where Δn/Δk = -20 cannot be used for phase modulation, owing to the high insertion loss associated with the phase change. Here, we show that we can leverage high-finesse ring resonators to achieve strong phase change with low optical loss. We achieve this by simultaneously modulating both the real and imaginary part of the effective index in the cavity to the same extent i.e. Δn/Δk ≈1. We design a hybrid SiN-2D platform that modulates the complex effective index of the propagating mode, by tuning the loss and index in monolayer graphene (Gr) and WSe₂ embedded on a SiN waveguide, respectively. We engineer the Gr-WSe₂ capacitor design to achieve a linear phase change of (0.50 ± 0.05)π radians with a low transmission modulation of 1.73 ± 0.20 dB and insertion loss of 2.96 ± 0.34 dB. We measure a 3 dB electro-optic bandwidth of 14.9 ± 0.1 GHz in the SiN-2D hybrid platform. We measure a phase modulation efficiency (V_(π/2)⋅L) of 0.045 V ⋅ cm with an insertion loss of 4.7 dB for a phase change of π/2 radians in the 25 μm SiN-2D platform. We show that the V_(π/2)⋅L for our SiN-2D hybrid platform is significantly lower than V_(π/2)⋅L of electro-refractive phase modulators based on silicon PN, PIN and MOS capacitors with comparable insertion loss. The TMD or TMD-graphene capacitor is incorporated as a post-fabrication process, transforming any passive substrate into an active photonic platform. The demonstrated enhanced light-matter interaction in monolayer TMDs could open up routes to a range of novel applications with these 2D materials and enable highly reconfigurable photonic circuits with low optical loss and power dissipation. We estimate that the efficiency of our TMD platform can be improved by optimizing the optical mode overlap with the monolayer through photonic mode optimization or reducing the dielectric thickness. For large-scale photonic systems, wafer-scale integration of TMD materials with silicon photonics can be done either as a direct TMD growth process on silicon wafers or a post-processing step where large wafer-scale TMD films are transferred onto a silicon photonics platform fabricated in a standard foundry.

Silicon photonics accelerated the advent of complex integrated photonic systems where multiple devices and elements of the circuits synchronize to perform advanced functions such as beam formation for range detection, quantum computation, spectroscopy, and high-speed communication links. The key ingredient for silicon's growing dominance in integrated photonics is scalability: the ability to monolithically integrate large number of devices. There are emerging device designs and material platforms compatible with silicon photonics that offer performances superior to silicon alone, yet their lack of scalability often limits the demonstrations to device-level. Here we discuss two of such platforms, suspended air-cladded microresonators and graphene modulators. In this thesis, we demonstrate methods to scale these devices and enable more complex applications and higher performance than a single device can ever acheive. We present an effective method to thermally tune optical properties of suspended and air-cladded devices. We utilize released MEMs-like wire structures and integrated heaters and demonstrate efficient thermo-optic tuning of suspended microdisk resonators without affecting optical performance of the device. We further scale this method to a system of two evanescently coupled resonators and demonstrate on-demand control of their coupling dynamics. We present an approach to achieve large yield of high bandwidth graphene modulators to enable Tbits/s data transmission. Despite their high performance, graphene modulators have been demonstrated at single device-level primarily due to low yield, ultimately limiting their total data transmission capacity. We achieve large yield by minimizing performance variation of graphene modulators due to random inhomogeneous doping in graphene by optimizing device design and leveraging state-of-the-art electrochemical delamination graphene transfer. We present for the first time, to the best of our knowledge, a statistical analysis of graphene photonic devices. Finally, we present a graphene modulator that is versatile for photonic links at cryogenic temperature. We demonstrate the operation of high bandwidth graphene modulator at 4.9 K, a feat that is fundamentally challenging other electro-optic materials. We describe its performance enhancement at cryogenic temperature compared to ambient environment unlike modulators based on other electro-optic materials whose performance degrades at cryogenic temperature.

Photonic lattices consisting of arrays of evanescently coupled waveguides fabricated with precisely controlled parameters have enabled the study of discrete optical phenomena, both classical and quantum, and the simulation of other physical phenomena governed by the same dynamics. In this dissertation, I have experimentally demonstrated transverse Anderson localization of classical light in arrays with off-diagonal coupling disorder and investigated theoretically and experimentally the propagation of entangled photon pairs through such disordered systems. I discovered a new phenomenon, Anderson co-localization, in which a spatially entangled photon pair in a correlated transversally extended state localizes in the correlation space, though neither photon localizes on its own. When the photons of a pair are in an anti-correlated state, they maintain their anti-correlation upon transmission through the disordered lattice, exhibiting Anderson anti-localization. These states were generated by use of parametric down conversion in a nonlinear crystal. The transition between the correlated and anti-correlated states was also explored by using a lens system in a configuration intermediate between imaging and Fourier transforming. In the course of this research, I discovered a curious aspect of light transmission through such disordered discrete lattices. An excitation wave of a single spatial frequency (transverse momentum) is transmitted through the system and is accompanied by another wave with the same spatial frequency but opposite sign, indicating some form of internal reflection facilitated by the disordered structure.

The dissertation is concerned with the design of high-efficiency permanent magnet synchronous machinery and the control system. The dissertation first talks about the basic concept of the permanent magnet synchronous motor (PMSM) design and the mathematics design model of the advanced design method. The advantage of the design method is that it can increase the high load capacity at no cost of increasing the total machine size. After that, the control method of the PMSM and Permanent magnet synchronous generator (PMSG) is introduced. The design, simulation, and test of a permanent magnet brushless DC (BLDC) motor for electric impact wrench and new mechanical structure are first presented based on the design method. Finite element analysis based on the Maxwell 2D is built to optimize the design and the control board is designed using Altium Designer. Both the motor and control board have been fabricated and tested to verify the design. The electrical and mechanical design are combined, and it provides an analytical IPMBLDC design method and an innovative and reasonable mechanical dynamical calculation method for the impact wrench system, which can be used in whole system design of other functional electric tools. A 2kw high-efficiency alternator system and its control board system are also designed, analyzed and fabricated applying to the truck auxiliary power unit (APU). The alternator system has two stages. The first stage is that the alternator three-phase outputs are connected to the three-phase active rectifier to get 48V DC. An advanced Sliding Mode Observer (SMO) is used to get an alternator position. The buck is used for the second stage to get 14V DC output. The whole system efficiency is much higher than the traditional system using induction motor.

Liquid crystal (LC) has been widely used for displays, spatial light modulators, variable optical attenuators (VOAs) and other tunable photonic devices. The response time of these devices is mainly determined by the employed liquid crystal material. How to obtain fast response for the LC devices is a fundamentally important and technically challenging task. In this dissertation, we investigate several methods to improve liquid crystal response time, for examples, using dual-frequency liquid crystals, polymer stabilized liquid crystals, and sheared polymer network liquid crystals. We discover a new class of material, denoted as sheared polymer network liquid crystal (SPNLC) which exhibits a submillisecond response time. First, dual-frequency liquid crystals and polymer network methods are demonstrated as examples for the variable optical attenuators. Variable optical attenuator (VOA) is a key component in optical communications. Especially, the sheared PNLC VOA shows the best result; its dynamic range reaches 43 dB while the response time is in the submillisecond range at 1550 nm wavelength, which is 50 times faster than the commercial LC-based VOA. Second, we report a new device called axially-symmetric sheared polymer network liquid crystals (AS-SPNLC) and use it as LC devices. An axially-symmetric sheared polymer network liquid crystal has several attractive features: 1) it is polarization independent, 2) it has gradient phase change, and 3) its response time is fast. It can be used for polarization converter and divergent LC lens. In addition, a new method for simultaneously measuring the phase retardation and optic axis of a compensation film is demonstrated using an axially-symmetric sheared polymer network liquid crystal. This simple technique can be used for simultaneously measuring the optic axis and phase retardations of both A- and C-plates. These compensation films have been used extensively in wide-view LCD industry. Therefore, this method will make an important impact to the LCD industry.

Aside from energy, light carries linear and angular momenta that can be transferred to matter. The interaction between light and matter is governed by conservation laws that can manifest themselves as mechanical effects acting on both matter and light waves. This interaction permits remote, precise, and noninvasive manipulation and sensing at microscopic levels. In this dissertation, we demonstrated for the first time a complete set of opto-mechanical effects that are based on nonconservative forces and act at the interface between dielectric media. Without structuring the light field, forward action is provided by the conventional radiation pressure while a backward movement can be achieved through the natural enhancement of linear momentum. If the symmetry of scattered field is broken, a side motion can also be induced due to the transformation between spin and orbital angular momenta. In experiments, these opto-mechanical effects can be significantly amplified by the long-range hydrodynamic interactions that provide an efficient recycling of energy. These unusual opto-mechanical effects open new possibilities for efficient manipulation of colloidal microparticles without having to rely on intricate structuring or shaping of light beams. Optically-controlled transport of matter is sought after in diverse applications in biology, colloidal physics, chemistry, condensed matter and others. Another consequence of light-matter interaction is the modification of the optical field itself, which can manifest, for instance, as detectable shifts of the centroids of optical beams during reflection and refraction. The spin-Hall effect of light (SHEL) is one type of such beam shifts that is due to the spin-orbit transformation governed by the conservation of angular momentum. We have shown that this effect can be amplified by the structural anisotropy of random nanocomposite materials.

The main purpose of this dissertation to investigate photophysical properties, third order nonlinearity and free carrier absorption and refraction in organic materials and semiconductors. Special emphasis of this dissertation is on characterization techniques of molecules with enhanced intersystem crossing rate and study of different approaches of increasing triplet quantum yield in organic molecules. Both linear and nonlinear characterization methods are described. Linear spectroscopic characterization includes absorption, fluorescence, quantum yield, anisotropy, and singletoxygen generation measurements. Nonlinear characterization, performed by picosecond and femtosecond laser systems (single and double pump-probe and Z-scan measurements), includes measurements of the triplet quantum yields, excited-state absorption, two-photon absorption, nonlinear refraction and singlet and triplet-state lifetimes. The double pump-probe technique is a variant of the standard pump-probe method but uses two pumps instead of one to create two sets of initial conditions for solving the rate equations allowing a unique determination of singlet- and triplet-state absorption parameters and transition rates. The advantages and limitations of the the double pump-probe technique are investigated theoretically and experimentally, and the influences of several experimental parameters on its accuracy are determined. The accuracy with which the double pump-probe technique determines the triplet-state parameters improves when the fraction of the population in the triplet state relative to the ground state is increased. Although increased accuracy is in iv principle achievable by increasing the pump fluence in the reverse saturable absorption range, it is shown that the DPP is optimized by working in the saturable absorption regime. Two different approaches to increase intersystem crossing rates in polymethine-like molecules are presented: traditional heavy atom substitution and molecular levels engineering. Linear and nonlinear optical properties of a series of polymethine dyes with Br- and Se- atoms substitution, and a series of new squaraine molecules, where one or two oxygen atoms in a squaraine bridge are replaced with sulfur atoms, are investigated. A consequence of the oxygento-sulfur substitution in squaraines is the inversion of their lowest lying ππ* and nπ* states leading to a significant reduction of singlet-triplet energy difference and opening of an additional intersystem channel of relaxation. Experimental studies show that triplet quantum yields for polymethine dyes with heavy-atom substitutions are small (not more than 10%), while for sulfurcontaining squaraines these values reach almost unity. Experimental results are in agreement with density functional theory calculations allowing determination of the energy positions, spinorbital coupling, and electronic configurations of the lowest electronic transitions. For three different semiconductors: GaAs, InP and InAsP two photon absorption, nonlinear refraction and free carrier absorption and refraction spectrums are measured using Zscan technique. Although two photon absorption spectrum agrees with the shape of theoretical prediction, values measured with picosecond system are off by the factor of two. Nonlinear refraction and free carrier nonlinearities are in relatively good agreement with theory. Theoretical values of the third order nonlinearities in GaAs are additionally confirmed with femtosecond Z-scan measurements. v Due to large spectral bandwidth of femtosecond laser, three photon absorption spectrum of GaAs was additionally measured using picosecond Z-scan. Again, spectral shape is in excellent agreement with theory however values of three photon absorption cross sections are larger than theory predicts.

Efficient computation in deterministic and uncertain electromagnetic propagation environments, tackled by parabolic equation methods, is the subject of interest of this dissertation. Our work is comprised of two parts. In the first part we determine efficient absorbing boundary conditions for propagation over deterministic terrain and in the second part we study techniques for efficient quantification of random parameters/outputs in volume and surface based electromagnetic problems. Domain truncation by transparent boundary conditions for open problems where parabolic equation is utilized to govern wave propagation are in general computationally costly. For the deterministic problem, we utilize two approximations to a convolution-in-space type discrete boundary condition to reduce the cost, while maintaining accuracy in far range solutions. Perfectly matched layer adapted to the Crank-Nicolson finite difference scheme is also verified for a 2-D model problem, where implemented results and stability analyses for different approaches are compared. For the random problem, efficient moment calculation of electromagnetic propagation/scattering in various propagation environments is demonstrated, where the dimensionality of the random space varies from N = 2 to N = 100. Sparse grid collocation methods are used to obtain expected values and distributions, as a non-intrusive sampling method. Due to the low convergence rate in the sparse grid methods for moderate dimensionality and above, two different adaptive strategies are utilized in the sparse grid construction. These strategies are implemented in three different problems. Two problems are concerned with uncertainty in propagation domain intrinsic parameters, whereas the other problem has uncertainty in the boundary shape of the terrain, which is realized as the perfectly conducting (PEC) Earth surface.