Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2004. / Includes bibliographical references (leaves 52). Also available in electronic version. Access restricted to campus users.

Silicon has been the material of choice of the photonics industry over the last decade due to its easy integration with silicon electronics as well as its optical transparency in the near-infrared telecom wavelengths. Besides these, it has very high refractive index, and also a broad optical transparency window over the entire mid-IR till about 8[Mu]m. Photonic crystal is well known that it can slow down the speed of light. It also can provide a universal platform for microcavity optical resonators with high quality factor Q and small modal volumes. The slow light effect, high Q and small modal volumes enhance light-matter interaction, together with high refractive index of silicon can be utilized to build a highly sensitive, high throughput sensor with small footprint. In this research, we have demonstrated highly compact and sensitive silicon based photonic crystal biosensor by engineering the photonic crystal microcavity in both cavity size and cavity-waveguide coupling condition. We have developed solutions to increase biosensor throughput by integrating multimode interference device and improving the coupling efficiency to a slow light photonic crystal waveguides. We have also performed detailed investigations on silicon based photonic devices at mid-infrared region to develop an ideal platform for highly sensitive optical absorption spectroscopy on chip. The studies have led to the demonstration of the first slot waveguide, the first photonic crystal waveguide, and the first holey photonic crystal waveguide and first slotted photonic crystal waveguide in silicon-on-sapphire at mid-infrared. The solutions and devices we developed in our research could be very useful for people to realize an integrated photonic circuit for biological and chemical sensing in the future. / text

Recent impactful advances in integrated photonics undoubtedly owe much to silicon and its associated enabling platform (SOI). Although silicon has proved to be an indispensable element in many photonic systems yet it seems that it is not the ultimate solution to address all the challenges facing the photonics community. Therefore, integration of silicon with other optical materials featuring diverse properties is highly desirable. Such integration will be conducive to platforms which are naturally more capable and are suited for implementation of a wider range of optical devices and diverse functionalities. This dissertation is dedicated to design and implementation of integrated optical elements for hybrid material platforms. The basic theoretical foundation of integrated photonics is laid out in Chapter 2. In Chapter 3, an interlayer grating coupler for a specific hybrid material platform is designed, and demonstrated. Considering the fact that in almost all integrated photonic platforms, fabrication imperfections lead to an unpredictable shift in the wavelength of operation of individual devices, post fabrication tuning/trimming is inevitable. A number of widely used post fabrication trimming/tuning methods are briefly reviewed in Chapter 4 with special emphasis on a method based on electron beam exposure. In Chapter 5, an ultra-fast, low-power, and self-trimmable electro-optic modulator in demonstrated on a Si-based multilayer platform. Due to its remarkable optical and electronic properties, graphene has become a valuable material for opto-electronic applications. Integration of this novel 2D material with SOI platform is investigated in Chapter 6. Graphene-based electro-optic modulation through absorption and refractive-index change is successfully demonstrated using electrostatic gating mechanism. Chapter 7 is devoted to demonstration of a field-programmable 2 by 2 optical switch on a vertically stacked Si/SiO2/SOI platform. In Chapter 8, the peak-dragging phenomenon in a nanobeam photonic crystal cavity is studied. The optical bistability associated with this nonlinear phenomenon is of great interest for all-optical processing and sensing application. Future directions of this thesis are also discussed in the last Chapter.

The mid-infrared wavelength region (2-20 µm) is of great utility for a number of applications, including chemical bond spectroscopy, trace gas sensing, and medical diagnostics. Despite this wealth of applications, the on-chip mid-IR photonics platform needed to access them is relatively undeveloped. Silicon is an attractive material of choice for the mid-IR, as it exhibits low loss through much of the mid-IR. Using silicon allows us to take advantage of well-developed fabrication techniques and CMOS compatibility, making the realization of on-chip integrated mid-IR devices more realistic. The mid-IR wavelengths also afford the opportunity to exploit Si's high third-order optical nonlinearity for nonlinear frequency generation applications. In this work, we present a Si-based platform for mid-IR photonics, with a special focus on micro-resonators for strong on-chip light confinement in the 4-5 μm range. Additionally, we develop experimental optical characterization techniques to overcome the inherent difficulties of working in this wavelength regime. First, we demonstrate the design, fabrication, and characterization of photonic crystal cavities in a silicon membrane platform, operational at 4.4 μm (Chapter 2). By transferring the technique known as resonant scattering to the mid-IR, we measure quality (Q) factors of up to 13,600 in these photonic crystal cavities. We also develop a technique known as scanning resonant scattering microscopy to image our cavity modes and optimize alignment to our devices. Next, we demonstrate the electro-optic tuning of these mid-IR Si photonic crystal cavities using gated graphene (Chapter 3). We demonstrate a tuning of about 4 nm, and demonstrate the principle of on-chip mid-IR modulation using these devices. We then investigate the phenomenon of optical bistability seen in our photonic crystal cavities (Chapter 4). We discover that our bistability is thermal in origin and use post-processing techniques to mitigate bistability and increase Q-factors. We then demonstrate the design, fabrication, and characterization grating-coupled ring resonators in a silicon-on-sapphire (SOS) platform at 4.4 μm, achieving intrinsic Q-factors as high as 278,000 in these devices (Chapter 5). Finally, we provide a quantitative analysis of the potential of our SOS devices for nonlinear frequency generation and describe ongoing experiments in this regard (Chapter 6). / Engineering and Applied Sciences

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Under examensarbetet på Luftfartsverket i Norrköping har beräkningar, mätningar och teoretiska analyser gjorts på parallella seriesystem. Detta har givit kunskap om kablarnas uppbyggnad och användning samt induktiva kopplingen mellan de parallella kablarna. All nödvändiga fakta bygger på mina observationer och anteckningar från dessa beräkningar och teoretiska analyser. Utifrån teoretiska analyser och Maxwellsekvationer skall flera frågeställningar besvaras under förutsättningen att undersöka de för- och nackdelar som skärmade kablar ger gentemot oskärmade kablar i ett personsäkerhetsperspektiv och med avseende på störningskänslighet. Kalkyler har tagits ifrån olika litteratur, vilket har resulterat till olika uträkningar på skärmade kablar och oskärmade kablar. Sedan har de olika beräkningarna jämförts med praktiska mätningar som utfördes ute på två flygplatser, nämligen Norrköpings flygplats (med typen oskärmade kablar) och Jönköpings flygplats (med typen skärmade kablar). Personsäkerheten kunde sedan klarläggas utifrån resultaten av såväl beräkningar som mätningar. Resultaten och slutsatser har tagits fram enligt olika matematiska presentationer och teoretiska analyser, då jämförandet mellan skärmade och oskärmade kablar har gjords. Reduktionsfaktor ger en storlek på hur effektivt skärmen är, dvs. för en kabel utan metallmantel är reduktionsfaktorn k=1. Om kabel däremot omsluts av en metallskärm, är reduktionsfaktorn kə. Reduktionsfaktor: 0.9995 (Utan jordade brunnar) Reduktionsfaktor: 0.91 (Med jordade brunnar) Reduktionsfaktor: 0.82 (Mätningar) Med hänsyn till resultaten ser man att reduktionsfaktorn är mindre än 1 för alla tre ovan nämnda, vilket innebär att kabeln är en ganska bra skärm. Samtidigt är reduktionsfaktorn ganska nära 1, vilket indikerar att skillnaden mellan skärmade och oskärmade kablar inte är stort. Detta leder till att man i praktiken inte bör räkna med någon reduktion. Beräkningarna och mätningar som har gjords på inducerad spänning och inducerad ström indikerar att den induktiva kopplingen mellan de parallella kablarna är låg. Den inducerade spänningen blev 14V och inducerade strömmen 156mA för oskärmad kabel och 12V samt 80mA för skärmad kabel.

Plasmonic resonances are characterized by enhanced optical near field and subwavelength power confinement. Light is not only scattered but also simultaneously absorbed in the metal nanostructures. With proper structural design, plasmonic-enhanced light absorption can generate nanoscopically confined heat power in metallic nanostructures, which can even be temporally modulated by varying the pump light. These intrinsic characters of plasmonic nanostructures are investigated in depth in this thesis for a range of materials and nanophotonic applications.   The theoretical basis for the photothermal phenomenon, including light absorption, heat generation, and heat conduction, is coherently summarized and implemented numerically based on finite-element method. Our analysis favours disk-pair and particle/dielectric-spacer/metal-film nanostructures for their high optical absorbance, originated from their antiparallel dipole resonances.   Experiments were done towards two specific application directions. First, the manipulation of the morphology and crystallinity of Au nanoparticles (NPs) in plasmonic absorbers by photothermal effect is demonstrated. In particular, with a nanosecond-pulsed light, brick-shaped Au NPs are reshaped to spherical NPs with a smooth surface; while with a 10-second continuous wave laser, similar brick-shaped NPs can be annealed to faceted nanocrystals. A comparison of the two cases reveals that pumping intensity and exposure time both play key roles in determining the morphology and crystallinity of the annealed NPs.   Second, the attempt is made to utilize the high absorbance and localized heat generation of the metal-insulator-metal (MIM) absorber in Si thermo-optic switches for achieving all-optical switching/routing with a small switching power and a fast transient response. For this purpose, a numerical study of a Mach-Zehnder interferometer integrated with MIM nanostrips is performed. Experimentally, a Si disk resonator and a ring-resonator-based add-drop filter, both integrated with MIM film absorbers, are fabricated and characterized. They show that good thermal conductance between the absorber and the Si light-guiding region is vital for a better switching performance.   Theoretical and experimental methodologies presented in the thesis show the physics principle and functionality of the photothermal effect in Au nanostructures, as well as its application in improving the morphology and crystallinity of Au NPs and miniaturized all-optical Si photonic switching devices. / <p>QC 20140331</p>

The goal of this thesis is to design both liquid crystal hosts and photochromic dopants terminated with short siloxane oligomers in order to produce homogeneous liquid crystal mixtures containing a photochromic component for liquid crystal photoswitches. Some of the liquid crystals terminated with short siloxane oligomers were also found to form 'de Vries'-type SmA phases, which minimize the formation of chevrons and zigzag defects that severely degrade the quality of electro-optic devices. In the first part of the thesis, siloxane-terminated phenylpyrimidine liquid crystals were synthesized and characterized. They form SmC phases and, in some cases, SmA phases. Addition of a terminal halogen substituent on the alkoxy side-chain broadens the SmA temperature range. It was shown that combining a structural element that promotes the formation of a SmC phase with one that promotes the formation of a SmA phase in a mesogen with a 2-phenylpyrimidine core results in a maximum layer contraction of 1.6% for 2-(4-(11-(1,1,1,3,3,5,5-heptamethyltrisiloxanyl)undecyloxy)phenyl)-5-(1-chlorooctyloxy)pyrimidine (33a), which may be considered a ‘de Vries’ material. As an extension of the result obtained in the first project, siloxane-terminated biphenyl benzoate and phenyl benzoate liquid crystals were synthesized and their phase behavior studied. They form SmC phases and, in some cases, SmA and SmI phases. Addition of a terminal chloro substituent on alkoxy side-chain results in a broader SmA temperature range and, in some cases, also affects the nature of the mesophase formed. The compound 4-[6-(1,1,1,3,3,5,5-heptamethyltrisiloxanyl)hexanoyloxy]phenyl 4-(8-chlorooctyloxy)benzoate (40b) is characterized by a maximum layer shrinkage of only 1.7%, which may be considered to possess some ‘de Vries’ character. Finally, siloxane-terminated fulgide derivatives were designed as photochromic dopants for liquid crystal photoswitches. Compound 41 was designed and synthesized and proved to be an oil at room temperature. Solid fulgide precusors 42, 43a and 44b were then assessed as photochromic dopants in terms of fast switching and high quantum yield requirements of a photoswitch, and their photophysical properties were studied in solution. The isomer composition at the photostationary state suggests that the competition from E-Z isomerization is likely too high for compounds 42, 43a and 44b to be suitable as photochromic dopants for photoswitches. / Thesis (Ph.D, Chemistry) -- Queen's University, 2009-05-28 12:46:13.992

We derive an analytical model for the depletion capacitance of silicon-on-insulator (SOI) optical modulation diodes. This model accurately describes the parasitic fringe capacitances due to a lateral pn junction and can be extended to other geometries, such as vertical and interleaved junctions. Analytical results show excellent agreement with numerical simulations. The model is used to identify the waveguide slab to rib height ratio as a key geometric scaling parameter for the modulation e ciency and bandwidth for lateral diodes. We characterise the fringe capacitance as a parasitic e ffect that leads to a decrease of about 20% in modulation bandwidth of typical SOI diodes without a corresponding increase in modulation effi ciency. From the scaling relations, the most e ffective way to increase the modulation bandwidth is to reduce the series resistance of the diode. In the light of our analysis, we propose high-speed and low power microdisk structures for future SOI modulators.

We derive an analytical model for the depletion capacitance of silicon-on-insulator (SOI) optical modulation diodes. This model accurately describes the parasitic fringe capacitances due to a lateral pn junction and can be extended to other geometries, such as vertical and interleaved junctions. Analytical results show excellent agreement with numerical simulations. The model is used to identify the waveguide slab to rib height ratio as a key geometric scaling parameter for the modulation e ciency and bandwidth for lateral diodes. We characterise the fringe capacitance as a parasitic e ffect that leads to a decrease of about 20% in modulation bandwidth of typical SOI diodes without a corresponding increase in modulation effi ciency. From the scaling relations, the most e ffective way to increase the modulation bandwidth is to reduce the series resistance of the diode. In the light of our analysis, we propose high-speed and low power microdisk structures for future SOI modulators.