In this work, we study the properties and device applications of MoS2, black phosphorus, MoOx, and NbSe2. We first start with the design, fabrication, and characterization of ultra-high responsivity photodetectors based on mesoscopic multilayer MoS2. The device architecture is comprised of a metal-semiconductor-metal (MSM) photodetector, where Mo was used as the contact metal to suspended MoS2 membranes. The dominant photocurrent mechanism was determined to be the photoconductive effect, while a contribution from the photogating effect was also noted from trap-states that yielded a wide spectral photoresponse from UV-to-IR with an external quantum efficiency (EQE) ~ 104. From time-resolved photocurrent measurements, a fast decay time and response time were obtained with a stream of incoming ON/OFF white light pulses. Another interesting semiconductor 2D material that has attracted special attention due to its small bandgap and ultra-high hole mobility is the black phosphorus. An analysis of the optoelectronic properties and photocurrent generation mechanisms in two-dimensional (2D) multilayer crystallites of black phosphorus (BP) was conducted from 350 K down to cryogenic temperatures using a broad-band white light source. The Mo-BP interface yielded a low Schottky barrier "φ" _"SB" ~ -28.3 meV and a high photoresponsivity R of ~ 2.43 x 105 A/W at a source-drain bias voltage of ~ 0.5 V (300 K, and incident optical power ~ 3.16 μW/cm2). Our report is the first to highlight the empirical use of Mo as a contact metal with BP. From the analysis conducted on the BP devices, the thermally driven photocurrent generation mechanism arising from the photobolometric effect (PBE) dominated the carrier dynamics for T > 181 K since the photocurrent Iph and the bolometric coefficient β undergo a transition in polarity from positive to negative. Our results show the promise of BP to potentially advance thermoelectric and optoelectronic devices stemming from this mono-elemental, direct bandgap 2D van der Waals solid. Another intriguing metallic 2D material is superconducting 2H-NbSe2. Here we present the temperature-dependent Raman spectroscopy and electronic transport on bulk NbSe2, carried out to investigate the scattering mechanisms. We report on the photoresponse of direct probed mesoscopic 2H-NbSe2 as a function of laser energy for lasers at 405 nm, 660 nm, and 1060 nm wavelengths used to irradiate the device, where the modulation from the superconducting-to-normal-state is detected through photomodulation. Additionally, the various oxidation levels of molybdenum oxide have interesting optical and electrical properties as a function of the oxygen vacancy and stoichiometry. The substoichiometric MoOx (2 < x < 3) behaves as a high work function conductor due to its metallic defect band. As a result, one of the potential applications of MoOx is for electrical contacts providing high hole injection or extraction. In this work, we have synthesized MoOx nanosheets via chemical vapor deposition and a four-terminal device was fabricated via e-beam lithography and electronic transport was measured as a function of temperature. Outstanding properties were obtained from our MoOx nanosheets, including a high conductivity of ~ 6,680.3 S cm-1, a superior temperature coefficient of resistance ~ -0.10%, and a high sensitivity based on the bolometric coefficient β of ~ 0.152 mS K-1. In summary, this work pushes the state-of-the-art in enabling 2D van der Waals materials for next-generation high-performance detectors.

全光信息處理被認為是其中一種改善當今計算機網絡性能的方法。而高效率的全光信息處理需要使用可用低強度的控制激光來控制的全光學開關。最近有人提出利用橫向光學圖案製造低強度全光學開關，並已通過原子蒸氣系統的實驗證明這個計劃的可行性。此外，相關的研究正在半導體量子阱微腔中進行。 / 這篇論文以微觀多體理論研究被激光正向入射的半導體量子阱微腔系統中產生的自發性橫向光學圖案。入射光會在一定條件下於半導體量子阱微腔中發生極化子場之間的自發四波混頻，並產生橫向光學圖案。我們分別以半分析和數值模擬的方法研究這些圖案的形成和選擇方式。本論文亦研究了如何用離軸激光和腔的各向異性來控制這些圖案。 / 我們分別用「多- / Processing information all-optically is thought to be one way to improve the performance of present-day computational network. Low intensity all-optical switches are desirable for effective all-optical information processing. Recently, low intensity all-optical switching schemes utilizing transverse optical patterns have been proposed. One such scheme was successfully demonstrated experimentally in an atomic vapour system, and a similar scheme is being studied both theoretically and experimentally in semiconductor quantum well micro-cavities. / In this thesis, we present our theoretical studies on the spontaneous transverse optical patterns produced by a semiconductor quantum well microcavity, pumped by a normally incident laser, using a microscopic many-body theory. Far field transverse optical patterns are formed under certain conditions by spontaneous four-wave mixing of the exciton-photon polariton field. The formation and the selection of these patterns are studied by both semi-analytical calculations and numerical simulations. The controls of transverse patterns using anisotropy in the microcavity and an o-axis control beam are also being studied in this thesis. / Two reduced models, the ‘multi- / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Luk, Ming Ho = 對半導體量子阱微腔中橫向光學圖案的控制 / 陸名浩. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references (leaves 136-141). / Abstracts also in Chinese. / Luk, Ming Ho = Dui ban dao ti liang zi jing wei qiang zhong heng xiang guang xue tu an de kong zhi / Lu Minghao. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Pattern formation and nonlinear optics --- p.5 / Chapter 1.2 --- All-optical switching --- p.8 / Chapter 1.3 --- Semiconductor quantum well microcavity --- p.9 / Chapter 2 --- Semiconductor quantum well microcavity --- p.13 / Chapter 2.1 --- The structure of semiconductor quantum well microcavity --- p.14 / Chapter 2.2 --- Coupling between the cavity mode and external fields --- p.18 / Chapter 2.3 --- Microscopic theory in the microcavity --- p.22 / Chapter 3 --- Linear stability analysis and reduced models --- p.32 / Chapter 3.1 --- Pump only system - steady state solution --- p.32 / Chapter 3.2 --- Pump only system - stability analysis --- p.37 / Chapter 3.3 --- Off-axis stability studies --- p.39 / Chapter 3.3.1 --- Stability analysis without phase-space filling --- p.40 / Chapter 3.3.2 --- Linear stability analysis with phase-space filling --- p.54 / Chapter 3.4 --- Reduced models --- p.59 / Chapter 3.4.1 --- The multi- --- p.63 / Chapter 3.4.2 --- The ring model --- p.68 / Chapter 3.5 --- Effects of system parameters --- p.71 / Chapter 3.5.1 --- Radiative loss --- p.72 / Chapter 3.5.2 --- Incident laser field/intensity --- p.73 / Chapter 3.5.3 --- Fluctuations/weak constant sources --- p.78 / Chapter 4 --- Single-hexagon model --- p.82 / Chapter 4.1 --- Numerical results of single-hexagon model --- p.82 / Chapter 4.2 --- Pattern and time scale variations with parameters --- p.86 / Chapter 4.2.1 --- Anisotropy in the cavity mode energy --- p.87 / Chapter 4.2.2 --- Control beam intensity --- p.90 / Chapter 5 --- Dynamical analysis and interplay of wave-mixing processes --- p.93 / Chapter 5.1 --- Dynamical analysis --- p.93 / Chapter 5.2 --- Interplay of wave mixing processes --- p.99 / Chapter 5.3 --- Switching between hexagons --- p.103 / Chapter 6 --- Full two-dimensional simulation --- p.111 / Chapter 6.1 --- Convolution theorem and Fast Fourier Transform --- p.112 / Chapter 6.2 --- Simulation result and difficulties --- p.114 / Chapter 7 --- Other approaches --- p.119 / Chapter 7.1 --- Real Space Simulation --- p.119 / Chapter 7.2 --- Mode competition model --- p.121 / Chapter 7.3 --- Transfer Matrix --- p.123 / Chapter 8 --- Conclusion and outlook --- p.125 / Chapter 8.1 --- Future work --- p.128 / Chapter 8.1.1 --- Double Cavities --- p.128 / Chapter 8.1.2 --- The Gross-Pitaevskii Equation and Bose-Einstein Condensation --- p.131 / Bibliography --- p.136 / Chapter A --- Dispersion of cavity photon --- p.142

The ever-growing need for high speed data transmission is driven by multimedia and telecommunication demands. Traditional metallic media, such as copper coaxial cable, prove to be a limiting factor for high speed communications. Fiber optic methods provide a feasible solution that lacks the limitations of metallic mediums, including low bandwidth, cross talk caused by magnetic induction, and susceptibility to static and RF interferences. The first scientists to work with fibers optics started in 1970. One of the early challenges they faced was to produce glass fiber that was pure enough to be equal in performance with copper based media. Since then, the technology has advanced tremendously in terms of performance, quality, and consistency. The advancement of fiber optic communication has met its limits, not in the purity of its fiber media used to guide the data-modulated light wave, but in the conversion back and forth between electric signals to light. A high speed optic receiver must be used to convert the incident light into electrical signals. This thesis describes the design of a 2.5 GHz Optoelectronic Amplifier, the front end of an optic receiver. The discussion includes a survey of feasible topologies and an assessment of circuit techniques to enhance performance. The amplifier was designed and realized in a TSMC 0.18 µm CMOS process.

The conventional methods for diagnosing pathological conditions of the tympanic membrane (TM) and other abnormalities require measuring its motion while responding to acoustic excitation. Current methodologies for characterizing the motion of the TM are usually limited to either average acoustic estimates (admittance or reflectance) or single-point mobility measurements, neither of which is sufficient to characterize the detailed mechanical response of the TM to sound. Furthermore, while acoustic and single-point measurements are useful for the diagnosis of some middle ear disorders, they are not useful in others. Measurements of the motion of the entire TM surface can provide more information than these other techniques and may be superior for the diagnosis of pathology. In this Thesis, the development of an optoelectronic holographic otoscope (OEHO) system for characterization of nanometer scale motions in TMs is presented. The OEHO system can provide full-field-of-view information of the sound-induced displacements of the entire surface of the TM at video rates, allowing rapid quantitative analysis of the mechanical response of normal or pathological TMs. Preliminary measurements of TM motion in cadaveric animals helped constrain the optical design parameters for the OEHO, including the following: image contrast, resolution, depth of field (DOF), laser power, working distance between the interferometer and TM, magnification, and field of view (FOV). Specialized imaging software was used in selecting and synthesizing the various components. Several prototypes were constructed and characterized. The present configuration has a resolution of 57.0 line pairs/mm, DOF of 5 mm, FOV of 10 ´ 10 mm2, and a 473 nm laser with illumination power of 15 mW. The OEHO system includes a computer controlled digital camera, a fiber optic subsystem for transmission and modulation of laser light, and an optomechanical system for illumination and observation of the TM. The OEHO system is capable of operating in two modes. A 'time-averaged' mode, processed at video rates, was used to characterize the frequency dependence of TM displacements as tone frequency was swept from 500 Hz to 25 kHz. A 'double-exposure' mode was used at selected frequencies to measure, in full-field-of-view, displacements of the TM surface with nanometer resolution. The OEHO system has been designed, fabricated, and evaluated, and is currently being evaluated in a medical-research environment to address basic science questions regarding TM function. Representative time-averaged holographic and stroboscopic interferometry results in post-mortem and live samples are herein shown, and the potential utilization discussed.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographies. / by Erik Karl Antonsson. / Ph.D.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1979. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by David Howard Turkel. / B.S.

Besides colorless ONUs, we investigate potentially low cost, high speed vertical-cavity-surface-emitting lasers (VCSELs) for use in future access networks. VCSELs are attractive because they may meet the stringent size, power dissipation and cost constraints of access network components. We carry out experiments to demonstrate that up to 20 Gb/s direct modulation of long wavelength VCSEL is possible and evaluate their performance as high-speed transceivers. / In order to reduce the complexity and costs of ONU transceiver, we propose a scheme based on a nonreciprocal optical modulator and a linear loop mirror for receiving downstream and sending upstream data We show that the nonreciprocity of traveling wave electrodes can selectively impress signal modulation onto the reflected upstream signals only. Monolithic integrated transceivers may thus remodulate downstream signals for upstream data transmission without needing integrated optical circulators. The proposed ONU is thus compatible with monolithic integration. / In this thesis, we describe our research on photonic devices and subsystems for future access networks. Since optical network units (ONUs) are the most cost-sensitive parts, we first investigate the use of advanced modulation format in colorless ONU structure. We implement a scheme which uses dark return-to-zero (DRZ) for downstream transmission and remodulation of it using a differential-phase-shift-keying (DPSK) for upstream both at 10 Gb/s. We also experimentally demonstrate silicon microring based optical frequency discriminators for use in demodulating DPSK and differential-quadrature-phase-shift-keying (DQPSK) signals. We show that the scheme is robust to variations in bit-rates in contrast with conventional Mach-Zehnder delay interferometer scheme. / Internet traffic has undergone tremendous growth in the past decades and has already penetrated into the daily lives of the general population. Demand for new high bandwidth services is beginning to drive the deployment of optical fiber-based access networks to solve the so-called last mile bottleneck around the world. Passive optical networks (PON) are attractive because there are no active components in the transmission line, thus reducing operational and deployment costs. Time-division-multiplexing (TDM) used in currently deployed PON, in which the bandwidth is shared among the users by time domain multiplexing, does not fully utilize the bandwidth potential of optical fibers and will not be able to satisfy the bandwidth demand in access networks in the near future. Among the advanced multiplexing techniques, wavelength-division-multiplexing (WDM) PON is a good candidate technology for providing sustained bit-rates beyond 10 Gb/s in access networks. However, reduction of costs in WDM PON remains a key challenge for their practical deployment. / Wired and wireless hybrid optical access networks are also investigated. Radio-over-fiber is one low-cost approach to deliver broadband wireless services, in which radio signals at the carrier frequency are delivered over optical networks from a central office to remote antenna base stations. Generation of high frequency carrier and radio frequency fading are the main research challenges. We propose and demonstrate frequency upconversion based on frequency doubling and quadrupling. Novel wired and wireless hybrid subsystems that mitigate millimeter-wave signal distortion are also demonstrated. / Xu, Lin. / Adviser: H. K. Tsang. / Source: Dissertation Abstracts International, Volume: 72-04, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. Ann Arbor, MI : ProQuest Information and Learning Company, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

Lee Ka-lun. / "September 2003." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Lo, Ming Gai Stanley. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 131-135). / Abstracts in English and Chinese. / Title Page --- p.i / Abstract --- p.ii / Acknowledgements --- p.v / Table of Contents --- p.vii / List of Figures --- p.ix / List of Tabic --- p.xiv / Chapter Chapter 1: --- Introduction --- p.1 / Chapter 1.1 --- Photonic Integrated Circuits --- p.1 / Chapter 1.2 --- Silicon Photonics --- p.7 / Chapter 1.3 --- Optical Modulators --- p.15 / Chapter 1.4 --- Modulation Mechanisms in Silicon --- p.19 / Chapter 1.5 --- Motivation --- p.27 / Chapter 1.6 --- Thesis Outline --- p.28 / Chapter Chapter 2: --- Use of Silicon-bascd Modulators in Radio-over-fiber Optical Links --- p.29 / Chapter 2.1 --- Modeling of Linearity of Silicon Carrier Depletion-based Modulators --- p.31 / Chapter 2.2 --- Modeling of Dependence of Linearity on Various Diode Structures --- p.45 / Chapter 2.3 --- Experiment of Radio-over-Fiber Signal Transmission by a Carrier-Injection Silicon Microring Modulator --- p.52 / Chapter 2.3.1 --- Device Fabrication --- p.53 / Chapter 2.3.2 --- Experimental Setups --- p.59 / Chapter 2.3.3 --- Experimental Results --- p.61 / Chapter 2.4 --- Summary --- p.66 / Chapter Chapter 3: --- Novel Diode Structures and T-Rail Travelling-Wave Electrodes to Enhance the Performance of Depletion-based Modulators --- p.67 / Chapter 3.1 --- Requirements of Diode Design for Depletion-based Optical Modulators --- p.70 / Chapter 3.2 --- Diode Design Principle --- p.72 / Chapter 3.3 --- Modeling Results of Vertical-Junction p-n Diodes --- p.79 / Chapter 3.4 --- Fabrication Process of the Silicon Modulator --- p.88 / Chapter 3.5 --- Experimental Results of the Fabricated Devices --- p.92 / Chapter 3.6 --- T-Rail Travelling-Wave Electrodes --- p.102 / Chapter 3.6.1 --- The Limiting Factors to the Speed of Depletion-based Modulators --- p.102 / Chapter 3.6.2 --- The Design Principle of T-Rail Travelling-Wave Electrodes --- p.104 / Chapter 3.6.3 --- The Fabricated Devices --- p.111 / Chapter 3.7 --- Summary --- p.112 / Chapter Chapter 4: --- Conclusion and Future Work --- p.113 / Chapter 4.1 --- Conclusion --- p.113 / Chapter 4.1.1 --- Use of Silicon-based Modulators in Radio-over-fiber Optical Links --- p.113 / Chapter 4.1.2 --- Novel Diode Structures and T-Rail Travelling-Wave Electrodes to Enhance the Performance of Depletion-based Modulators --- p.114 / Chapter 4.2 --- Future Work --- p.116 / Chapter Appcndix-A --- List of Symbols --- p.118 / Chapter Appcndix-B --- List of Abbreviations --- p.120 / Chapter Appcndix-C --- Principles of Various Optical Structures of Modulators --- p.123 / Chapter Appcndix-D --- Modeling of Refractive Index Change by Free-Carrier Plasma Dispersion Effcct --- p.127 / Reference --- p.131 / Publication List --- p.136

Graded InGaN buffers were employed to relax the strain arising from the lattice and thermal mismatch in GaN/InGaN epilayers grown on sapphire. An enhanced strain relaxation was observed in GaN grown on a stack of five InGaN layers, each 200 nm thick with the In content increased in each layer, and with an intermediate thin GaN layer, 10 nm thick inserted between the InGaN layers, as compared to the conventional two-step growth of GaN epilayer on sapphire. The function of the intermediate layer is to progressively relax the strain and to annihilate the dislocations that build up in the InGaN layer. If the InGaN layers were graded too rapidly, more dislocations will be generated. This increases the probability of the dislocations getting entangled and thereby impeding the motion of the dislocations to relax the strain in the InGaN layer. The optimum growth conditions of the intermediate layer play a major role in promoting the suppression and filling of the V-pits in the GaN cap layer, and were empirically found to be a thin 10 nm GaN grown at 750 0°C and annealed at 1000 0°C. / Singapore-MIT Alliance (SMA)