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M.Sc. (Physics) / Please refer to full text to view abstract

M.Sc. (Physics) / Silicon thin films can be manufactured with the aid of various deposition techniques, each with its own unique properties. In this study the optical properties of silicon manufactured with physical vapour deposition from an electron beam source were studied as a function of layer thickness, deposition rate and substrate temperature. The index of refraction (n and k) as well as optical gap eg. were determined with the aid of characterization models derived specific for optical techniques. These models are covered extensively in the thesis. It was found that the layers were homogeneous and stable, but that the deposition rate and substrate temperature did have a large influence on the properties of the layers. The results show that structural changes, first from the collumnar structure to an amorphous structure and with a further increase in substrate temperature, also a transition from the amorphous to a microcrystalline structure do occure at temperatures considerably lower than what was previously anticipated. With variations in deposition rate it was found that the disorder in the coating will increase with an increase in rate resulting in a reverse transition from the microcrystalline structure to the amorphous structure. Optical gaps in the range 1. 12eV to approximately 1. 38eV were found to be possible with the correct choice of deposition parameters...

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近年在矽光子學方面的研究日漸增多，主要原因是在高效能電腦，低成本通訊接取網絡及集成光學感應器等各方面有很大的潛在應用。以矽為原材料的各種光學器件已經被廣泛研究，包括電光調制器，光感應器和各式各樣主動及被動器件。但是由於矽是一種間接能隙的物質，即是由電子激發的電子電洞的結合是屬於非輻射躍遷，所以不可以得到光放大和激光器的效果。為了製作集成激光器，已經有很多不同的研究方案，例如在矽波導上摻雜鉺或是混合集成矽和-族半導體。在這篇論文中，我們提出並且論証了一個創新的方案去製作由光纖和矽波導混合而成的激光器，大大簡化了設計和生產過程。 / 在論文中，我們會集中討論選取光波長的器件及整體結構的設計。在首次的結構設計上，我們利用了分佈在矽波導兩側的布拉格反射鏡作為選取光波長的器件和一小段以鉺摻雜的光纖作為放大器。我們將會詳細形容該器件的設計、模擬效果和實驗結果。我們已經透過實驗証明了單波長的光纖－矽波導混合激光器，其側模抑制超過35分貝。 / 另一方面，為了製作多波長的光纖－矽波導混合激光器，我們利用微環諧震器來取代分佈在矽波導兩側的布拉格反射鏡作為選取光波長的器件。我們將會討論微環諧震器的設計以及達到穩定多波長的光纖和矽波導混合激光器的設計要求。 / Motivated by potential applications for optical interconnects in high performance computing, low cost optical access networks in telecommunications and integrated optical sensors, there has been much research in recent years on silicon photonics. Different silicon-based photonic devices have been studied, including optical modulators, detectors and various types of active and passive components. However, since the bandgap of silicon is indirect, the recombination of carriers injected by electrical pumping is dominated by non-radiative transitions and thus it is not possible to get optical gain via current injection into silicon diodes. / To implement integrated laser, different approaches such as erbium doping on silicon waveguide and hybrid integration of III-V semiconductors on silicon have been investigated. In this thesis, we propose and demonstrate a novel approach for making a hybrid fiber-silicon laser to simplify the design and fabrication processes. We propose the use of Erbium-doped fiber (EDF) to provide gain and silicon devices to provide all the other functionalities needed for a modulated laser. / The thesis focuses on the design of wavelength selective element and the structure of hybrid fiber-silicon laser. The first design includes a silicon waveguide side-cladding distributed Bragg reflector (WSC-DBR) as the wavelength selective component on silicon-on-insulator (SOI) wafer and a short length of EDF as the gain medium. The details of design, simulation and experimental results of the WSC-DBR will be described. Single wavelength WSC-DBR hybrid fiber-silicon laser is demonstrated with a side mode suppression ratio (SMSR) of over 35dB. / We also investigate the use of a micro-ring resonator to replace WSC-DBR for selecting multiple wavelengths. Details of the micro-ring resonator are given and we discuss the requirement and design criteria to achieve stable multi-wavelength lasing. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Fung, Ka Yan. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references. / Abstracts also in Chinese. / ABSTRACTOF THESIS ENTITLED: --- p.ii / ACKNOWLEDGEMENT --- p.v / TABLE OF CONTENT --- p.vii / Chapter 1 --- INTRODUCTION --- p.10 / Chapter 1.1 --- Photonic Integrated Circuits --- p.10 / Chapter 1.2 --- Silicon Photonics --- p.13 / Chapter 1.3 --- Lasers in Silicon --- p.20 / Chapter 1.4 --- Motivation --- p.27 / Chapter 1.5 --- References --- p.29 / Chapter 2 --- ERBIUM DOPED FIEBR AND FIBER LASERS --- p.34 / Chapter 2.1 --- Erbium doped fiber --- p.34 / Chapter 2.2 --- Multi-wavelength lasers --- p.45 / Chapter 2.3 --- References --- p.54 / Chapter 3 --- SINGLE CHANNEL HYBRID FIBER-SILICON LASER --- p.59 / Chapter 3.1 --- Introduction of Distributed Bragg reflector --- p.60 / Chapter 3.2 --- Design of waveguide side-cladding distributed Bragg reflector --- p.63 / Chapter 3.3 --- Simulation results of waveguide side-cladding distributed Bragg reflector --- p.66 / Chapter 3.4 --- Device fabrication --- p.69 / Chapter 3.5 --- Experimental results of waveguide side-cladding distributed Bragg reflector --- p.71 / Chapter 3.6 --- Experimental results of hybrid fiber-silicon laser --- p.77 / Chapter 3.7 --- Introduction of micro-ring resonator --- p.81 / Chapter 3.8 --- Design of race track micro-ring resonator --- p.85 / Chapter 3.9 --- Experimental results of race track micro-ring resonator --- p.88 / Chapter 3.10 --- Experimental results of hybrid fiber-silicon laser with ring resonator --- p.95 / Chapter 3.11 --- Summary --- p.99 / Chapter 3.12 --- References --- p.101 / Chapter 4 --- DUAL WAVELENGTH HYBRID FIBER SILICON LASER --- p.102 / Chapter 4.1 --- Design of micro-ring resonator for dual wavelength --- p.103 / Chapter 4.2 --- Experimental results of micro-ring resonator --- p.104 / Chapter 4.3 --- Experimental results of dual wavelength hybrid fiber-silicon laser --- p.108 / Chapter 4.4 --- Summary --- p.119 / Chapter 4.5 --- References --- p.121 / Chapter 5 --- DUAL WAVELENGTH VERTICAL GRATING COUPLER --- p.123 / Chapter 5.1 --- Introduction of grating coupler --- p.123 / Chapter 5.2 --- Design of dual wavelength vertical grating coupler --- p.125 / Chapter 5.3 --- Simulation of dual wavelength vertical grating coupler --- p.127 / Chapter 5.4 --- Experimental results of dual wavelength vertical grating coupler --- p.135 / Chapter 5.5 --- Summary --- p.138 / Chapter 5.6 --- References --- p.139 / Chapter 6 --- CONCLUSION AND FUTURE WORK --- p.141 / Chapter 6.1 --- Conclusion --- p.141 / Chapter 6.2 --- Future work --- p.144 / Chapter 6.3 --- References --- p.146 / Chapter APPENDIX A: --- PUBLICATION LIST --- p.147 / Chapter APPENDIX B: --- LIST OF TABLES --- p.149 / Chapter APPENDIX C: --- LIST OF FIGURES --- p.150 / Chapter APPENDIX D: --- METHODS OF LINEWIDTH MEASUREMENT --- p.155 / Chapter APPENDIX E: --- EQUIPMENT INFORMATION --- p.164

從上世紀80年代中期開始，矽光子學在研究與工業界都有快速的發展。矽光子學有望實現電子與光子電路的一體化集成，從而使得光電子系統的價格和能耗大大地降低。基於這樣的特性，矽光子學被提出用於當前的光通信系統。 / 在這篇論文中，我們將研究矽波導在光信號的成型和重定時中的應用。首先，我們研究基於自由載流子色散效應的矽調製器。調製器的原理和設計方法將會詳細地討論。我們所設計的調製器是基於馬赫-曾德爾干涉儀。實驗表明，製作好的調製器的3dB電光帶寬達到了5GHz。當調製器進行非歸零開關鍵控調製時，調製器的速率可以達到12.45GHz，且誤碼率在10⁻⁹以下。同時，調製器用於正交頻分複用調製格式的結果也會給出。接著，我們研究矽波導中產生的四波混頻效應如何增強信號消光比和減少時域抖動。我們通過實驗表明了，矽波導中的四波混頻效應可以增強單通道的10和40Gb/s歸零開關鍵控信號的消光比。我們接著將四波混頻效應應用於時域交叉的雙通道歸零開關鍵控信號。實驗結果也表明，兩個通道的消光比都能得到增強。我們也通過實驗表明，四波混頻效應可以減少10Gb/s歸零開關鍵控信號的時域抖動。最後，我們用矽波導和chirped光纖光栅實現了一套可調光延遲系統。當這套系統分別應用於10Gb/s的光脈衝、非歸零開關監控信號和歸零的差分相位鍵控信號時，延遲效果都一致。 / Emerging from the mid-1980s, the field of silicon photonics has been rapidly growing, in both research and industry. Silicon photonics has the great potential of monolithic integration of both electronic and photonic circuits. With monolithic integration, the cost and power consumption of photonic systems can be cut down greatly. Due to these features, silicon photonics is proposed for applications in today’s optical communication systems. / In this thesis, silicon waveguide devices for shaping and retiming of optical signals will be investigated. Firstly, silicon Mach-Zehnder modulators based on free-carrier plasma dispersion effect are explored for amplitude modulation of optical signals. The principle and design of the modulators are discussed in details. Experimental results show that 3 dB electro-optic bandwidth of the modulators is 5 GHz, while 10⁻⁹ bit error rate can be obtained for up to 12.45 Gb/s modulated non-return-to-zero (NRZ) on-off keying (OOK) signal. Also, the results of the modulators for orthogonal frequency division multiplexing modulation will be given. Then, silicon waveguides are used as nonlinear medium of four-wave mixing (FWM) effect for extinction ratio enhancement and timing jitter reduction of optical signals. Extinction ratio enhancement of single channel 10 and 40 Gb/s return-to-zero (RZ) OOK signal is experimentally demonstrated. Following that we extend the scheme for two 40 Gb/s RZ-OOK channels which are time-interleaved and obtain extinction ratio enhancement for both. Timing jitter reduction of 10 Gb/s RZ-OOK signal is also achieved by FWM effect in silicon waveguides. Finally, a tunable delay line incorporating a silicon waveguide and a chirped fiber Bragg grating is realized for timing alignment of optical signals. The tunable delay line is used for 10 Gb/s optical pulse, NRZ-OOK signal and RZ differential phase-shift keying (DPSK) signal, showing consistent performance for all. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Chen, Yimin. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references. / Abstracts also in Chinese. / Acknowledgements --- p.ii / Abstract --- p.iv / Table of Contents --- p.vii / List of Tables --- p.x / List of Figures --- p.xi / Chapter Chapter 1 --- Introduction --- p.17 / Chapter 1.1 --- Research context --- p.17 / Chapter 1.2 --- Waveguides and modulators in silicon photonics --- p.18 / Chapter 1.2.1 --- Silicon photonics --- p.20 / Chapter 1.2.2 --- Silicon modulator --- p.23 / Chapter 1.2.3 --- Silicon waveguide as nonlinear medium --- p.24 / Chapter 1.3 --- Purpose and outline of this work --- p.26 / References --- p.26 / Chapter Chapter 2 --- Silicon modulators for optical communications --- p.28 / Chapter 2.1 --- Introduction --- p.28 / Chapter 2.1.1 --- Motivation for high capacity transmission system --- p.28 / Chapter 2.1.2 --- Literature review of silicon modulators --- p.30 / Chapter 2.2 --- Design of silicon modulators --- p.38 / Chapter 2.2.1 --- Optical circuit of silicon modulators --- p.38 / Chapter 2.2.2 --- p-n junction --- p.43 / Chapter 2.2.3 --- Electronic circuit --- p.44 / Chapter 2.3 --- Fabrication process --- p.46 / Chapter 2.4 --- Experimental results --- p.47 / Chapter 2.4.1 --- Testing results --- p.48 / Chapter 2.4.2 --- OFDM modulation --- p.58 / Chapter 2.5 --- Summary --- p.61 / References --- p.64 / Chapter Chapter 3 --- Signal quality enhancement using four-wave mixing in silicon waveguides --- p.68 / Chapter 3.1 --- Introduction --- p.68 / Chapter 3.1.1 --- All-optical wavelength conversion and all-optical regeneration --- p.68 / Chapter 3.1.2 --- Generic basics of four-wave mixing --- p.69 / Chapter 3.1.3 --- Four-wave mixing in silicon waveguides --- p.71 / Chapter 3.2 --- Extinction ratio enhancement using FWM in a silicon waveguide --- p.77 / Chapter 3.2.1 --- Extinction ratio enhancement of 10 and 40 Gb/s RZ-OOK signals --- p.77 / Chapter 3.2.1.1 --- Principle --- p.78 / Chapter 3.2.1.2 --- Experimental setup and results --- p.78 / Chapter 3.2.1.3 --- Discussion --- p.82 / Chapter 3.2.2 --- Extinction ratio enhancement of two 40 Gb/s RZ-OOK channels --- p.82 / Chapter 3.2.2.1 --- Principle --- p.83 / Chapter 3.2.2.2 --- Experimental setup and results --- p.84 / Chapter 3.2.2.3 --- Discussion --- p.89 / Chapter 3.3 --- Timing jitter reduction using FWM in silicon waveguides --- p.90 / Chapter 3.3.1 --- Principle --- p.91 / Chapter 3.3.2 --- Experimental setup and results --- p.92 / Chapter 3.3.2.1 --- Timing jitter reduction of RZ-OOK signal --- p.92 / Chapter 3.3.2.2 --- Timing jitter reduction of AMI signal --- p.96 / Chapter 3.3.3 --- Discussion --- p.101 / Chapter 3.4 --- Summary --- p.102 / References --- p.103 / Chapter Chapter 4 --- Optical tunable delay line incorporating a silicon waveguide and a chirped fiber Bragg grating --- p.106 / Chapter 4.1 --- Introduction --- p.106 / Chapter 4.1.1 --- Motivation --- p.106 / Chapter 4.1.2 --- Principle --- p.107 / Chapter 4.1.3 --- Characteristics of the silicon waveguide and chirped FBG --- p.108 / Chapter 4.2 --- Tunable delay line for 10 Gb/s optical signals --- p.111 / Chapter 4.2.1 --- 10 Gb/s optical pulse chain --- p.111 / Chapter 4.2.1.1 --- Experimental setup and results --- p.111 / Chapter 4.2.2 --- 10 Gb/s NRZ-OOK signal --- p.115 / Chapter 4.2.2.1 --- Experimental setup and results --- p.115 / Chapter 4.2.3 --- 10 Gb/s RZ-DPSK signal --- p.119 / Chapter 4.2.3.1 --- Experimental setup and results --- p.119 / Chapter 4.3 --- Summary --- p.124 / References --- p.126 / Chapter Chapter 5 --- Conclusions and future work --- p.129 / Chapter 5.1 --- Conclusions --- p.129 / Chapter 5.2 --- Future work --- p.131 / Chapter Appendix A. --- List of Symbols --- p.133 / Chapter Appendix B. --- Abbreviations --- p.135 / Chapter Appendix C. --- Publications --- p.139

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M.Sc. (Physics) / Please refer to full text to view abstract

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Silicon photonics is the study and application of photonic systems, which use silicon as an optical medium. Data is transferred in the systems by optical rays. This technology is seen as the substitutions of electric computer chips in the future and the means to keep tack on the Moore’s law. Cavity optomechanics is a rising field of silicon photonics. It focuses on the interaction between light and mechanical objects. Although it is currently at its early stage of growth, this field has attracted rising attention. Here, we present highly sensitive optical detection of acceleration using an optomechanical accelerometer. The core part of this accelerometer is a slot-type photonic crystal cavity with strong optomechanical interactions. We first discuss theoretically the optomechanical coupling in the air-slot mode-gap photonic crystal cavity. The dispersive coupling gom is numerically calculated. Dynamical parametric oscillations for both cooling and amplification, in the resolved and unresolved sideband limit, are examined numerically, along with the displacement spectral density and cooling rates for the various operating parameters. Experimental results also demonstrated that the cavity has a large optomechanical coupling rate. The optically induced spring effect, damping and amplification of the mechanical modes are observed with measurements both in air and in vacuum. Then, we propose and demonstrate our optomechanical accelerometer. It can operate with a resolution of 730 ng/Hz¹/² (or equivalently 40.1 aN/Hz¹/²) and with a transduction bandwidth of ≈ 85 kHz. We also demonstrate an integrated photonics device, an on-chip spectroscopy, in the last part of this thesis. This new type of on-chip microspectrometer is based on the Vernier effect of two cascaded micro-ring cavities. It can measure optical spectrum with a bandwidth of 74nm and a resolution of 0.22 nm in a small footprint of 1.5 mm².