by Chan Lai Yin, Simon. / "December 1998." / Thesis (Ph.D.)--Chinese University of Hong Kong, 1998. / 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.

Quantum Key Distribution (QKD) employs the laws of quantum mechanics for the purpose of cryptography. Two parties, commonly called Alice and Bob, are able to share a random key which is used to encrypt a message. Any eavesdropper trying to intercept their key will have to make measurements, thereby disturbing the system. This can be detected by Alice and Bob and they will then discard their key. Polarisation encoded QKD protocols use the polarisation of single photons as qubits to generate a cryptographic key. This can be implemented using a fibre optic link between Alice and Bob but the polarisation of light is altered when passed through a fibre due to birefringence caused by asymmetries in the fibre. This causes refractive differences for orthogonal components of the state of polarisation of light, so the polarisation is rotated as the photon is transmitted through the fibre. If the fibre is fixed, the change of polarisation will be unique and constant. This can be compensated by rotating each photon appropriately to its original state. Under typical environmental conditions, such as temperature changes and vibrations, the birefringence effects vary and should be compensated in real time. Therefore, an active polarisation controller is needed in order to maintain the state of polarisation of each qubit. An investigation was done to first track how the state of polarisation changes over time in a natural environment. Both wavelength-division multiplexing and time-division multiplexing were investigated as testing methods for the compensation system. A time-division multiplexed system was developed to compensate the changes in polarisation. Since QKD protocols such as BB84 and B92 utilise two non-orthogonal bases, two polarisation controllers are usually used for compensation. However, by using a search algorithm, one polarisation controller was able to isolate the plane on the Poincaré sphere that passes through both bases, thus compensating non-orthogonal states with one device. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2012.

by Kit Chan. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references. / Abstracts in English and Chinese. / Abstract --- p.ii / Acknowledgment --- p.v / Table of Contents --- p.vi / Chapter 1. --- Introduction --- p.1 / Chapter 1.1 --- Ultrashort Pulses Generation in Semiconductor Lasers and Fiber Lasers --- p.2 / Chapter 1.2 --- Wavelength Tunable Pulse Generation From Semiconductor Laser --- p.4 / Chapter 1.3 --- Wavelength Tunable Pulse Generation from Erbium Doped Fiber Lasers --- p.7 / Chapter 1.4 --- Structure of the thesis --- p.8 / Reference --- p.10 / Chapter 2. --- Principles and Theories --- p.14 / Chapter 2.1 --- Principle of Synchronous Injection Seeding --- p.15 / Chapter 2.2 --- Principle of Compensated Dispersive Tuning in Self-seeding Configuration --- p.18 / Chapter 2.3 --- Principle of Compensated Dispersive Tuning in Actively Mode-Locked Fiber Laser --- p.20 / Chapter 2.4 --- Principle of Wavelength Switching in Actively Mode-Locked Fiber Laser with Fiber Bragg Gratings in Cascaded Configuration --- p.24 / Chapter 3. --- Electrical Wavelength Tunable Pulses Generated From Two-way Synchronous Injection Seeded Fabry-Perot Laser Diodes --- p.26 / Chapter 3.1 --- Introduction --- p.27 / Chapter 3.2 --- Experimental Details --- p.28 / Chapter 3.3 --- Results and Discussion --- p.31 / Chapter 3.4 --- Summary --- p.38 / Reference --- p.39 / Chapter 4. --- Compensated Dispersive Tuning In Self-Seeding Configuration --- p.41 / Chapter 4.1 --- Introduction --- p.42 / Chapter 4.2 --- Experimental Details --- p.43 / Chapter 4.3 --- Results and Discussion --- p.46 / Chapter 4.4 --- Summary --- p.55 / Reference --- p.56 / Chapter 5. --- Compensated Dispersive Tuning in Actively Mode-Locked Fiber Laser --- p.57 / Chapter 5.1 --- Introduction --- p.58 / Chapter 5.2 --- Experimental Details --- p.59 / Chapter 5.3 --- Results and Discussion --- p.61 / Chapter 5.4 --- Summary --- p.69 / Reference --- p.70 / Chapter 6. --- Compensated Dispersive Tuning in Actively Mode-Locked Fiber Laser Using Linearly Chirped Fiber Bragg Grating --- p.71 / Chapter 6.1 --- Introduction --- p.72 / Chapter 6.2 --- Experimental Details --- p.73 / Chapter 6.3 --- Results and Discussion --- p.75 / Chapter 6.4 --- Summary --- p.77 / Reference --- p.78 / Chapter 7. --- Electrically Wavelength Switching in Actively Mode- locked Fiber Laser Using Fiber Bragg Gratingsin Cascaded Configuration --- p.79 / Chapter 7.1 --- Introduction --- p.80 / Chapter 7.2 --- Experimental Details --- p.81 / Chapter 7.3 --- Results and Discussion --- p.83 / Chapter 7.4 --- Summary --- p.87 / Reference --- p.88 / Chapter 8. --- Conclusion and Future Works --- p.89 / Chapter 8.1 --- Conclusion --- p.89 / Chapter 8.2 --- Possible Future Works --- p.92 / Appendices --- p.A-l / Chapter Appendix A. --- List of Publications --- p.A-l / Chapter Appendix B. --- List of Figures --- p.A-2

Lee Ka-lun. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references. / Abstracts in English and Chinese. / Abstract --- p.ii / Acknowledgment --- p.v / Table of contents --- p.vi / List of figure --- p.viii / Chapter 1. --- Introduction --- p.1 / Chapter 1.1. --- Generation of picosecond pulses from semiconductor laser and fiber laser --- p.2 / Chapter 1.2. --- Wavelength tunable pulse generated from semiconductor laser --- p.5 / Chapter 1.3. --- Wavelength tunable pulse generated from erbium doped fiber laser --- p.7 / Chapter 1.4. --- Structure of the thesis --- p.8 / Chapter 2. --- Principles and Theories --- p.13 / Chapter 2.1. --- Principle of dispersion tuning --- p.15 / Chapter 2.1.1. --- Dependence on the strength of dispersion --- p.16 / Chapter 2.1.2. --- Wavelength selection in time domain --- p.18 / Chapter 2.1.3. --- Compensated dispersion tuning in a dispersion balanced fiber ring --- p.20 / Chapter 2.2. --- Optical gating using Nonlinear Optical Loop Mirror (NOLM) incorporated with nonlinear element --- p.22 / Chapter 2.3. --- Principle of compensated dispersion tuning in harmonically mode- locked fiber laser incorporated with linearly chirped fiber grating (LCFG) --- p.26 / Chapter 2.4. --- Principle of compensated dispersion tuning in self-seeding configuration --- p.29 / Chapter 2.5. --- Principle of dual-wavelength operation in harmonically mode-locked fiber laser --- p.31 / Chapter 3. --- Preliminarily experimental study --- p.33 / Chapter 3.1. --- Wavelength selection using strong and weak dispersive medium --- p.34 / Chapter 3.2. --- NOLM as a fast optical modulator --- p.38 / Chapter 4. --- Self-compensated dispersion-tuning in mode-locked fiber laser using bi- directional transit in a linearly chirped fiber grating --- p.41 / Chapter 4.1. --- Introduction --- p.42 / Chapter 4.2. --- Experimental Details --- p.43 / Chapter 4.3. --- Results and discussion --- p.47 / Chapter 4.4. --- Summary --- p.54 / Chapter 5. --- Generation of wavelength tunable pulses from a self-seeded semiconductor laser using an optically controlled Nonlinear Optical Loop Modulator (NOLM) incorporated with a Semiconductor Optical Amplifier (SOA) --- p.56 / Chapter 5.1. --- Introduction --- p.57 / Chapter 5.2. --- Experimental Details --- p.58 / Chapter 5.3. --- Results and discussion --- p.64 / Chapter 5.4. --- Summary --- p.71 / Chapter 6. --- Alternate and Simultaneous Generation of 1 GHz Dual-Wavelength Pulses from an Electrically-Tunable Harmonically Mode-locked Fiber Laser --- p.74 / Chapter 6.1. --- Introduction --- p.75 / Chapter 6.2. --- Experimental Details --- p.76 / Chapter 6.3. --- Results and discussion --- p.80 / Chapter 6.4. --- Summary --- p.87 / Chapter 7. --- Conclusion and Future works --- p.89 / Chapter 7.1. --- Conclusion --- p.89 / Chapter 7.2. --- Future works --- p.93 / Appendix --- p.A-l / List of Publication --- p.A-l

by Sui-Pan Yam. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1998. / Includes bibliographical references. / Abstract also in Chinese. / Acknowledgements --- p.V / Abstract --- p.VI / Chapter Chapter 1 --- Introduction --- p.1-1 / Chapter 1.1) --- Tunable Multi-Wavelength Optical Sources --- p.1 -1 / Chapter 1.2) --- All-Optical Switching --- p.1 -3 / Chapter 1.2.1) --- Nonlinear Effect / Chapter 1.2.2) --- Special Design of the Laser Structure / Chapter 1.2.3) --- Self-Injection Seeding of Fabry-Perot Laser Diode / Chapter 1.3) --- About This Project --- p.1-6 / Chapter Chapter 2 --- Basic Theory --- p.2-1 / Chapter 2.1) --- Mechanism of Gain-Switching --- p.2-1 / Chapter 2.1.1) --- General Description / Chapter 2.1.2) --- "Optical Pulsewidth, Spectra, and Frequency Chirping of Gain-Switched Pulses" / Chapter 2.2) --- Mechanism of Self-Injection Seeding --- p.2-8 / Chapter 2.2.1) --- General Description / Chapter 2.2.2) --- Dynamics of Single-Mode Formation / Chapter 2.2.3) --- Frequency Evolution of the Laser Diode for Cavity Mode Selection / Chapter 2.2.4) --- Turn-On Delay Time Jitter (TOJ) / Chapter 2.3) --- Mechanism of Injection Seeding --- p.2-17 / Chapter 2.3.1) --- General Description / Chapter 2.3.2) --- The Model of Weak Injection / Chapter 2.3.3) --- The Model of Strong Injection / Chapter Chapter 3 --- Single- and Multi-wavelength Optical Pulses Generated by a Diffraction Grating --- p.3-1 / Chapter 3.1) --- Introduction --- p.3-1 / Chapter 3.2) --- Basic Principle --- p.3-2 / Chapter 3.3) --- Experimental Setup --- p.3-5 / Chapter 3.4) --- Results and Discussion --- p.3-7 / Chapter 3.4.1) --- Spectral Characteristics Analysis / Chapter 3.4.2) --- Individually Access of the Four-Wavelength Output / Chapter 3.4.3) --- The Optical Pulsewidth Characteristics / Chapter 3.4.4) --- Discussion / Chapter 3.5) --- Summary --- p.3-14 / Chapter Chapter 4 --- Using a Highly Dispersive Fiber for Tunable Multi-Wavelength Pulse Generation --- p.4-1 / Chapter 4.1) --- Introduction --- p.4-1 / Chapter 4.2) --- Basic Principle --- p.4-2 / Chapter 4.3) --- Experimental Setup --- p.4-5 / Chapter 4.4) --- Experimental Results --- p.4-7 / Chapter 4.4.1) --- Spectral and Temporal Characteristics / Chapter 4.4.2) --- Wavelength Tuning / Chapter 4.4.3) --- Individually Access of Two Wavelength Channels / Chapter 4.4.4) --- Multi-Wavelength Generation / Chapter 4.5) --- Summary --- p.4-13 / Chapter Chapter 5 --- Comparison of Two Self-Seeding Configurations --- p.5-1 / Chapter 5.1) --- Introduction --- p.5-1 / Chapter 5.2) --- Polarization Sensitivity --- p.5-1 / Chapter 5.3) --- Stability --- p.5-2 / Chapter 5.4) --- Tunability --- p.5-2 / Chapter 5.5) --- Simplification --- p.5-3 / Chapter 5.6) --- Summary of the advantages and disadvantages of Two Configurations --- p.5-4 / Chapter Chapter 6 --- All-Optical Wavelength Switching achieved by Self-Seeding and External Injection-Seeding --- p.6-1 / Chapter 6.1) --- Introduction --- p.6-1 / Chapter 6.2) --- Experimental Setup --- p.6-2 / Chapter 6.3) --- Results and Discussion --- p.6-4 / Chapter 6.3.1) --- Spectral Characteristics / Chapter 6.3.2) --- The Optical Pulsewidth / Chapter 6.3.3) --- The Optical Switching Behaviors / Chapter 6.3.4) --- The Detail Information of Switching / Chapter 6.3.5) --- Optical Power / Chapter 6.4) --- Summary --- p.6-10 / Chapter Chapter 7 --- A Novel Self-Injection Seeding Scheme --- p.7-1 / Chapter 7.1) --- Introduction --- p.7-1 / Chapter 7.2) --- Basic Principle --- p.7-2 / Chapter 7.3) --- Experimental Setup --- p.7-9 / Chapter 7.4) --- Results and Discussion --- p.7-11 / Chapter 7.4.1) --- Spectral and Temporal Characterizations of Two-Wavelength Switching / Chapter 7.4.2) --- Different Wavelength Selection / Chapter 7.4.3) --- Operation Frequency Against the Fiber Length / Chapter 7.4.4) --- Multi-Wavelength Generation / Chapter 7.5) --- Discussion --- p.7-20 / Chapter 7.6) --- Summary --- p.7-22 / Chapter Chapter 8 --- Comparison of Switching Methods --- p.8-1 / Chapter 8.1) --- Introduction --- p.8-1 / Chapter 8.2) --- Switching between Self-Seeding and Injection-Seeding --- p.8-1 / Chapter 8.3) --- Switching by Self-Seeding of a F-P Laser Diode --- p.8-2 / Chapter 8.4) --- Summary --- p.8-3 / Chapter Chapter 9 --- Conclusion --- p.9-1 / References / Figure Captions / Appendix 一 Equipment Descriptions / List of Accepted and Submitted Publications

by Ka-Suen Lee. / "June 1998." / Thesis (Ph.D.)--Chinese University of Hong Kong, 1998. / 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.

The purpose of this study is to determine the relationship of light wave length to tissue differentiation in sunflower seedlings.

In this thesis, wave propagation through acoustic materials with subwavelength slits structures is studied. Guided by the findings, acoustic wave focusing is achieved with a specific material design. By using a parameter retrieving method, an effective medium theory for a slab with periodic subwavelength cut-through slits is successfully derived. The theory is based on eigenfunction solutions to the acoustic wave equation. Numerical simulations are implemented by the finite-difference time-domain (FDTD) method for the two-dimensional acoustic wave equation. The theory provides the effective impedance and refractive index functions for the equivalent medium, which can reproduce the transmission and reflection spectral responses of the original structure. I analytically and numerically investigate both the validity and limitations of the theory, and the influences of material and geometry on the effective spectral responses are studied. Results show that large contrasts in impedance and density are conditions that validate the effective medium theory, and this approximation displays a better accuracy for a thick slab with narrow slits in it. Based on the effective medium theory developed, a design of a at slab with a snake shaped" subwavelength structure is proposed as a means of achieving acoustic focusing. The property of focusing is demonstrated by FDTD simulations. Good agreement is observed between the proposed structure and the equivalent lens pre- dicted by the theory, which leads to robust broadband focusing by a thin at slab.

by Chow Kin Kee. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references. / Abstracts in English and Chinese. / Abstract --- p.ii / Acknowledgment --- p.v / Table of Contents --- p.vi / Chapter 1. --- Introduction --- p.1 / Chapter 1.1 --- Ultra-short Pulse Generation in Semiconductor Lasers --- p.2 / Chapter 1.2 --- Wavelength Selection and Switching in Short Pulses Generated from Semiconductor Laser --- p.4 / Chapter 1.3 --- Structure of the Thesis --- p.6 / Reference --- p.8 / Chapter 2. --- Principles and Theories --- p.10 / Chapter 2.1 --- Principle of Wavelength Switching in Self-Seeded Laser --- p.11 / Chapter 2.2 --- Principle of Synchronous Injection Seeding of two Lasers --- p.15 / Chapter 2.3 --- Principle of Fast Spectral Improvement in DFB Laser with Optical Feedback --- p.17 / Chapter 2.4 --- Principle of Spectrally Resolved Analysis --- p.19 / Reference --- p.24 / Chapter 3. --- Switching Dynamics between Single-Mode and Dual-Mode Pulse Emissions from a Self-Seeded Laser Diode --- p.25 / Chapter 3.1 --- Introduction --- p.26 / Chapter 3.2 --- Experimental Details and Discussion --- p.28 / Chapter 3.3 --- Summary --- p.37 / Reference --- p.38 / Chapter 4. --- Spectrally Resolved Analysis of Fast Tuning in Single-Mode Pulses Generated from Mutually Injection-Seeded Fabry- Perot Laser Diodes --- p.40 / Chapter 4.1 --- Introduction --- p.41 / Chapter 4.2 --- Experimental Details and Discussion --- p.42 / Chapter 4.3 --- Summary --- p.51 / Reference --- p.52 / Chapter 5. --- Fast Spectral Improvement in Gain-Switched Pulses Generated from a Distributed Feedback Laser with Weak Optical Feedback --- p.54 / Chapter 5.1 --- Introduction --- p.55 / Chapter 5.2 --- Experimental Details and Discussion --- p.57 / Chapter 5.3 --- Summary --- p.65 / Reference --- p.66 / Chapter 6. --- Conclusion and Future Work --- p.67 / Chapter 6.1 --- Conclusion --- p.67 / Chapter 6.2 --- Future Works --- p.69 / Reference --- p.71 / Appendices --- p.A-l / Appendix A. List of Publications --- p.A-l / Appendix B. Modeling of Self-Seeded Fabry-Perot Laser --- p.A-2 / Appendix C. List of Figures --- p.A-4

Made available in DSpace on 2017-07-24T19:22:16Z (GMT). No. of bitstreams: 1 MilkoJavier.pdf: 902702 bytes, checksum: 627c849996015406ece5d6f3423376ae (MD5) Previous issue date: 2004-09-30 / The purpose of this study was to evaluate the generated fluorescence during ultraviolet light exposure on five metal-free ceramics. Samples were grouped according to the brand: Group I Classic (Ivoclar-Vivadent); Group II IPS Empress 2 (Ivoclar-Vivadent); Group III In-Ceram Alumina (Vita); Group IV In-Ceram Spinell (Vita) and Group V IPSd.SING (Ivoclar-Vivadent). A spectrofluorometer (Fluorescence Spectrophotometer F 4500 Hitachi) was used as the measuring tool. The test samples consisted of discs (15mm diameter and 2mm thick) made form each ceramic brand following the manufacturer specifications. Each disc was attacked by ultraviolet rays with a wave length of 390nm to register fluorescence from a 400nm to 700nm range. The fluorescence present was registered as a Fluorescence Intensity curve and as wave length. The data was analyzed applying ANOVA (test Nueman-Keuls) with a significance level of p<0,05. The fluorescence intensity mean found was: Group I-2432au; Group II-3216au; Group III-398au; Group IV -408au and Group V-2839au. The wave length mean obtained was: Group-I 447.6nm; Group II-450.1nm; Group III-459.7nm; Group IV-458.9nm and Group V-449.2nm. It was concluded that there was significant difference between the fluorescence intensity where groups III and IV presented the least values and group II the highest value. With respect to wave length, no significant difference was found between groups II and V and between III and IV. From the five groups analyzed, IPS Empress 2 and IPS d-SIGN presented wave length values similar to natural dentition data found in the literature. / O objetivo deste trabalho foi avaliar a fluorescência de cinco cerâmicas livres de metal gerada durante a exposição de uma fonte de luz UV, sendo: Grupo I Classic (Ivoclar-Vivadent); Grupo II IPS Empress 2 (Ivoclar-Vivadent); Grupo III In-Ceram Alumina (Vita); Grupo IV In-Ceram Spinell (Vita) e Grupo V IPS d.SING (Ivoclar-Vivadent). Utilizou-se um espectrofluorímetro (Fluorescence Spectrophotometer F 4500 Hitachi). Os espécimes de prova foram obtidos pela confecção de discos de cerâmicas livres de metal, segundo as especificações dos fabricantes, cada um deles possuía 15mm de diâmetro e 2mm de espessura tendo como característica uma superfície de espelho. O equipamento foi calibrado para que o raio incidente de luz UV nos corpos-de-prova fosse emitido com um comprimento de onda de 390nm e para que todo fenômeno de fluorescência em uma faixa de 400 até 700nm de comprimento de onda fosse registrado pelo equipamento. A fluorescência gerada durante o teste foi registrada em uma curva de Intensidade de Fluorescência x Comprimento de Onda permitindo obter os valores dos picos máximos de Intensidade de Fluorescência e Comprimento de Onda. A análise estatística deu-se através do teste ANOVA (test Nueman-Keuls), utilizando-se um nível de significância de p<0,05. A média dos grupos para Intensidade de Fluorescência (u.a) foi: Grupo I 2432; Grupo II 3216; Grupo III 398; Grupo IV 408 e Grupo V 2839. A média dos grupos para Comprimento de Onda (nm) foi: Grupo I 447.6; Grupo II 450.1; Grupo III 459.7; Grupo IV 458.9 e Grupo V 449.2. De acordo com a metodologia empregada, com os resultados obtidos no presente trabalho, concluiu-se que houve diferenças em relação à intensidade de fluorescência em todos os grupos, sendo que os menores valores foram obtidos no grupo III (In-Ceram Alumina) e no grupo IV (In-Ceram Spinell), e os maiores valores encontrados no grupo II (IPS Empress 2), houve diferenças em relação ao comprimento de onda em todos os grupos, não havendo diferenças significativas entre os grupos II (IPS Empress 2) e V (IPS d.SIGN), bem como entre os grupos III (In-Ceram Alumina) e IV (In-Ceram Spinell) e os valores de comprimento de onda mais próximos aos dentes naturais foram encontrados no grupo II (IPS Empress 2) e no grupo V (IPS d-SIGN), quando comparados com dados encontrados na literatura