Dissertations / Theses on the topic 'Guided wave devices'

Thesis (Ph. D.)--West Virginia University, 2009.
Title from document title page. Document formatted into pages; contains vi, 84 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 79-84).

Integrated optics-based approaches to beam steering, beam shaping, beam collimation, and quasi-phasematched (QPM) second harmonic generation (SHG) of light offer significant advantages over conventional approaches based on bulk optics. The research in this dissertation addresses the analysis and design of optical guided-wave devices for both efficient quasi-phasematched second harmonic generation in diffused channel waveguides, as well as Bragg deflection of beams in planar waveguides. It is known that the normalized SHG efficiency depends on the linear properties of the waveguide through the overlap of the modal fields at the fundamental and second harmonic wavelengths. To analyze the linear modal properties, a fast and accurate modeling tool, based on an improved, semi-vector, Fourier method of analysis, is presented. The tool incorporates the Wentzel-Kramers-Brillouin (WKB) and effective index methods to accurately determine the computational parameters required for the numerical calculation in the Fourier method so that automatic variation of the waveguide parameters is permitted. Using the modeling tool, the dependence of the SHG process on the waveguide parameters is investigated in detail, leading to waveguide designs with improved mode confinement, and consequently higher SHG efficiency. The phasematching characteristics of these improved designs are also calculated, and it is found that non-critical phasematching, or phasematching with wide tolerances to variations in the waveguide parameters, is possible in certain cases. The analysis of the waveguide-SHG process also indicates that efficiency can be improved by utilizing thin films on the waveguide surface to ensure that the peaks of the fundamental and second harmonic modes are coincident. This contributes to higher SHG efficiency through improved mode overlap as well, but it is demonstrated that this approach is clearly distinct from and independent of the mode-confinement approach. The analysis of planar overlays is based on recursion relations for the phase shift upon reflection at interfaces. The significance of this approach is demonstrated through the "matching" of the diffused waveguide to an independently-designed, multilayer overlay for the purposes of obtaining specific modal characteristics in the "integrated" structure. On a different note but incorporating similar approaches for analysis and design, beam shaping, steering, and collimation in planar waveguides, using Bragg gratings with finite area and non-uniform depth variation, are also discussed.

The properties of all-optical nonlinear waveguide devices are investigated. In particular, the nonlinear directional coupler (NLDC) and nonlinear Mach-Zehnder interferometer (NLMZ) are analyzed using perturbation theory. The perturbation theory provides differential equations that describe the amplitude of the waveguide modes as a function of the propagation distance. To be practical, these waveguide devices require nonlinear phase shifts of π or more. Therefore, the theoretical investigation of these devices emphasizes their fabrication in bulk and multiple-quantum-well (MQW) gallium arsenide (GaAs). For the first time, absorption, carrier diffusion, and thermal effects are included in the theoretical investigation of the NLMZ and NLDC. The nonlinear dependence of the coupling terms, which has been neglected in all previous work, is shown to be significant for semiconductor based NLDC's. The effects of carrier diffusion on the nonlinear response of a GaAs waveguide is demonstrated using a self-consistent numerical method. The effects are heavily dependent on the waveguide geometry, and, therefore, should be included in the analysis of nonlinear semiconductor waveguide devices. However, if the diffusion length is large compared to the mode width, carrier diffusion simplifies the investigation since the nonlinear absorption and index change are uniform across the mode. This important conclusion is used in the models for the NLMZ and NLDC. The theoretical models predict the NLMZ and NLDC should work in bulk and MQW GaAs. To demonstrate that the required nonlinear phase shifts for the NLMZ and NLDC are indeed possible in bulk and MQW GaAs, the first experimental observation of electronic optical bistability in a MQW GaAs strip-loaded waveguide is recounted. This original research illustrated that phase shifts in excess of 2π are possible in MQW GaAs waveguides and, therefore, the future of all-optical waveguide devices in semiconductors is optimistic.

Thesis (Ph.D.)--City University of Hong Kong, 2009.
"Submitted to Department of Mathematics in partial fulfillment of the requirements for the degree of Doctor of Philosophy." Includes bibliographical references (leaves [85]-91)

Photonic crystals have allowed unprecedented control of light and have allowed bringing new functionalities on chip. Photonic crystal waveguides (PCWs), which are linear defects in a photonic crystal, have unique features that distinguish these waveguides from other waveguides. The unique features include very large dispersion, existence of slow light, and the possibility of tailoring the dispersion properties for guiding light. In my research, I have overcome some of the challenges in using slow light in PCWs. In this work, I have demonstrated (i) high efficiency coupling of light into slow group velocity modes of a PCW, (ii) large bandwidth high transmission and low dispersion bends in PCWs, (iii) accurate modeling of pulse propagation in PCWs, (iv) high efficiency absorbing boundary conditions for dispersive slow group velocity modes of PCWs. To demonstrate the utility of slow light in designing high efficiency devices, I have demonstrated refractive index sensors using slow light in PCWs. In the end, a few high efficiency devices based on slow light in PCWs are mentioned. The remaining issues in the widespread use of PCW are also discussed in the last chapter.

Thesis (PhD)--Stellenbosch University, 2002.
ENGLISH ABSTRACT: Multi-mode coupled cavity filters have been the mainstay of commercial satellite communications systems since their introduction in 1970. Multi-mode filters use more than one resonant mode in a single cavity resonator, thereby reducing the size and weight of the filter. This is especially advantageous for satellite applications where the size and weight of the communications payload must be minimised. The use of more modes also increases the complexity of the filter design. Iris design plays an integral part in the design of multi-mode coupled cavity filters. Currently, irises are mostly designed using either the small aperture theory derived by Bethe, or a standard numerical technique. A recent study comparing these two techniques shows that approximations made in standard correction factors applied to small aperture theory, can lead to unacceptable errors. While numerical techniques are clearly required for the accurate design of complex irises, the standard numerical technique is only suited to the design of relatively simple iris structures. This dissertation presents three new CAD procedures for the design of irises in multi-mode coupled cavity devices. The new procedures are verified by numerical examples and measurements. Two new multi-mode coupled cavity devices were designed and tested using the CAD procedures developed in this work. The first is a new diplexer structure that realises two fourth order Chebyschev filter channels in three quadruple-mode cavities. Through correct placement and accurate design of irises, channel isolation was increased beyond that of existing multi-mode diplexer structures. The second application is the development of a new coupling structure for the replacement of coupling and tuning screws. A third order triple-mode cavity filter, including this new fixed coupling element, was designed using the CAD procedures developed in this dissertation.
AFRIKAANSE OPSOMMING: Multi-modale gekoppelde resoneerder filters word reeds vanaf die eerste verskyning van kommersiele sateliet-kommunikasiestelsels in 1970 gebruik. Vir hierdie toepassing is die fisiese grootte en massa van die filters in die kommunikasiestelsels van groot belang. Multimodale filters gebruik meer as een resonante modus in ‘n golfgeleier resoneerder om die fisiese grootte en massa van die filter te verminder. Hoe meer resonante modusse in een golfgeleier resoneerder, hoe kleiner en ligter die filter. Die gebruik van meer modusse kompliseer egter die ontwerp van die filter. ‘n Baie belangrike aspek van multi-modale filterontwerp is die ontwerp van die irisse wat die golfgeleier resoneerder skei. Die irisse word tans ontwerp, of deur middel van Bethe se klein iris teorie, of met die gebruik van ‘n standaard numeriese metode. ‘n Onlangse studie toon aan dat sekere standaard toevoegings tot Bethe se teorie, benaderings bevat wat tot foutiewe iris ontwerp kan lei. Numeriese metodes is dus noodsaaklik vir akkurate iris ontwerp. Hierdie studie wys egter dat die bestaande numeriese tegnieke beperk is tot die ontwerp van relatief eenvoudige irisse. Hierdie proefskrif bied drie nuwe rekenaargesteunde ontwerpsprosedures vir die doeltreffende ontwerp van verskillende klasse irisse in multi-modale golfgeleier resoneerder filters. Die nuwe metodes word getoets aan die hand van numeriese voorbeelde, en/of gemete resultate. Twee nuwe komplekse multi-modale golfgeleier resoneerder filter toepassings is ontwerp deur gebruik te maak van die nuwe ontwerpsprosedures. Die eerste is ‘n nuwe diplekser struktuur met twee vierde-orde Chebyschev filterkanale in drie golfgeleier resoneerders wat elk vier resonante modusse ondersteun. Deur korrekte en akkurate plasing van die irisse word ‘n groot verbetering in kanaalisolasie bo ‘n bestaande multi-modale diplekser verkry. Die tweede toepassing is die ontwikkeling van ‘n nuwe koppelstruktuur vir die vervanging van die gebruiklike koppel- en aanpassingskroewe. ‘n Derde-orde trippel-modus filter, gebaseer op hierdie nuwe struktuur, is ook ontwerp deur van die nuwe ontwerpsalgoritmes gebruik te maak.

Thesis (Ph.D)--Electrical and Computer Engineering, Georgia Institute of Technology, 2010.
Committee Chair: Prof. Ali Adibi; Committee Member: Prof. Joseph Perry; Committee Member: Prof. Stephen Ralph; Committee Member: Prof. Thomas Gaylord. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Numerical analysis of the electromagnetic fields in large, complex structures is very challenging due to the high computational overhead. Recently, it has been shown that a new method called Trefftz-FLAME ( Flexible Local Approximation MEthod) is suitable for problems where there exist a large number of similar structures.
This thesis develops Trefftz-FLAME in two areas. First, a novel 2D Trefftz-FLAME method incorporates the modal analysis and port boundary condition that are essential to an accurate calculation of reflection and transmission coefficients for photonic crystal devices. The new technique outperforms existing methods in both accuracy and computational cost.
The second area pertains to the 3D, vector problem of electromagnetic wave scattering by aggregates of identical dielectric particles. A methodology for the development of local basis functions is introduced, applicable to particles of any shape and composition. Boundary conditions on the surface of the finite FLAME domain are described, capable of representing the incident wave and absorbing the outgoing radiation. A series of problems involving dielectric spheres is solved to validate the new method. Comparison with exact solutions is possible in some cases and shows that the method is able to produce accurate near-field results even when the computational grid spacing is equal to the radius of the spheres.

The objective of this research is to investigate the use of laser direct writing to micro-pattern low loss passive optical channel waveguide devices using a new hybrid organic/inorganic polymer. Review of literature shows previous methods of optical waveguide device patterning as well as application of other non-polymer materials. System setup and design of the waveguide components are discussed. Results show that laser direct writing of the hybrid polymer produce single mode interconnects with a loss of less 1dB/cm.

Ce travail de thèse, qui se rattache au domaine des composants télécom, concerne l'étude de composants passifs élémentaires constitués de lignes de transmission coplanaires alliant ferrite et métamatériaux. Ces composants sont susceptibles de réaliser de nouvelles fonctions en électronique des hautes fréquences en combinant plusieurs phénomènes comme ceux de non réciprocité, des comportements main droite - main gauche et l'agilité en fréquence. Les applications visées portent sur un grand champ de composants microondes comme des antennes, des isolateurs, déphaseurs, coupleurs, filtres - agiles et performants. La modélisation, la fabrication et la caractérisation de ces composants ont été effectuées dans le cadre d'une collaboration entre l'INL et le LT2C. Les outils mis en œuvre dans ce travail comprennent la réalisation de ces composants en salle blanche, leur caractérisation en hyperfréquences (en général jusqu'à 20 GHz), leur simulation par un logiciel commercial de simulation par éléments finis (COMSOL) ainsi que le développement de techniques d'extraction de paramètres (Matlab). La mise en œuvre de ces outils a permis d'appréhender le comportement de ces lignes en termes de constante de propagation et de diagramme de dispersion. Sur le plan pratique, des composants inductifs et/ou capacitifs (capacités à fente ou interdigitées) ont été intégrés à des lignes de transmission coplanaires sur 2 types de substrats. Le premier substrat, diélectrique (Al203), sert de référence, tandis que le second est ferrimagnétique (YIG ou Y3Fe5O12) et présente un effet de non-réciprocité de la propagation du signal dans la configuration retenue. Sur alumine, les valeurs des capacités et des inductances intégrées atteignent 80 fF et 400 pH respectivement. Sur YIG, à partir d'études paramétriques originales sur différentes topologies de structures de test, les effets de non réciprocité attendus ainsi que les phénomènes de résonance gyromagnétique ont bien été mis en évidence. La simulation électromagnétique des structures est validée par un accord correct entre simulations et mesures. Il ressort de cette étude que la non réciprocité d'une ligne sur YIG chargée par des inductances parallèles peut être améliorée jusqu'à 15 dB environ par rapport à une simple ligne coplanaire sur YIG pour certaines bandes de fréquences. Enfin l'agilité en fréquence de la structure de bande des lignes CRLH est établie. Ces travaux ouvrent de très intéressantes perspectives pour le développement de nouveaux composants microondes et sont susceptibles de constituer un socle solide pour une suite des activités dans cette thématique.

La réduction des dimensions des composants optoélectroniques constitue une contrainte importante pour un couplage optimal avec la fibre optique. Le but recherché étant de focaliser le maximum de lumière à l'intérieur de la couche intrinsèque de la photodiode, il faudrait donc envisager de réduire le diamètre de la fibre optique. Une étude du bout de la fibre est également menée et montre que pour une forme lentillée appropriée, il est possible d'adapter la distribution d'énergie entre fibre optique et photodiode. Le calcul du champ le long de ce guide de dimensions lentement décroissantes utilise la méthode des modes locaux. Cette méthode est employée car il n'y a pas de solutions exactes aux équations de Maxwell. En réalité, le champ total est la superposition des champs locaux et du champ radiatif. Les pertes d'énergie le long de ce guide sont analysées avec la théorie du couplage des modes locaux. On obtient alors un bilan le long de ce guide que l'on cherche à optimiser. La comparaison de ces résultats avec la simulation numérique quasi 3 D de la propagation optique guidée sur ALCOR est également réalisée. Ceci permet de définir la structure la mieux adaptée pour un couplage optimum entre la fibre et le composant

This thesis investigates a novel optoelectronic platform based on the integration of superconductive structures, such as thin films and micro-constrictions, with optical waveguides for ultra-fast and ultra-sensitive devices with applications including high-speed optical communications, quantum optical information processing, and terahertz (THz) devices and systems. The kinetic-inductive photoresponse of superconducting thin films will be studied as the basic optoelectronic process underlying the operation of these novel devices. Analytical formulation for the non-bolometric response is presented, and experimental photodetection in YBCO meander-line structures will be demonstrated. A set of superconducting coplanar waveguides (CPW) are designed and characterized, which support the operation of the devices at microwave frequencies. Microwave-photonic devices comprising a microwave transmission line and a light-sensitive element, such as a meander-line structure, are designed and measured for implementation of optically tunable microwave components. In order to support low-loss and low-dispersion propagation of millimeter-wave and THz signals in ultra-fast and wideband kinetic-inductive devices, surface-wave transmission lines are proposed, incorporating long-wavelength Surface Plasmon Polariton (SPP) modes in planar metal-dielectric waveguides. The theory of superconducting optical waveguides, including analytical formulation and numerical methods, is developed in detail. The implementation of superconducting optical waveguides is discussed thoroughly, employing conventional dielectric-waveguide techniques as well as optical SPP modes. Superconductive traveling-wave photodetectors (STWPDs) are introduced as a viable means for ultra-fast and ultra-sensitive photodetection and photomixing. A modified transmission line formalism is developed to model STWPDs, where light is guided through an optical waveguide and photodetection is distributed along a transmission line. As an appendix, a systematic approach is developed for the analysis of carrier transport through superconducting heterostructures and micro-constrictions within the Bogoliubov-de Gennes (BdG) framework. The method is applied to study the role of Andreev reflection and Josephson-like phenomena in the current-voltage characteristics of inhomogeneous superconducting structures. I-V characteristics are experimentally demonstrated in YBCO micro-constrictions with potential applications in millimeter-wave and THz devices.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1991.
Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Huang, Xiaobo.
Thesis (Ph.D.)--Chinese University of Hong Kong, 2011.
Includes bibliographical references (leaves 108-111).
Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Abstract also in Chinese.

表面電漿是由貴金屬表面電荷密度漲落引起的沿著金屬表面傳播的電磁波。在過去十年裡，表面電漿效應因其在光子器件，傳感，表面增強螢光，尤其是表面增強拉曼散射(SERS) 方面的應用而引起了廣泛的關注.許多著作中的結論已經證實了的預期的SERS 強度，因此使得基於各種不同納米結構中的熱點的SERS變成一種下一代超敏感生物傳感平臺。因為表面電漿的波長和材料介電性質密切相闕，受f於此，難以進一步減小，所以對於進一步的各種應用來說，保證產生高強度的表面電漿使至關重要。同時，用電漿實現納米光子器件已經引起了研完者長久的興趣。例如，基於等問距規則排列的密置金屬納米顆粒之間突破衍射極限的的近場耕合已經被用於傳輸光信號。但是，輻射和吸收損耗在此類波導中是很嚴重的。因此，設計新概念的電漿器件是急需的。
有鑒於上述種種問題，本論文集中于總結構和材料兩方面剪裁表面電漿以期達到下面的要點和目的:
(1)基於傳播電漿(PSPs) ，或者傳播電漿同局域電漿(LPRs) 的結合而發展新的簡單的器件，由此提供顯著的聚焦、電磁場和場強增強。這種器件可以應用於很多方面，包括依賴強場的生物分子傳感探測，以及非線性光學效應。
(2) 設計基於增益介臂的低損耗的納米光子學器件，這種器件能夠為納米光子器件提供切實的可行性。針對表面電漿共振和電漿結構植于的介電環境之間聯繫，獲得其理論闡釋。這一工作將可以為傳感和器件設計提供深入的理解。
本論文中我們已經得到了如下的成果:
(1)一種基於將表面電漿聚焦到金屬盤中心孔而實現級聯放大增強的SERS 激勵源被提出和理論研究。這種器件提供了準均勻，水平偏振，較大面積的強SERS 激勵源。如時域有限差分(FDTD) 方法所揭試，強度譜線和波長範圍在650-1000 nm的近場性質展混出了一系列增強模式。在最佳的增強模式下，孔洞中的電場可以使得SERS 信號獲得四次方的進一步增強。同時一種解析模型也被提出來給FDTD結果以精確的解釋。我們的模型同時揭示了通過侵化金屬盤尺度而得到八次方場增強的可能性。我們的結果表明極強的電場增強，並且聚焦的電場是平行于金屬盤平面的效果，只能在中間包含一個孔洞的中空金屬盤(HMDs) 中才可能實現。這是因為金屬盤中間絶悸的問時的存在使得孔洞邊棒的電子不能流通間隙，進進而使得高強度的電場可以存在。另一方面，在實心的金屬盤的情形下，電子流會傾向於抑制到達中心的表面電漿的強度。除了產生高度優化的SERS 熱點，這種大面積的活性孔洞在螢光增強和非線性光學中也提供了一些潛在的應用。
除了中空金屬盤，基於經由增孟輔助下PSPs 的LPRs 之間的衍射共掠，我們開發了另一種一種高度侵化的熱點。由此得到的器件被理論上分析。衍射共振的過程是經由下述過程實現的:由LPRs 實現的光場局域化， LPRs 和PSPs 相互作用，以及通過PSPs 的能量傳遞。我們的研究表明通過給PSPs 引入光學增孟，可以從一種激光過程中的到LPRs 非常強的電磁場增強。我們發現通過現實的增豆豆水平，局域電場的增強引子可以達到10⁷。因此，我們為實現依賴強電場的單分子SERS提供了一種理想的方案，並且這種方案也是一種納米激光的新機制。
(2) 基於增孟輔助的電漿共振金屬納米顆粒鏈，我們提出了一種低損耗納米尺度的波導。我們證明通過引入增孟材料或者引入適當的介電材料作為周圍環境，波導的損耗可以顯著減小。為了得到低損耗傳翰的復介電譜，我們開發了一種高效的膺正交基展開(POBE) 方法。本徵模式分析揭示了低損耗模式的物理源頭，同時給出了除了基於單體偶極共振傳輸之外能量傳輸的可能性。我們提出一種基於電子書刻蝕和化學合成納米顆粒的一種製備方案。這種電漿波導可以構成納米光學器件的基石，尤其是用於集成納米光子學線路。同時，我們原創的揭示表面電漿的物理機理的POBE 方法可以用於進一步研究優化增豆豆輔助的電漿結構，進而設計良好的納米光子器件。
本論文始於一個古老問題:宏觀尺度下基於傳統介電材料光聚焦和傳導，并最後終結於納米尺度內經由增益材料和電漿結構的表面電漿的聚焦、和引導。論文結尾，本文給出了展望以及幾種可能的器件實現方案。
Surface plasmons (SPs) are electromagnetic waves that propagate along the surface of a noble metal via fluctuations in electron density. In the last decade, SPs effects gained widespread attention for their potential application in photonic devices, sensing, surface-enhanced fluorescence, especially Surface-Enhanced Raman Scattering (SERS). Many published results have confirmed the expected strengths of SERS, hence making it possible for SERS to become a next generation ultra-sensitive biosensing platform, which may take the form of various nano-structures in order to achieve optimized hot spots. While the wavelength of SPs is closely related to material dielectric properties and has limited scope for further reduction, it is of critical importance to ensure that SPs are being generated with the highest intensity before any further application advancement is possible. Meanwhile, plasmonics has aroused longstanding interests among researchers to realize nanophotonic devices. For example, ordered arrays of closely spaced metallic nanoparticles (MNP) have been employed to transport optical signals via near-field coupling below the diffraction limit. However, radiation and absorption losses in these waveguides can be serious. New concepts for novel plasmonic devices are essential.
In light of these issues, this thesis focuses on tailoring SPs from the viewpoints of structural and material properties with the following objectives:
(1) To develop a new class of simple plasmonic devices based on tailoring of propagating surface plasmons (PSPs) or cooperation between PSPs and localized plasmon resonance (LPRs) to offer significant field focusing and intensity enhancement. It can serve a wide range of applications, including high field related biomolecular sensing and detection as well as non-linear optical effects.
(2) To design low loss nanophotonic wave guides based on gain medium, which may offer real opportunity for practical nanophotonic devices. To obtain a theoretical interpretation of relationship between surface plasmon resonance and host environment where the plasmonic structure embedded. This study should provide further insight towards sensing and device design.
We have achieved the following results in this project:
(1) A novel SERS excitation source based on focusing of surface plasmons around the center hole of a metal disk for cascaded enhancement is put forward and studied theoretically. The device offers intense SERS excitation with quasi-uniformity and horizontal polarization over a comparatively large hole. As revealed by fmite-difference time-domain (FDTD) method, the intensity spectra and the characteristics of the near field for the wavelength range of 650-1 000 nm exhibit a number of enhancement modes. Electric field intensity of the optimal mode enhances the SERS signal inside the hole by over four orders. An analytical model was also developed to gain precise interpretation on FDTD results. Our model also reveals the possibility of achieving eight orders of enhancement by optimizing the scale of the disk. Our results indicate that much higher electric field enhancement in hollow metal disks (HMDs) can only be possible when we have a hole at the centre and the direction of the focusing field is parallel to the surface of the plasmonic device. This is because of the presence of an insulating gap at the center, that higher level of electric field can exist as electrons are not allowed to flow pass the gap. On the other hand, in the case of a solid metal disk, the flow of mobile electron will tend to dampen the amplitude of the arriving SPs. In addition to generation of highly optimized hot spots for SERS, the large active hole also offers potential applications in fluorescence enhancement and nonlinear spectroscopy.
In addition to HMDs, we also develop a kind of highly optimized hot spots based on diffraction coupling between LPRs via gain-assisted PSPs. Thus derived device was theoretically analyzed. The process of diffraction coupling is achieved via localization of light by LPRs, LPRs-PSPs interplay and PSPs transfer. Our study shows that by incorporating optical gain to PSPs, a very strong boost of the electromagnetic enhancement of LPRs can be expected from a lasing process. We find that with a practical gain level, the enhancement factor of local electric field intensity can be larger than 10⁷. Hence, we offer an ideal configuration to realize high-field dependent single molecule SERS and also a newly applied physical scheme for nano-Iaser.
(2) We propose a low-loss nanoscale wave guide based on gain-assisted plasmonic resonance MNP chain. We demonstrate that by employing a gain material or even an appropriate dielectric for the host environment, waveguide loss can be reduced dramatically. A highly efficient pseudo-orthonormal basis expansion (POBE) method for obtaining the complex dielectric spectra of the low-loss transmission has been developed. Eigenmode analysis revealed the physical origin of those low-loss wave guiding modes, which opens the possibility to achieve waveguiding other than using conventional dipolar resonances of individual particles. A scheme based on electron beam lithography and chemically synthesized nanoparticles has been proposed to fabricate the device. Such plasmonic waveguides may serve as building blocks for making nanoscale optical devices especially for integrated nanophotonic circuits. Meanwhile, the originally developed POBE method, which reveals the general physical mechanism of SPs, can be used to further explore optimized gain-assisted plasmonic structures to design favorable nanophotonic devices.
This thesis begins with an old problem: light focusing and guiding in macroscopic scale with traditional dielectric, and sum up finally with SPs focusing and guiding in nanoscale with gain material and plasmonic material. An outlook is presented at last with several potential schemes for the device realization.
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Zhang, Haixi.
"September 2011."
Thesis (Ph.D.)--Chinese University of Hong Kong, 2012.
Includes bibliographical references (leaves 124-139).
Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Abstract also in Chinese.
Chapter Chapter1 --- Introduction --- p.1
Chapter 1.1 --- Towards field intensity focusing and guiding of electromagnetic wave --- p.1
Chapter 1.2 --- Surface plasmons as a route to realize electromagnetic field focusing and waveguiding in nanoscale --- p.3
Chapter 1.3 --- Structure of this thesis --- p.10
Chapter Chapter2 --- Plasmonic near field engineering: structural and material aspects --- p.13
Chapter 2.1 --- Light focusing using near field oflocalized plasmon resonances --- p.13
Chapter 2.2 --- Plasmonic near field focusing through propagating surface plasmons --- p.30
Chapter 2.3 --- Various schemes for near field focusing through surface plasmons --- p.33
Chapter 2.4 --- Guiding surface plasmons in nanoscale --- p.35
Chapter 2.5 --- Gain-assisted surface plasmons: a different path to field enhancement and guiding --- p.38
Chapter Chapter3 --- Surface plasmons: characteristics and methodology --- p.42
Chapter 3.1 --- Characteristics of localized plasmon resonance --- p.42
Chapter 3.2 --- Localized plasmon resonance: Mie theory and its variations --- p.44
Chapter 3.3 --- Characteristics of propagating surface plasmons --- p.49
Chapter 3.4 --- Reflection Pole Method for studying propagating surface plasmons in multilayer structures --- p.55
Chapter 3.5 --- Pseudo-orthonormal basis expansion method: a new mathematical scheme for modeling surface plasmons --- p.58
Chapter Chapter4 --- High field generation through intensity focusing of propagating surface plasmons --- p.62
Chapter 4.1 --- Introduction --- p.62
Chapter 4.2 --- The hollow metal disk design and its characteristics --- p.64
Chapter 4.3 --- Quasi-uniform excitation source based on focusing of propagating surface plasmons for cascade enhancement of surface enhanced Raman scattering --- p.68
Chapter 4.4 --- Conclusions and outlook --- p.78
Chapter Chapter5 --- High field generation through intensity enhancement of localized plasmon resonance from gain-assisted diffraction coupling --- p.81
Chapter 5.1 --- Introduction --- p.81
Chapter 5.2 --- Diffraction excitation of localized plasmon resonance from propagating surface plasmons --- p.83
Chapter 5.3 --- Diffraction coupling of localized plasmon resonance through gain-assisted propagating surface plasmons --- p.89
Chapter Chapter6 --- Gain-assisted plasmonic waveguides based on nanoparticle chains: an effective device approach for achieving low loss in nanoscale dimensions --- p.97
Chapter 6.1 --- Introduction --- p.97
Chapter 6.2 --- Theoretical study of near-field particle interactions in active plasmon wave guides --- p.99
Chapter 6.3 --- Routing and splitting of electromagnetic energy in nanosphere plasmon waveguides --- p.103
Chapter 6.4 --- Conclusions --- p.107
Chapter Chapter7 --- Conclusions and outlook --- p.109
Appendix --- p.117
Bibliography --- p.124

Structural Health Monitoring (SHM) systems for future structures and vehicles would involve a process of damage identification and prediction of certain quantities of interest that concerns the function and safety. This process provides SHM systems the ability to not only save cost but also enhance the service life, safety and reliability of the structures and vehicles. Integrated SHM system (ISHM) is an advancement of SHM system that has additional capability of predicting the component life/failure. ISHM system development involves detailed understanding of diagnostic waves, hardware components, signal processing paradigms and intelligent use of algorithms. Diagnostic waves like the guided waves are the elastic waves that propagate in a direction defined by the material boundaries. These waves have the capability of traveling large distance probing the entire thickness in plates/shells. Thus, they are widely used by SHM systems in monitoring the plate structures. Piezoelectric transducers are often employed in the interrogation using guided waves. Most SHM systems employing guided waves are designed for specific structures. Current paradigms of SHM systems are unable to enable the transition from simple or ideal structures to realistic and complicated structures. This is due to the challenges at the fundamental level involving transducer, wave propagation and phenomena of guided wave scattering with damages to evaluate the possible solutions through mathematical modeling and signal analysis capability required by ISHM systems. This thesis aims to develop understanding of these problems at a fundamental level. Complex system level understanding is still needed which is left out as open problem. A primary requirement in designing SHM system is the proper understanding of wave characteristics such as number of modes, wavelength and dispersiveness. Although three-dimensional elasticity solution and simplified theories are available to understand them, their applicability in SHM problem requires a much more detailed look. Effort toward this direction has led to the development of simpler models. However, mathematical models are not available for understanding the wave characteristics in complex structures involving stiffeners and adhesive joints. This problem is addressed in this thesis. There is a fair amount of understanding developed regarding transducer characteristics. This is accomplished by analytical and finite element models of transducers in the past. However, simplified transducer model that are computationally fast to suit SHM system requirements needs to be developed. The development of such model is presented in this thesis. Apart from modeling the transducers and wave scattering due to damage, signal correlation and calibration are needed for practical implementation in SHM. Characterization studies reported in published literature are limited to quasi-static and low frequencies applications. However, SHM of aerospace structures employ guided waves typically in the frequency range of 100-500 kHz. Methods to characterize the transducers at this frequency range needs to be developed, which is addressed in this thesis. Another major requirement of SHM system is the design and development of sensor-actuator network and appropriate algorithm. Techniques developed earlier involving transducer arrays in this regard have limitation due to complexity of geometry and signal interpretation that needs to be addressed. The network with suitable algorithm should ideally monitor large area including the critical areas of failure with minimum number of transducers. ISHM systems further require some capability to estimate the useful life of the damaged structure in order to take suitable decisions. Efficient techniques to achieve these are not developed. Overall, there is a need to improve highly interdisciplinary areas involving mathematical modeling, transducer design, fabrication and characterization, damage detection and monitoring strategies. In this thesis, various novel techniques to combine mathematical model with experimental signals to enhance the damage detection capability are presented. In this thesis, developments in the three main aspects of SHM systems are focused upon. They are (1) development of mathematical models of sensors/actuators, wave propagation and scattering due to damage (2) characterization and calibration of transducers and (3) development of technique to monitor wide variety of damages within the scope of ultrasonic guided wave based SHM. The thesis comprises of ten chapters. First chapter is devoted to the background and motivation for the problem addressed in this thesis. In second chapter, brief overview of available mathematical models and conventional damage monitoring strategy is presented. The significant contributions reported in the subsequent chapters in this thesis are outlined below In chapter 3, a reduced-order model of guided wave propagation in thick structures with reduced-order approximation of higher-order elasto-dynamic field is formulated. The surface normal and shear tractions of the thick structure are satisfied in a closed form. The time-frequency Fourier spectral finite element is developed and is validated using detailed and computationally intensive finite element simulations. Natural frequencies obtained from the developed spectral finite element and the detailed finite element simulations are compared. Transient response due to broad frequency band and narrow frequency band excitations given in the form of surface tractions are validated by comparing with the detailed finite element simulations. Using the developed spectral finite element, wave scattering from a free edge and a notch are simulated and validated by comparing with the detailed finite element simulations. In chapter 4, two-dimensional plane wave and flexural wave scattering models for more complicated features such as stiffener with delamination and stiffener with bolt failures in a stiffened panel are derived using ultrasonic ray tracing based approach combined with wave-field representation. Dispersion relations are reformulated for the base plate where it is bolted with the stiffener. Surface conditions due to contact stiffness and contact damping are modeled by introducing springs and dampers. Scattering coefficients for the bonded and bolted stiffeners are derived. The scattering coefficients are evaluated for various different frequencies. Results are compared for different stiffener parameters. In chapter 5, a simplified analytical model of a piezoelectric actuator with uniform electrodes is modeled. The problem is to determine the launched guided wave characteristics in the structure. The analytical model is derived considering two-dimensional elasticity based approach and Airy’s stress function. The actuator model is used to specify the displacement boundary conditions in the detailed finite element model. The radiated wave patterns in a plate due to actuation from transducers of different shapes are obtained and validated with experiments. Phased array actuators are modeled in the detailed finite element model using the displacements estimated from the actuator model. The radiated wave pattern from the detailed finite element simulations are validated with experiments. Chapter 6 is devoted to the design and characterization of transducers for ultrasonic guided wave applications. The characterization techniques involve the estimation of voltage response for the induced strain by the guided wave at various different frequencies. First, a novel removable bonding technique and a calibration technique are demonstrated and related advantages are discussed. Performance of the piezoelectric thin film under quasi-static, dynamic and transient impact loadings are analyzed first. Next, a guided wave technique is developed to characterize piezoelectric thin film sensors and actuators at ultrasonic frequencies. The transducers with inter digital electrodes are characterized for frequency tuning and directional sensitivity. This characterization study enables in the selection of optimal frequency bands for interrogation. Further, the characterization of transducers with thermal degradation is presented. In chapter 7, a novel guided wave technique to calibrate the thin film sensors for ultrasonic applications is presented. Calibration procedure involves the estimation of the piezoelectric coefficient at ultrasonic range of frequencies. Calibration is done by the measurement of voltage generated across thin films when guided waves are induced on them. With the proposed technique, piezoelectric coefficient can be estimated accurately at any frequency of the propagating wave. Similarly, the measurement of piezoelectric coefficient of thin films with inter digital electrodes is presented. The estimation of piezoelectric coefficient at various different directions using laser Doppler vibrometer is presented. Lastly, the degradation of piezoelectric coefficient is studied for increasing thermal fatigue. In chapter 8, toward SHM methodology development, a guided wave based technique to detect and monitor cracks in a structure is presented. To establish the methodology, a detailed study is carried out on the effect of crack and specimen size on the guided wave propagation characteristics. Using the wave characteristics, an analytical way of modeling Lamb wave propagation in the specimen with plastic zone is proposed. The feasibility to determine plastic zone and fatigue crack propagation with integrated piezoelectric transducers is demonstrated experimentally and the results are verified analytically. A method is further established to detect damage at initial stage and crack-tip plastic zone size along with crack length for a given stress amplitude or vice-versa. An approach to estimate fatigue life from the transducer signals is also proposed. In chapter 9, a compact circular array of sensor-actuator network and an algorithm is presented to monitor large plate structures. A method based on the wavelet transforms of transducer signals is established to localize and estimate the severity of damages. Experiments are conducted to demonstrate the capability of the circular array based method in the localization and quantification of various types of damages like debonding of stiffeners, failure of bolted joints, corrosion and hole-enlargement. A damage index is then computed from wavelet time-frequency map that indicates the severity of damage. Chapter 10 ends with the concluding remarks on the work done with simultaneous discussion on the future scope. The work reported in this thesis is interdisciplinary in nature and it aims to combine the modeling and simulation techniques with realistic data in SHM to impart higher confidence levels in the prediction of damages and its prognosis. The work also aims in incorporating various mathematical models of wave propagation and ray tracing based algorithm to optimize the detection scheme employed in SHM. The future direction based on this study could be aimed at developing intelligent SHM systems with high confidence levels so that statistical machine learning would be possible to deal with complex real-world SHM problems.

Structural Health Monitoring (SHM) systems for future structures and vehicles would involve a process of damage identification and prediction of certain quantities of interest that concerns the function and safety. This process provides SHM systems the ability to not only save cost but also enhance the service life, safety and reliability of the structures and vehicles. Integrated SHM system (ISHM) is an advancement of SHM system that has additional capability of predicting the component life/failure. ISHM system development involves detailed understanding of diagnostic waves, hardware components, signal processing paradigms and intelligent use of algorithms. Diagnostic waves like the guided waves are the elastic waves that propagate in a direction defined by the material boundaries. These waves have the capability of traveling large distance probing the entire thickness in plates/shells. Thus, they are widely used by SHM systems in monitoring the plate structures. Piezoelectric transducers are often employed in the interrogation using guided waves. Most SHM systems employing guided waves are designed for specific structures. Current paradigms of SHM systems are unable to enable the transition from simple or ideal structures to realistic and complicated structures. This is due to the challenges at the fundamental level involving transducer, wave propagation and phenomena of guided wave scattering with damages to evaluate the possible solutions through mathematical modeling and signal analysis capability required by ISHM systems. This thesis aims to develop understanding of these problems at a fundamental level. Complex system level understanding is still needed which is left out as open problem. A primary requirement in designing SHM system is the proper understanding of wave characteristics such as number of modes, wavelength and dispersiveness. Although three-dimensional elasticity solution and simplified theories are available to understand them, their applicability in SHM problem requires a much more detailed look. Effort toward this direction has led to the development of simpler models. However, mathematical models are not available for understanding the wave characteristics in complex structures involving stiffeners and adhesive joints. This problem is addressed in this thesis. There is a fair amount of understanding developed regarding transducer characteristics. This is accomplished by analytical and finite element models of transducers in the past. However, simplified transducer model that are computationally fast to suit SHM system requirements needs to be developed. The development of such model is presented in this thesis. Apart from modeling the transducers and wave scattering due to damage, signal correlation and calibration are needed for practical implementation in SHM. Characterization studies reported in published literature are limited to quasi-static and low frequencies applications. However, SHM of aerospace structures employ guided waves typically in the frequency range of 100-500 kHz. Methods to characterize the transducers at this frequency range needs to be developed, which is addressed in this thesis. Another major requirement of SHM system is the design and development of sensor-actuator network and appropriate algorithm. Techniques developed earlier involving transducer arrays in this regard have limitation due to complexity of geometry and signal interpretation that needs to be addressed. The network with suitable algorithm should ideally monitor large area including the critical areas of failure with minimum number of transducers. ISHM systems further require some capability to estimate the useful life of the damaged structure in order to take suitable decisions. Efficient techniques to achieve these are not developed. Overall, there is a need to improve highly interdisciplinary areas involving mathematical modeling, transducer design, fabrication and characterization, damage detection and monitoring strategies. In this thesis, various novel techniques to combine mathematical model with experimental signals to enhance the damage detection capability are presented. In this thesis, developments in the three main aspects of SHM systems are focused upon. They are (1) development of mathematical models of sensors/actuators, wave propagation and scattering due to damage (2) characterization and calibration of transducers and (3) development of technique to monitor wide variety of damages within the scope of ultrasonic guided wave based SHM. The thesis comprises of ten chapters. First chapter is devoted to the background and motivation for the problem addressed in this thesis. In second chapter, brief overview of available mathematical models and conventional damage monitoring strategy is presented. The significant contributions reported in the subsequent chapters in this thesis are outlined below In chapter 3, a reduced-order model of guided wave propagation in thick structures with reduced-order approximation of higher-order elasto-dynamic field is formulated. The surface normal and shear tractions of the thick structure are satisfied in a closed form. The time-frequency Fourier spectral finite element is developed and is validated using detailed and computationally intensive finite element simulations. Natural frequencies obtained from the developed spectral finite element and the detailed finite element simulations are compared. Transient response due to broad frequency band and narrow frequency band excitations given in the form of surface tractions are validated by comparing with the detailed finite element simulations. Using the developed spectral finite element, wave scattering from a free edge and a notch are simulated and validated by comparing with the detailed finite element simulations. In chapter 4, two-dimensional plane wave and flexural wave scattering models for more complicated features such as stiffener with delamination and stiffener with bolt failures in a stiffened panel are derived using ultrasonic ray tracing based approach combined with wave-field representation. Dispersion relations are reformulated for the base plate where it is bolted with the stiffener. Surface conditions due to contact stiffness and contact damping are modeled by introducing springs and dampers. Scattering coefficients for the bonded and bolted stiffeners are derived. The scattering coefficients are evaluated for various different frequencies. Results are compared for different stiffener parameters. In chapter 5, a simplified analytical model of a piezoelectric actuator with uniform electrodes is modeled. The problem is to determine the launched guided wave characteristics in the structure. The analytical model is derived considering two-dimensional elasticity based approach and Airy’s stress function. The actuator model is used to specify the displacement boundary conditions in the detailed finite element model. The radiated wave patterns in a plate due to actuation from transducers of different shapes are obtained and validated with experiments. Phased array actuators are modeled in the detailed finite element model using the displacements estimated from the actuator model. The radiated wave pattern from the detailed finite element simulations are validated with experiments. Chapter 6 is devoted to the design and characterization of transducers for ultrasonic guided wave applications. The characterization techniques involve the estimation of voltage response for the induced strain by the guided wave at various different frequencies. First, a novel removable bonding technique and a calibration technique are demonstrated and related advantages are discussed. Performance of the piezoelectric thin film under quasi-static, dynamic and transient impact loadings are analyzed first. Next, a guided wave technique is developed to characterize piezoelectric thin film sensors and actuators at ultrasonic frequencies. The transducers with inter digital electrodes are characterized for frequency tuning and directional sensitivity. This characterization study enables in the selection of optimal frequency bands for interrogation. Further, the characterization of transducers with thermal degradation is presented. In chapter 7, a novel guided wave technique to calibrate the thin film sensors for ultrasonic applications is presented. Calibration procedure involves the estimation of the piezoelectric coefficient at ultrasonic range of frequencies. Calibration is done by the measurement of voltage generated across thin films when guided waves are induced on them. With the proposed technique, piezoelectric coefficient can be estimated accurately at any frequency of the propagating wave. Similarly, the measurement of piezoelectric coefficient of thin films with inter digital electrodes is presented. The estimation of piezoelectric coefficient at various different directions using laser Doppler vibrometer is presented. Lastly, the degradation of piezoelectric coefficient is studied for increasing thermal fatigue. In chapter 8, toward SHM methodology development, a guided wave based technique to detect and monitor cracks in a structure is presented. To establish the methodology, a detailed study is carried out on the effect of crack and specimen size on the guided wave propagation characteristics. Using the wave characteristics, an analytical way of modeling Lamb wave propagation in the specimen with plastic zone is proposed. The feasibility to determine plastic zone and fatigue crack propagation with integrated piezoelectric transducers is demonstrated experimentally and the results are verified analytically. A method is further established to detect damage at initial stage and crack-tip plastic zone size along with crack length for a given stress amplitude or vice-versa. An approach to estimate fatigue life from the transducer signals is also proposed. In chapter 9, a compact circular array of sensor-actuator network and an algorithm is presented to monitor large plate structures. A method based on the wavelet transforms of transducer signals is established to localize and estimate the severity of damages. Experiments are conducted to demonstrate the capability of the circular array based method in the localization and quantification of various types of damages like debonding of stiffeners, failure of bolted joints, corrosion and hole-enlargement. A damage index is then computed from wavelet time-frequency map that indicates the severity of damage. Chapter 10 ends with the concluding remarks on the work done with simultaneous discussion on the future scope. The work reported in this thesis is interdisciplinary in nature and it aims to combine the modeling and simulation techniques with realistic data in SHM to impart higher confidence levels in the prediction of damages and its prognosis. The work also aims in incorporating various mathematical models of wave propagation and ray tracing based algorithm to optimize the detection scheme employed in SHM. The future direction based on this study could be aimed at developing intelligent SHM systems with high confidence levels so that statistical machine learning would be possible to deal with complex real-world SHM problems.

碩士
國立臺灣大學
光電工程學研究所
91
In recent years the finite-difference time-domain (FDTD) method has been extensively used for electromagnetic field simulation. The FDTD method seeks the direct solution to the Maxwell's time-dependent curl equations numerically. The FDTD method first discretizes the problem in space and time into rectangular cells and intervals, respectively, and then solves the time variation of the field components at each grid point. The FDTD method has many advantages compared to other methods. It is directly used to solve Maxwell's equations and does not need the derivation of Green's functions nor require solving a large number of linear equations. The FDTD method was introduced by Yee [1966]. Yee's method implemented the spatial derivatives of the curl operators using finite differences in Cartesian space meshes for the electric and magnetic fields. Yee's method was ignored for a long time because it requires large computer storage and long CPU time to be implemented, which was not available at that time. One way to reduce the required memory is to lower the dimensions of the problem, such as considering the two-dimensional (2-D) problem instead of the full 3-D one. Nowadays, the 2-D version of the method is indispensable in optoelectronics for the analysis of problems involving reflected waves and for study of the performance of devices with elaborate structures. Although the actual optical integrated circuits have 3-D structures, most of the existing theoretical studies replace the structures by the corresponding 2-D ones by using the effective-index method. For the emerging demand for the information-carrying capacity and the class of micrometer- and nanometer-scale integrated optical devices, FDTD modeling has the potential to play a useful role in practical design of such devices. Recent advances in nanofabrication techniques permit optical devices with physical dimensions on the order of the optical wavelength to be components in high-density photonic integrated circuits. Strongly guided waves in high index-contrast structures allow the design of complex waveguide intersections within a small area. In order to obtain an optimal packaging and reduction of the area occupied by waveguides on a substrate, waveguides must be bent to accommodate practical structures in integrated optical circuits. To form power diveders and combiners, single-mode T-junctions are basic elements. Because radiation losses of the simple 90-bend and T-junction are excessive, simple structures are not proper elements in fabricating optical circuits. It needs some modification or speccific structure applied at the waveguide discontinuity. Manolatou et al. [1999] proposed several modified 90-bend waveguides and modified T-junctions with resonator cavities in order to increase the transmittance performance, and near 100% transmission has been achieved in the simulation. Complicated optical signal processing and switching functions require waveguide crossings with negligible crosstalk. Manolatou et al. [1999] also designed three modified structures with cavities applied to the simple waveguide crossing. In this thesis the structures designed by Manolatou et al. [1999] are analyzed with emphasis on suitable arrangement of the numerical scheme to maintain second order covnergence trend such that numerical results can be trusted.

博士
大同工學院
電機工程學系
85
There have been gradually increasing requirements in transmission capacity for the data and network communications, accompanied with the gradually matured technologies relevant to the light-wave communication in recent years, so that the fiber- optic communication has become one of the most popular communication technologies nowadays. Of today''s light-wave communication systems, optical active devices are still under maturity; hence, it is desired to investigate new material or new technology, or combination of both, in order to promote the performance of the whole system. Due to the fact that liquid crystal (LC) is possessed of a number of advantages, such as large birefringence, large electro-optic effect, and ease to fabricate, accompanied with the highly developed liquid crystal display (LCD) technology, it offers us a new research field for application in guided-wave and Fabry-Perot-etalon based light- wave devices. In this dissertation, we made best use of LC to build various kinds of the crucial components for optic communications as follows, which were analyzed, designed, fabricated, measured, and discussed. First of all, we fabricated a prototype of LC waveguide switch (LC-WS), which consists of an LC cell as the active overcladding and a polymer film as the waveguide layer. Its advantages include ease to fabricate and a low driving voltage (< 5 volts); while the measured extinction ratio (about 3 dB) is quite low and should be further improved. Secondly, a novel integrated-optic polarization splitter using nematic LC as the coupling layer was proposed, based on the vertical type of directional coupler. The idea of the device is originated from the operational analysis of LC-WS. The beam propagation method (BPM) was used to investigate the propagating behaviors of the device. An LC polarization splitter with an ultrashort device length of 140 (m is achieved at a high extinction ratio of 28 dB. With respect to the tunable wavelength-selective filter, an LC cell was used to construct the cavity of a Fabry-Perot interferometer (FPI). We proposed the "equivalent refractive index" model to analyze the electro- optic characteristics; moreover, a novel measurement method was proposed, based on this model. Only a usual set of a monochromatic light source and an optical power meter are needed. Besides, we successfully fabricated an electronically tunable LC-FPI filter with free spectral range of 9 nm, bandwidth of 1.2 nm, and finesse of 7.

By means of numerical simulations, the thesis aims at improvements in the understanding of light propagation in dielectric optical waveguides, with emphasis on nonreciprocal integrated magnetooptic devices. The results include: Proposal, implementation, and assessment of the WMM mode solver (Wave Matching Method) For waveguides with piecewise constant, rectangular permittivity profiles, the calculation of guided modes can be based on a local expansion into factorizing harmonic or exponential trial functions. A least squares expression for the mismatch in the continuity conditions at dielectric boundaries connects the fields on neighbouring regions. Minimization of this error allows to compute propagation constants and mode fields. The procedure has been implemented both for semivectorial and fully vectorial mode analysis. The piecewise defined trial fields are well suited to deal with field discontinuities or discontinuous derivatives. Numerical assessment shows excellent agreement with accepted previous results from other methods. The WMM turns out to be effective especially for structures described by only a few rectangles. It yields semianalytical mode field representations which are not restricted to a computational window. The fields are therefore perfectly suited for further processing, e.g. in the framework of various kinds of perturbation theory. Perturbational geometry tolerancing procedure Shifting the location of a dielectric boundary in the cross section of a waveguide with piecewise constant refractive index profile results in a permittivity perturbation in a layer along the discontinuity line. On the basis of these thin layer perturbations, perturbational expressions for the derivatives of the propagation constants with respect to geometry parameters are discussed. The approach provides direct access to wavelength dependences. Comparison with rigorously calculated data shows that the accuracy is sufficient to yield reasonable tolerance estimates for realistic integrated optical devices, at almost no extra computational cost. This perturbational approach allows to establish and to quantify guidelines for geometry tolerant devices. Numerical assessment of nonreciprocal wave propagation The coefficients of coupled mode theory for the magnetooptic permittivity contribution allow a classification of the influences of gyrotropy on guided wave propagation. For mirror symmetric waveguides, one identifies the dominant effects of TE phase shift, TM phase shift, and TE/TM polarization conversion, for polar, equatorial, and longitudinal magnetooptic configurations, respectively. Layered equatorial magnetooptic profiles lead to the well known phase shifters for TM modes. Analogously, sliced asymmetric polar magnetooptic profiles yield phase shifts for TE polarized modes. Simulations of rib waveguides with a magnetooptic domain lattice predict effects of the same order of magnitude as the phase shift for TM modes. Phase matching as a condition for complete polarization conversion in longitudinally magnetized waveguides can be realized with selected geometries of raised strip waveguides or embedded square waveguides. Based on coupled mode theory for hybrid fundamental modes, the analysis of the performance of such devices in an isolator setting includes birefringence, optical absorption, and an explicit perturbational evaluation of fabrication tolerances. A magnetooptic waveguide which is magnetized at a tilted angle may perform as a unidirectional polarization converter. The term specifies a device that converts TE to TM light for one direction of propagation, while it maintains the polarization for the opposite direction. A double layer setup with two magnetooptic films of opposite Faraday rotation is proposed and simulated. Designs of three waveguide couplers for applications as isolators/circulators and polarization splitters Three-guide couplers with multimode central waveguides allow for a remote coupling between the outer waveguides. While the power transfer is a truly multimode interference process, one can identify two different regimes where either two or three supermodes dominate the coupling behaviour. Numerical simulations show reasonable agreement between the main coupling features in planar an three dimensional devices. The specific form of the relevant modes suggests the design of integrated optical isolators and circulators. Both planar and three dimensional concepts are investigated. A radiatively coupled waveguide polarization splitter should be designed such that the entire dynamic range of the coupling length variations is exploited. This is easily possible with a three dimensional raised strip configuration. Combination of two magnetooptic unidirectional polarization converters and two radiatively coupled waveguide based polarization splitters leads to a concept for a polarization independent integrated four port circulator device. The simulation predicts a total length of about three millimeters.

by Loi Kwok Kwong.
Thesis (M.Phil.)--Chinese University of Hong Kong, 1992.
Includes bibliographical references (leaves 197-222).
Chapter Chapter 1 --- Introduction --- p.1
Chapter 1.1 --- An Overview of Integrated Optics --- p.1
Chapter 1.2 --- Application of Lithium Niobate Integrated Optical Circuit --- p.4
Chapter 1.3 --- Summary --- p.5
Chapter Chapter 2 --- Optical Waveguide Theory --- p.7
Chapter 2.1 --- Introduction --- p.7
Chapter 2.2 --- Ray Optics Treatment of Planar Waveguide --- p.7
Chapter 2.2.1 --- Step-index Waveguide --- p.8
Chapter 2.2.2 --- Graded-index Waveguide --- p.13
Chapter 2.3 --- Optical Channel Waveguide --- p.20
Chapter 2.3.1 --- Marcatili's Method --- p.22
Chapter 2.3.2 --- Effective Index Method --- p.26
Chapter 2.4 --- Summary --- p.30
Chapter Chapter 3 --- Waveguide Fabrication Technology --- p.32
Chapter 3.1 --- Properties of Substrate Materials --- p.32
Chapter 3.1.1 --- Glass --- p.32
Chapter 3.1.2 --- Semiconductor --- p.34
Chapter 3.1.3 --- Ferroelectric Material --- p.35
Chapter 3.2 --- Waveguide Fabrication Techniques --- p.40
Chapter 3.2.1 --- Ion Implantation --- p.40
Chapter 3.2.2 --- Titanium Indiffusion --- p.41
Chapter 3.2.3 --- Proton Exchange --- p.44
Chapter 3.3 --- Summary --- p.48
Chapter Chapter 4 --- Fabrication and Measurement of Optical Waveguides --- p.49
Chapter 4.1 --- Fabrication of Optical Waveguides --- p.49
Chapter 4.1.1 --- Planar Waveguides --- p.49
Chapter 4.1.1.1 --- Substrate Cutting --- p.49
Chapter 4.1.1.2 --- Substrate Cleaning --- p.49
Chapter 4.1.1.3 --- Proton Exchange --- p.50
Chapter 4.1.1.4 --- Post-exchange Annealing --- p.51
Chapter 4.1.2 --- Channel Waveguides --- p.51
Chapter 4.1.2.1 --- Patterning Technique: Photolithography and Lift-off --- p.51
Chapter 4.1.2.2 --- Proton Exchange and Annealing --- p.56
Chapter 4.1.2.3 --- Lapping and Polishing --- p.56
Chapter 4.2 --- Measurement of Waveguide Parameters --- p.57
Chapter 4.2.1 --- Coupling of Light into Optical Waveguide --- p.57
Chapter 4.2.1.1 --- Prism Coupling --- p.58
Chapter 4.2.1.2 --- End-fire Coupling --- p.60
Chapter 4.2.2 --- Effective Index --- p.63
Chapter 4.2.3 --- Refractive Index Profile --- p.63
Chapter 4.2.4 --- Waveguide Depth --- p.67
Chapter 4.2.5 --- Propagation Loss --- p.67
Chapter 4.2.6 --- Near-field Intensity Profile --- p.69
Chapter 4.3 --- Summary --- p.74
Chapter Chapter 5 --- Results and Discussions --- p.75
Chapter 5.1 --- Proton-exchanged Waveguides Using Phosphoric Acid --- p.75
Chapter 5.2 --- Proton-exchanged LiNb03 Waveguides Using Toluic Acid --- p.112
Chapter 5.3 --- Proton-exchanged LiNb03 Waveguides Using Stearic Acid --- p.127
Chapter 5.4 --- Proton-exchanged LiNb03 Waveguides Using Cinnamic Acid --- p.148
Chapter 5.5 --- Structural Characteristics of Proton-exchanged Waveguides --- p.174
Chapter 5.5.1 --- Thermogravimetric Analysis --- p.174
Chapter 5.5.2 --- Raman Spectroscopy --- p.174
Chapter 5.5.3 --- Infrared Spectrometry --- p.179
Chapter 5.5.4 --- Double Crystal X-ray Diffractometry --- p.185
Chapter 5.6 --- Summary --- p.190
Chapter Chapter 6 --- Conclusions --- p.192
References --- p.197
Chapter Appendix 1 --- Error Estimations --- p.219
Chapter Appendix 2 --- List of Publications --- p.221

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

Integrated photonics is the field of shrinking and simplifying the fabrication of devices that guide and manipulate light. It not only offers to greatly lower the size and cost of systems used in optical communications it also offers a platform on which new physical phenomenon can be explored by being able to fabricate and manipulate structures on the scale of the wavelength of light. One such platform in integrated photonics is that of two-dimensional slab photonic crystals. These structures exhibit a photonic band-gap, a band of optical frequencies that are prohibited from propagating within the medium, that can be used to guide and confine light. When used to create photonic crystal waveguides these waveguides exhibit unique dispersion properties that demonstrate very low optical group velocities, so called "slow-light". This dissertation begins with the practical realization of design and fabrication of such waveguides using the silicon-on-insulator material system using conventional deep-UV photolithography fabrication techniques. It will detail and demonstrate the effect physical dimensions have on the optical transmission of these devices as well as their optical dispersion. These photonic crystal waveguides will then be used to demonstrate the enhancement of nonlinear optical phenomenon due to the slow-light phenomenon they exhibit. First spontaneous Raman scattering will be theoretically demonstrated to be enhanced by slow-light and then experimentally shown to be enhanced in a practical realization. The process of four-wave mixing will be demonstrated to be enhanced in these devices and be shown to be greatly affected by the unique optical dispersion within these structures. Additionally, we will examine the dispersion that exists in silicon nitride microring resonators and the effect it has on the use of these devices to generate optical frequency combs. This is done by leveraging the dispersion measurement methods used to characterize photonic crystal waveguides. We conclude this work by examining the avenues of future work that can be explored in the area of photonic crystal waveguides.

Zhang Ailing.
"September 2004."
Thesis (Ph.D.)--Chinese University of Hong Kong, 2004.
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.