Dissertations / Theses on the topic 'LEAKY WAVEGUIDE'

Film display holograms typically diffract light over a wide enough view-angle to be viewed, directly, without intervening optics. However, all holographic video displays must use optics beyond the hologram surface to overcome the challenges of small display extent and low diffraction angle by using some form of demagnification and derotation. We report a leaky mode waveguide spatial light modulator (SLM) with sufficiently high angular diffraction to obviate the need for demagnification in scanned aperture systems. This was achieved by performing a number of experiments to determine the depth of the annealed, proton-exchanged waveguide which corresponded to a maximized diffracted angle. Diffraction sweeps were recorded in excess of 19.5° for 632.8 nm light which is above the 15° required for direct view display. Moreover, we present a paired set of waveguide SLMs capable of a maximum light deflection nearing 28° for red. This deflection, which is several times larger than the angular sweep of current, state-of-the-art modulators, is made possible by the unilateral, near-collinear waveguide nature of the leaky mode interaction. The ability to double angular output in this way, which is either not possible or not practical in other SLMs, is possible in leaky mode devices, thanks to the absence of zero-order light and the lack of high-order outputs. This combined structure has angular deflection high enough to enable color holographic video monitors that do not require angular magnification. Furthermore, the low cost and high angular deflection of these devices may make it possible to make large arrays for flat-screen video holography. One improvement that could be made to the current setup would be to increase the device's diffraction efficiency. One highly influential factor of diffraction efficiency for a Bragg-regime surface acoustic wave (SAW) grating is the length of the interaction between the light and the grating. In this work, we have shown that guided light in a reverse proton exchanged (RPE) waveguide experiences less loss. This enables us to create longer devices which eventually results in devices with higher diffraction efficiency. We have also researched on LCoS SLMs and used them for two different applications: (a) photophoretic-trap volumetric displays and (b) holographic video displays. In the first case, aberrations including spherical, astigmatism, and coma can make particles to trap tighter in the focal point of the beam. Also, a new approach for holographic computations is presented which uses the electromagnetic nature of light in Maxwell Equations to find a unique phase map for every specific 3D object in space.

This thesis describes the development of antennas suitable for mobile coinmunication systems based on a dielectric rod antenna fed from circular waveguide. Pattern control of the antenna is implemented using a combination of Frequency Selective Surface (FSS) elements and metallic endcaps placed on the antenna Both linear and circular polarised feeds have been made for these antennas to ensure they are suitable for a wide range of applications. The suitability of the dominant and next, higher order, waveguide mode were investigated and conclusions drawn as to their suitability for this type of antenna. The antennas were extensively modelled using a commercial TLM based solver and the results of these simulations were compared to the comprehensive set of antenna pattern measurements and S-parameter measurements obtained for the prototype antennas.

In dieser Arbeit wird der Einsatz von Leckwellenleiter (engl. Leaky Coaxial Cable, LCX) zur funkgestützten Indoor-Positionierung in Fahrgastzellen untersucht. Mit Hilfe eines erstellten Vorgehensmodells werden zwei unterschiedliche LCX-Prototypen speziell für den Ortungseinsatz entwickelt. Hierbei wird die elektromagnetische Feldberechnung verwendet, um sowohl Leckwellenleiterstrukturen als auch deren Einsatz in einer Fahrgastzelle zu bewerten. Nach Fertigung beider Leckwellenleiter erfolgt eine messtechnische Validierung in einer vordefinierten Fahrgastzellenumgebung. Der Einsatz dieser Prototypen zur Indoor-Positionierung wird sowohl in Modell- als auch in realen Fahrzeugumgebungen, wie der AutoTram Extra Grand des Fraunhofer IVI, durchgeführt. Eine statistische Betrachtung von Messergebnissen sowie die Vorstellung eines zonenselektiven Positionierungsansatzes schließen diese Arbeit.

本論文では，遮断周波数以下のTE・TMモードを利用した右手/左手系複合円筒導波管および方形導波管を提案する．この提案したCRLH導波管にスリットまたはスロットを設けることで構成された導波管型漏洩波アンテナの放射特性について述べている．最後に，CRLH導波管を試作し解析結果と実験結果の比較を行うことで，CRLH方形・円筒導波管の構成法の有用性を明らかにする．<br>This paper proposes a composite right/left-handed cylindrical and rectangular waveguides using the cutoff TE and TM modes. The CRLH waveguides can be successfully applied to radiation characteristics of leaky-wave antenna by setting slits or slots. Finally, usefulness of the proposed CRLH waveguides is verified by comparison between the calculated and the measured values.<br>博士(工学)<br>Doctor of Philosophy in Engineering<br>同志社大学<br>Doshisha University

De nombreux éléments de structures de génie civil sont élancés et partiellement enfouis dans un milieu solide. Les ondes guidées sont souvent utilisées pour le contrôle non destructif (CND) de ces éléments. Ces derniers sont alors considérés comme des guides d’ondes ouverts, dans lesquels la plupart des ondes sont atténuées par des fuites dans le milieu environnant. D’autre part le problème est non borné, ce qui le rend difficile à appréhender sur le plan numérique. La combinaison d’une approche par éléments finis semi-analytique (SAFE) et de la méthode des couches parfaitement adaptées (PML) a été utilisée dans une thèse antérieure pour calculer numériquement trois types de modes (modes piégés, modes à fuite et modes de PML). Seuls les modes piégés et à fuite sont utilisés pour la représentation des courbes de dispersion. Les modes de PML sont non intrinsèques à la physique. L’objectif premier de cette thèse est d’obtenir, par superposition modale sur les modes calculés, les champs émis et diffracté dans les guides d’ondes ouverts. Nous montrons dans un premier temps que les trois types de modes appartiennent à la base modale. Une relation d’orthogonalité est obtenue dans la section du guide(incluant la PML) pour garantir l’unicité des solutions. La réponse forcée du guide peut alors être calculée rapidement par une somme sur les modes en tout point du guide. Des superpositions modales sont également utilisées pour construire des frontières transparentes au bord d’un petit domaine élément fini incluant un défaut, permettant ainsi de calculer le champ diffracté. Au cours de ces travaux, nous étudions les conditions d’approximation des solutions par des superpositions modales, limitées seulement aux modes à fuite, ce qui permet de réduire le coût des calculs. De plus, la généralité des méthodes proposées est démontrée par des calculs hautes fréquences (intéressantes pour le CND) et sur des guides tridimensionnels. Le deuxième objectif de cette thèse est de proposer une méthode d’imagerie pour la localisation de défauts. La méthode de l’imagerie topologique est appliquée aux guides d’ondes. Le cadre théorique général, de type optimisation sous contrainte, est rappelé. Le formalisme modal permet un calcul rapide de l’image. Nous l’appliquons pour simuler un guide d’onde endommagé, et nous montrons l’influence du type de champ émis (monomodal, dispersif,multimodal) ainsi que des configurations de mesure sur la qualité de l’image obtenue<br>Various elements of civil engineering structures are elongated and partially embedded in a solid medium. Guided waves can be used for the nondestructive evaluation (NDE) of such elements. The latteris therefore considered as an open waveguide, in which most of waves are attenuated by leakage losses into the surrounding medium. Furthermore, the problem is difficult to solve numerically because of its unboundedness. In aprevious thesis, it has been shown that the semi-analytical finite-element method (SAFE) and perfectly matched layers(PML) can be coupled for the numerical computation of modes. It yields three types of modes: trapped modes,leaky modes and PML modes. Only trapped and leaky modes are useful for the post-processing of dispersion curves. PML modes are non-intrinsic to the physics. The major aim of this thesis is to obtain the propagated and diffracted fields, based on modal superpositions on the numerical modes. First, we show that the three types of modes belong to the modal basis. To guarantee the uniqueness of the solutions an orthogonality relationship is derived on the section including the PML. The forced response can then be obtained very efficiently with a modal expansion at any point of the waveguide. Modal expansions are also used to build transparent boundaries at the cross-sections of a small finite-element domain enclosing a defect, thereby yielding the diffracted field. Throughout this work, we study whether solutions can be obtained with modal expansions on leaky modes only, which enables to reduce the computational cost. Besides, solutions are obtained at high frequencies (which are of interest for NDE) and in tridimensional waveguides, which demonstrates the generality of the methods. The second objective of this thesis is to propose an imaging method to locate defects. The topological imaging method is applied to a waveguide configuration. The general theoretical framework is recalled, based on constrained optimization theory. The image can be quickly computed thanks to the modal formalism. The case of a damaged waveguide is then simulated to assess the influence on image quality of the emitted field characteristics (monomodal, dispersive or multimodal)and of the measurement configuration

碩士<br>國立交通大學<br>電信工程研究所<br>104<br>Conductor-backed coplanar waveguide (CBCPW) propagates electromagnetic waves via dominant modes (coplanar waveguide mode), and excites leaky wave which propagates toward both sides despite the value of the frequency. In general, there are two applications based on this structure: first is to use such property to design the antenna; the other is to suppress the leaky wave through some methods in order to decrease the unnecessary couplings and crosstalk. Implementing the full wave analysis (Spectral Domain Approach) on the CBCPW structure, we can discover that the leaky wave propagates along a particular angle relative to the main CPW line, causing the wave to propagate as if in a parallel plate waveguide (PPW). Therefore, we can etch rectangular slots along the ground planes with the angle we have acquired. If the length of the slot is significantly longer than the width and approximately equals to half the guided wavelength, the slots fed by CBCPW will radiate power efficiently .We can thus obtain a centralized broadside radiation pattern and a dual-polarization antenna.

We propose a leaky channel waveguide for large-mode-area extended single-mode operation. The proposed structure is characterized by specially designed guiding core and multilayer cladding. Specially designed cladding enables all the supported modes except fundamental modes leaky. Leakage loss of the higher-order mode which is key factor of single-mode operation is calculated by solving the profile by effective index method in conjunction with transfer matrix method. Dispersive cladding of the proposed design makes this design enable to show extended single mode operation in the entire wavelength range beyond 900 nm with a mode area as large as 100μm2. Such a large confinement area for mode propagation can effectively suppress non linear optical effects. The waveguide is expected to find application in the design of high power lasers and amplifiers.

Integrated-optic waveguide lasers have drawn considerable attention for their compactness and possibility of device integration. A lot of interest has been shown to increase the mode area of waveguide for applications in optical communication and high-power laser and amplifier. For waveguide laser and amplifier applications, it is preferable to use a waveguide that supports only one mode to avoid instability arising from intermodal dispersion and mode competition. A conventional single-mode waveguide has a small guiding core. The tight light confinement in such a waveguide can reduce the optical damage threshold of the waveguide and at the same time, give rise to significant nonlinear optical effects, which limit ultimately the power handling capability of the waveguide. A preferred structure for high-power applications should be one that has a large core and yet supports only a single mode. Here a novel cladding design in which the refractive index is uniform but the geometry is so designed that all the modes are leaky. Such a geometrically shaped cladding is highly dispersive and can also lead to singlemode operation over an extended range of wavelengths. Using properly chosen parameters, the waveguide can exhibit single-mode operation in the wavelength range 900–1600nm with a large core area.

In urban rail transit, systems using communication based train control (CBTC), it uses high accuracy of train locating, realizes a continuous automatic train control system. High resolution of locating the train permits the high line capacity and fewer Infrastructures is required than Track circuit based system therefore all over the world countries have more concerned about this technology. DCS system plays an important role in the information interaction between ground equipment and vehicle equipment in CBTC. DCS is WLAN which is short range radio networks based on IEEE 802.11, complete communication network is built with many closely deployed AP (Access Point). IEEE 802.11b is a physical layer amendment for operation in the 2.4 GHz band, adopted in CBTC system in which data transmits at 11Mbps and uses DSSS modulation. Data communications systems based in the 2.4 GHz ISM band has raised the concern of RF interference between CBTC equipped trains and the variety of new and existing users of this band. The reliability and safety of information transmission can be improved when leaky waveguide is used as transmission medium of train-ground wireless communication in CBTC (Communication Based Train Control), also it can provide better performance and stronger anti-interference ability than free space. These benefits of leaky waveguide insisting the research scholar of communication field to intervene in CBTC system. Wireless LAN technologies are adopted in most train wayside communication systems in CBTC. Successful handoff plays an indispensable role in wireless communications. Running through the large wireless networks with numerous APs in urban mass transit, a train equipped with CBTC systems inevitably encounters the problems of handoff. Against the possibly negative phenomena such as Ping-Pong effect, handoff delay, packet loss and so on. Frequency Combination and Location based Handover scheme are analysed, both handover scheme are also correlated with Leaky waveguide based CBTC system. After analysis, it is realized that Location Based Handover Scheme is best suited for Leaky waveguide based CBTC system in many aspects. Leaky waveguide also limits the implementation of various handover schemes.

博士<br>國立交通大學<br>電信工程系所<br>93<br>In this dissertation, we presented a beam adjustable antenna made up of a slitted waveguide and a dielectric slab. In order to steer the radiation main-beam angle, we changed the phase constant of the waveguide mode by inserting a dielectric slab to perturb its field distribution. The direction of radiation main-beam can be steered by dynamically changing the position of the dielectric slab. In the theoretical analysis, the dispersion relation including the phase and attenuation constants, were determined by solving the transverse resonance equation. An agreement between the theoretical and experimental radiation pattern verifies the beam-steering mechanism. Up to 23o beam-steering angle can be achieved using this approach.

碩士<br>國立交通大學<br>電信工程研究所<br>99<br>This thesis gives a study on two techniques to suppress the side lobes and enhance the gain of a half mode substrate integrated waveguide leak wave antenna, respectively. In this thesis, we are aware of two phenomenon that may spoil the performance of a leaky wave antenna: 1. Due to the traveling wave nature of the leaky wave antennas, the remaining power at the end of the leaky wave antenna should always be carefully guided and terminated or the reflected wave will be excited with the corresponding back lobes that may spoil the radiation pattern. 2. Even if one can guide the wave in the leaky wave antenna to avoid reflections, an ideal leaky wave line source may still introduce side lobes due to the effect of the finite uniform illumination of the aperture antennas. We would here give a study on two methods accompanied with a proposed transition dedicated for a half mode substrate integrate waveguide leaky wave antenna to handle the problems mentioned above. First, a transition to efficiently convert the input power to construct the leaky mode of the leaky wave antenna is proposed to enhance the efficiency of the leaky wave antenna and avoid possible reflections at the terminal of the leaky wave antenna. This transition can be considered as a stepping stone to facilitate the later analysis and design of the leaky wave antenna. Secondly, a cosine-shaped tapering profile is proposed to taper the waveguide width of the half mode substrate integrated waveguide. Since one can thus shape the aperture field of the leaky wave antenna to satisfy the Taylor’s rules, the side lobes of the radiation pattern can having a better chance to be suppressed. Finally, a feed-back network is proposed to guide the non-radiated power back to the feed of the leaky wave antenna. The gain is expected to be enhanced with the aid of the non-radiated power. These two methods accompanied with the proposed transition can improve the performance of the leaky wave antenna at an arbitrary frequency range easily and thus has great potential in many applications.

碩士<br>國立臺灣大學<br>電信工程學研究所<br>102<br>This thesis is divided into two parts, the first part is a design of CRLH dual band leaky wave antenna by substrate integrated waveguide (SIW). Energy is radiated from the top slots of the SIW. By adding transmission line differs from SIW structure on both sides of SIW, the dual band design can be more flexible and the size of antenna can be reduced. VIAs are added near the slot for adjusting the operating frequency. Dual slots on the top of SIW for enhancing the gain of antenna is also proposed in this thesis. Design theory, antenna structure, simulation and measurement verification of these three antennas, are discussed in the second and the third chapter in the thesis. The second part is the verification of embedded end-fire antenna in LTCC for V-band. Two different type of antenna, monopole and slot, are proposed. Considering the variation in the manufacturing process, the impact of different design parameters on the reflection coefficient and the isolation are analyzed. The comparison of simulation and measurement result are discussed in the fourth and fifth chapter.

博士<br>國立中山大學<br>光電工程研究所<br>93<br>We have developed a rigorous leaky-mode analysis on the antiresonant reflecting optical waveguides (ARROW’s) using a so-called “coupled electric (CE) coupled magnetic (CH) field method.” Radiation loss characteristics and the field distribution of the ARROW are analyzed in detail. Meanwhile, both the refractive indices and the thickness dependence for the isolation and distinction of modes are also investigated in this thesis. From the CE–CH method, the associated complex symmetric tridiagonal matrices are derived to solve the modal solutions via the eigenvalue-eigenvector technique. The uniquely designed formulation of CE–CH method yields better numerical properties, specifically in calculating the field distribution. This is suitable for any combination of materials and is capable of handling complex problems such as the leaky characteristics for both lossless and lossy cases. To quickly solve the complex roots of the ARROW, a set of accurate closed-form approximations for estimating both the field distribution and complex propagating constant have been derived from the CE–CH matrices. These first-order approximations provide six significant figures of the real part of the propagation constant

碩士<br>國立臺灣大學<br>電信工程學研究所<br>92<br>Abstract Due to its simplicity and efficiency, a full-vectorial mode solver based on a finite difference scheme is applied to investigate the propagation characteristics of optical waveguides. Since uniform meshes are used in the numerical implementation, it is very easy to divide the computational window of any arbitrary cross-sectional geometries of the waveguides. An index averaging technique is employed to deal with curved dielectric interfaces for stabilizing the numerical calculation and accelerating convergence. In addition, for solving leaky-mode problems, such as the investigation of waveguide confinement loss, the perfectly matched layer (PML) absorbing boundary condition is incorporated into our finite difference formulations. The influence of the index averaging technique on the leaky-mode analysis is also discussed. We employ the shift inverse power method (SIPM) for solving the formulated eigenvalue problems. In this work, both one-dimensional and two-dimensional problems are considered, including the slab waveguide, the antiresonant reflecting optical waveguide (ARROW), the step-index optical fiber, the rectangular channel waveguide, the anisotropic embedded-channel LiNbO3 integrated optical waveguide, and microstructured optical fibers (MOFs). Comparsion of our calculation with other methods is discussed.

碩士<br>國立中山大學<br>電機工程研究所<br>82<br>In this study, the effects of finite metalization thickness on dispersion characteristics and leaky waves of coplanar waveguides are presented and discussed in detail. We first derive the spectral domain integral equations by using network analytical method, an extension of spectral domain approach, to take metalization thickness into account. By applying the Galerkin's procedure to these integral equations, we can solve the complex propagation constant of this coplanar waveguide structure. Thus, the transmission characteristics of the coplanar waveguide can be obtained, i.e., effective dielectric constants and normalized attenuation constants. Numerical results show that the normalized attenuation constant varies significantly with the dielectric substrate thickness. Changing the center strip width or the slot width has similar influence on the normalized attenuation constant. The normalized attenuation constant is found to increase with increasing metalization thickness.

碩士<br>國立清華大學<br>電機工程學系<br>85<br>A simple, generalized method of analyzing the light transmission in leaky and absorbing planar waveguides is proposed in this thesis. We use a straightforward and intuitive manner to derive the analytical expression of the power transmission discussed. By utilizing the well-known law for the partial reflection of a plane wave at an interface and the Goos-Hanchen shift happened for the case of total internal reflection, the associated power transmission of the above structure is derived. Advantages of the present method are simple and applicable to multilayer structures with ease. For comparisons, the existing formula for this waveguiding structures is overviewed, and numerical calculations are compared well with our and the other method. An extension of this approach is applied to a medium-clad side-polished single-mode fiber. Calculations based on our simplified method and an expression derived from the sophisticated coupled-mode theory are also made. Our results can explain the behaviors of the light transmission in the above structure. It is still far from satisfaction because some assumptions are made too rough, however. Further works in this subject are needed. In summary, this thesis introduces a simple and interesting approach to analyze the light transmission in leaky and absorbing planar and fiber-optic waveguides. The previous subject is important in designing and analyzing optical waveguide components.