Dissertationen zum Thema „Subwavelength photonics“

Les effets Pockels de deuxième ordre et les effets Kerr de troisième ordre font partie des effets importants exploités pour la modulation de la lumière et la génération de sources dans les plateformes technologiques de la photonique intégrée. Pour tirer parti de ces non-linéarités en photonique au silicium, l'utilisation de structures optiques sub-longueurs d'onde a été explorée. Dans ce contexte, ce travail de thèse s'est concentré sur deux aspects principaux, notamment : 1) L’exploration d'un nouveau schéma de cavité photonique pour tirer profit de l'effet Pockels électro-optique dans les structures de silicium contraint pour la réalisation de modulateurs ultra-rapides à faible consommation ; 2) L’exploration d'une nouvelle famille de guides d'ondes conduisant à une satisfaction automatique des lois de conservation énergie/vecteur d’onde pour la génération de peignes de fréquence Kerr au sein des plateformes photoniques intégrées (notamment silicium).Pour améliorer les performances des modulateurs optiques Si résonants intégrés, nous avons mis au point un nouveau résonateur à cavité de Fano qui, grâce à une ingénierie sub-longueur d'onde (λ=1.55µm), a permis d'obtenir simultanément un taux d'extinction élevé (23 dB) avec un faible facteur Q de seulement 5600, et caractérisé par une très faible consommation électrique inférieure à 5 fj/bit quand on utilise l'effet de modulation par dispersion plasma des porteurs libres. Nous avons étendu la méthode à la conception d'une structure de modulation Fano en silicium contraint dont les performances souffrent traditionnellement de la faible amplitude de l'effet Pockels induit par la déformation exploitée et des pertes micro-ondes considérables dues à des composants de grande surface. Au moyen du résonateur Fano ultra-compact à structuration sub-longueur d'onde, une amélioration d'environ 200 fois/60 fois (facteurs Q de 32000/5600) du rapport d'extinction de modulation avec la même tension de commande a été théoriquement prévue. Pour améliorer l'exploitation des non-linéarités Kerr des structures silicium, nous avons proposé une nouvelle famille de guides d'ondes optiques pour satisfaire automatiquement les lois de conservation de l'énergie et du vecteur d’onde des procédés de mélange à quatre ondes (FWM). La conception de la section des guides d'ondes est basée sur un principe hérité des puits quantiques et des concepts hérités des structures sub-longueur d'onde pour la réalisation des profils d'indice particuliers. En nous basant sur ces guides d'ondes spécifiques en terme de dispersion chromatique, nous les avons appliqués à la modélisation des micro peignes de fréquence (en utilisant des résonateurs à micro anneaux) en résolvant l’équation non linéaire pertinente (Lugiato-Lefever) pour analyser de façon dynamique le processus de génération du spectre des peignes à solitons dans diverses configurations. En complément de ce modèle, les guides d'ondes sub-longueur d'onde à accord de phase automatique ont été considérés pour étendre la largeur de bande des peignes de fréquence à solitons, démontrant une largeur de bande élargie et une meilleure flexibilité dans la réalisation des peignes de fréquence relativement aux démonstrations des travaux précédents. Dans l'ensemble, l'une des caractéristiques dominantes de notre étude a été de contribuer à montrer que les structures photoniques sub-longueur d'onde pouvaient apporter des solutions concrètes aux problèmes utiles à la réalisation de fonctions non linéaires sur puce. Les nano-structures sub-longueur d’onde permettent non seulement une amélioration des circuits photoniques passifs, sujet intensivement développé depuis dix ans, mais ont également un fort potentiel pour la réalisation des fonctions actives. Cette boîte à outils de structures sub-longueur d'onde est décisive dans la pratique pour la réalisation concrète de fonctions optiques nonlinéaires intégrées, en particulier en photonique silicium
Second-order Pockels and the third-order Kerr effects are among the important effects exploited for light modulation and light generation in integrated photonic platforms. To take advantage of these nonlinearities in silicon photonics, especially due to the lack of second order effect in bulk Si, the use of subwavelength optical structures is explored. In this context, this thesis work has focused on two main aspects, including: 1) Exploration of a novel photonic cavity scheme to take benefit of the electro-optical Pockels effect in strained Si structures for the realization of ultra-fast lower-consumption compact silicon modulators; 2) Exploration of a new family of waveguides leading to an automatic satisfaction of energy/momentum conservation for the purpose of Kerr frequency comb generation in integrated photonic platforms. For improving the performances of integrated silicon resonant optical modulators, we have developed a novel Fano cavity resonator enabled by sub-wavelength engineering, leading simultaneously to high extinction ratio (23 dB) with a small Q factor of only 5600, and characterized by an ultra-low power consumption of less than 5 fj/bit when relying on the free carrier plasma dispersion effect. We have further extended the method to design a strained silicon Fano modulation structure which performances traditionally suffer from the weak amplitude of the exploited strain-induced Pockels effect and from considerable microwave losses due to large footprint components. By means of the proposed ultra-compact subwavelength structured Fano resonator, around 200-fold/60-fold (Q factor of 32000/5600) improvement on the modulation extinction ratio with the same driven voltage was theoretically predicted. For improving the exploitation of silicon Kerr nonlinearities, we have proposed a novel family of graded index optical waveguides intending to automatically fulfill the energy and momentum conservation laws of four-wave mixing processes. The design of the waveguide section is based on a principle inherited from quantum wells of wave mechanics and concepts inherited from subwavelength structures for the practical realization of the rather particular index profiles. Standing on these specific waveguides in term of light dispersion, we have applied them to the modeling of frequency micro-combs (e.g. frequency combs generated using micro-ring resonators and a CW light source) by solving the nonlinear relevant equations (Lugiato-Lefever) to dynamically analyze the soliton comb spectrum generation process in various configurations. On top of this model, the specifically automatically phase-matched sub-wavelength-enabled graded-index waveguides were considered to trim and extend the bandwidth of silicon soliton frequency combs, demonstrating enlarged bandwidth and improved spectrum design flexibility with respect to previous works. Overall, one of the dominant features of our study was to contribute to showing that sub-long wavelength photonic structures could provide concrete solutions to problems useful for the realization of on-chip non-linear functions. Subwavelength/nano structures not only benefit to passive photonic circuits which have been intensively developed in the past ten years, but also show strong potentials in the realization of active functions. This subwavelength toolbox is decisive in practice for the concrete achievement of the objectives pursued

Les antennes optiques sont des structures qui permettent de convertir, dans les deux sens, l'énergie électromagnétique entre un faisceau lumineux et une source (ou un absorbeur) localisée en son sein. L'utilisation de résonateurs de taille inférieure à la longueur d'onde permet de réaliser cette fonction de manière efficace, sur une bande spectrale relativement étendue, et d'avoir une antenne compacte.La bonne connaissance des propriétés optiques de ces résonateurs, pris séparément, et de leurs couplages entre eux, est nécessaire pour pouvoir proposer des designs d'antenne efficaces.Dans cette thèse, en se basant sur la décomposition multipolaire des champs et sur la méthode de la matrice-T, on obtient des solutions analytiques rigoureuses pour des résonateurs sphériques et homogènes, dont on tire des modèles simplifiés, intuitifs, et proches de la solution exacte des équations de Maxwell.Entre autre résultats, ces modèles nous ont permis de proposer un design d'antenne optique compacte, directive, à taux de désexcitation et rendement quantique élevés en utilisant une structure hybride métal-diélectrique. Des collaborations avec des expérimentateurs ont permis de valider, d'une part les caractéristiques de chromophores auto-assemblés par ADN (S. Bidault à Paris), et d'autre part, la possibilité d'utiliser plusieurs résonances électriques et magnétiques combinées (supportées par des sphères diélectriques d'indice modéré, n=2,45) pour réfléchir ou bien collecter le rayonnement d'un émetteur dipôle électrique placé à proximité (expérience menée dans le régime micro-ondes par R. Abdeddaim et J-M. Geffrin)
Optical antennas are structures able to convert, in both ways, electromagnetic energy between a light beam and a source (or absorber) placed in the structure. The use of sub-wavelength resonators enables one to realize this function in an efficient way, on relatively broad bandwidths, and to have a compact design. A good understanding of the optical properties of such resonators, taken individually, and of their couplings, is thus necessary in order to propose efficient optical antenna designs. In this manuscript, using a multipole decomposition of the fields and a T-matrix method, we obtain rigorous analytical solutions for spherical, homogeneous resonators, from which we deduce simplified, intuitive models that are still very close to the exact resolution of the Maxwell equations.Among other results, those models enabled us to propose a nanoantenna design that is at once compact, radiative and efficient, by using a hybrid metallo-dielectric structure. Some collaborations with experimental groups enabled us to validate, on the one hand, the optical characteristics of hybrid chromophores that are self-assembled using a DNA template (S. Bidault, Paris), and on the other hand, the possibility of using multiple combined electric and magnetic resonances (supported by dielectric spheres of moderate refractive index, n=2.45) in order to reflect, or more importantly collect, radiation coming from an electric dipole emitter placed nearby (the experiment was realized in the microwave regime by R. Abdeddaim and J-M. Geffrin)

Generation and detection of circularly-polarized (CP) radiation in the 8- to 12-micrometers] band of the infrared (IR) spectrum is crucial for polarization sensing and imaging scenarios. There is very little naturally occurring CP radiation in the long-wave IR band, so that useful functionalities may be obtained by exploiting preferential radiation and transmission characteristics of engineered metamaterials. Conventional CP devices in the IR utilize birefringent crystals, which are typically bulky and expensive to manufacture. The operation of these devices is generally optimized at a single wavelength. Imaging in the long-wave IR is most often broadband, so that achromatic CP-device behavior is highly desirable from a flux-transfer viewpoint. Also, size, weight and cost are significant drivers in the design of practical IR systems. Thus a solution is sought with a convenient thin planar form factor. This dissertation will demonstrate a novel planar periodic subwavelength-microstructured approach derived from classical radiofrequency meanderline designs that are able to generate CP radiation over a broad IR band while maintaining a low fabrication profile. We investigate issues regarding efficiency as a function of the number of layers in the device structure; reflective, transmissive, and emissive behavior; strategies for broadband achromatization; and thermal-isolation requirements between the active blackbody reservoir and the top of the planar device, to achieve a given degree of polarization. Theoretical, numerical, and experimental findings are presented that confirm the feasibility of this class of devices for use in a wide variety of situations, from polarization imaging and spectroscopy to industrial laser processing and machining.
ID: 030422966; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2011.; Includes bibliographical references (p. 169-181).
Ph.D.
Doctorate
Optics and Photonics

Reliability and sensitive information protection are critical aspects of integrated circuits. A novel technique using near-field evanescent wave coupling from two subwavelength gratings (SWGs), with the input laser source delivered through an optical fiber is presented for tamper evidence of electronic components. The first grating of the pair of coupled subwavelength gratings (CSWGs) was milled directly on the output facet of the silica fiber using focused ion beam (FIB) etching. The second grating was patterned using e-beam lithography and etched into a glass substrate using reactive ion etching (RIE). The slightest intrusion attempt would separate the CSWGs and eliminate near-field coupling between the gratings. Tampering, therefore, would become evident. Computer simulations guided the design for optimal operation of the security solution. The physical dimensions of the SWGs, i.e. period and thickness, were optimized, for a 650 nm illuminating wavelength. The optimal dimensions resulted in a 560 nm grating period for the first grating etched in the silica optical fiber and 420 nm for the second grating etched in borosilicate glass. The incident light beam had a half-width at half-maximum (HWHM) of at least 7 µm to allow discernible higher transmission orders, and a HWHM of 28 µm for minimum noise. The minimum number of individual grating lines present on the optical fiber facet was identified as 15 lines. Grating rotation due to the cylindrical geometry of the fiber resulted in a rotation of the far-field pattern, corresponding to the rotation angle of moiré fringes. With the goal of later adding authentication to tamper evidence, the concept of CSWGs signature was also modeled by introducing random and planned variations in the glass grating. The fiber was placed on a stage supported by a nanomanipulator, which permitted three-dimensional displacement while maintaining the fiber tip normal to the surface of the glass substrate. A 650 nm diode laser was fixed to a translation mount that transmitted the light source through the optical fiber, and the output intensity was measured using a silicon photodiode. The evanescent wave coupling output results for the CSWGs were measured and compared to the simulation results.

The present work aims at enhancing the external quantum efficiencies of ultra-violet (UV) sensitive photodetectors (PDs) and light emitting diodes (LEDs)for any light polarization. Deep UV solid state devices are made out of AlGaN or MgZnO and their performances suffer from the high resistivity of their p-doped regions. They require transparent p-contacts; yet the most commonly used transparent contacts have low transmission in the UV: indium tin oxide (ITO) and nickel-gold (Ni/Au 5/5 nms) transmit less than 50% and 30% respectively at 300 nm. Here we investigate the use of surface plasmons (SPs) to design transparent p-contacts for AlGaN devices in the deep UV region of the spectrum. The appeal of using surface plasmon coupling arose from the local electromagnetic field enhancement near the metal surface as well as the increase in interaction time between the field and semiconductor if placed on top of a semiconductor. An in/out-coupling mechanism is achieved by using a grating consisting of two perpendicularly oriented sets of parallel aluminum lines with periods as low as 250 nm. The incident light is first coupled into SPs at the air/aluminum interface which then re-radiate at the aluminum/AlGaN interface and the photons energy is transferred to SP polaritons (SPPs) and back to photons. High transmission can be achieved not only at normal incidence but for a wider range of incident angles. A finite difference time domain (FDTD) package from R-Soft was used to simulate and design such aluminum gratings with transparency as high as 100% with tunable peak wavelength, bandwidth and angular acceptance. A rigorous coupled wave analysis (RCWA) was developed in Matlab to validate the FDTD results. The high UV transparency meshes were then fabricated using an e-beam assisted lithography lift-off process. Their electrical and optical properties were investigated. The electrical characterization was very encouraging; the sheet resistances of these meshes were lower than those of the conventionally used transparent contacts. The optical transmissions were lower than expected and the causes for the lower measurements have been investigated. The aluminum oxidation, the large metal grain size and the line edge roughness were identified as the main factors of inconsistency and solutions are proposed to improve these shortcomings. The effect of aluminum oxidation was calculated and the passivation of aluminum with SiO[sub2] was evaluated as a solution. A cold deposition of aluminum reduced the aluminum grain size from 60 nm to 20 nm and the roughness from 5 nm to 0.5 nm. Furthermore, replacing the conventional lift-off process by a dry back-etch process led to much smoother metal line edges and much high optical transparency. The optical measurements were consistent with the simulations. Therefore, reduced roughness and smooth metal line edges were found to be especially critical considerations for deep UV application of the meshes.
ID: 029810223; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Thesis (Ph.D.)--University of Central Florida, 2011.; Includes bibliographical references (p. 140-145).
Ph.D.
Doctorate
Optics and Photonics

La photonique au silicium suscite un immense intérêt dans la recherche fondamentale et le développement technologique et commercial en raison de sa compatibilité avec les techniques de fabrication et de traitement standard de l'industrie électronique. Traditionnellement développée pour les applications de télécommunication de données, la photonique au silicium explore aujourd'hui d'autres domaines, tels que le traitement des signaux sur puce, la détection, les communications entre la puce et l'espace libre, et même l'informatique quantiques. Ce large éventail d'applications est possible grâce à de nouveaux phénomènes physiques. Dans ce contexte, la diffusion Brillouin apparaît comme un outil prometteur pour la prochaine génération de circuits intégrés. Cette interaction non linéaire entre la lumière et les modes mécaniques d'une structure couple des photons optiques (dans le régime THz) avec des phonons MHz et GHz, ce qui permet une conversion de fréquence très efficace. Cette propriété est essentielle pour le traitement des signaux micro-ondes et la transduction quantique entre les qubits supraconducteurs et les fibres optiques. Ces deux technologies devraient révolutionner les télécommunications au cours des prochaines décennies. Depuis le début des années 2000, de nouvelles conceptions intégrées permettant un fort couplage optomécanique ont fait l'objet d'une recherche active. En raison de leur petite taille, du confinement étroit de la lumière et de l'interaction optique importante avec les limites de la structure, ces nouvelles géométries promettent une réponse optomécanique exceptionnelle. Nous contribuons à cet effort en utilisant des structures sub-longueur d'onde pour maximiser l'effet Brillouin en exploitant le contrôle indépendant des modes optiques et mécaniques. Les structures sub-longueur d'onde, c'est-à-dire les géométries périodiques dont le pas est inférieur à la moitié de la longueur d'onde optique, offrent un contrôle unique de la propagation de la lumière, de l'anisotropie et de l'ingénierie des modes optiques. Grâce à de récents développements dans les installations de fabrication, ces structures promettent une nouvelle génération de dispositifs compacts en silicium sur isolant dotés de capacités inédites sans incorporer de nouveaux matériaux
Silicon photonics attracts immense interest in fundamental research and technological and commercial development due to its compatibility with the electronics industry's standard fabrication and processing techniques. Traditionally developed for datacom applications, nowadays, silicon photonics is exploring more fields, such as on-chip signal processing, sensing, on-chip to free-space communications, and even quantum information and computing. This wide range of applications is possible thanks to novel physical phenomena. In this context, Brillouin scattering emerges as a promising tool for the next generation of integrated circuits. This nonlinear interaction between light and mechanical modes of a structure couples optical photons (in the THz regime) with MHz- and GHz-phonons, allowing a very efficient frequency conversion. This property is critical for microwave signal processing and quantum transduction between superconducting qubits and optical fibres. These two technologies are set to revolutionise telecommunications in the coming decades. Novel integrated designs yielding strong optomechanical coupling have been an active research field since the early 2000s. Due to their small size, tight light confinement, and large optical interaction with the structure boundaries, these new geometries promise an exceptional optomechanical response. We contribute to this effort by utilising subwavelength structures to maximise the Brillouin effect by harnessing independent control over optical and mechanical modes. Subwavelength structures, i.e., periodic geometries with a pitch smaller than half the optical wavelength, offer unique control of light propagation, anisotropy, and optical mode engineering. Thanks to recent developments in fabrication facilities, these structures promise a new generation of silicon-on-insulator compact devices with novel capabilities without incorporating new materials

Optical interconnects based on CMOS compatible photonic integrated circuits are regarded as a promising technique to tackle the issues traditional electronics faces, such as limited bandwidth, latency, vast energy consumption and so on. In recent years, plasmonic integrated components have gained great attentions due to the properties of nano-scale confinement, which may potentially bridge the size mismatch between photonic and electronic circuits. Based on silicon nanowire platform, this thesis work studies the design, fabrication and characterization of several integrated plasmonic components, aiming to combine the benefits of Si and plasmonics. The basic theories of surface plasmon polaritons are introduced in the beginning, where we explain the physics behind the diffraction-free confinement. Numerical methods frequently used in the thesis including finite-difference time-domain method and finite-element method are then reviewed. We summarize the device fabrication techniques such as film depositions, e-beam lithography and inductively coupled plasma etching as well as characterization methods, such as direct measurement method, butt coupling, grating coupling etc. Fabrication results of an optically tunable silicon-on-insulator microdisk and III-V cavities in applications as light sources for future nanophotonics interconnects are briefly discussed. Afterwards we present in details the experimental demonstrations and novel design of plasmonic components. Hybrid plasmonic waveguides and directional couplers with various splitting ratios are firstly experimentally demonstrated. The coupling length of two 170 nm wide waveguides with a separation of 140 nm is only 1.55 µm. Secondly, an ultracompact polarization beam splitter with a footprint of 2×5.1 μm2 is proposed. The device features an extinction ratio of 12 dB and an insertion loss below 1.5 dB in the entire C-band. Thirdly, we show that plasmonics offer decreased bending losses and enhanced Purcell factor for submicron bends. Novel hybrid plasmonic disk, ring and donut resonators with radii of ~ 0.5 μm and 1 μm are experimentally demonstrated for the first time. The Q-factor of disks with 0.5 μm radii are                         , corresponding to Purcell factors of . Thermal tuning is also presented. Fourthly, we propose a design of electro-optic polymer modulator based on plasmonic microring. The figure of merit characterizing modulation efficiency is 6 times better comparing with corresponding silicon slot polymer modulator. The device exhibits an insertion loss below 1 dB and a power consumption of 5 fJ/bit at 100 GHz. At last, we propose a tightly-confined waveguide and show that the radius of disk resonators based on the proposed waveguide can be shrunk below 60 nm, which may be used to pursue a strong light-matter interaction. The presented here novel components confirm that hybrid plasmonic structures can play an important role in future inter- and intra-core computer communication systems.

QC 20140404

Thesis: M. Eng., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 110-117).
Three applications of the interaction of light with periodic dielectric structures are investigated. The first application is large-area spectroscopy, for which we use the mid-field diffraction pattern generated by the light source passing through a transmission grating to determine its spectral composition. By utilizing a large grating size, we are able to achieve resolutions of < 4 nm experimental while having an etendue of roughly 0.033 mm2. Furthermore, since we are sampling the mid-field light pattern as opposed to the farfield, the entire spectrometer can fit within a 10 mm by 10 mm by 5 mm volume. The second application are barcodes based on the wavelength-dependent back-scattering off of a photonic crystal resonant cavity. The challenge is that we want to observe high quality factor resonant peaks while reducing the size of the crystal to less than 10 microns. So far the highest quality factor observed was about 800. The third application is a Fano silicon photonic crystal modulator waveguide device. The resonant cavity of the modulator is a 1D photonic crystal cavity. If we excite the fundamental and first excited mode of the waveguide, we obtain a Fano resonance that can potentially increase modulation depth and efficiency. We investigated how to improve the modulator architecture to reliably design resonators with sharp Fano resonance peaks. Those these applications are still in their early stages, the are promising for furthering each technology.
by Erika Ye.
M. Eng.

The widespread adoption of photonic circuits requires the economics of volume manufacturing offered by integration technology. A Complementary Metal-Oxide Semiconductor compatible silicon material platform is particularly attractive because it leverages the huge investment that has been made in silicon electronics and its high index contrast enables tight confinement of light which decreases component footprint and energy consumption. Nevertheless, there remain challenges to the development of photonic integrated circuits. Although the density of integration is advancing steady and the integration of the principal components – waveguides, optical sources and amplifiers, modulators, and photodetectors – have all been demonstrated, the integration density is low and the device library far from complete. The integration density is low primarily because of the difficulty of confining light in structures small compared to the wavelength which measured in micrometers. The device library is incomplete because of the immaturity of hybridisation on silicon of other materials required by active devices such as III-V semiconductor alloys and ferroelectric oxides and the difficulty of controlling the coupling of light between disparate material platforms. Metamaterials are nanocomposite materials which have optical properties not readily found in Nature that are defined as much by their geometry as their constituent materials. This offers the prospect of the engineering of materials to achieve integrated components with enhanced functionality. Metamaterials are a class of photonic crystals includes subwavelength grating waveguides, which have already provided breakthroughs in component performance yet require a simpler fabrication process compatible with current minimum feature size limitations. The research reported in this PhD thesis advances our understanding of the structure-property relations of key planar light circuit components and the metamaterial engineering of these properties. The analysis and simulation of components featuring structures that are only just subwavelength is complicated and consumes large computer resources especially when a three dimensional analysis of components structured over a scale larger than the wavelength is desired. This obstructs the iterative design-simulate cycle. An abstraction is required that summarises the properties of the metamaterial pertinent to the larger scale while neglecting the microscopic detail. That abstraction is known as homogenisation. It is possible to extend homogenisation from the long-wavelength limit up to the Bragg resonance (band edge). It is found that a metamaterial waveguide is accurately modeled as a continuous medium waveguide provided proper account is taken of the emergent properties of the homogenised metamaterial. A homogenised subwavelength grating waveguide structure behaves as a strongly anisotropic and spatially dispersive material with a c-axis normal to the layers of a one dimensional multi-layer structure (Kronig-Penney) or along the axis of uniformity for a two dimensional photonic crystal in three dimensional structure. Issues with boundary effects in the near Bragg resonance subwavelength are avoided either by ensuring the averaging is over an extensive path parallel to boundary or the sharp boundary is removed by graded structures. A procedure is described that enables the local homogenised index of a graded structure to be determined. These finding are confirmed by simulations and experiments on test circuits composed of Mach-Zehnder interferometers and individual components composed of regular nanostructured waveguide segments with different lengths and widths; and graded adiabatic waveguide tapers. The test chip included Lüneburg micro-lenses, which have application to Fourier optics on a chip. The measured loss of each lens is 0.72 dB. Photonic integrated circuits featuring a network of waveguides, modulators and couplers are important to applications in RF photonics, optical communications and quantum optics. Modal phase error is one of the significant limitations to the scaling of multimode interference coupler port dimension. Multimode interference couplers rely on the Talbot effect and offer the best in-class performance. Anisotropy helps reduce the Talbot length but temporal and spatial dispersion is necessary to control the modal phase error and wavelength dependence of the Talbot length. The Talbot effect in a Kronig-Penny metamaterial is analysed. It is shown that the metamaterial may be engineered to provide a close approximation to the parabolic dispersion relation required by the Talbot effect for perfect imaging. These findings are then applied to the multimode region and access waveguide tapers of a multi-slotted waveguide multimode interference coupler with slots either in the transverse direction or longitudinal direction. A novel polarisation beam splitter exploiting the anisotropy provided by a longitudinally slotted structure is demonstrated by simulation. The thesis describes the design, verification by simulation and layout of a photonic integrated circuit containing metamaterial waveguide test structures. The test and measurement of the fabricated chip and the analysis of the data is described in detail. The experimental results show good agreement with the theory, with the expected errors due to fabrication process limitations. From the Scanning Electron Microscope images and the measurements, it is clear that at the boundary of the minimum feature size limit, the error increases but still the devices can function.

Quarter-wave retarders (QWR) that employ total internal reflection (TIR) and interference of light in a transparent thin-film coating at the base of a prism are presented. Explicit equations that guide the optimal design are provided. The optimal refractive index and normalized thickness of QWR coatings on glass and ZnS prisms are determined as functions of the internal angle of incidence from 45o to 75o. An achromatic QWR that uses an Si3N4- coated N-BK10-Schott glass prism is also presented with retardance error of 3o over the 400-600 nm wavelength range. An iterative procedure for the design of a polarizing beam splitter (PBS) that uses a form-birefringent, subwavelength-structured, one-dimensional photonic-crystal layer (SWS 1-D PCL) embedded in a high-index cubical prism is presented. The PBS is based on index matching and total transmission for the p polarization and total internal reflection for the s polarization at the prism-PCL interface at a 45o angle of incidence. A high extinction ratio in reflection ( 50 dB) over the 4-12 μm IR spectral range is achieved using a SWS 1-D PCL of ZnTe embedded in a ZnS cube within an external field of view (FOV) of ±6.6o and in the presence of grating filling factor errors of up to ±10%. Comparable results, but with a wider field of view, are also obtained with a Ge PCL embedded in a Si prism. A design for visible spectrum (553–713 nm) PBS SWS 1-D PCL of ZnTe embedded in a ZnS cube is also presented. The PBS shows a FOV of ±7o. A circular polarizing beam splitter (CPBS) with equal throughput for p and s polarization using SWS 1-D PCL embedded in a high-index cubical prism is introduced. A dual QWR in transmission and reflection with 50–50% CPBS is designed using the PCL. Such a CPBS shows large deviation from the design point as a result of small changes in the design parameters; e.g. a change of 10% in the filling factor results in 12o shift from the 90o phase shift between p and s polarizations, which limits the practical utility of the device.

An innovative approach for characterization of one dimensional Photonic Band Gap structures comprised of metallic inclusions (i.e. subwavelength dipole elements or resonant ring elements) is presented. Through an efficient S- to T-parameters conversion technique, a detailed analysis has been performed to investigate the variation of the dispersion characteristics of 1-D PBG structures as a function of the cell element configuration. Also, for the first time, the angular sensitivity of the structure has been studied in order to obtain the projected band diagrams for both TE and TM polarizations. Polarization sensitivity of the subwavelength cell element is exploited to propose a novel combination of elements which allows achieving PBGs with simultaneous frequency and polarization selectivity. The proposed approach demonstrates that the dispersion characteristic of each orthogonal polarization can be independently adjusted with dipole elements parallel to that same polarization. Generally, the structure has potential applications in orthomode transducer, and generally whenever the polarization of the incoming signal is to be used as a means of separating it from another signal in the same frequency band that is of orthogonal polarization. The current distribution and the resonance behavior of the ring element is studied and the effect of resonance on dispersion characteristics of 1-D PBGs composed of rings is investigated for the first time, for both individual and coupled rings. Interestingly, it is observed that 1-D PBG composed of resonant elements consistently has a bandgap around the resonant frequency of the single layer structure.

Tesis por compendio
[ES] La fotónica de silicio es una tecnología emergente clave en redes de comunicación e interconexiones de centros de datos de nueva generación, entre otros. Su éxito se basa en la utilización de plataformas compatibles con la tecnología CMOS para la integración de circuitos ópticos en dispositivos pequeños para una producción a gran escala a bajo coste. Dentro de este campo, los interferómetros integrados juegan un papel crucial en el desarrollo de diversas aplicaciones fotónicas en un chip como sensores biológicos, moduladores electro-ópticos, conmutadores totalmente ópticos, circuitos programables o sistemas LiDAR, entre otros. Sin embargo, es bien sabido que la interferometría óptica suele requerir caminos de interacción muy largos, lo que dificulta su integración en espacios muy compactos. Para mitigar algunas de estas limitaciones de tamaño, surgieron varios enfoques, incluyendo materiales sofisticados o estructuras más complejas, que, en principio, redujeron el área de diseño pero a expensas de aumentar los pasos del proceso de fabricación y el coste. Esta tesis tiene como objetivo proporcionar soluciones generales al problema de tamaño típico de los interferómetros ópticos integrados, con el fin de permitir la integración densa de dispositivos basados en silicio. Para ello, aunamos los beneficios tanto de las guías de onda bimodales como de las estructuras periódicas, en términos de la mejora del rendimiento y la posibilidad para diseñar interferómetros monocanal en áreas muy reducidas. Más específicamente, investigamos los efectos dispersivos que aparecen en estructuras menores a la longitud de onda y en las de cristal fotónico, para su implementación en diferentes configuraciones interferométricas bimodales. Además, demostramos varias aplicaciones potenciales como sensores, moduladores y conmutadores en tamaños ultra compactos de unas pocas micras cuadradas. En general, esta tesis propone un nuevo concepto de interferómetro integrado que aborda los requisitos de tamaño de la fotónica actual y abre nuevas vías para futuros dispositivos basados en funcionamiento bimodal.
[CA] La fotònica de silici és una tecnologia emergent clau en xarxes de comunicació i interconnexions de centres de dades de nova generació, entre altres. El seu èxit es basa en la utilització de plataformes compatibles amb la tecnologia CMOS per a la integració de circuits òptics en dispositius diminuts per a una producció a gran escala a baix cost. Dins d'aquest camp, els interferòmetres integrats juguen un paper crucial en el desenvolupament de diverses aplicacions fotòniques en un xip com a sensors biològics, moduladors electro-òptics, commutadors totalment òptics, circuits programables o sistemes LiDAR, entre altres. No obstant això, és ben sabut que la interferometría òptica sol requerir camins d'interacció molt llargs, la qual cosa dificulta la seua integració en espais molt compactes. Per a mitigar algunes d'aquestes limitacions de grandària, van sorgir diversos enfocaments, incloent materials sofisticats o estructures més complexes, que, en principi, van reduir l'àrea de disseny però a costa d'augmentar els processos de fabricació i el cost. Aquesta tesi té com a objectiu proporcionar solucions generals al problema de grandària típica dels interferòmetres òptics integrats, amb la finalitat de permetre la integració densa de dispositius basats en silici. Per a això, combinem els beneficis tant de les guies d'ones bimodals com de les estructures periòdiques, en termes de funcionament d'alt rendiment per a dissenyar interferòmetres monocanal compactes en àrees molt reduïdes. Més específicament, investiguem els efectes dispersius que apareixen en estructures menors a la longitud d'ona i en les de cristall fotònic, per a la seua implementació en diferents configuracions interferomètriques bimodals. A més, vam demostrar diverses aplicacions potencials com a sensors, moduladors i commutadors en grandàries ultres compactes d'unes poques micres cuadrades. En general, aquesta tesi proposa un nou concepte d'interferòmetre integrat que aborda els requisits de grandària de la fotònica actual i obri noves vies per a futurs dispositius basats en funcionament bimodal.
[EN] Silicon photonics is a key emerging technology in next-generation communication networks and data centers interconnects, among others. Its success relies on the ability of using CMOS-compatible platforms for the integration of optical circuits into small devices for a large-scale production at low-cost. Within this field, integrated interferometers play a crucial role in the development of several on-chip photonic applications such as biological sensors, electro-optic modulators, all-optical switches, programmable circuits or LiDAR systems, among others. However, it is well known that optical interferometry usually requires very long interaction paths, which hinders its integration in highly compact footprints. To mitigate some of these size limitations, several approaches emerged including sophisticated materials or more complex structures, which, in principle, reduced the design area but at the expense of increasing fabrication process steps and cost. This thesis aims at providing general solutions to the long-standing size problem typical of optical integrated interferometers, in order to enable the densely integration of silicon-based devices. To this end, we combine the benefits from both bimodal waveguides and periodic structures, in terms of high-performance operation and compactness to design single-channel interferometers in very reduced areas. More specifically, we investigate the dispersive effects that arise from subwavelength grating and photonic crystal structures for their implementation in different bimodal interferometric configurations. Furthermore, we demonstrate various potential applications such as sensors, modulators and switches in ultra-compact footprints of a few square microns. In general, this thesis proposes a new concept of integrated interferometer that addresses the size requirements of current photonics and open up new avenues for future bimodal-operation-based devices.
Financial support is also gratefully acknowledged through postdoctoral FPI grants from Universitat Politècnica de València (PAID-01-18). European Commission through the Horizon 2020 Programme (PHC-634013 PHOCNOSIS project). The authors acknowledge funding from the Generalitat Valenciana through the AVANTI/2019/123, ACIF/2019/009 and PPC/2020/037 grants and from the European Union through the operational program of the European Regional Development Fund (FEDER) of the Valencia Regional Government 2014–2020.
Torrijos Morán, L. (2021). Photonic Applications Based on Bimodal Interferometry in Periodic Integrated Waveguides [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/172163
TESIS
Compendio

碩士
國立中山大學
光電工程學系研究所
104
This thesis focuses on the design and simulation of subwavelength waveguide gratings, which reflect the light at its Bragg wavelength, implemented on silicon-on-insulator (SOI) platform. This photonic device has been utilized as an optical filter, a wavelength division multiplexer, and a sensing element. However, the strong side-lobe ripples arise from the waveguide gratings would cause serious channel crosstalks once the waveguide gratings are used to implement wavelength division multiplexing devices. In this work, we incorporate Gaussian-apodized structure in the waveguide grating design to reduce the side-lobe ripples by means of grating width modulation. Apodized grating is able to obtain a side-lobe suppression ratio of larger than 20 dB. Such an apodization structure is successfully implemented in strip-type and cladding-modulated waveguide gratings for side-lobe suppression. It works for not only uniform gratings but also phase-shifted gratings and sampled gratings. In addition, the moiré grating design, which is composed of two grating periods, is also implemented on SOI waveguides. This moiré grating has a π phase shift just like a phase-shifted grating, but more importantly this grating provides a tunable resonant bandwidth, which can not be achieved by a conventional phase-shifted grating. A resonant bandwidth of 0.18, 0.6 and 1.09 nm can be realized by cascading one, two, and three moiré gratings, respectively. Performance variation of the moiré gratings against the fabrication errors is finally investigated.

This thesis work is located within the framework of light localization in all-dielectric nanostructures, from single Mie resonators to correlated disordered media. The application of groundbreaking imaging techniques like Near-field and Dark-field hyperspectral imaging on such complex architectures, is here proven to be a fascinating tool not only for the optical characterization, extremely important to understand their fundamental physical properties, but also an efficient vehicle for probing their practical potentialities. The presented experimental results are carefully supported by theory and numerical calculations.

Large on-chip bandwidths required for high performance electronic chips will render optical components essential parts of future on-chip interconnects. Silicon photonics enables highly integrated photonic integrated circuit (PIC) using CMOS compatible process. In order to maximize the bandwidth density and design flexibility of PICs, vertical integration of electronic layers and photonics layers is strongly preferred. Comparing deposited silicon, single crystalline silicon offers low material absorption loss and high carrier mobility, which are ideal for multi-layer silicon PIC. Three different methods to build multi-layer silicon PICs based on single crystalline silicon are demonstrated in this dissertation, including double-bonded silicon-on-insulator (SOI) wafers, transfer printed silicon nanomembranes, and adhesively bonded silicon nanomembranes. 1-to-12 waveguide fanouts using multimode interference (MMI) couplers were designed, fabricated and characterized on both double-bonded SOI and transfer printed silicon nanomembrane, and the results show comparable performance to similar devices fabricated on SOI. However, both of these two methods have their limitations in optical interconnects applications. Large and defect-free silicon nanomembrane fabricated using adhesive bonding is identified as a promising solution to build multi-layer silicon PICs. A double-layer structure constituted of vertically integrated silicon nanomembranes was demonstrated. Subwavelength length based fiber-to-chip grating couplers were used to couple light into this new platform. Three basic building blocks of silicon photonics were designed, fabricated and characterized, including 1) inter-layer grating coupler based on subwavelength nanostructure, which has efficiency of 6.0 dB and 3 dB bandwidth of 41 nm, for light coupling between layers, 2) 1-to-32 H-tree optical distribution, which has excess loss of 2.2 dB, output uniformity of 0.72 dB and 3 dB bandwidth of 880 GHz, 3) waveguide crossing utilizing index-engineered MMI coupler, which has crossing loss of 0.019 dB, cross talk lower than -40 dB and wide transmission spectrum covering C-band and L-band. The demonstrated integration method and silicon photonic devices can be integrated into the CMOS back-end process for clock distribution and global signaling.
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The objective of this dissertation work is to examine light localization in semiconductors provided by a complete photonic bandgap via three-dimensional (3D) woodpile photonic crystals. A 3D photonic crystal is a periodic nanostructure that demonstrates omni-directional Bragg reflection. These materials are anticipated to become a powerful tool for engineering light propagation and localization within subwavelength scales due to their complete photonic bandgap and the distinctive dispersion relation.

The approach of realizing microcavities in this dissertation is to combine multi-directional etching fabrication methods with mode gap design. Modulation of unit cell size along a line-defect 3D waveguide could bring a guiding mode into the mode gap region of the waveguide and form a microcavity with a resonance inside the complete photonic bandgap. The designed microcavities could be fabricated by multi-directional etching methods because they can structurally be decomposed into two sets of connected and straight dielectric rods.

Ultra-high-quality factor microcavities and sub-wavelength-scale waveguides are designed without introduction of local disorders. Monopole, dipole, and quadrupole resonant modes are demonstrated with a small modal volume. The smallest modal volumes obtained are 0.36 cubic half-wavelengths for a resonance field in vacuum, and 2.88 cubic half-wavelengths for a resonance field in a dielectric. Direct metal contacts with the microcavities do not significantly deteriorate the quality factors because the resonant fields are located inside the microcavities. Single-mode woodpile waveguides are also designed in both lateral and vertical propagation directions.

The multi-directional etching method is a simple approach to the fabrication of woodpile photonic crystals and designed optical components with a variety of crystal orientations and surfaces, including (110), (001), (100), and (010) planes. An arbitrary surface plane (mn0) is obtained with this method, where m and n are integers. Moreover, it can also produce large area woodpile photonic crystals with high precision in silicon and GaAs materials.

These optical components in woodpile photonic crystals would be building blocks of high-density, low-loss 3D integrated optics, cavity quantum electrodynamics (QED), nonlinear optics, and enable the realization of current-injection optical devices.

Dissertation

碩士
國立中山大學
光電工程學系研究所
104
This thesis focuses on the modification of our mirror-tunable laser interference system for short-period (200~400 nm) grating formation over a large sample area with superior uniformity. Experimental results indicate that the resist gratings have a fill factor variation of < 1.3%, a thickness variation of < 3%, and a grating period variation of < 0.15%. Such a superior grating structure then serves as the building block to realize RGB reflective filters and wire-grid optical polarizers. The gratings are also applied for liquid crystal alignment on a flexible substrate. The RGB reflective filter is based on a guided-mode resonance mechanism and the grating is made of high-refractive-index silicon material. According to the rigorous coupled-wave analysis, the reflecting wavelength of a Si grating can be adjusted by changing the grating period. A reflection bandwidth of > 80 nm and a reflectivity of > 75% are predicted and experimentally demonstrated. Wire-grid optical polarizer is realized by oblique depositing Aluminum atop the resist gratings. The resultant optical polarizer enables an optical transmission of 60% and an extinction ratio of about 40:1. The alignment of liquid crystal by grating allows an optical transmission of up to 95%. After assembling RGB reflective filter with standard liquid crystal cell, we show that color mixing can be achieved by adjusting the voltage applied to the cell. We believe that the proposed all-grating-based reflective display concept could be a high-efficiency and low-cost choice.

Near-field light confinement on scanning probe is the backbone technology for near-field imaging with subwavelength resolution that overcomes the diffraction limit by exploiting the properties of evanescent waves. The fusion of the photonics and the latest nanofabrication technology creates emerging frontier for near-field light confinement research with new design approach. The propagation of light can now be controlled by periodical structure at subwavelength scale with low loss in the artificially synthesized dielectric material. New light propagation patterns can now be implemented in subwavelength structure, such as directional free space light focus grating coupler, photonic bandgap material like photonic crystal by permitting light propagation at certain wavelength while prohibiting light outside of bandgap, and nano-slot light resonator for increased light-matter interaction at nanometer scale. Advances in this research area will have tremendous impact on electromagnetic modeling and biomedical technology for probe based subwavelength optical detection. My doctoral research focused on investigating highly efficient, nanofabrication compatible directional light coupling structure and near-field subwavelength light focus through photonic crystal material. The distinct significance of this research was placed on exploitation of the embedded metallic grating coupler of high free space directivity and subwavelength light processing circuit of enhanced near-field transmission rate, the two most dominating basic elements of the scanning optical imaging system. First, I designed a compact elliptical grating coupler based on embedded noble metal such as gold or silver that efficiently interconnects free space with dielectric rectangular waveguide. The dense system integration capability shows the application potential for on-chip interfacing subwavelength light processing circuits and near-field fluorescent biosensors with far-field detection of superb radiation directivity and coupling efficiency. Second, a novel all-dielectric light confinement probe designed by slotted photonic crystal waveguide provides a light confinement mechanism on the lateral plane. The resonating nano-cavities and the λ/4 nano-slot are used to enlarge the light throughput while as the nano-slot waveguide provides single subwavelength center lobe. The impetus of this research is the growing interests by near-field imaging researchers to obtain a low loss visible light confinement probe designs through mass production.
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Tese no âmbito do Doutoramento em Engenharia Electrotécnica e de Computadores, ramo de especialização em Telecomunicações, orientada pelos Professores Doutores Mário Gonçalo Mestre Veríssimo Silveirinha e Tiago André Nogueira Morgado e apresentada no Departamento de Engenharia Electrotécnica e de Computadores da Faculdade de Ciências e Tecnologia da Universidade de Coimbra.
Nanophotonics is a field of research dedicated to study the interactions of nanosized-objects with light. One of the goals of nanophotonics is to enable the miniaturization of optical components at a competitive scale with microelectronics. There are several rewards in using light based technologies, such as building photonic circuits that are not only smaller but faster and more efficient than the electronic counterparts, new solar cells that have enhanced energy absorption, nano-optical sensors able to detect ultralow concentrations of molecules in chemical solutions, amongst many others. My work aims to contribute to this field of research by exploring new mechanisms to accomplish an efficient spatial confinement of light. This thesis is devoted to the analytical and numerical study of three different ways to confine light in the nanoscale. First, we investigate light trapping in open plasmonic resonators (metaatoms) with different shapes. It is found that in some conditions complexshaped dielectric cavities may support discrete light states screened by volume plasmons that in the limit of a vanishing material loss have an infinite lifetime. The embedded eigenstates can be efficiently pumped with a plane wave excitation when the meta-atom core has a nonlinear response, such that the trapped light energy is precisely quantized. Then, we investigate how the spatial dispersion effects, e.g., caused by the electron-electron interactions in a metal, affect these trapped eigenstates in three-dimensional open plasmonic resonators. Heuristically, one may expect that the repulsive-type electron-electron interactions should act against light localization, and thereby that they should have a negative impact on the formation of the embedded eigenstates. Surprisingly, it is found that the nonlocality of the material response creates new degrees of freedom and relaxes the requirements for the observation of trapped light. In particular, a zero-permittivity condition is no longer mandatory and the same resonator shell can potentially suppress the radiation loss at multiple frequencies. The possibility to trap and guide light in wire metamaterials is also investigated. Specifically, we investigate the guided modes supported by a metamaterial slab formed by two mutually orthogonal and nonconnected sets of parallel metallic wires. It is demonstrated that the wire medium slab has a peculiar comb-like dispersion diagram. In the continuum approximation, the metamaterial supports a diverging number of guided mode branches that accumulate near the light line due to a strong hyperbolic response in the static limit. In a realistic system, the number of guided modes branches is finite and is determined by the density of wires. Remarkably, the guided modes may be characterized by a fast field variation along the transverse direction, which can be exploited to detect subwavelength particles or defects. Lastly, we investigated topological trapped states in photonic crystals. We show that in one-dimensional periodic systems the number of bands below a band gap determines the topological Chern number of an extended system with a synthetic dimension. It is theoretically and numerically demonstrated that in real-space the Chern number gives the number of gapless trapped state branches localized at the interface of the photonic crystal, when its geometry is continuously displaced by one lattice period. Furthermore, we introduce a novel class of topological systems with inversion-symmetry and fractional (non-integral) Chern numbers. It is proven that the non-integral topological number arises due to the discontinuous behaviour of the Hamiltonian in the spectral domain. We introduce a bulk-edge correspondence that links the number of edge-states with the fractional topological number.
A nano-fotónica é uma área de investigação dedicada ao estudo das interacções da luz com objectos nanométricos. Um dos objectivos da nanofotónica é possibilitar a miniaturização de componentes ópticos para uma escala competitiva com a microelectrónica. Existem vários benefícios em usar tecnologia fotónica, como a construção de circuitos fotónicos com pequenas dimensões que não são apenas mais rápidos mas também mais eficientes do que as suas contrapartes eletrónicas, novas células solares com uma maior absorção energética, sensores nano-ópticos capazes de detectar concentrações extremamente baixas de moléculas em soluções químicas, entre outros. O objectivo principal do meu trabalho é contribuir para esta área de investigação, explorando novos mecanismos de confinamento espacial da luz de forma eficiente. Esta tese é dedicada ao estudo analítico e numérico de três mecanismos diferentes de confinar a luz à nano-escala. Em primeiro lugar, é investigado o aprisionamento da luz em ressoadores plasmónicos abertos (meta-átomos) de diferentes geometrias. É mostrado que, em certas condições, cavidades dieléctricas de geometrias complexas podem suportar estado fotónicos discretos que, no limite em que as perdas materiais são nulas, possuem tempos de vida infinitos. Estes estados surgem devido à acção dos plasmões de volume suportados pela camada plasmónica exterior do meta-átomo e podem ser excitados eficientemente por uma onda plana quando o núcleo do ressoador possui uma resposta não-linear. Demonstra-se que a energia aprisionada no núcleo do ressoador é precisamente quantizada. Depois, é investigado o impacto dos efeitos de dispersão espacial, causados por exemplo pelas interacções electrão-electrão em metais, nos estados próprios embebidos suportados por ressoadores abertos plasmónicos tridimensionais. Heuristicamente, seria de esperar que as interacções repulsivas electrão-electrão agissem de maneira deteriorante no mecanismo de localização de luz e, portanto, tivessem um impacto negativo na formação dos estados próprios embebidos. Surpreendentemente, é mostrado neste trabalho que a dispersão não-local do material que encapsula o meta-átomo dá origem a novos graus de liberdade e relaxa os requisitos necessários ao aprisionamento da luz. Em particular, a condição que exige que o material da cápsula exiba uma permitividade exactamente igual a zero deixa de ser obrigatória, passando a ser possível que a mesma cápsula suprima a perda por radiação em várias frequências. É estudada de seguida a possibilidade de aprisionar e guiar luz em metamateriais de fios metálicos. Especificamente, investigamos os modos guiados suportados por um metamaterial formado por dois planos de fios metálicos mutuamente ortogonais. É demonstrado que o meio de fios tem um diagrama de dispersão peculiar, semelhante a um pente. No limite em que o material é visto como um meio contínuo (homogeneizado), o metamaterial suporta um número divergente de “ramos” de modos guiados que se acumulam junto à linha da luz devido à forte resposta hiperbólica do metamaterial no limite estático. Num sistema realista, o número de ramos é finito e determinado pela densidade de fios. Curiosamente, os modos são caracterizados por uma variação do campo rápida na direcção transversal, que pode ser explorada na detecção de partículas e defeitos de dimensão sub-lambda. Por último, são investigados modos de luz topologicamente aprisionados em cristais fotónicos. São estudadas as propriedades topológicas de sistemas periódicos unidimensionais, e é mostrado que o número de bandas abaixo do hiato de frequências determina o número de Chern de um sistema extendido com uma dimensão sintética. É demonstrado teórica e numericamente que, no espaço-real, o número de Chern determina o número de estados aprisionados na interface de um cristal fotónico no intervalo de frequências da banda não-propagante, quando a sua geometria sofre uma deslocação contínua de um período de estrutura. Além disso, é introduzida uma nova classe de sistemas topológicos com inversão de simetria e números de Chern fraccionários. É provado que o número topológico fraccionário é devido às descontinuidades do Hamiltoniano no domínio espectral. É introduzida uma correspondência volume-interface que liga o número de estados de interface com o número topológico fraccionário.
Instituto de Telecomunicações

碩士
國立清華大學
原子科學系
93
Owing to the vigorous development of nano-technology, the bandgap region of photonic crystals or electro-optical devices can be shifted from microwave to infrared or visible light and applications of photonic crystals(PBG) are more extensively and practically. Nano-technology can apply to fabricate many kinds of novel electro-optical devices. Most importantly, it can reduce the volume of these devices substantially and thus will be engaged in highly concentrated integration of electro-optical devices. In this thesis, we study three kinds of subwavelength structure electro-optical devices. First, we use HDPCVD(High Density Plasma Chemical Vapor Deposition) to improve conventional autocloning method and expect to fabricate 2-D PCs waveguide by simpler, reproducible and flexible process. Second, we use autocloning method to fabricate the antireflection layer of solar cell. We also discuss negative refraction lens in this study. We successfully fabricate 2-D PCs waveguide and the antireflection layer of solar cell by using autocloning method. We also use 2D FDTD(Finite-difference time-domain) to simulate negative refraction phenomenon of low-index material, and apply to the fabrication of negative refraction lens. Many characteristics of electro-optical devices are obtained and the valuable applications are also analyzed.

碩士
長庚大學
電子工程學系
101
For last few years, the GaN-based light emitting diodes(LEDs) have great developed. But in the illumination applications, light extraction of GaN-based LEDs remains limited, one of the most significant problem is the total internal reflection of trapped light within GaN material with high refractive index. In this dissertation, for improving the light extraction efficiency, electron-beam lithography and inductively plasma dry etching were used to achieve sub-wavelength grating-periodic structures with exact dimensions on the p-side of nitride-based LEDs with multiple quantum wells. The main focus of the dissertation can be divided into two parts. First, fixed the Air duty cycle, change the period of structure, to find the best period. Second, fixed the period of structure, change the part of air, to find the best air duty cycle. Done for different periods and air duty cycle in discussion.