Pages (41,133,161,209) were omitted from the thesis as they were completely blank pages. / <p> In this thesis, we propose efficient approaches for design optimization of passive and active photonic devices. These approaches are based on utilizing gradient based optimization algorithms for efficient optimization of photonic devices. Some of the proposed approaches obtain the required gradient (sensitivity) information efficiently using adjoint variable method (AVM) applied directly to the exploited numerical techniques. Other approaches are based on formulating the design problem as an optimization problem using convex programming. These approaches utilize the gradient-based interior point method (IPM) for solving the design.</p> <p> The AVM aims at efficiently obtaining the sensitivity information using the numerical technique. This technique requires a solution of an additional simulation of the adjoint system. The information obtained from the original and the adjoint simulation is sufficient to obtain the response and the sensitivity of the response with respect to all the design parameters. The AVM technique differs for different numerical method. </p> <p> The obtained sensitivity using the AVM approach is not only useful for exploiting gradient based optimization for design optimization, but also for yield and tolerance analyses of the newly proposed designs. </p> <p> We proposed a second order accurate approach to obtain the sensitivity information using finite difference time domain (FDTD) technique. This approach utilizes the AVM to efficiently obtain the sensitivity information. This approach is exploited for efficiently obtaining the sensitivity of the power reflectivity and coupling coefficient of various devices. This approach has been also utilized for obtaining the sensitivity of the dispersion characteristics of different guided wave structures.</p> <p> We also introduce a novel approach for sensitivity analysis of photonic devices using the beam propagation method (BPM). This approach is simple and easy to implement. It exploits the existing factorization of the system matrices for efficient calculation of the sensitivity of the required objective function. This approach is also utilized for sensitivity analysis of the vectorial modal properties of different guided wave structures. This approach is also exploited for sensitivity analysis of various surface plasmon devices. </p> <p> This AVM approach is also exploited to propose a novel design of an optical switch with wide working wavelength band and compact size. The switch is based on the self imaging theory in multimode waveguide with a refractive index has approximate parabolic profile. The design problem is formulated as two stage optimization procedure. The optimization algorithm exploits the efficiently obtained sensitivity information from a BPM simulation. The final design has interesting characteristics.</p> <p> An efficient approach is also proposed to obtain the sensitivity of the energy levels and wavefunctions of different quantum structures obtained using time dependent and time independent Schrodinger equation. This approach is exploited for design optimization of different quantum well lasers.</p> <p> We also propose a convex formulation for the design problem of multilayer optical coatings. This formulation allows for efficient design of structures with large number of layers in fractions of a second without an initial design.</p> / Thesis / Doctor of Philosophy (PhD)

As optical interconnects make their paces to replace traditional electrical interconnects, implementing low cost optical components and hybrid optic-electronic systems are of great interest. In the research work described in this dissertation, we are making our efforts to develop several practical optical components using novel printing technologies including imprinting, ink-jet printing and a combination of both. Imprinting process using low cost electroplating mold is investigated and applied to the waveguide molding process, and it greatly reduces the surface roughness and thus the optical propagation loss. The imprinting process can be applied to photonic components from multi-mode waveguides with 50[mu]m critical dimension down to photonic crystal structures with 500nm hole diameter. Compared to traditional lithography process, imprinting process is featured by its great repeatability and high yield to define patterns on existing layers. Furthermore we still need an approach to deposit layers and that is the reason we integrate the ink-jet printing technology, another low-cost, low material consumption, environmental friendly process. Ink-jet printing process is capable of depositing a wide range of materials, including conductive layer, dielectric layer or other functional layers with defined patterns. Together with molding technology, we demonstrate three applications: proximity coupler, thermo-optic (TO) switch and electro-optic (EO) polymer modulator. The proximity coupler uses imprinted 50[mu]m waveguide with embedded mirrors and ink-jet printed micro-lenses to improve the board-to-board optical interconnects quality. The TO switch and EO modulator both utilize imprinting technology to define a core pattern in the cladding layer. Ink-jet printing is used to deposit the core layer for TO switch and the electrode layers for EO modulator. The fabricated TO switch operates at 1 kHz with less than 0.5ms switching time and the EO modulator shows V[pi][middle dot]L=5.68V[middle dot]cm. To the best of our knowledge, these are the first demonstrations of functional optical switches and modulators using printing method. To further enable the high rate fabrication of ink-jet printed photonic and electronic devices with multiple layers on flexible substrate, we develop a roll-to-roll ink-jet printing system, from hardware integration to software implementation. Machine vision aided real time automatic registration is achieved when printing multiple layers. / text

La thèse montre des solutions pour la réalisation de circuits photoniques intégrés utilisant le caractère volumétrique et les très faibles pertes en propagation des solitons spatiaux . On s'intéresse aux élément de base: interconnections, sources et router optique (comme dispositif d'élaboration). Interconnections et sources sont réalisé dans le niobat de lithium (LN) qui fournis des structures avec une très longe durée temporelle. Le fonctionnement d'un router optique est démontré dans le semiconducteur photorefractif (PR) InP:Fe en raison de sa sensitivité aux longueurs d'onde infrarouges (IR) et à son temps de réponse rapide. On montre que les pertes en propagation dans les interconnections solitoniques peuvent être réduites à nouveau en utilisant un faisceau en polarisation ordinaire qui augmente la variation d'indice de réfraction induite. La réalisation de sources intégrées solitoniques est étudié pour avoir émission en bleu à 400nm et en IR à 1530nm. Celles en bleu sont obtenues par génération de deuxième harmonique ; le rôle du bleu pour la formation des solitons est montré et ses propriété physiques étudiées. Celles en IR sont obtenues en dopant le LN avec des ions (actifs) d'erbium. Leurs effets sur les paramètres PR sont présentés et les solitons spatiaux sont obtenus en excitant l'absorption soit du LN soit de l'erbium. L'amplification de la luminescence est étudié numériquement. Le routage optique dans le InP :Fe est obtenu en faisant interagir deux solitons cohérents et en changeant leur phase relative. L'augmentation de la séparation ou leur fusion est analysé en fonctionne de la distance entre eux, température et intensité de la lumière.

This thesis describes work to create a variety of thin-film photonic devices based upon liquid crystalline materials. Firstly, a variety of liquid crystal phases are polymer- templated by combining a liquid crystalline material with photo-polymerisable reactive mesogens. Upon photo-curing, a polymer scaffold, which is a template of the original phase, is formed with liquid crystal molecules in interstitial sites. This liquid crystal is removed to yield a polymer scaffold which can be used to template the original phase. Here, polymer-templating is used to template the smectic A liquid crystal alignment onto nematic liquid crystals for the first time; this results in materials with improved contrast ratios and faster response times than conventional nematic devices. Next, a study is performed to compare the electro-optic properties of polymer-templated and polymer-stabilised chiral nematic liquid crystals. The enhanced tuning range of polymer-templated liquid crystals is applied to create a polymer-templated liquid crystal laser and to electrically tune its emission wavelength. Subsequently, thin-film elastomeric liquid crystal lasers are created. The lasing wavelength of these films can be reversibly and selectively tuned without hysteresis by subjecting them to a mechanical stress. Finally, work is performed to study the potential of inorganic materials for use in liquid crystal lasers. Transition metal clustomesogens (liquid crystalline materials that contain highly emissive molybdenum clusters) and inorganic-organic perovskites are considered here. The dispersal and emissive properties of clustomesogens in liquid crystals are studied, and they are used to create circularly polarised light sources with a polarisation that can be controlled using electric fields. Layered structures of inorganic- organic perovskite and liquid crystal are created; these exhibit enhanced amplified spontaneous emission. Then, perovskites are used as the gain materials in distributed feedback lasers for the first time. These lasers may be wavelength-tuned by varying the grating spacing of the structure.

Optical waveguide structures and devices are the fundamental basic building blocks of photonic cireuits which play important roles in modern telecommunication and sensing systems. With the fast development of fabrication technologies and in response to the needs of miniaturization and fast increased functionality in future integrated photonic chips, various structures based on high-index contrast waveguides, surface plasmonic polaritons structures, etc., have been widely proposed and investigated. Modeling and simulation methods, as efficient and excellent cost performance tools comparing to costly facilities and time-consuming fabrication procedures, are demanded to explore and design the devices and circuits before their finalization. This thesis covers a series of techniques for modeling, simulation and design of photonic devices and circuits with the emphasis of handling of radiation wave and the related power couplings. The fundamental issue in optical waveguide analysis is to obtain the complete mode spectrum. In principle, we need the radiation modes to expand the arbitrary fields of an open waveguide. In practice, however, the continuum nature of the radiation modes makes them hard to use. The discrete leaky modes may approximately represent a cluster of radiation modes under some circumstance and can be utilized in mode expansion together with guided modes to significantly simplify the analysis of mode coupling problems in optical waveguides. However, the leaky modes are unbounded by nature and hence lack the usual characteristics of normal guided modes in terms of normalization and orthogonality. Recently a novel scheme for handling of radiation optical fields was proposed and demonstrated by applying perfectly matching layers (PML) terminated with a perfectly reflecting boundary (PRB) condition. In this scheme, the radiation fields are represented in terms of a set of complex modes, some of which resemble the conventional leaky modes and others associated with the interaction between the PML media and the reflecting numerical boundaries. The mode spectrum is therefore split into the guided modes and complex modes which possess the normal mode features such as normalization and modal orthogonality. The seemingly paradoxical application of both the PML and PRB in the new method has in fact overcome one of the main challenges assoiated with this traditional method, i.e., the desire for discrete, orthogonal, and normalized modes to represent radiation fields and the need for elimination and reduction of spurious reflections from the edges of the finite computation window. With the understanding of mode spectrum, a full vector mode matching method and a complex coupled mode method for analyzing the wave propagation in optical waveguides under the framework of PRL and PRB computation model have been proposed. The methods have been validated through various structures such as waveguide facet, polarization rotators, long/short period gratings etc. Then the proposed techniques have been utilized to design a series of waveguide structures based on surface plasmonic polaritons, slot waveguides etc. / Thesis / Doctor of Philosophy (PhD)

[pt] Polimeros orgânicos de natureza conjugada têm despertado bastante interessante como materiais ópticos não-lineares por serem extremamente promissores para o desenvolvimento de dispositivos fotônicos, como por exemplo dispositivos de comunicações. Além de possuírem resposta óptica não - linear intensa e rápida, seu modo de preparação e sua forma final apresentam grande flexibilidade. Do ponto de vista de aplicação, os parâmetros do material mais importantes são : a susceptibilidade não-linear de terceira ordem (x (3)) cuja parte real está relacionada com o índice de refração não-linear e a parte imaginária relacionada com o coeficiente de absorção não-linear; o tempo de resposta; o coeficiente de absorção linear no comprimento de onda de operação (alfa L); a capacidade de processamento; o limiar de dano e a estabilidade térmica. Dentre os polímeros conjugados, destaca-se a família dos politiofenos, compostos heterocíclicos de elevada estabilidade, que exibem interessantes propriedades de transporte e acentuada não-linearidade de terceira ordem. Neste trabalho as propriedades ópticas do politiofeno: X (3), partes real e imaginária; alfaL; e tempo de resposta, foram investigadas experimentalmente. A técnica utilizada para medida dos efeitos não-lineares de terceira ordem foi a técnica de Z-scan convencional. Os valores absolutos e s sinais do índice de refração não - linear e do coeficiente de absorção não-linear foram encontrados como sendo da ordem de - 10 -12 cm 2/W e - 10 - 8 cm/W, respectivamente. Para analisar os resultados experimentais foi necessário utilizar um tratamento teórico relativamente novo. Esta abordagem teórica é diferente da convencional e fornece resultados satisfatórios que descrevem bem os resultados experimentais. O tempo de resposta da não-linearidade do politiofeno foi obtido com a técnica de Z-scan resolvida no tempo, utilizando um único comprimento de onda e polarizações cruzadas. O valor obtido foi inferior à 100 os. Além de caracterizar o politiofeno, foi também demonstrada a utilização dexte polímero comoporta lógica E (AND)m através de uma medida envolvendo chaveamento Kerr. Este experimento mostrou que é possível realizar um chaveamento total óptico onde um feixe de luz é controlado por um outro feixe de luz, com duração de algumas dezenas de picossegundos. / [en] Conjugated organic polymers are of wide interest as nonlinear optical materials because of their potential applications in photonic devices, such as communication devices. They have a large and fast nonlinear optical response, as well as a great flexibility in their preparing method. For device applications, the most important parameters are: third-order optical nonlinear susceptibility X(3), which real part is related with nonlinear refractive index and imaginary part is related with nonlinear absorption coefficient; response time; absorptioon at operating wavelength alfaL; processability; damage threshold; and thermal stability. There are many conjugated polymers, and the polythiophene class, which includes high stabilityn heterocyclic compunds, is one of the most impoant because of its interesting transport properties and large third-order nonlinearity. In this work the optical properties of polythiophene: X (3), real and imaginary parts; alfaL and time response, were investigated experimentally. The Z-scan technique was used to measure the third-order nonlinear effects. The value and the sign of the nonlinear refractive index and nonlinear absorption coefficient of the polythiophene were found to be around -10 -12cm2/W and -10-8 cm/W, respectively. To analyze the experimental data it wass necessary to use a new theoretical approach. This approach is different from the conventional one and produces better fitting of the experimental results. The nonlinear response time of the polythiophene was measured using the time-resolved Z-scan technique, using a single waveguide and perpendicular polarizations. The time response is smaller than 100 ps. Besides the polythiophene characterization, it was demonstrated that this polymer can work like an AND logical gate using Kerr switching. This wxperiment showed that it is possible to make a fast (picoseconds) all- optical switch using a light beam to control another light beam.

Pages viii, xii, xiv, 32, 110, 182, 188, 194 were blank and therefore omitted. / <p> The functional density of photonic integrated circuits can be significantly increased by stacking multiple waveguide layers. These vertically-integrated devices require optical couplers to switch light signals between their layers. In this thesis, optical coupling between two stacked silicon-on-insulator slab waveguides has been demonstrated with a coupling efficiency of 68±4%, obtained with a coupler length of 3535 μm. The main advantage of using a silicon-based material system for photonic integrated circuits is its compatability with existing electronics manufacturing processes, facilitating cost-effective fabrication and the monolithic integration of both photonics and electronics on a single device. </p> <p> Coupling between more complex silicon-on-insulator waveguide structures with lateral confinement was then demonstrated. The coupling ratio between stacked silicon rib wavelengths was measured to be 54±4%, while ratios of 71±4% and 93±4% were obtained for stacked channel waveguide and multimode interferometer-based couplers respectively. The corresponding coupler lengths for these three designs were 572 μm, 690 μm and 241 μm respectively. The sensitivity of these couplers to the input wavelength and polarization state has also been evaluated. These vertical-integrated couplers, along with other structures, have been thoroughly simulated, including their tolerance to fabrication errors. Novel fabrication processes used to demonstrate coupling in proof-of-concept devices have been developed, including an in-house wafer bonding procedure. </p> / Thesis / Doctor of Philosophy (PhD)

This thesis describes the outcome of study to investigate methods of broadband matching to photonic devices such as lasers and high speed detectors. The thesis is divided into two areas of interest relating to the design of broadband fiber optic links. The first area is the application of numerical methods and commensurate line methods to the design of compact equalisers which allow an improved transducer power gain over a wide band. It is shown that physically small equalisers can yield an improvement of 4 dB over a 2 GHz bandwidth. The second area considered is the distortion inherent in a laser diode. Detailed measurements of the second order and intermodulation products are given. A small signal perturbation analysis is presented which helps to explain the observed distortion products. The results of numerical simulation of the distortion using a state variable implementation of the full rate equations and related first, second and intermodulation equations is presented and possible methods of reducing the distortion are explored. It is shown that in principle the distortion could be reduced by pre-generating the distortion and adding an inverted form of the distortion to the transmitted signal. The distortion can then be corrected in the fiber and simulation studies suggest that an improvement of 13 dB optical or 26 dB electrical may be possible.

The field of Information and Communication Technologies is witnessing a development speed unprecedented in history. Moore’s law proves that the processor speed and memory size are roughly doubling each 18 months, which is expected to continue in the next decade. If photonics is going to play a substantial role in the ICT market, it will have to follow the same dynamics. There are mainly two groups of components that need to be integrated. The active components, including light sources, electro-optic modulators, and detectors, are mostly fabricated in III-V semiconductors. The passive components, such as waveguides, resonators, couplers and splitters, need no power supply and can be realized in silicon-related semiconductors. The prospects of silicon photonics are particularly promising, the fabrication is mostly compatible with standard CMOS technology and the on-chip optical interconnects are expected to increase the speed of microprocessors to the next generation. This thesis starts with designs of various silicon-based devices using finite-difference time-domain simulations. Parallel computation is a powerful tool in the modeling of large-scale photonic circuits. High Q cavities and resonant channel drop filters are designed in photonic crystal platform. Different methods to couple light from a single mode fiber to silicon waveguides are studied by coupled-mode theory and verified using parallel simulations. The performance of waveguide grating coupler for vertical radiation is also studied. The fabrication of silicon-based photonic devices involves material deposition, E-beam or optical lithography for pattern defining, and plasma/wet-chemistry etching for pattern transfer. For nanometer-scaled structures, E-beam lithography is the most critical process. Depending on the structures of the devices, both positive resist (ZEP520A) and negative resist (maN2405) are used. The proximity and stitch issues are addressed by careful dose correction and patches exposure. Some examples are given including photonic crystal surface mode filter, micro-ring resonators and gold grating couplers. In particular, high Q (2.6×105), deep notch (40 dB) and resonance-splitting phenomenon are demonstrated for silicon ring resonators. It is challenging to couple light into photonic integrated circuits directly from a single-mode fiber. The butt-coupled light-injecting method usually causes large insertion loss due to small overlap of the mode profiles and large index mismatch. Practically it is not easy to cleave silicon sample with smooth facet where the waveguide exposes. By adding gold gratings to the waveguides, light can be injected and collected vertically from single-mode fiber. The coupling efficiency is much higher. There is no need to cleave the sample. The access waveguides are much shortened and the stitch problem in E-beam lithography is avoided. In summary, this thesis introduces parallel simulations for the design of modern large-scale photonic devices, addresses various issues with Si-based fabrication, and analyses the data from the characterization. Several novel devices using silicon nanowire waveguides and 2D photonic crystal structures have been demonstrated for the first time. / QC 20100923

Coherent optical signal processing systems typically require dynamic, low-loss phase changes of an optical signal. Waveform generation employing phase modulation is an important application area. In particular, laser radar systems have been shown to perform better with non-linear frequency chirps. This work shows how dynamically tunable integrated optical ring resonators are able to produce such phase changes to a signal in an effective manner and offer new possibilities for the detection of phase-modulated optical signals. When designing and fabricating dynamically tunable integrated optical ring resonators for any application, system level requirements must be taken into account. For frequency chirped laser radar systems, the primary system level requirements are good long range performance and fine range resolution. These mainly depend on the first sidelobe level and mainlobe width of the autocorrelation of the chirp. Through simulation, the sidelobe level and mainlobe width of the autocorrelation of the non-linear frequency modulated chirp generated by a series of integrated optical ring resonators is shown to be significantly lower than the well-known tangent-FM chirp. Proof-of-concept experimentation is also important to verify simulation assumptions. A proof-of-concept experiment employing thermally tunable Silicon-Nitride integrated optical ring resonators is shown to generate non-linear frequency modulated chirp waveforms with peak instantaneous frequencies of 28 kHz. Besides laser radar waveform generation, three other system level applications of dynamically tunable integrated optical ring resonators are explored in this work. A series of dynamically tunable integrated optical ring resonators is shown to produce constant dispersion which can then help extract complex spectral information. Broadband photonic RF phase shifting for beam steering of a phased array antenna is also shown using dynamically tunable integrated optical ring resonators. Finally all-optical pulse compression for laser radar using dynamically tunable integrated optical ring resonators is shown through simulation and proof-of-concept experimentation.