In this work, we investigate several aspects of photonic crystal waveguides through modeling and simulation. We introduce a one-dimensional model for two-dimensional photonic crystal fibers (PCFs), analyze tapered PCFs, analyze planar photonic crystal waveguides and one-dimensional PCFs with infinite periodic cladding, and investigate transmission properties of a novel type of fiber, referred to as Fresnel fiber. A simple, fast, and efficient one-dimensional model is proposed. It is shown that the model is capable of predicting the normalized propagation constant, group-velocity dispersion, effective area, and leakage loss for PCFs of hexagonal lattice structure with a reasonable degree of accuracy when compared to published results that are based on numerical techniques. Using the proposed model, we investigate tapered PCFs by approximating the tapered section as a series of uniform sections along the axial direction. We show that the total field inside the tapered section of the PCF can be evaluated as a superposition of local normal modes that are coupled among each other. Several factors affecting the adiabaticity of tapered PCFs, such as taper length, taper shape, and number of air hole rings are investigated. Adiabaticity of tapered PCFs is also examined. A new type of fiber structure, referred to as Fresnel fiber, is introduced. This fiber can be designed to have attractive transmission properties. We present carefully designed Fresnel fiber structures that provide shifted or flattened dispersion characteristics, large negative dispersion, or large or small effective area, making them very attractive for applications in fiber-optic communication systems. To examine the true photonic crystal modes, for which the guidance mechanism is not based on total internal reflection, photonic crystal planar waveguides with infinite periodic cladding are studied. Attention will be focused on analytical solutions to the ideal one-dimensional planar photonic crystal waveguides that consist of infinite number of cladding layers based on an impedance approach. We show that these solutions allow one to distinguish clearly between light guidance due to total internal reflection and light guidance due to the photonic crystal effect. The analysis of one-dimensional PCFs with infinite periodic cladding is carried out in conjunction with an equivalent T-circuits method to model the rings that are close to the core of the fiber. Then, at sufficiently large distance from the core, the rest of the cladding rings are approximated by planar layers. This approach can successfully estimate the propagation constants and fields for true photonic crystal modes in both solid-core and hollow-core PCFs with a high accuracy. <i>Original file (released May 10, 2007) replaced Oct. 3, 2012 GMc per DePauw]</i> / Ph. D.

Photonic crystals (PCs) are structures with spatially periodic variations in dielectric constants. The prime property of PCs is the existence of the photonic band gaps (PBGs) which could prohibit the propagation of light within a certain frequency range. Once the PC structures are fabricated, it is hard to tune their optical properties for the fixed geometries. Thus, it is important to develop tunable PC waveguide devices for the applications in the photonic integrated circuits. We utilize the mode-gap effect to design two-dimensional (2-D) tunable Y-shaped PC waveguides with the polyaniline type electrorheological (ER) fluids. The propagation of light on the Y-shaped waveguide can be controlled by applying the electric field in specific regions. Besides, we also propose a tunable multi-channel PC waveguide with the polyaniline type ER fluids. We then investigate the tunable propagation characteristics of a 2-D single line-defect PC waveguide with liquid crystals (LCs) by varying the direction of LCs and the hole sizes. We also simulate the tunable optical properties of a 2-D Y-shaped PC waveguide utilizing LCs. Finally, we consider a 3-D Y-shaped PC slab waveguide with LCs. The effects of the direction of LCs and the slab thickness are discussed.

A theoretical investigation of one-dimensional planar photonic crystal waveguides is carried out. These waveguides consist of a dielectric layer sandwiched between two semiinfinite periodic dielectric structures. Using a novel approach, exact analytical solutions for guided modes in such waveguides are presented. The se rigorous solutions allow one to distinguish clearly between the index-guiding regime and guidance due to the photonic crystal effect. In the first part of this investigation, a rigorous analysis of the reflection of uniform plane waves from a semi- infinite periodic dielectric structure is undertaken. Both parallel and perpendicular polarizations for the incident plane wave are considered. Exact expressions for the reflection coefficients corresponding to two polarization cases are obtained using an impedance approach. The results for the reflection coefficient are then used to study propagation properties of guided modes in one-dimensional photonic crystal waveguides with semiinfinite periodic cladding regions. Characteristic equations, from which propagation constants of guided modes can be obtained, and solutions for electromagnetic fields of these modes are derived. Solutions for both TE (transverse electric) and TM (transverse magnetic) modes are presented. Numerical results for the propagation constant and field distributions of several lower-order modes are presented. The solutions unique to photonic crystal waveguides are emphasized. / Master of Science

Microstructure and photonic crystal fibers with periodic as well as random refractive-index distributions are investigated. Two cases corresponding to fibers with one-dimensional (1D) radial index distributions and two-dimensional (2D) transverse index distributions are considered. For 1D geometries with an arbitrary number of cladding layers, exact analytical solutions of guided modes are obtained using a matrix approach. In this part, for random index distributions, the average transmission properties are calculated and the influence of glass/air ratio on these properties is assessed. Important transmission properties of the fundamental mode, including normalized propagation constant, chromatic dispersion, field distributions, and effective area, are evaluated. For 2D geometries, the numerical techniques, FDTD (Finite-Difference Time-Domain) method and FDM (Finite Difference Method), are utilized. First, structures with periodic index distributions are examined. The investigation is then extended to microstructure optical fibers with random index distributions. Design of 2D microstructure fibers with random air-hole distributions is undertaken with the aim of achieving single-mode guiding property and small effective area. The former is a unique feature of the holey fiber with periodic air-hole arrangement and the latter is a suitable property for nonlinear fiber devices. Measurements of holey fibers with random air-hole distributions constitute an important experimental task of this research. Using a section of a holey fiber fabricated in the draw tower facility at Virginia Tech, measurements of transmission spectra and fiber attenuation are performed. Also, test results for far-field pattern measurements are presented. Another objective of this dissertation is to explore new applications for holey fibers with random or periodic hole distributions. In the course of measuring the holey fibers, it was noticed that robust temperature-insensitive pressure sensors can be made with these fibers. This offers an opportunity for new low-cost and reliable pressure fiber-optic sensors. Incorporating gratings into holey fibers in conjunction with the possibility of dynamic tuning offers desirable characteristics with potential applications in communications and sensing. Injecting gases or liquids in holey fibers with gratings changes their transmission characteristics. These changes may be exploited in designing tunable optical filters for communication applications or making gas/liquid sensor devices. / Ph. D.

Silicon is the dominant material in Microelectronics. Building photonic devices out of silicon can leverage the mature processing technologies developed in silicon CMOS. Silicon is also a very good waveguide material. It is highly transparent at 1550nm, and it has very high refractive index of 3.46. High refractive index enables building high index contrast waveguides with dimensions close to the diffraction limit. This provides the opportunity to build highly integrated photonic integrated circuit that can perform multiple functions on the same silicon chip, an optical parallel of the electronic integrated circuit. However, silicon does not have some of the necessary properties to build active optical devices such as lasers and modulators. For Example, silicon is an indirect band gap material that can’t be used to make lasers. The centro-symmetric crystal structure in silicon presents no electro-optic effect. By contrast, electro-optic polymer can be engineered to show very strong electro-optic effect up to 300pm/V. In this research we have demonstrated highly compact and efficient devices that utilize the strong optical confinement ability in silicon and strong electro-optic effect in polymer. We have performed detailed investigations on the optical coupling to a slow light waveguide and developed solutions to improve the coupling efficiency to a slow light photonic crystal waveguides (PCW). These studies have lead to the demonstration of the most hybrid silicon modulator demonstrate to date and a compact chip scale true time delay module that can be implemented in future phased array antenna systems. In the future, people may be able to realize a photonic integrated circuit for optical communication or sensor systems using the devices we developed in our research. / text

The necessity of using extremely high sensitivity biosensors in certain research areas has remarkably increased during the last two decades. Optical structures, where light is used to transduce biochemical interactions into optical signals, are a very interesting approach for the development of this type of biosensors. Within optical sensors, photonic integrated architectures are probably the most promising platform to develop novel lab-on-a-chip devices. Such planar structures exhibit an extremely high sensitivity, a significantly reduced footprint and a high multiplexing potential for sensing applications. Furthermore, their compatibility with CMOS processes and materials, such as silicon, opens the route to mass production, thus reducing drastically the cost of the final devices. Optical sensors achieve their specificity and label-free operation by means of a proper chemical functionalization of their surfaces. The selective attachment of the receptors allows the detection of the target analytes within a complex matrix. This PhD Thesis is focused on the development of label-free photonic integrated sensors in which the detection is based on the interaction of the target analytes with the evanescent field that travels along the structures. Herein, we studied several photonic structures for sensing purposes, such as photonic crystals and ring resonators. Photonic crystals, where their periodicity provokes the appearance of multiple back and forth reflections, exhibits the so-called slow-light phenomenon that allows an increase of the interaction between the light and the target matter. On the other hand, the circulating nature of the resonant modes in a ring resonator offers a multiple interaction with the matter near the structure, providing a longer effective length. We have also proposed a novel approach for the interrogation of photonic bandgap sensing structures where simply the output power needs to measured, contrary to current approaches based on the spectral interrogation of the photonic structures. This novel technique consists on measuring the overlap between a broadband source and the band edge from a SOI-based corrugated waveguide, so that we can determine indirectly its spectral position in real-time. Since there is no need to employ tunable equipment, we obtain a lighter, simpler and a cost-effective platform, as well as a real-time observation of the molecular interactions. The experimental demonstration with antibody detection measurements has shown the potential of this technique for sensing purposes / García Castelló, J. (2014). A Novel Approach to Label-Free Biosensors Based on Photonic Bandgap Structures [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/35398 / TESIS

Les guides à cristaux photoniques sont des guides optiques structurés à des échelles inférieures à la longueur d’onde. La vitesse de groupe de l’onde guidée y est ralentie. L’intensité du champ électromagnétique est ainsi exaltée et permet d’envisager de nombreuses applications pour le traitement optique de l'information. Cependant cette exaltation rend aussi les guides particulièrement sensibles aux imperfections de fabrication. Nous réalisons ici une étude théorique, numérique et expérimentale du transport de la lumière lente dans ces guides en présence de désordre. Le travail théorique propose une extension des méthodes perturbatives (de type Born) au cas des modes de Bloch électromagnétiques et un outil numérique original pour prendre en compte la diffusion multiple, qui devient déterminante lorsque la vitesse diminue. Les prédictions de ces deux types d'analyse ont été confrontées à des résultats expérimentaux. Pour la première fois dans les guides à cristaux photoniques, nous avons mesuré les statistiques d'ensemble du transport, en recoupant des mesures réalisées sur 18 échantillons identiques au désordre de fabrication près. Nous mettons en évidence les véritables limites de fonctionnement de ces guides. Ils ne sont limités ni par la dispersion, ni par leur atténuation moyenne. Les phénomènes de diffusion multiple modifient par contre considérablement la loi de probabilité de transmission. Pour pouvoir utiliser les guides à cristaux photoniques, il faut donc rester dans des régimes de fonctionnement où la diffusion multiple est négligeable, c’est-à-dire soit pour des vitesses de groupe relativement grandes (vg > c/20), soit pour des longueurs de guide faibles. / Photonic crystals are optical materials in which patterning of dielectric materials on a sub-wavelength scale creates unusual optical properties such as propagation speeds that are much slower than the speed of light. Electromagnetic fields are locally enhanced and light-matter interactions are thereby increased. However, because of this enhancement, the waveguides are much more sensitive to fabrication disorder. In this manuscript, we develop a theoretical, numerical and experimental analysis of the light transport in disordered waveguides. The theoretical work proposes an extension of the Born approximation to the case of electromagnetic Bloch modes and a new numerical tool which considers the multiple-scattering that becomes dominant when the group velocity decreases. Predictions of both models have been compared to experimental results. For the first time in photonic crystal waveguides, we measured ensemble-averaged quantities of photonic transport, collected on a series of 18 waveguides that are nominally identical and that only differ by statistical structural imperfections. We deduced the actual working limitations of these guides: they are limited neither by their GVD nor by their averaged losses. However multiple-scattering processes change the transmission probability density function dramatically. In order to use photonic crystal waveguides, it is therefore necessary to keep within regimes, where multiple scattering can be neglected, i.e. for relatively high group velocities (vg > c/20), or for short waveguide lengths.