Numerical modelling of photonic crystal based switching devices

In the last few years research has identified Photonic Crystals (PhCs) as promising material that exhibits strong capability of controlling light propagation in a manner not previously possible with conventional optical devices. PhCs, otherwise known as Photonic Bandgap (PBG) material, have one or more frequency bands in which no electromagnetic wave is allowed to propagate inside the PhC. Creating defects into such a periodic structure makes it possible to manipulate the flow of selected light waves within the PhC devices outperforming conventional optical devices. As the fabrication of PhC devices needs a high degree of precision, we have to rely on accurate numerical modelling to characterise these devices. There are several numerical modelling techniques proposed in literature for the purpose of simulating optical devices. Such techniques include the Finite Difference Time Domain (FDTD), the Finite Volume Time Domain (FVTD), and the Multi-Resolution Time Domain (MRTD), and the Finite Element (FE) method among many others. Such numerical techniques vary in their advantages, disadvantages, and trade-offs. Generally, with lower complexity comes lower accuracy, while higher accuracy demands more complexity and resources. The Complex Envelope Alternating Direction Implicit Finite Difference Time Domain (CE-ADI-FDTD) method was further developed and used throughout this thesis as the main numerical modelling technique. The truncating layers used to surround the computational domain were Uniaxial Perfectly Matched Layers (UPML). This thesis also presents a new and robust kind of the UPML by presenting an accurate physical model of discretisation error. iv This thesis has focused on enhancing and developing the performance of PhC devices in order to improve their output. An improved and new design of PhC based Multiplexer/Demultiplexer (MUX/DEMUX) devices is presented. This is achieved using careful geometrical design of microcavities with respect to the coupling length of the propagating wave. The nature of the design means that a microcavity embedded between two waveguides selects a particular wavelength to couple from one waveguide into the adjacent waveguide showing high selectivity. Also, the Terahertz (THz) frequency gap, which suffers from a lack of switching devices, has been thoroughly investigated for the purpose of designing and simulating potential PhC based switching devices that operate in the THz region. The THz PhC based switching devices presented in this thesis are newly designed to function according to the variation of the resonant frequency of a ring resonator embedded between two parallel waveguides. The holes of the structures are filled with polyaniline electrorheological fluids that cause the refractive index of the holes to vary with applied external electric field. Significant improvements on the power efficiency and wavelength directionality have been achieved by introducing defects into the system

Design, analysis, and optimization of photonic crystal Sensors

It has been more than 30 years that Photonic Crystal (PhC) have been used in wide variety of applications. The photonic bandgap phenomenon and the flexibility of such structures to manipulate the light have made them popular. PhC sensors are popular because of their promising characteristics like high measurement sensitivity, ultra-compact size, suitability for monolithic integration, and flexibility in structural design. In this thesis, a novel framework for designing optimized PhC sensors has been proposed. The complexity of such structures resulted in the lack of an analytical method to design the structures. Therefore, this framework aims to provide a comprehensive and automatic method to find the best values for the structural parameters without human involvement. The framework is explained with an example of designing a PhC liquid sensor. In the framework, an optimizer called Multi-Objective Gray Wolf Optimizer is utilized. However, a diverse range of multi-objective optimizer algorithms could be utilized. The results show that the proposed framework can design any kind of PhC sensor. Simplicity, being straightforward, and no human involvement are the advantages of the proposed framework. In addition, a significantly wide range of optimal designs will be found which are suitable for general and specific applications

Sonic and Photonic Crystals

Sonic/phononic crystals termed acoustic/sonic band gap media are elastic analogues of photonic crystals and have also recently received renewed attention in many acoustic applications. Photonic crystals have a periodic dielectric modulation with a spatial scale on the order of the optical wavelength. The design and optimization of photonic crystals can be utilized in many applications by combining factors related to the combinations of intermixing materials, lattice symmetry, lattice constant, filling factor, shape of the scattering object, and thickness of a structural layer. Through the publications and discussions of the research on sonic/phononic crystals, researchers can obtain effective and valuable results and improve their future development in related fields. Devices based on these crystals can be utilized in mechanical and physical applications and can also be designed for novel applications as based on the investigations in this Special Issue

Metamaterial

In-depth analysis of the theory, properties and description of the most potential technological applications of metamaterials for the realization of novel devices such as subwavelength lenses, invisibility cloaks, dipole and reflector antennas, high frequency telecommunications, new designs of bandpass filters, absorbers and concentrators of EM waves etc. In order to create a new devices it is necessary to know the main electrodynamical characteristics of metamaterial structures on the basis of which the device is supposed to be created. The electromagnetic wave scattering surfaces built with metamaterials are primarily based on the ability of metamaterials to control the surrounded electromagnetic fields by varying their permeability and permittivity characteristics. The book covers some solutions for microwave wavelength scales as well as exploitation of nanoscale EM wavelength such as visible specter using recent advances of nanotechnology, for instance in the field of nanowires, nanopolymers, carbon nanotubes and graphene. Metamaterial is suitable for scholars from extremely large scientific domain and therefore given to engineers, scientists, graduates and other interested professionals from photonics to nanoscience and from material science to antenna engineering as a comprehensive reference on this artificial materials of tomorrow

First order Bragg grating filters in silicon on insulator waveguides.

The subject of this thesis is the design; analysis, fabrication and characterisation of first order Bragg Grating optical filters in Silicon-on-Insulator (SOI) planar waveguides. It is envisaged that this work will result in the possibility of Bragg Grating filters for use in Silicon Photonics. It is the purpose of the work to create as far as is possible flat surface waveguides so as to facilitate Thermo-Optic tuning and also the incorporation into rib-waveguide Silicon Photonics. The spectral response of the shallow Bragg Gratings was modelled using Coupled Mode Theory (CMT) by way of RSoft Gratingmod TM. Also the effect of having a Bragg Grating with alternate layers of refractive index 1.5 and 3.5 was simulated in order to verify that Silica and Silicon layered Bragg Gratings could be viable. A series of Bragg Gratings were patterned on 1.5 micron SOI at Philips in Eindhoven to investigate the variation of grating parameters with a) the period of the gratings b) the duty cycle (or mark to space ratio) of the gratings and c) the length of the region converted to Bragg Gratings (i.e. the number of grating period repetitions). One set of gratings were thermally oxidised at Philips in Eindhoven (this was to simulate the effects of oxidising Porous Silicon) and another set were ion implanted with Oxygen ions at the Ion Beam Facility, University of Surrey. The gratings were tested and found to give transmission minima at approximately 1540 nanometres and both methods of creating flat surfaces were found to give similar minima. Atomic Force Microscopy was applied to the grating area of the Ion as Implanted samples in the ATI, University of Surrey, which were found to have surface undulations in the order of 60 nanometres

Slab photonic crystal demultiplexers : analysis and design

The exploitation of the superprism phenomenon for optical demultiplexing using a slab photonic crystal on the silicon on insulator platform is the main subject of this thesis. The S-vector and k-vector superprisms are considered. Design equations for the S-vector superprism demultiplexer which fully take into account the nonlinear spectral dependence of beam propagation and dispersion are introduced. This allows wide-band coarse wavelength division multiplexing (CWDM) demultiplexers to be designed. Selecting minimum prism area as a metric, the best photonic crystal lattice, design parameters and prism geometry is sought. A full 3-D modeling approach using the plane wave expansion method is employed to ensure the practicality of the design. We show that the slab 1-D photonic crystal can provide the smallest superprism. Based on our result, an area of 1367 mum2 is sufficient to resolve 4 standard CWDM channels (20nm channel spacing). We extend this approach by proposing a stratified photonic crystal which has 5 times less area for an 8 channel CWDM design.We then propose the first fully integrated k-vector superprism layout. Design rules and equations are presented and we use these to obtain the design parameters that result in a minimum prism area. We show that an optimized 1-D photonic crystal k-vector superprism with the area of less than 0.1 mm2 is sufficient to resolve 32 standard dense wavelength division multiplexing (DWDM) channels (100GHz channel spacing). The resulting chip size is approximately 4.5 times less than an equivalent etched grating demultiplexer.We also demonstrate that fast lenses can be made using slab 1-D photonic crystal with an periodicity.We introduce an analytical approximation technique for slab 1-D photonic crystals based on the weighted index method. The variational nature of the method leads to acceptable results for moderate refractive index contrast materials. The method can also be extended to 2-D cases and to nonlinear systems.The plane wave expansion (PWE) method and field matching have been combined to obtain a new method which is capable of obtaining all types of modes including the leaky modes of slab 1-D photonic crystals. The method requires fewer plane waves than the conventional PWE method but provides a better approximation. We compare our results with an accurate finite element method as a benchmark.A report of our first attempt for the fabrication, post-possessing and optical characterization of the proposed k-vector superprism demultiplexer is also presented. We recommend the development of a cladding, and more accurate fabrication procedures for future investigations

Designing periodic and aperiodic structures for nanophotinic devices.

330 p.Future all--optical networks will require to substitute the present electronic integrated circuitry by optical analogous devices that satisfy the compactness, throughput, latency and high transmission efficiency requirements in nanometer scale dimensions, outperforming the functionality of current networks. Thereby, existing dielectric materials do not confine light in a sufficiently small scale and so the physical size of these links and devices becomes unacceptable. In fact, if the optical chip does not exist in the liking of the electronic chip, photonic crystals have recently led to great hopes for a large-scale integration of optoelectronic components. Two-dimensional photonic crystals slabs obtained through periodic structuring of a planar optical waveguide, feature many characteristics which bring them closer to electronic micro-and nanostructures. This thesis explores non-trivial periodic and aperiodic dielectric nano-structures and to do so, we pose a photonic crystal design process guided by non-convex combinatory optimization techniques. In addition, this thesis proposes some novel coupling devices optimized to minimize insertion losses between silicon-on-insulator integrated waveguides and single mode optical fibers. Last but not least, this thesis explores periodic arrangements from a new perspective and reports on the first experimental evidence of topologically protected waveguiding in silicon. Furthermore, we propose and demonstrate that, in a system where topological and trivial defect modes coexist, we can probe them independently. Tuning the configuration of the interface, we observe the transition between a single topological defect and a compound trivial defect state