Sharif Digital Repository

Nonuniform superconducting microstrip transmission lines in microwave regime have been investigated. Nonuniform transmission lines provide the capability of controlling line parameters. Photonic structures with subwavelength features can be homogenized and thus be accurately approximated by homogeneous yet spatially dispersive structures. This idea is here applied to nonuniform superconducting transmission lines with subwavelength nonuniformities, i.e. subcentimeter features in the microwave regime. This modelling is quite useful in geometrical and optical control of quasi-TEM wave propagation and dispersion engineering along microwave superconducting lines. This approach has applications... 

Ring and disk resonator are studied in this thesis. First, the complex resonance frequencies of two-dimensional homogeneous ring and disk resonators are extracted by following the standard approach and then a novel method is proposed to extract the complex eigen-frequencies of two-dimensional inhomogeneous ring and disk resonators. The inhomogeneity of the refractive index is arbitrary along the radial direction. The proposed method is shown to be more efficient than the standard approach based on the stair-case approximation. It is therefore appropriate for resonator design and is thus employed for systematic study of the opposing trends of geometrical parameters in maximization of... 

Full numerical methods are usually used for the analysis of periodic structures such as photonic crystals and diffraction gratings. The main drawback of these methods is that they are time-consuming and thus are not appropriate for the design process. In this thesis, approximate and fast methods, based on transmission line models, for the analysis of periodic structures are proposed. To this end, in the first part of the thesis, we investigate one-dimensionally periodic metallic gratings. Longitudinally homogenous metallic gratings, enhanced reflection phenomenon and longitudinally inhomogenous metallic gratings are examined, and simple, and efficient transmission line models for these cases... 

Today’s technological trend towards higher performance microwave and digital circuits at increasingly smaller sizes poses new challenges to both the microwave and high-speed VLSI designers. One aspect of these challenges lies in the fact that nonuniform transmission structures must often be used to reduce circuit sizes, to increase circuit bandwidth, to reduce discontinuity effects, and to optimize the overall circuit performance. Coupled microwave transmition lines are one of most common microwave circuits, that are use to design couplers, power dividers, hybrids, baluns, filters, phase shifters, matching circuts and so on. The broadband tight couplers are one of interesting devices that... 

In this thesis a rigorous approach toward systematic quantification of qualitative fea-tures in a three-dimensional (3D) integral imaging is proposed. Incorporating the concepts of sampling rays and sampling points, the first approach is based on geo-metrical optics and quantifies the lateral and depth resolutions of the system within the field-of-view (FOV) and depth-of-field (DOF). The obtained results are justified through experiments. In the next step, the principals of wave optics are employed to measure the lateral and depth resolutions of the system. To this end, the concept of point-spread function is generalized to three-dimensional imaging systems. Through this systematic approach the... 

Because of widespread use of optical communication systems, analysis of optical wavepacket behavior during propagation in optical devices is of great importance. On the other hand, constant demand for improving the quality of data transmission and increasing data processing speed raises the necessity of studying novel electromagnetic structures for the purpose of designing new optical devices. Therefore, Photonic Crystal (PC) based structures, for their unique optical properties, have been subject of vast investigation in last two decades. Control of optical wavepacket behavior in photonic crystal based structures is considered in the present dissertation. Depending on the structure under... 

In recent years, thin-film photovoltaic cells with thicknesses of less than 1-2 µm have been developed with potentially lower production costs. Due to the small thickness of the absorbing semiconductor in these cells, the absorption is inevitably low at energies close to the electronic band gap of the semiconductor. This is particularly a problem for thin-film devices. Recently، periodic metallic nanostructures supporting surface plasmons have been introduced as alternative solutions to achieve light trapping in thin-film solar cells.Full numerical methods are usually used for the analysis of these periodic structures. The main drawback of these methods is that they are time-consuming and... 

In several electro-optic and optoelectronic devices, we require the structures with simultaneous high electrical conductivity and optical transparency so as to transmit the incident light. Transparent Conductive Electrodes (TCEs) that are both highly conductive and transparent were introduced to be an answer to the mentioned challenge. Periodic arrays of metallic holes are amongst the most important structures that are used as transparent electrodes. Using the metals with low electrical resistivity, such as Au and Ag, provides these structures with high electrical conductance. On the other hand, since these micro/nano structures support the propagation of guided electromagnetic waves, light... 

Due to the growing need for plasmonic wavs in microwave and terahertz spectra, a periodic arrangement of one-dimensional cut-through slits is investigated and an equivalent model based on the effective medium theory is derived. In contrast to the all previous attempts that were successful in mimicking only the zeroth-order diffracted waves, the proposed effective medium is capable of mimicking all diffraction orders. The parameters of the equivalent model are established by comparing the scattered waves of the semi-homogeneous medium and those of the main structure obtained by invoking the rigorous mode matching approach based on the single mode approximation inside the slits. This medium is... 

Despite of significant developments of optical trapping in past decays, trapping of small nanometer-sized particle faces some difficulties. Optical force reduces rapidly by decreasing the size of the particle because of reducing the particle’s polarizability. So, it is necessary to increase the intensity of incident beam to attain a stable trap. However, it can lead to damage of particle before getting trapped. Self induced back-action(SIBA) is one of the proposed solutions to overcome this problem. In this phenomena particle plays an active role in trapping by changing the surrounding electromagnetics field. In this thesis, we show that SIBA is a phenomenon that appears when we extend the... 

Subwavelength localization of electromagnetic energy with intense local fields, also known as electromagnetic hotspots, has received significant attention over the past few decades. In most cases the hotspot is achieved through the resonant concentration of electromagnetic fields. One way recently considered to get hotspot is through reflection of electromagnetic waves in nonreciprocal one-way structures, in plasmonics and via magneto optic effect.However these hotspots are less confined compared to hotspots caused by resonances. So combining nonreciprocal structures with resonance can provide better hotspots.Our aim in this thesis is to study nonreciprocal resonant structures using coupled... 

Semi-analytical solutions for the nonlinear, one dimensional wave equation have been investigated. The aim of this procedure is to deliver fast and yet accurate approaches for solving the abovementioned equasions. These solutions make a good alternative for full-numerical methods, which are usually time consuming and combersome. Therefore the proposed methods may find complete priority, considering design goals. Lack of a fast numerical method for solving the nonlinear, steady state cases, make the proposed approaches relevant, dealing theses problems. By employing the presented methods, It is possible to effieciently simulate the behavior of the space-wave packet, incident on the nonlinear... 

Diabetes is one of the most catastrophic diseases in the world. There will be an end to patients’ problems if scientists can invent the artificial pancreas, but there is no implantable sensing core available. All of the sensors used for measuring blood glucose level were based on an electrochemical sensor which will generate a glucose level dependent electric current. The chemical structure of that sensor will deny its usability for in vivo applications. By exploring several biological and electrical literatures we introduced a fully electrical method for sensing the blood glucose level by impedance measurement. In this thesis we introduced a new method for sensing the blood glucose... 

Impedance spectroscopy is known as one of the important integrated sensing methods in micro scale Biosensors and electrochemical sensors. Recently, Impedance spectroscopy has been noticed in many micro scale applications. These micro scale applications is being developed specially in bioelectronics and biomedical. The goal of this thesis is designing an on-chip impedance spectroscope system for high frequency with 10 bits resolution via fully electrical blood glucose concentration measurement. This system extracts the blood glucose concentration data through measuring the permittivity coefficient of blood at 1 GHz frequency. In this thesis, new method for high frequency high resolution... 

The Bragg reflection mechanism is in this thesis employed to design optical fibers with specific characteristics. First, optical Bragg fibers (BF) with radial periodicity are considered and optimized to have the minimum leakage loss by introduction of a new parameter referred to as the point-wise wave-number. In this fashion, the optical effects of geometrical factors of the to-be-designed fiber are brought together in the point-wise wave-number and the sought-after parameters of the fiber are thus analytically found. Despite a few approximations made in extraction of optimum parameters, rigorous numerical analysis of the here-proposed optical BF clearly demonstrates that it outperforms... 

In this thesis, the unwanted effects of diffraction and defocus aberration in three-dimensional (3D) integral imaging are taken into account by using the principles of Fourier optics approach. First, the indirect reconstruction of 3D images is simulated by using the geometrical optics and then the direct reconstruction process is simulated via Fourier optics. The role of diffraction and defocus aberration in deterioration of the depth of field is studied for both real/virtual and focused modes of integral imaging. The extent of image deterioration in 3D integral imaging is compared against the extent of deterioration in conventional single lens imaging. The field of view of the 3D integral... 

In this thesis, while a comprehensive study of different methods for the characterization of the optical fibers is done, a unique and effective method is being introduced for the characterization of the dispersion coefficient of Highly Nonlinear Fibers (HNLFs). The proposed method is based on the Brillouin Optical Time Domain Analysis (BOTDA) of a wave generated by the Four Wave Mixing (FWM) interaction. The current method, which includes an experimental scheme and an algorithm for solving the inverse problem, offers high sensitivity and experimental accuracy at the longitudinal resolution of 1 meter. The noise level has been considerably reduced by understanding different sources of the... 

Reservoir Computing is a novel computing paradigm that uses a nonlinear recurrent dynamical system to carry out information processing. Recent electronic and optoelectronic Reservoir Computers based on an architecture with a single nonlinear node and a delay loop have shown performance on standardized tasks comparable to state-of-the-art digital implementations. Here we report an all-optical implementation of a Reservoir Computer, made of off-the-shelf components for optical telecommunications. It uses a semiconductor optical amplifier as nonlinearity, and a Fabry-Perot Resonator as a key element to establish the virtual nodes, connecting them and consequently, build the virtual neural... 

Structures with time-varying electromagnetic properties can potentially yield non-reciprocity, amplification, harmonic generation, and other interesting wave propagation phenomena. To date, some studies have dealt with time-varying media and circuits, including time-varying optical ring resonators having degenerate travelling wave resonances. In time-varying ring resonators, the clockwise and counter clockwise resonances lose their degeneracy, and non-reciprocity is observed. One of the main challenges of such research is the need to induce time-variations in the entirety of the resonator or structure, which makes their implementation very limited or impossible in practice. The purpose of... 

In this thesis, the Maxwell's equations are transformed into a set of ordinary differential equations and then solved in periodic structures by using the differential method (DM). The periodic structures considered in this thesis are carved in linear anisotropic, nonlinear isotropic and nonlinear anisotropic media. Different numerical issues, e.g. stability and convergence rate, are addressed by following the conventional methods, e.g. S- and R- matrix formalism, and Fourier factorization. In addition, an algorithm is proposed for fast and efficient analysis of periodic structures with identical layers. Binary gratings and photonic crystals are examples of such structures. In this algorithm,...