Sharif Digital Repository

An approximate and accurate enough multi-conductor transmission line model is developed for analysis of side-coupled metal-insulator-metal (MIM) waveguides. MIM waveguides have been already modeled by single conductor transmission lines. Here, the side coupling effects that exist between neighboring plasmonic structures are taken into account by finding appropriate values for distributed mutual inductance and mutual capacitance between every two neighboring conductors in the conventional single-conductor transmission line models. In this manner, multi-conductor transmission line models are introduced. Closed-form expressions are given for the transmission and reflection of miscellaneous MIM... 

A coupled transmission line model whose parameters are analytically given is provided for fast and accurate analysis of miscellaneous plasmonic structures with metal-dielectric-metal (MDM) arrangement. The coupling of surface plasmons supported by the planar metal-dielectric interfaces is included in the proposed model and thereby the effects of the first non-principal mode of the MDM waveguide are considered. In particular, MDM bends, junctions, and stubs are studied. Using rigorous numerical solutions, e.g., the finite-element method and the finite-difference time-domain, it is shown that the proposed model is accurate in all those cases  

Bluetooth headsets are one of the popular accessories of mobile phones because of their convenience. It is necessary to assess the impact of electromagnetic waves on the human head when a person is using a headset. In this paper different scenarios closely modeling the situations that a subject may use the headset in real life are simulated. Simulations are performed for two types of materials commonly used to manufacture the headsets, namely silicone and acetal, and for two different orientation angle of the headset on the ear. Specific Absorption Rate (SAR) and path loss values are then obtained for two different environments, the open space and inside a car. SEMCAD-X software is used as a... 

It has been proposed that emission spectrum of random lasers with magnetically active semiconductor constituents can be made tunable by external magnetic fields. By employing the FDTD method, the spectral intensity and spatial distribution of electric field are calculated in the presence of an external magnetic field. It is numerically shown that due to the magneto-optical Voigt effect, the emission spectrum of a semiconductor-based random laser can be made tunable by adjusting the external magnetic field. The effect of magnetic field on the localization length of the laser modes is investigated. It is also shown that the spatial distribution of electric field exhibited remarkable... 

Time-dependent model is presented to simulate random lasers in the presence of an inhomogeneous gain medium. PbSe quantum dots (QDs) with an arbitrary size distribution are treated as an inhomogeneous gain medium. By introducing inhomogeneity of the PbSe QDs in polarization, rate, and Maxwell's equations, our model is constructed for a one-dimensional disordered system. By employing the finite difference time-domain method, the governing equations are numerically solved and lasing spectra and spatial distribution of the electric field are calculated. The effect of increasing the pumping rate on the laser characteristics is investigated. The results show that the number of lasing modes and... 

We substitute different types of photonic crystal waveguide components by approximate transmission line circuits. The proposed distributed circuits exploit the analogy of wave propagation in photonic crystal waveguides and transmission lines. They are either cascaded to each other or inserted like stubs to imitate wave propagation within the photonic structure. Notable examples, e.g. coupled waveguide-cavity systems, sharp 90° bends, and T-junctions, are studied in detail. It is shown that analysis of the proposed circuits here can yield accurate enough results and thus substitute the brute-force numerical methods. The privilege of having analytical models is exploited to improve the... 

Many standards are not considering Specific Absorption Rate (SAR) measurements with the use of mobile headsets.In this paper a simulation of mobile headset effects on a human head is done using FDTD-based platform, SEMCAD-X software.We designed two headset models with different case materials to observe their interaction with a Specific Anthropomorphic Mannequin (SAM) phantom as a human head model.Both headset models are installed in the left ear and the human head is rotated by 30±.As headset communicates via Bluetooth at the frequency of 2.4 GHz, we chose a suitable planar inverted F antenna (PIFA) to use with both the headset models.Spatial peak SAR values averaged over 1 g and 10 g for... 

A transmission line model is developed for coupled plasmonic metal-insulator-metal (MIM) waveguides. In the proposed model coupling between electric fields of two plasmonic waveguides is modeled by distributed mutual capacitor while distributed mutual inductor accounts for magnetic field coupling. These mutual elements are determined using propagation constants of supermodes of coupled waveguides. The model is applied to analyze coupled line directional coupler and side-coupled rectangular resonators. The effectiveness of the model is assessed using fully numerical finite-difference time-domain (FDTD) technique. The results have excellent agreement with the numerical methods  

We theoretically demonstrate the tunabiltiy of terahertz random lasers composed of high temperature superconductor YBCO and ruby layers as active medium. The considered system is a one-dimensional disordered medium made of ruby grain and YBCO. Finite-difference time domain method is used to calculate the emission spectrum and spatial distribution of electric field at different temperatures. Our numerical results reveal that the superconductor based random lasers exhibit large temperature tunability in the terahertz domain. The emission spectrum is significantly temperature dependent, the number of lasing modes and their intensities increase with decreasing temperature. Also, we make some... 

We propose that spectral intensity of superconductor based random lasers can be made tunable by changing temperature. The two fluid model and wavelength dependent dispersion formula have been employed to describe the optical response of the superconducting materials. Random laser characteristics have been calculated using the one dimensional FDTD method. Our simulation results reveal that the emission spectrum can be manipulated through the ambient temperature of the system. It is observed that transition from metal phase to pure superconducting phase leads to the enhancement of the laser emission. Furthermore, spatial distribution of the fields in one dimensional disordered media is very... 

In this paper, the lasing action in three-dimensional active random systems has been numerically investigated. Here, random systems of spherical dielectric particles imbedded in an active medium are considered. The quasi steady state approximation for the population inversion of the active medium is applied to solve three dimensional governing equations. Results show that when the density of particles increases to an upper limit, the intensity of lasing modes is enhanced. Also, the effects of pumping rate and particle size on the number of lasing modes and their intensity are studied. Lasing threshold of laser modes in different disordered systems is calculated and it is shown that by an... 

Split-field finite-difference time-domain (SF-FDTD) method can overcome the limitation of ordinary FDTD in analyzing periodic structures under oblique incidence. On the other hand, huge run times of 3D SF-FDTD, is practically a major burden in its usage for analysis and design of nanostructures, particularly when having dispersive media. Here, details of parallel implementation of 3D SF-FDTD method for dispersive media, combined with totalfield/ scattered-field (TF/SF) method for injecting oblique plane wave, are discussed. Graphics processing unit (GPU) has been used for this purpose, and very large speed up factors have been achieved. Also a previously reported formulation of SF-FDTD based... 

We propose a new method to extract the modes of photonic crystal slabs and, thus, obtain their band structures. These slabs, which are 2-D periodic structures with finite thickness, can completely confine light and have the important advantage of simple construction for applications in integrated optic devices. In this paper, reflection pole method (RPM) is utilized to analyze photonic crystal slabs. Modes are poles of reflection and transmission coefficients of multilayered structures. According to this principle, modes can be detected by only pursuing phase variations of transmission coefficients that are equal to π rad. Therefore, extraction of modes becomes fast and simple through... 

A new method for fluorescent microscopy has been proposed. Proposed method uses indirect excitation of fluorophores with nanometer localized illuminating source. Localized source is created at corners of gold nanotriangles which are deposited on glass substrate. Actually the combination of gold nanotriangle (deposited on glass) acts as active substrate (where species will be placed) for our proposed method. The structure will be scanned with a focused beam of laser (or combination of beams). Due to electric field enhancement in corners and edges of nanotringle (because of surface plasmons), third order nonlinear effect will be enhanced accordingly. Enhancement in third order nonlinearity... 

The three-dimensional split-field finite-difference time-domain (SF-FDTD) method is combined with the totalfield- scattered-field method for injecting a plane wave. A formulation is derived for calculating the incidence transformed fields of SF-FDTD on a one-dimensional auxiliary grid. The resulting fields obtained in the scattered zone are used to calculate the far fields, based on a proposed fully time-domain near-to-far-field transformation. The far-field information is used to calculate the extinction cross section of the periodic structure under oblique incidence. To analyze metallic periodic structures, a formulation with a reduced number of variables is proposed based on the auxiliary... 

A novel approach for phototherapy is proposed. The proposed method is based on cell apoptosis according to halting activation of cancer cell membrane receptor by exposure to UV light pulses without any side effect. In the proposed method, gold nanoparticles are directed to cancerous cells by conjugating their surface with specific ligands. UV light is created locally adjacent to cells around the gold nanoparticles. UV light is generated due to nonlinear interaction of visible light with gold nanoparticles because of enhancement in third order nonlinear effects. For example, by using 780 nm laser, 260 nm UV will be generated around the nanoparticle because of third harmonic generation... 

Effect of relaxation time on the performance of photonic crystal optical bistable switches based on Kerr nolinearity is discussed. This paper deals with optical pulses with the duration of about 50 ps. In such cases the steady state response of the optical device can be used to approximate the pulse evolution if the nonlinearity is assumed instantaneous, hence analytical solutions such as the coupled mode theory can be used to obtain the time evolution of the electromagnetic fields. However if the relaxation time of the material nonlinear response is also considered, changes in the power levels and in the shape of the hystersis loop is observed. In this case, we use the nonlinear finite... 

SFDTD was first introduced as modified Finite Difference Time Domain method by Aminian et al in [1]. They used this method to calculate the TE reflection coefficient for grounded slab and also for periodic array of metallic patches. Later Aminian et al used SFDTD for bandwidth determination of soft and hard ground planes [2] and for determination of permittivity of metamaterials [3]. Yunfei Mao et al also used SFDTD for Solving Oblique incident wave on other kind of patches array [4]  

Third order nonlinear effects and its enhancement in gold nanostructures has been numerically studied. Analysis method is based on computationally solving nonlinear Maxwell's equations, considering dispersion behavior of permittivity described by Drude model and third order nonlinear susceptibility. Simulation is done by method of nonlinear finite difference time domain method, in which nonlinear equations of electric field are solved by Newton-Raphshon method. As the main outcomes of third order nonlinear susceptibility, four wave mixing and third harmonic generation terms are produced around gold nanostructures. Results of analysis on different geometries and structures show that third... 

A simple approach is extended for the simulation of Kerr-nonlinear and/or dispersive media through the finite-difference time-domain method. The scheme is able to include different types of linear and nonlinear dispersion in a single and unified formulation. It also provides a method for the simulation of nonlinear dispersive media in such a way that saving time is possible. Also, a new simple technique is presented for the implementation of sources having arbitrary profiles and arbitrary radiation angles. The technique is particularly suited for easy modeling of unidirectional sources like Gaussian beams