Sharif Digital Repository

In this paper, the excitation of surface waves in the presence of interface charges is discussed. Interface charges affect the dispersion of surface waves, and therefore they can be used in various applications such as optical modulators, switches, sensors and filters. These waves can be superior to surface plasmon waves since they are not lossy. The lossless property is satisfied in a limited range of millimetre waves to far infrared  

In this paper, the effect of two-dimensional electron plasma formed on the surface of a semiconductor on the refraction phase of an optical beam is investigated. Both the density and effective mass of the surface state electrons can be controlled by a transverse electric field. While the surface density of electrons varies slowly with the applied field, their effective mass changes instantaneously. Therefore, a high bandwidth for the phase modulation can be obtained. It is expected that the device operates in the far-infrared region with a semiconductor as the base material. GaAs is one of the best candidates having both large dynamic range, and large ratio of free electron to the crystal... 

In this article, a time-domain non-linear model is proposed for quantum dynamics of interface traps. This model includes the effects of thermoionic emission, combined with the drift and tunneling currents. The model is simplified for the case of interface traps of the directly bonded Silicon wafers, and linearized. Therefore, an equivalent electrical circuit is obtained being composed of two resistive and capacitive branches. The theory predicts a close spacing between the corresponding zero and pole in the frequency response of the system, being justified by experiment on directly bonded n-type Silicon wafers. The low frequency response to a square-wave is quite in agreement with the... 

In this report, the time-dependent carrier concentration in electrolytic cells, due to some basic periodic shapes, has been studied. Exact analytical solutions for step, sinusoidal and periodic pulse reverse inputs are derived. The effect of frequency, forward and reverse amplitudes, and pulse modulation width are investigated. Analytical solution of the model is obtained as a Fourier series, using Laplace transformations applied to a one-dimensional model with linearized Butler-Volmer electrode kinetics. The results are applied to an acid-copper bath and discussed. It is shown that there exist optimal operation points or optimal current waveforms to obtain efficient and enhanced deposition... 

Line nanopatterns are produced on the positive photoresist by scanning near-field optical microscope (SNOM). A laser diode with a wavelength of 450 nm and a power of 250 mW as the light source and an aluminum coated nanoprobe with a 70 nm aperture at the tip apex have been employed. A neutral density filter has been used to control the exposure power of the photoresist. It is found that the changes induced by light in the photoresist can be detected by in situ shear force microscopy (ShFM), before the development of the photoresist. Scanning electron microscope (SEM) images of the developed photoresist have been used to optimize the scanning speed and the power required for exposure, in... 

An analytic formulation revealing exact contribution of different factors affecting the interference interaction between eigenmodes of a scatterer is presented by utilizing our previously reported modal scattering power formula. For special case of arbitrary multilayer concentric and nonconcentric nanoshells, a recursive method for analytically calculating the T-matrix, and each of these factors is derived. Results for a three layer structure showing the conditions for constructive and destructive interference interactions are discussed in details. It is shown that the interference interaction can occur in the vicinity of the overlapping resonance frequencies of the two spatially overlapping... 

A band structure of one-dimensional periodic media having an arbitrary inhomogeneous refractive index profile is extracted based on the modification committed on the differential-transfer-matrix method (DTMM). Furthermore, the most recently modified differential transfer matrix is improved by reshaping the formulation in terms of which the electromagnetic fields are expanded and closed form formulas, providing the allowed values of Bloch wavenumbers, which were not available before. Although the frequency gaps in previously published results that we derived by using the conventional DTMM were not in agreement with the well-known Bragg law at the edge of each Brillouin zone, the new results... 

Modified forms of WKB expansion of electromagnetic field distribution with variable coefficients are proposed for both TE and TM polarizations. Based on a method similar to the previously reported differential transfer matrix method [1,2], the analytical expressions of those aforementioned coefficients are then derived. The applicability and accuracy of the presented method are shown via some numerical examples. © 2007 EuMA  

Modified forms of WKB expansion of electromagnetic field distribution with variable coefficients are proposed for both TE and TM polarizations. Based on a method similar to the previously reported differential transfer matrix method [1,2], the analytical expressions of those aforementioned coefficients are then derived. The applicability and accuracy of the presented method are shown via some numerical examples. © 2007 EuMA  

A new analytical method for finding the general solution of the nth-order linear differential equation with variable coefficients is given based on generalizing the idea of differential transfer matrix method already proposed for solving the second order Helmholtz equation. Our generalization has two aspects. First, the given formulation copes with the nth-order linear differential equations, rather than the special case of second order wave equations. Second, the proposed approach is generalized in several different ways each yielding different types of differential transfer matrices with correspondingly different numerical accuracies. The presented methods can be applied to problems such... 

In this article, a new variational approach for extraction of leaky modes in layered waveguides is proposed. To verify the method, results of analysis of a typical test case is compared to the other references, being in agreement with them. The efficiency of the proposed approach is compared to other reported methods  

In this article, a new variational approach for extraction of guided and leaky modes in layered waveguides is proposed. To verify the method, results of analysis of a typical test case is compared to the other references, being in agreement with them. The efficiency of the proposed approach is compared to other reported methods  

Planar grating diffraction analysis based on Legendre expansion of electromagnetic fields is reported. In contrast to conventional RCWA in which the solution is obtained using state variables representation of the coupled wave amplitudes; here, the solution is expanded in terms of Legendre polynomials. This approach, without facing the problem of numerical instability and inevitable round off errors, yields well-behaved algebraic equations for deriving diffraction efficiencies, and can be employed for analysis of different types of gratings. Thanks to the recursive properties of Legendre polynomials, for longitudinally inhomogeneous gratings, wherein differential equations with non-constant... 

In this paper, distribution of voltage along a general nonuniform transmission line is expanded in an appropriate form, and by employing an approach similar to conventional and modified differential transfer matrix methods already proposed for optical structures, analytical expressions are obtained for voltage/current distributions and reflection/transmission coefficients. This method shows great accuracy in different test cases and has been found to be superior to the well-known analytical method of small reflections. Notwithstanding, the overall accuracy of proposed approach is further improved by introducing the technique of multiple divisions. In particular, lossy/lossless tapered... 

The performance of conventional imaging lenses, relying on the phase transformation of propagating waves, is impairing due to the aberration and diffraction limits. For imaging beyond the diffraction limit, different superlens designs have been proposed. Although subdiffraction resolution imaging in the near field has been realized by the superlenses with negative refractive index, magnification of the subwavelength objects into the far field has not been fulfilled. Imaging using “hyperlens” is promising to overcome the energy spreading associated with diffraction, by utilizing negative permittivity parallel to the optical axis, and positive permittivity perpendicular to it. Among various... 

Using a model reduction method, a formula for the ideality factor of a pn junction as a function of the diffusion and generation terms of its reverse current is derived. Using this formula a method for separate computation of these two currents for a pn junction is presented. The validity of the method is investigated using computer simulations for an assumed diode with known ideality factor and total leakage current. Experimental results for two commercially available diodes validate the proposed technique  

A new formulation for the solution of wave propagation in inhomogeneous optical systems, based on the extension of conventional differential-transfer matrices into modified differential-transfer matrices, is given. In justification of our proposed method, several examples are presented, and the greater accuracy of our modified differential transfer matrices compared with that of conventional differential-transfer matrices is observed in several cases. It is also shown that the modified differential-transfer-matrix method is accurate enough even in those cases that the conventional differential-transfer-matrix method fails to yield acceptable results. © 2005 Optical Society of America  

The feasibility of an integrated optical memory is explored. This memory cell is based on the plasma wave modulator/switch1, which has a horizontal layered structure. A transverse voltage maintains a bias for the structure and can be used for electrical write cycle. The cell content is then read by a propagating guided optical wave across the structure. It is also possible to apply full optical read/write/clear cycles as discussed. The read cycle can be either destructive or nondestructive, depending on the wavelength. A modification of this device may be considered as an opto-transistor, in which an optical signal controls the flow of another optical beam