Sharif Digital Repository

In this research, we present the results of applying simulated annealing (SA) which is a heuristic optimization algorithm for focusing light through a turbid media. The performance of this algorithm on both phase optimization and amplitude optimization has been demonstrated. A guideline to set up the SA parameters is also suggested. The performance of SA algorithm in different levels of measurement noise has been also explored. The results showed that the SA algorithm performs effectively in measurement noises as high as 0.3(I0). © COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only  

In this paper, we design a dimming compatible visible light communication (VLC) system with asynchronous and optimum indoor positioning method in a standard office room in combination with asynchronous and optimum indoor positioning method according to illumination standards under channel constraints. We use overlapping pulse position modulation (OPPM) to support dimming control by changing the code weights. The system parameters such as a valid interval for dimming together with an upper bound for bit rate according to the channel delay spread are investigated. Moreover, considering the dispersive VLC channel and using Monte Carlo (MC) simulations, a method is proposed to determine the... 

Here, an in-depth study of a novel electro-optic phenomenon suggested earlier in optical waveguides, referred to as the conducting interfaces, is carried out. It is shown that it would be possible to achieve a very strong optical modulation effect in slab waveguides fabricated on the standard III-V InAlGaAs compound platform. The electro-optic effect is obtained by controlling the density and population of the electron and hole states in the well layer. The additional phase shift contributed to the reflection phase of the guided electromagnetic wave constitutes an ultrastrong source of optical modulation and phase control. It is estimated that a Mach-Zhender configuration based on this... 

We propose and theoretically and experimentally demonstrate a novel tunable spurious-free single-loop optoelectronic oscillator (OEO) with low drift and low-phase noise. In the proposed transposed-frequency OEO (TF-OEO), a nonreciprocal bias unit and an optical phase modulator in a fiber Sagnac interferometer function jointly as an intrinsically drift-free intensity modulator, which improves the long-term drift. Besides, a transposed-frequency low-noise filtered amplifier is used which replaces the conventional radio frequency (RF) bandpass filter (BPF) and RF amplifier with an intermediate frequency (IF) BPF, an ultralow phase noise IF amplifier, and a tunable local oscillator, to attain... 

In this paper we examine the transmission of two types of ultra-wideband (UWB) signals, multiband orthogonal frequency division multiplexing (MB-OFDM) and impulse radio ultra-wideband (IR-UWB), over single mode fiber at 1550 nm. In order to investigate the impact of optical components such as laser diode, external modulator and single mode fiber on UWB signals, we develop mathematical models for these components. These models are experimentally verified and corresponding numerical parameter values are obtained by experiment. Using these models we discuss the transmission of two types of UWB signals over single mode fiber. A new figure of merit namely distortion factor is defined. Using this... 

Tunability of fiber Bragg grating (FBG) in transition region is used to implement wavelength-selective optical intensity modulator, which superimposes a secondary low-speed data on the transit high-speed payload optical signal. Theoretical model of the device is developed and verified by measurements in the linear and nonlinear slopes of the FBG. Experiments with strong and relatively weak gratings confirm the wavelength-selectivity and stability of modulation. The fiber-based modulator is employed for optically tagging or labeling individual wavelength channels using baseband and amplitude-shift keying (ASK) modulated signals. The wavelength-selective channel labeling scheme is useful for... 

This paper introduces the concept of on-chip temporal optical computing, based on dispersive Fourier transform and suitably designed modulation module, to perform mathematical operations of interest, such as differentiation, integration, or convolution in time domain. The desired mathematical operation is performed as signal propagates through a fully reconfigurable on-chip photonic signal processor. Although a few numbers of photonic temporal signal processors have been introduced recently, they are usually bulky or they suffer from limited reconfigurability which is of great importance to implement large-scale general-purpose photonic signal processors. To address these limitations, this... 

To improve the range resolution in inexpensive conventional long pulse optical time domain reflectometer (OTDR) for application in structural health monitoring (SHM) and robotic neural network, the Fourier Wavelet Regularized Deconvolution (ForWaRD) based on the adaptive wavelet method is employed. Since Deconvolution is a noise sensitive process, employing the (ForWaRD) method enhances the signal to noise ratio. Simulation for long pulse OTDR system is done and ForWaRD method is employed to improve the resolution of the OTDR system to the order of several centimeters. In this method the resolution is limited by the bandwidth of detector, bandwidth of electronic circuit, and the sampling... 

Feed-forward is one of the main methods for linearising microwave power amplifiers. The level of inter-modulation rejection (IMR) values can be predicted by appropriate modelling of the feed-forward microwave amplifier. Here, we have presented closed form expressions, which can be used for predicting the IMR for the first and second adjacent channels. Fifth- and third-order nonlinear models have been used for the main and error amplifiers, respectively. The predicted values have been verified using ADS simulator and a MATLAB program. © The Institution of Engineering and Technology 2007  

Field analysis of ring resonator modulators based on p-i-n diodes has been dissected in this paper. This analysis is performed in time and frequency domains. The conformal transformation method has been used for solving 3-D wave equation. Coupling coefficient between the ring and straight waveguides are obtained by developing the coupled-mode assumption. In the resonant wavelength of 1573.91 nm, a drop of more than 15 dB in frequency spectrum of the device has been observed. Time domain simulation shows that this modulator could support up to 0.4 Gb/s and up to 1.5 Gb/s for NRZ and RZ signals, respectively. Obtained simulation results in both domains have been properly complied with... 

We analyze the interaction of a propagating guided electromagnetic wave with a quantum well embedded in a dielectric slab waveguide. First, we design a quantum well based on InAlGaAs compounds with the transition energy of 0.8 eV corresponding to a wavelength of 1.55 μm. By exploiting the envelope function approximation, we derive the eigenstates of electrons and holes and the transition dipole moments. Next, we calculate the electrical susceptibility of a three-level quantum system (as a model for the 2-D electron gas trapped in the waveguide), by using phenomenological optical Bloch equations. We show that the 2-D electron gas behaves as a conducting interface, whose conductivity can be... 

Recently, a group of novel devices based on conducting interfaces has been proposed. These conducting interfaces can be implemented, for example, by using the inversion layer of MOS structures, trapped charges, or depletion layer charges. It has been shown that these structures can support surface electromagnetic waves. In this paper, the coupling of surface electromagnetic waves supported by conducting interfaces is first analysed. Next, by direct solution of Maxwell's equations and applying appropriate boundary conditions; exact analytical formulation of the dispersion equation has also been derived. Results driven by a coupled mode theory approach are justified by solving the exact... 

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  

Material design and input field properties limit high-harmonic excitation efficiency of surface-plasmon polaritons (SPPs) in a nanoscopic device. We remedy these limitations by developing a concept for a plasmonic waveguide that exploits spatiotemporal control of a weak surface polaritonic field to create efficient four-wave mixing (FWM) and periodic phase singularities. Our configuration comprises four-level double 3-type atomic medium (43 As) doped in a lossless dielectric situated above a negative-index metamaterial (NIMM) layer. We report the coherent excitation and propagation of the multiple surface polaritonic shock waves (SWs) and establish the highly efficient frequency combs by... 

Limitations imposed by the non-linearity of optical links, in the front end of a receiving array antenna, on the performance of a pulse compression radar are studied. Particularly linear frequency-modulated waveforms backscattered from a pair of targets are inspected. Inter-modulation and gain compression by noise are presented as two remarkable phenomena. For an interconnection of two dual-drive Mach-Zehnder modulators, the sensitivity of the compressed echo at the output of a matched filter receiver to certain tunable parameters is studied numerically. Finally, certain values of DC bias and phase shift between the modulators' electrodes are recommended  

In this paper, we present an optical computing method for string data alignment applicable to genome information analysis. By applying moire technique to spatial encoding patterns of deoxyribonucleic acid (DNA) sequences, association information of the genome and the expressed phenotypes could more effectively be extracted. Such moire fringes reveal occurrence of matching, deletion and insertion between DNA sequences providing useful visualized information for prediction of gene function and classification of species. Furthermore, by applying a cylindrical lens, a new technique is proposed to map two-dimensional (2D) association information to a one-dimensional (1D) column of pixels, where... 

In this study, we simulated and analyzed a plasmonic waveguide modulator based on a single layer of graphene. It includes a graphene sheet, which sandwiches between two layers of silicon dioxide. Then, some gates are arranged on either side of the waveguide on a periodic structure. When an electric field is applied perpendicular to the waveguide plate, the Fermi level of graphene under the gates changes. Detailed analysis is performed by the method of lines based on Maxwell's equations along the propagation direction of the waveguide. Computation of the multi-gate device starts by examining the effect of the Fermi level. The transmission coefficient of the magnetic-field norms of the...