Sharif Digital Repository

Nowadays, ultra-high bandwidths and speed are essential for information processing and transmission. Also, we know optical systems have these properties. Therefore, we use optical systems to provide these essentials. We need optical devices to obtain all optical systems. Optical buffers and memories are examples of optical devices which realization of them is still an unsolved challenge. The slow light is suitable method to realize optical buffers. To realize slow light, different methods have been introduced. One of these methods is slowing down of the group velocity of light pulses in a medium which we use that in this thesis. To realize these, many different methods and material systems... 

It is well known that arrays of antennas make it possible to steer the radiation pattern without steering a physical structure. For the past few decades this has been considered for many civil and military communication systems. Recently, ultra-short pulses are considered for high resolution radars and ultra-wideband communication systems. Systems with short pulses and large antenna arrays may benefit from high resolution in both temporal and spatial domains. But the implementation of the ultra-wideband feeding circuits for such antenna arrays is a hard job even with state of the art electronics. Optical technology has been applied, successfully, to a number of radio applications such as... 

High-power (108 – 109 W) RF pulses with a carrier frequency of C band and a duration of several oscillation periods can be produced through direct energy conversion of a travelling high-voltage pulse with the use of nonlinear elements.
Nonlinear transmission lines consist either of lumped nonlinear elements and provide spatial dispersion of excited oscillations or of elements uniformly distributed on a certain line segment. The first type of NLTL’s can be referred to NLTL’s with spatial dispersion. The second type of NLTL’s is ensemble of nonlinear oscillators with a characteristic natural frequency and temporal dispersion. In the first case, the duration of electromagnetic pulses is... 

The colloidal crystals are formed of spherical particles and can be fabricated using simple and low-cost chemical methods. Optical properties of colloidal crystals should be recognized properly in order to design optical devices based on these nano-structures. Reflection and transmission coefficients of these multilayer structures are very important for understanding their properties. Semi-analytical methods like Fourier Modal method (FMM) can be very useful to obtain their reflection and transmission properties of these multilayer structures. In this thesis, we try to implement Matched Coordinate (MC) and Adaptive Spatial Resolution (ASR) techniques in the FMM. These techniques increase... 

To design and identify specific properties of Metamaterials we need methods that accurately and quickly provide precise information about these composite materials for engineers. In this thesis we use FMM method with ASR technique for the analysis of Metamaterials and photonic crystals in three dimensional structures. In the second chapter FMM method is described briefly and then ASR technique for applying in the FMM method is introduced. ASR approach has large convergence rates in all types of gratings particularly metallic ones and with optimization that we have done for two dimensional periodic gratings convergence speed is increased more. In the third chapter using ASR reflection and... 

This thesis includes five major parts and eight chapters. In the first part, the literature of arbitrary waveform generation is reviewed. The expansion and diversity of telecommunication services like WIMAX , UWB , RoF , satellite telemetry methods and sensor networks require ultra-broadband arbitrary waveform generation methods. The ultra-broadband signals are those signals with normalized bandwidth (%BW is the ratio of signal’s bandwidth to the central frequency) over 15%. The main approach to enjoy the advantages of photonic processing is to modulate microwave signal with the light and then feed it to the optical signal processor. This light processor in case of linearity is called... 

The Fourier modal method is one of the most important methods in the analysis of flat periodic structures (gratings). Using this method, the problem of wave propagation in the periodic medium leads to an eigenproblem, in which eigenvalues represent the propagation constants and eigenvector or eigenfunctions determine the filed distribution of the modes. On the other side, considering all the generalizations and modifications reported so far, the Fourier modal method still faces two fundamental problems. First, for problems involving large dielectric constants or high contrasts, the matrix form of the eigenproblem (the modal matrix) can be large, dense, and require a high computational cost.... 

Time-Modulated Array is known as an electrical beamforming technique that has lower cost and complexity compared to the conventional beamforming techniques. In a Time-Modulated Array, the antennas are turned on and off periodically, so the harmonics of the switching appear in the spectrum of the signal. The radiation characteristics of the array such as Side Lobe Level and beam orientation can be controlled at these harmonics, also known as sidebands. The capability of the array in creating multiple simultaneous radiation patterns has paved the way toward employing this technique in wireless communication applications. In this thesis we explore the basic fundamentals and the characteristics... 

The Deep Fading Effect is a destructive factor in communication systems, one of the solutions to eliminate it is the use of Diversity, and there are two types of indicators of Diversity, Spatial Diversity and Polarization Diversity. Spatial Diversity is a common method to reduce the Fading Effect while increasing the cost and increasing the volume of the communication station, which to optimize the cost and reduce the volume of the communication station, the Polarization Diversity Structure is added to the telecommunication system. To apply Spatial Diversity, several Antennas with different Polarizations are used, which The most common method in mobile telecommunication station systems is... 

This paper presents a scalable and ultrasensitive magnetic biosensing scheme based on on-chip LC resonance frequency-shifting. The sensor transducer gain is demonstrated as being location-dependent on the sensing surface and proportional to the local polarization magnetic field strength |B|2 generated by the sensing inductor. To improve the gain uniformity, a periodic coil is proposed as a substitution for the standard process coil. As an implementation example, the circuit is designed in a 65nm CMOS process. The spatially uniform sensor gain of the array is verified by COMSOL simulations. Overall, the presented sensor demonstrates an improvement in the uniformity of the inductor’s magnetic... 

If the size of the conventional telecommunication antennas -that are widely used in transmitting broadcasted radio and TV messages- is reduced by a nanometer size these antennas can be used at optical frequencies. Dimensions of these optical nanoantennas -that made of nanoparticles with highly permittivity- can be smaller than half of the wavelength. Based on this capability, optical nanoantennas have some important applications such as optical communication, photovoltaic devices, non-classical light, and optical sensing. After studying on optical nanoantennas and their features, in this project, we present distinctions between optical NAs and MW antennas and then investigate about different...