Completed Projects




















    1. Design a proper switching sequence for Array of Antenna Using Time Modulation
      Phd Research Project done by Mr. Mohammad Hossein Mazaheri,
      Abstract : The conventional time-modulated arrays (TMAs) have a low radiation efficiency, since each antenna turns off at specific time slots. In this paper, first, the efficiency of TMA is investigated analytically. Next, the optimized switching sequences are proposed to enhance the radiation efficiency of a specific sideband, while preserving the level of the other sidebands. The practical hardware limitations are considered in the switching sequence design. Moreover, a low-cost flexible eight-element printed dipole array operating at 1.2–1.4 GHz is implemented to verify the proposed algorithms. The measured radiation patterns indicate that by applying the proposed sequences, the TMA efficiency improves by 8.3 dB for the fundamental frequency. The efficiency enhancement for the first and second sidebands is 2.9 and 2.95 dB, respectively. In addition, a fast and lowcost setup for TMA measurement using the commercial software defined radio dongle is implemented in this work.
      Keywords: Array efficiency, complementary mode switching (CMS), software defined radio (SDR), time-modulated arrays (TMAs), wireless communication.

    2. Analysis and design of optical devices by colloidal nano-structures
      Phd Research Project done by Mr. Amir Hossain Nekuee
      Abstract : 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 convergence rate and the accuracy of numerical results in the analysis of two-dimensional colloidal crystals especially hybrid colloidal crystals. In the following, guided modes of two-dimensional colloidal structures are extracted using phase changes of transmission and reflection coefficients and then band structures of these structures and their inverse replica are obtained. The existence of band gap for odd or even modes in these structures is very important. These gaps confine guided modes in the horizontal plane while the control of light in the vertical direction is done by the principle of total internal reflection. Therefore by these structures we can made waveguides that control light in three-dimensions. Hybrid colloidal crystals that are made of colloidal particles and a material with plasmonic properties can be important in optical devices. Graphene is one of these materials that due to its unique properties, has been highly interested. In this thesis, by modelling the graphene as a surface conductivity, FMM formulation is modified in such a way that Fourier factorization rules have been applied correctly. This new formulation greatly reduce the computational cost and running time. This formulation can be used in the analysis of hybrid colloidal structures that are designed by graphene such as broadband absorbers. Hybrid colloidal crystals can be fabricated by combining the colloidal crystals and the metasurfaces. In this chapter new boundary conditions using the susceptibility distribution of the metasurafce are introduced such that without solving any eigenvalue equation the characteristics of the metasurface such as reflection, transmission and absorption can be calculated easily. Correct Fourier factorization rules are also applied in the proposed boundary conditions that increase the convergence rate of this method in comparison with the previous works. This formalism can be used in the analysis of hybrid colloidal structures that are made by metasurfaces.
      Keywords: colloidal crystal, semi-analytical method, Fourier factorization rules, reflection, transmission

    3. Design a proper switching sequence for Array of Antenna Using Time Modulation
      Phd Research Project done by Mr. Mostafa Shabani,
      Abstract : This project aims to consider optical beamforming as a promising solution for future wideband and ultra wideband electronically steering array antennas. This is a part of a broader interesting subject entitled "optical signal processing". Low weight, high instantaneous bandwidth, immunity to radio frequency interference and low prices in ever increasing volume of optical and photonic devices are strong driving forces toward optical beamforming networks.
      Keywords: Fiber gratings , Microwave photonics signal processing , Electro-optical systems , Optical beam-forming , Group delay ripple

    4. Photonic Methods Ultra-Ultra-Broadband RF Arbitrary Waveform Generation
      Phd Research Project done by Mr. Arash Mokhtari,
      Abstract : There is an ever-increasing need for ultra-Broadband arbitrary waveform generation (AWG) due to evolution of telecommunication services such as WIMAX1, UWB2, ROF3, Satellite communication and sensor networks. UWB signals are coined for waveforms with fractional bandwidth of over 15% (%BW is defined as the ratio of signal’s bandwidth to its central frequency). The emphasis on the “broadband” techniques is to distinguish them form conventional narrowband techniques. Femtosecond pulse shaping techniques for waveform generation are relatively mature and have numerous applications ranging from ultra-Broadband communications to the coherent control of chemical reactions. Recently, ideas have been proposed on techniques for generation of RF ultra-Broadband pulses employing femtosecond pulse shaping and optical-electrical conversion such as different waveforms with a diversity of amplitude, phase and frequency modulation in GHz or even THz range. Recruiting appropriate light source, optical pulse shaper and optical-electrical converters helps generating waveforms with arbitrary temporal and spectral characteristics. In order to enjoy the optical processing advantages, another approach also has been shown to be useful; that is to modulate processor microwave signals with a light source and employ an optical processor. With the assumption of processor’s linearity, it is called a microwave photonic filter.In order to realize an arbitrary frequency response (transfer function), we propose two degrees of freedom to be controlled:
      1) Taps’ amplitudes by tunable attenuators or amplifiers or even spatial light modulator (SLM
      2) Tunable delays by dispersion control and change of group velocity by methods such as current injection in semiconductor waveguides, variation of
      dimension in photonic crystals or resonator structure, stimulated Brillouin and Raman processes and optical parametric amplifications. In this proposal, we attempt to offer a temporal arbitrary waveform generation scheme for standard pulses for UWB communications such as monocycle or doublet Gaussian.
      Keywords:Analog optical signal processing; Radio frequency photonics; Frequency filtering; Dispersion compensation devices.




    1. Analysis and Design of Nanoantenna Arrays
      MSc. Thesis defined for Mr. Ayoob Dehmollaian
      Abstract : 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 types of NAs and their applications. Raman spectroscopy and its applications in medical fields and detection of various tissues is an important application of NAs. Therefore we focus on investigation about different types of NAs that used in Surface Enhanced Raman Spectroscopy (SERS). By studying on SERS and reviewing various types of NAs in this area, a new design of NA is obtained. Based on interesting idea of Internet of Nano-Thing (IoNT) we focus on deployment of carbon nanotubes (CNT) in the NA’s structures. By applying the CNTs instead of metals in structure of optical NAs we can use NAs in nanonetworks and terahertz band.
      Keywords:Optical Nanoantennas, Antenna Array, Plasmonics, SERS, CNT, Nanotechnology

    2. Reducing Mutual Coupling between Millimeter Wave Antenna Arrays Using MetaMaterial Absorbers
      MSc. Thesis defined for Mr. Hamed Ghaffarzadeh Derakhshan
      Abstract : Until now, array antennas have high utilization rates and radiation guidance for many applications in communication and defense industries. With the advancement of the telecommunication industry and the emergence of new requirements in the fifth generation of telecommunications, imaging and the Internet of Things, array antennas in many forms, with a variety of operating frequencies and specific specifications, are highly needed. One of the major challenges in using these types of antennas is unwanted couplings in these systems. These couplings can occur between the elements of an array or between two or more arrays that are adjacent to each other and seriously affect the performance of the system. For example, the coupling of electromagnetic fields between transmitter and receiver arrays reduces the level of image quality reconstructed in an imaging system. Therefore, reducing the coupling level should be done in such a way that the antenna specifications are not significantly altered. The goal of this project is to reduce the coupling level using periodic surface structures. These structures are positioned in the imaging system between transmitter and receiver arrays, such as filters or electromagnetic absorbers at a specific bandwidth. These structures, known as 1FSS structures, display abnormal behavior in some frequency bands and are known as commands. Inventories have a negative permeability and permitivity. Attenuated and absorbent precipitators attract much attention in microwave frequencies and terahertz. The absorbent is made up of metal plates separated by insulating blades. These structures operate extensively and at the resonance frequency, the imaginary part of the impedance is zero and its real part is matched to the free space impedance. In this case, the electromagnetic wave is absorbed into the adsorbent and dissolved in the structure. Recently, single-frequency, two-phase and multi-frequency metamaterial absorbents are designed and one of the challenges of these structures is the dependence of the resonant frequency and the absorption rate on the change in the polarization angle and the angle of radiation of the fields. In this dissertation, there are two types of adsorbents that have a high absorption capability at 29 GHz central frequency, and their absorption rate is favorable for polarization angle and angle variation.
      Keywords: Array Antennas, Absorbers, BandStop Filters, Coupling, Imaging, MetaMaterial Periodic Structures

    3. Spur level reduction in direct digital synthesizer
      MSc. Thesis defined for Mr. Behnam Sabouri
      Abstract : Direct digital synthesizers (DDS) are one type of frequency synthesizer that used for creating arbitrary waveforms from a reference clock with fixed-frequency and have various applications in signal generators, local oscillators in telecommunication systems, mixers, modulators and part of phase-locked loop.Despite of numerous advantages of direct digital synthesizers like high accuracy, fast switch ability, low power consumption and etc, beause of some available alternative errors in it's structure like phase truncation, In side band of desired output signal, independent troubler signals namely spur were created. Spurs put trouble in the use of sensor or radar systems and limit the performance and efficiency of radar or sensor. This project's goal is spurs level reduction in direct digital synthesizer's output by one technic namely dithering and implementation it by one system based FPGA. For this opinion, one minimal noise is created by linear feedback shift register as pseudo random number generator and this random numbers is added to direct digital synthesizer's phase or amplitude for destroying the periodicity of errors and reducing the level of spurs’s power.
      Keywords: Frequency syntesizer, Direct digital synthesizer,Spur level reduction,Spur,Dither

    4. Analysis and simulation of micrometre-scale silicon electro-optic modulators based on ring resonators
      MSc. Thesis defined for Mr. Omid Jafari
      Abstract : Metal–interconnection imposes many limitations to electronic system, such as high loss and low transformation speed. Due to these limitations, optical–interconnection has seen more consideration, and replaced metal–interconnection. Constructing a suitable optical– interconnection is based on development of micro optic devices technologies. Recent developmental demonstrations of laser, silicon low loss waveguide, light emitters, amplifiers, modulators, and detector approach this purpose. Optical modulator is one of the most important component in optic communication, and causes the main limitations in communication system when it is not properly designed. Generally, the optical modulators are divided into old generation and new generation. The old generation optical modulators are divided into these three popular groups: direct modulator laser (DML), electro–absorption modulator (EAM), and electro–optic modulator (EOM). The weakness of DMLs is insufficiencies in high bitrate. EAMs are PIN semiconductor structures whose bandgap can be modulated by applying an external voltage, thus changing the device’s absorption properties. It includes wavelength–dependent absorption characteristics which is a major drawback. MZM is one of the kind EOM which most convenient in 3 LiN bO , Gallium arsenide (GaAs ), and indium phosphide ( InP ). This modulator is operating based on interface of two outlet waves which are modulated by phase variation. The old generation modulators have two main problems. First, they have structures with relatively large dimension of about centimeter or millimeter. Second, they are not capable of integration with other electronic devices. In order to resolve the second problem, optical modulators based on silicon are taken into consideration, but these modulators create two challenges due to silicon’s weak electro–optic properties. First, device dimensions are relatively large. Second, light control is very difficult in silicon media. To overcome these problems, the new generation modulators are taken into consideration. The new generation optical modulators can be classified into three common groups, optical modulators based on metal oxide semiconductor (MOS) capacitor, optical modulators based on PIN diode in forward bias, and optical modulators based on PN diode in reverse bias. Modulators based on MOS capacitor are embedded in a Mach-Zehnder interference (MZI) structure and they have a large effective area. Since MZI structure has less variation of refractive index versus drive voltage in active region, these modulators have high peak to peak voltage (Vpp) and high energy consumption. Modulators based on PN diode in reverse bias which is embedded in a MZI structure, similarly have energy consumption greater than 30 pJ per bit. Modulators based on PIN diode which is embedded in a ring resonator structure (ORRPIN modulator), have low power consumption and relatively low Vpp, since can effectively confine light inside the resonator. Since ORR–PIN modulators do not suffer from small optical confinement factor and shortage of carrier in active region, they have two advantages in comparison to the other silicon modulators. First, these modulators can provide higher changes in refractive index inside active region. Second, they can bring about high modulation depth in micro dimension structure. One of the purposes in this thesis, discusses the theory of optical modulators of ring resonators based on PIN diode in forward bias. It secondarily provides a full featured simulator to investigate the behavior of such modulators. Wave equation for ring structure will be solved by using the conformal transformation method. Power coupling between ring and straight waveguides will be calculated by coupled theory of nonparallel waveguides. The frequency spectrum analysis of device shows a 15 dB drop in transmission at the resonant wavelength of 1573.91nm . Experimental results in ref. 94 confirm the simulation results. Disadvantage of these modulators is its lower speed in comparison to MZM, since injection and extraction of minority and majority carriers are slow. Silicon optical modulator based on PN diode at reverse bias which is embedded in ring resonator structure can solve this problem. This structure has two main advantages. Energy consumption and Vpp of device are low because of the resonator’s structure. In order to modulate the ring refractive index, PN diode is embedded along ring which makes modulators capable of using width change of active area, instead of elimination /injection of free carriers in this region. Therefore, this device has higher speed compared to ORR-PIN modulator. Since width of active area changes with voltage, the refractive index of ring is modulated due to plasma dispersion effect. Other purpose in this thesis, primarily discusses the theory of silicon optical modulators of ring resonators based on PN diode in reverse bias. It secondarily provides a full featured simulator to investigate the behavior of such modulators. Wave equation for ring structure will be solved by using the conformal transformation method and the matrix method as used to analyze bent planar optical waveguides. Power coupling between ring and straight waveguides will be calculated by coupled theory of nonparallel waveguides based on experimental results. The time response demonstrates the capability of this device to operate correctly at up to 10 Gbps bitrate, and the frequency spectrum analysis of device shows a 17 dB drop in transmission at the resonant wavelength of ~ 1574.9nm .
      Keywords:

    5. Optimization of maximum frequency and power, extraction of parameter data and final publication design of high power microwave pulse generation using nonlinear transmission line with the periodic structure of the gas switch
      MSc. Thesis defined for Saeed Komeylian
      Abstract : 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 determined mainly by the number of lumped nonlinear elements, e. g. , gas gap switches. Circuits for producing high-voltage bipolar pulses, as a rule, contain two high-voltage gas gap switches. In this work, we report on an experiment in which the central conductor of the coaxial line has up to N gas gap switches with a rather low interelectrode capacitance. Relevant experiments show that increasing the number of the gaps causes an inversely proportional decrease in spectrum width. Because the average delay time of breakdown for a gap displays a nonlinearly relation to the amplitude of the applied field, including the RF component, the central frequency in the spectrum of the pulse is a function of the amplitude of the TEM wave incident on the line. Besides gas gap switches, nonlinear capacitances or inductances can be used as the lumped elements. For example, a periodic waveguide structure with ferrite-based nonlinear inductances and capacitive cross-couplings was used in.
      Keywords:

    6. Applications of Stimulated Brillouin Scattering effect in optical signal processing
      MSc. Thesis defined for Mr. Jaber Malekzadeh
      Abstract : 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 have been developed but due to its significant advantages the nonlinear effect of stimulated Brillouin scattering (SBS) is particularly promising. In this thesis the slow light effect on the basis of SBS is investigated.
      Keywords:

    7. An Optimization of ASR and combination with FMM for the analysis of Metamaterials and photonic crystals in three dimensional structures
      MSc. Thesis defined for Mr. Amir Hossain Nekuee, in cooperation with Prof. K. Mehrani, September 2010

    8. Open Metamaterial waveguide and nonlinear magnetic properties
      MSc. Thesis defined for Mr. Farid-Aldin Fayazbakhsh, December 2007

    9. Grating diffraction analysis based on legendre polynomial expansion
      MSc. Thesis defined for Mr.Meysamreza Chamanzar, in cooperation with Prof. B. Rashidian and Prof. K. Mehrani, 0ctober2005

    10. Analysis of photonic crystals with finite difference time domain method
      MSc. Thesis defined for Mr. Amir Hossain Atabaki , in cooperation with Prof. B. Rashidian and Prof. S. Khorasani, August 2005

    11. A rigorous vectorial analysis of photonic crystal fibers
      MSc. Thesis defined for Mr. Amin Khorshid Ahmad, December 2005

    12. Three dimensional field analysis of periodic structures utilizing modal transmission line theory
      MSc. Thesis defined for Mr. Ali. Dabirian, December 2004







    1. Analysis and Design of Vertical Cavity Lasers
      BSc. Thesis defined for Mr. Mohsen Arabgol, August 2010

    2. elevision Signals, Production and Propagation
      BSc. Thesis defined for Mr. Mohhamad Hossain Ashtari, August 2006

    3. Investigation on performance of mobile communication systems
      BSc. Thesis defined for Mr. Mohammad Ali Sebt, August 2005

    4. Periodic structures and its application on Vertical Cavity Surface Emitting Lasers
      BSc. Thesis defined for Mr. Farzad Tehranchi, July 2004