Golsa Mirbagheri

A new light responsive arylazopyrazole (AAP) containing polymer matrix thin film is fabricated by spincoating of different concentrations of the AAP azo dye into the polydimethylsiloxane (PDMS) polymer at 150°C. The new AAP molecular switch was also used to fabricate a solid-state PDMS-AAP waveguide by contact lithography and soft replica modeling methods in the micrometer scale. The refractive index of the spin-coated photoswitchable material can be modulated via the reversible trans-to-cis photoisomerization behavior of the AAP unit using different concentrations. When 0.01 M solution of the AAP unit was used, the refractive of the composite was 2.32 in the trans state and dropped to 1.85 in the cis state in the operating wavelength of 340 nm. At higher concentrations of 0.020 and 0.03 M, a wide refractive index tuning is achieved under the same wavelength. In 0.030 M the refractive index was 2.65 for the trans state and 2.0 for the cis state. The results suggest that the increase in refractive index tuning is related to the concentration of the AAP unit of the composite film. Theoretically, the spectral properties of the composite film are also simulated with two methods: 1) the Maxwell Equations; and 2) the frequency dependent finite element, showing excellent agreement for the different propagation modes of the proposed waveguide for regulated signals of 365/525 nm wavelengths. Furthermore, the photoisomerization of the PDMS-AAP thin film is analyzed with UV-vis spectroscopy to demonstrate the isomerization responses of the AAP moiety in the solid state. Additionally, preliminary photomechanical actuation properties of the composite film have been investigated. The PDMS-AAP waveguide described in this study provides a new approach for optically tunable photonics applications in the UV-Visible region.

Tunable dielectric meta-surface nanostructures offer incredible performance in optical application due to their extraordinary tunability of the polarization and engineering the dispersion of light with low loss in infrared range. In this article, we designed and experimentally measured the tunability of all-dielectric subwavelength silicon nanoparticles with the help of the temperature-based refractive index of the liquid crystal in the telecom regime. The proposed structure composed of high dielectric nanodisk surrounded by nematic liquid crystal (NLC) is simulated with numerical software, assembled with pre-alignment material, and optically measured by Fourier-transform infrared (FTIR) spectroscopy. The simulated result is compatible with the practical measurements, shows that the tunability of 30nm is achieved. Electric and magnetic resonance modes of the high dielectric nanodisks are tailored in different rates by anisotropic temperature dependent NLC. The phase switching of anisotropic to isotropic nematic liquid crystal enables spectral tunning of the two modes of all dielectric metasurface and modifies the symmetry of the optical response of the metamaterial structure.

In this project we propose and fabricate a hyperbolic metamaterials-based narrowband notch filter for the infrared regime with a center wavelength that remains fixed as the angle of incidence changes from 0 to 30 degrees for TM polarization. This novel device modifies a conventional Bragg reflector by including a middle resonance layer that opens up a narrow, highly transmissive band. To achieve angular independence, a subwavelength sized array of silver wires are inserted in a vertical orientation and permeate all 7 Si and SiO2 layers of the structure. In this work the theoretical underpinnings are explored using Maxwell-Garnett Theory, and simulated with 3D finite element full wave electromagnetic modeling software. Simulations demonstrate that the device is capable of up to 60% transmission at a fixed center wavelength for TM polarization in the infrared. The device is fabricated using typical microfabrication techniques. The silver nanowires are fabricated via DC electrodepositi...

Advances in Information Technology (IT) have solved information deficiency, but another problem has been brought about: information overload. One of the most appropriate methods to deal with this issue is the use of recommender systems. A recommender system can be used as a tool to support and even for decision-making. Although it can recommend the appropriate educational resources in e-learning system for the learners, so that they would be able to choose the best educational content, but according to the recent studies, such a recommender system has rarely been used in e-learning. A recommender system based on collaborative filtering methodology is introduced in this study to recommend the suitable resources to the learners and therefore save their precious time and facilitate the learning process. In this study, two groups of learners are selected from the same educational level. The first group will be given no recommendations at all and they themselves have to choose their educational resources. However, the second group will be supported by the proposed recommender system in order to select their appropriate resources. The obtained results show that the learners in the second group, who had been supported by the recommender system, outperform the first group and have a superior learning experience.

Concept maps are effective graphical tools for representing and organizing knowledge of learners and diagnosing students' misconception in educational environments. Considering the fact that constructing concept map manually is a complicated and time-consuming task and updating them is a boring job, they have not used widespread in educational environments. So constructing these maps in a semi-automated way is a preferable method. Another problem that learners in the e-learning environments may have is the growing amount of information and educational resources on the internet. Therefore, the use of guiding systems to introduce the resources to users is becoming more and more popular. Also, it's better if the materials proposed to the learners be in accordance with the level of their knowledge and learning situation. To end this, our paper suggests the construction of concept maps in semi-automated way and the use of a recommender system to propose appropriate resources. To make the learning guidance more understandable to the student, this study defines some fuzzy systems. In this paper, proposed recommender system suggests some resources to the users and then the users take part in the related test. Once the test is carried out, the users' learning level in each concept is determined and the initial concept map is drawn using the concepts which have been learned. Then this map is completed by the feedbacks given from the system to the learner, in each step and in this way the learning process completes. This procedure will continue until the completion of the concept map and the learning process finish.

In this project we design and fabricate a hyperbolic metamaterials-based narrowband notch filter for the mid-
wave infrared regime with an angle-of-incidence independent center-wavelength for TM polarized incident light.
To achieve angle of incidence independence, a subwavelength sized array of copper wires is inserted in a vertical
orientation and permeates the three middle layers of the seven layer Bragg stack filer. Analysis using Maxwell-
Garnett theory and full-wave electromagnetic modeling, and the fabrication progress to date are presented.
Narrowband notch filters have applications in optical communications systems, and remote sensors such as
hyperspectral and multi-spectral sensing and imaging.

With conventional narrowband filters, the center-wavelength of the narrow transmission band undergoes large shifts as the angle of incident light changes. In this project, we designed and experimentally verified a type of hyperbolic metamaterial Bragg stack that eliminates, or vastly reduces, this angle-of-incidence dependence (i.e., dispersion) of the transmission band for TM polarized beam. The filter developed in this project is composed of array of subwavelength sized metal wires vertically penetrating in the dielectric layers of the Bragg stack. We first discuss the physical reasons why such a structure is expected to minimize dispersion, then we performed detailed electromagnetic modeling, fabrication of proof-of-concept structures, and optical testing of the structures. The filter is fabricated by CMOS fabrication techniques at Cornell University’s Nanoscale Science and Technology Center, and optical characterized using Fourier-transform infrared spectroscopy. Both simulated and experimental data show that narrow band transmission filters can be designed such that the center-wavelength of the transmission peak for TM polarized incident light does not change as the angle of incidence of an incoming beam changes. These types of narrowband notch filters have been used in many sensing and imaging applications, including remote sensing and hyperspectral imaging.

Vanadium dioxide (VO2) as a phase-change material controls the transferred heat during phase transition process between metal and insulator states. At temperature above 68 C, the rutile structure VO2 keeps the heat out and increases the IR radiation reflectivity, while at the lower temperature the monoclinic structure VO2 acts as the transparent material and increase the transmission radiation. In this paper, we first present the metal-insulator phase transition (MIT) of the VO2 in high and low temperatures. Then we simulate the meta-surface VO2 of metamaterial reflector by Ansys HFSS to show the emittance tunability (Δε) of the rutile and monoclinic phase of the VO2. In next section, we will review the recent progress in the deposition of thermochromic VO2 on glass and silicon substrate with modifying the pressure of sputtering gases and temperature of the substrate. Finally, we present the results of the in-situ sputtered VOx thin film on thick SiO2 substrate in different combination of oxygen and argon environment by V2O5 target at temperature higher than 300C and then, analyze it with x-ray diffraction (XRD) method. The thermochromic VO2 based metamaterial structures open a new route to the passive energy-efficient optical solar reflector in the past few years.

Tunable dielectric meta-surface nanostructures offer incredible performance in optical application due to their extraordinary tunability of the polarization and engineering the dispersion of light with low loss in infrared range. In this article, we designed and experimentally measured the tunability of all-dielectric subwavelength silicon nanoparticles with the help of the temperature-based refractive index of the liquid crystal in the telecom regime. The proposed structure composed of high dielectric nanodisk surrounded by nematic liquid crystal (NLC) is simulated with numerical software, assembled with pre-alignment material, and optically measured by Fourier-transform infrared (FTIR) spectroscopy. The simulated result is compatible with the practical measurements, shows that the tunability of 30nm is achieved. Electric and magnetic resonance modes of the high dielectric nanodisks are tailored in different rates by anisotropic temperature dependent NLC. The phase switching of anisotropic to isotropic nematic liquid crystal enables spectral tunning of the two modes of all dielectric metasurface and modifies the symmetry of the optical response of the metamaterial structure.

Hyperbolic Metamaterials, as a non-magnetic anisotropic artificial structure, show metal properties in one direction and dielectric behavior in orthogonal directions. The proposed hyperbolic metamaterial filter in this project is designed with the metal wire mesh perpendicular to the alternative layers of dielectric materials, keeps TM center wavelength unchanged for the different angle of incident light in MDIR regime. The geometric size of this nanostructure is smaller than the working wavelength and supports big wavevectors due to hyperbolic dispersion. In contrast with conventional Bragg stack, the copper fakir bed makes the transmission properties of the filter the same. For this purpose, the stateof-the-art fabrication methods are required to make such small dimensions in alternative layers of amorphous silicon and silicon dioxide. In this work, first we demonstrate the simulation of Bragg stack with RCWA and finite element methods. Then we focus on our first-time multistep lithography method used to fabricate the filter at Cornell University's Nanoscale Science and Technology Center. Finally, we experimentally verify the optical characteristic of the fabricated filter using Fourier-transform infrared spectroscopy. The experimental and spectrometry data shows that transmission properties of the hyperbolic metamaterial filter remain the same for oblique TM polarized incident light.