Seyyed Keyhan Hosseini

With the increasing use of portable electronic devices and the need for more bandwidth, the limitation of radio frequency spectrum has become a serious challenge. Visible Light Communication (VLC) has emerged as an attractive option due to its broad bandwidth and the potential use of existing lighting equipment. This research focuses on the design and simulation of a broadband absorbing layer based on all-dielectric metasurfaces for use in VLC systems. The designed metasurfaces utilize all-dielectric nanorods with two different radii and heights, aimed at creating optical resonances at various wavelengths and enhancing the absorption bandwidth. This absorbing layer can also be applied in other uses, such as solar cells and photovoltaic devices. Simulations were conducted using Lumerical software and the Finite-Difference Time-Domain (FDTD) method. To optimize the structural parameters, an artificial neural network was used in MATLAB. The use of neural networks as an advanced tool allowed for precise modeling of complex relationships between control parameters and absorption performance, making the optimization of the structure more efficient, which reduced computational time and improved accuracy in predicting absorption. In this study, two structures were presented for different purposes. The first structure, with an average absorption of 99.50%, showed the best performance at normal incidence, outperforming previous structures, especially those based on metals. The second structure maintained a high absorption of over 90% up to an angle of 70 degrees, providing the highest angular stability. These absorbers, without the use of metal, achieve optimal performance across the wavelength range of 400 to 800 nanometers and are also independent of the light polarization angle.

Nowadays, with the widespread outbreak of viral diseases and cancer cells, the design of biosensors with optimal performance has become particularly important. The objective of this thesis is to design and simulate a one-dimensional photonic crystal biosensor based on surface plasmon waves, which is considered a cost-effective and efficient technology among sensors sensitive to changes in the refractive index of various materials. In this research, four pairs of layers made of titanium dioxide (TiO₂) and porous silicon dioxide (SiO₂) have been used. On top of these layers, two layers of magnesium fluoride (MgF₂) and another layer of porous SiO₂ have been applied. These structures are known as dielectric mirrors or Bragg reflectors. In this structure, the magnesium fluoride layer is considered as the defect layer. The last layer, which is porous SiO₂, acts as a protective layer against the reaction of the magnesium fluoride layer with the biological material and also ensures better adhesion between the sensor and the biological material. The proposed structure is stimulated by a light source with a wavelength of 1100 nanometers using a prism that serves as a coupler. In this biosensor, changes in the refractive index of the biological material lead to angular shifts in the resonance dip in the reflectance coefficient. The range of the biological material's refractive index varies from 1.33 to 1.34. During the simulation process, altering parameters such as layer thickness, material composition of the layers, the number of layers, and the type of prism considerably improves the sensitivity of the biosensor. The proposed sensor has achieved a sensitivity of 332 o/RIU and an FWHM close to 0.008° without using complex and heterogeneous structures like gratings.

One of the main problems in solar cells is low efficiency, which has challenged their development. The main reason for low efficiency in solar cells is their inability to trap and absorb photons emitted by the sun. In recent years, with the introduction of perovskite material, there have been many hopes for increasing the efficiency of solar cells. But perovskites do not absorb well at long wavelengths. For this reason, in order to increase the absorption and trapping of more photons in the structure of the solar cell, in this work, a combination of gold nanoparticles and perovskite is proposed to take advantage of the plasmonic effect of gold nanoparticles embedded in the perovskite layer. In the following, the proposed solar cell is compared with a perovskite solar cell and a solar cell with a conventional structure. The comparison results show that the proposed structure in low wavelengths is about 5% compared to the perovskite sample and 25% compared to the conventional sample and in high wavelengths it is about 10% compared to the perovskite sample and about 20% compared to The common sample absorbs more light. Therefore, from the obtained results, it can be concluded that the proposed solar cell performs better than the other two samples.

Due to the alarming increase in the prevalence of cancer, the development of early detection methods for this disease is of great importance. One of the promising technologies in this field is the use of optical biosensors. In this research, a metamaterial biosensor has been designed that is capable of accurately distinguishing between healthy and cancerous cells. Different geometric shapes were investigated for the metamaterial layer and the results related to each were analyzed. By examining the obtained results and comparing them, the symmetrical hexagonal ring structure with four veins was chosen for the geometric shape of the metamaterial layer, which had high sensitivity and efficiency. The primary proposed sensor unit cell is a symmetric hexagonal ring etched on a 150 nm thick silver layer, which rests on a 200 nm thick zirconium nitride (ZrN) layer. The zirconium nitride layer is placed on another layer of silver with a thickness of 100 nm and a silicon dioxide (SiO2) glass substrate with a thickness of 2000 nm. In the initial cell structure of the sensor unit, by scaling the dimensions of all the layers of the structure by a specific coefficient, the length and width of the layers were set equal to 1200 nm, and as a result, the working range of the sensor was placed in the optical telecommunication band. The resonance wavelengths of the sensor loaded with healthy cells and HeLa, Pc12 and MDA-MB231 cancer cells are 1445, 1486, 1489 and 1493 nm, respectively. The sensitivity and Figure of merit (FoM) of the proposed sensor were obtained as 986 (nm/RIU) and 417, respectively. Then, by performing numerical simulations, the effect of different thickness values of analyte, metamaterial, zirconium nitride, and silicon dioxide layers was observed, and the best values of thicknesses were obtained as 2000 nm, 150 nm, 100 nm, and 500 nm, respectively. The sensitivity and Figure of merit (FoM) of the final proposed sensor were obtained as 1016.42 (nm/unit of refractive index) and 3278.80, respectively. Comparison of the proposed hexagonal structure with existing sensors shows the superiority of the proposed sensor.

The increasing incidence of cancer in recent years has necessitated the development of early detection methods. In this regard, the use of optical biosensors, particularly surface plasmon resonance (SPR)-based biosensors, can serve as a reliable and effective technology. These biosensors offer low cost, small size, label-free detection, and high accuracy and sensitivity. An SPR biosensor was designed to detect Hela, Jurkat, PC-12, MDA-MB-231, and MCF-7 cancer cells, which have refractive index between 1368 and 1401. Two-dimensional numerical simulations were performed using COMSOL Multiphysics. The biosensor was meshed, and the Maxwell's equations were solved for each element using the finite element method. This analysis yielded the amount of light absorption, transmission, and reflection, as well as the electric field distribution. The operating range of the biosensor was designed to be within the optical communication band. Therefore, to prevent the resonance wavelength from shifting out of the communication band, the design of highly sensitive sensors was avoided. The presented SPR biosensor has a multilayer structure consisting of a prism/silver/titanium dioxide/di alumina trioxide grating. The structure is Stimulated using a BK7 prism at an incident angle of 75 degrees. The 37 nm thickness of silver layer is designed to generate surface plasmons, thereby inducing resonance in the biosensor and minimizing the reflection coefficient. The 22 nm thickness of titanium dioxide layer serves as a protective layer for silver against corrosion. Two types of di alumina trioxide gratings with asymmetric and triangular units were investigated. The gratings were employed to enhance the analyte-biosensor interface area. Simulations revealed that an equilateral triangular grating with a side length of 200 nm and a period of 300 nm exhibited the best performance. The proposed biosensor demonstrated a sensitivity of 12214 nm per refractive index unit, a full width at half maximum of 88 nm, a figure of merit of 122 per refractive index unit, a detection accuracy of 0.0113 nm, and a quality factor of 14.53. Additionally, the penetration depth of the electric field in the multilayer biosensor was calculated to be 500 nm. Comparisons with previous structures indicated improvements in all or some of the performance parameters.

In this thesis, an infrared plasmonic metamaterial absorber has been designed and simulated with the help of graphene for gas detection. The proposed plasmonic metamaterial consists of an alternating cubic cavity ring nanoantenna array made of gold (Au) with a thickness of td = 10 nm, diameter d = 300 nm and a cubic air cavity on the r side and a continuous gold layer of gold with a thickness of tau = 100 nm, which is separated from the nano antennas by a dielectric layer made of silicon dioxide (SiO2) with a thickness of tsi = 30 nm. A graphene layer with a thickness of Δ = 0.34 nm is embedded on the hollow nanodisks. This air cavity is filled with three materials: water, PMMA and AL2O3. The simulation results indicate that the highest sensitivity, the highest FOM and the smallest FWHM are related to the unfilled state for the air cavity. Gas measurement for the proposed structure is in the range of refractive index 1 to 1.12. The best result obtained for the proposed structure in this case is for gas with a refractive index of 1.06 for the parameters of sensitivity, FOM and FWHM are equal to S=3120nm/RIU, 59RIU-1 and 55nm, respectively.

The consumption of renewable energy is rapidly increasing. Additionally, limited non-renewable resources are available. Therefore, continuous research efforts are being made to generate energy from renewable sources such as solar, water, wind, etc. Photovoltaic cells, particularly perovskite solar cells, have gained popularity due to ease of fabrication, cost-effectiveness, high absorption coefficient, controllable energy gap, high charge carrier mobility, excellent power conversion efficiency (PCE), etc. The recent generation of perovskite solar cells are semi-transparent. In such solar cells, metallic back contacts are replaced by transparent contacts such as transparent conducting oxide (TCO) and thus they are able to absorb the solar light from both front and back contacts. In this regard, the incident light flux is enhanced which results in a higher absorption and PCE. In this research, optical and electrical modeling of a semi-transparent perovskite solar cell with a transparent back contact has been conducted using the COMSOL software. Finite Element Method (FEM) was employed to calculate absorption, reflection, light transmission, and the generation rate of electron-hole pairs. Electrical analysis was performed using the semiconductor module, obtaining characteristics such as the current-voltage (J-V) curve and photovoltaic parameters including short-circuit current, open-circuit voltage, filling factor, and PCE of the propose structure. Validating the simulation results, a semi-transparent solar cell with a MoOx/ITO back contact achieved a PCE of 13.87%. Removing the MoOx buffer layer increased PCE to 96.13%. Therefore, a buffer-less structure with high PCE was introduced, offering advantages such as simplified fabrication steps, accelerated manufacturing processes, reduced material requirements, and cost-effectiveness. In the following, different back contact materials (ITO, IZO, IOH) were tested, with IOH exhibiting the best performance with a PCE of 31.14%. Additionally, applying Albedo light to the back contact increased PCE from 14.31% to 18.21%. To further enhance PCE by minimizing losses from Fresnel reflection, MgF2 anti-reflection layers with an optimal thickness of 80 (100) nm were applied on front (back) contacts. Results showed that adding these layers increased PCE to 19.69%. Consequently, incorporating anti-reflection layers on both sides of the contacts resulted in an 8% increase in PCE.

The increasing growth of information technology and a tremendous speed in broadening the required traffic band of telecommunication networks and the Internet necessitates its continuous evolution. Given that optical telecommunications play a key role in the future of the communications industry, lasers are a key component of optical transmitters and their proper design has a significant impact on the performance of optical telecommunication systems. Distributed Bragg reflector (DBR) lasers play an important role in advanced optical communication networks due to their periodic structure which prevents the emission of power at unwanted wavelengths. The single mode operation of these single mode lasers is due to their frequency-selective nature. DBR lasers are designed based on InGaAs/InGaAsP/InP heterostructures. The key parameters in such lasers are the gain of the active medium, the current injected to the phase section, and the wavelength offered by the Bragg lattice. The gain medium and Bragg section are separated along the length of the laser suggesting more degrees of freedom in comparison with the distributed feedback lasers. In DBR lasers the Bragg wavelength λ_B has the highest reflection and the closest longitudinal cavity mode to λ_B has the lowest cavity losses. The structure of this type of laser is suitable for connection to other devices, such as separate sections for laser tuning or modulation. In this thesis, the Lumerical software of the Interconnect module is used for simulation and analysis of Fabry-Perot (FP) and DBR lasers. The design frequency is set at 1914.144 THz, and the Bragg grating section is designed to have a lattice constant of 194 nm and an effective refractive index of 4. A network optical analyzer is used to optically stimulate the active environment and to obtain FP laser transmissivity and DBR Reflectivity. In addition, the steady state spectrum, the instantaneous output power of the laser, and the instantaneous density of the carriers of the gain environment have been studied. Also, the effect of perturbing the lattice constant and temperature change on the output spectrum of lasers have been investigated. The power amplitude around the central frequency in the FP laser was achieved to be 4.48049 dBm, while the same quantity was reported to be 11.3619 dBm in the DBR laser with a 6.88 dB superiority in performance. Then, two optimal models were designed by tuning the currents injected to the Bragg lattice and the phase section compensating the perturbations in the lattice constant and the temperature