Seyyed Keyhan Hosseini

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.

رشد روزافزون فناوری اطلاعات و سرعت بالای افزایش حجم ترافیک شبکه‌های مخابراتی ‌و اینترنت مستلزم تکامل مستمر آن است. مخابرات نوری به دلیل پهنای باند زیاد آن در آینده‌ی صنعت ارتباطات نقش اساسی دارد و لیزرها بخش اصلی و کلیدی فرستنده‌های نوری را تشکیل می‌دهند. از این رو طراحی مناسب لیزر‌ها تاثیر به‌سزایی در عملکرد سیستم‌های مخابرات نوری دارد. در این میان، لیزرهای بازتابنده براگ توزیع‌شده (DBR) به دلیل دارا بودن ساختار تناوبی در شبکه‌های ارتباطات نوری پیشرفته نقش اساسی دارند؛ زیرا ساختار فرکانس‌گزین و تک‌مد آن‌ها از ارسال توان در فرکانس‌های ناخواسته جلوگیری می‌کند. معمولا ساختار لیزرهای بازتابنده ‌براگ‌ توزیع‌شده بر‌اساس چینش InGaAs/InGaAsP/InP طراحی می‌شود. اگر در یک لیزر فابری- پرو (FP) به‌جای یک یا هر دو آینه کاواک از بازتابنده‌های براگ توزیع‌شده استفاده شود، لیزر طراحی شده لیزر DBR نامیده می‌شود. این نوع لیزرها از سه بخش جدا تشکیل شده‌اند که هر بخش به‌طور جداگانه توسط یک الکترود برای کنترل بهره، فاز و طول موج توری براگ به‌‌طور مستقل قابل کنترل است. در این نوع لیزر طول موج براگ (λ_B) بیشترین بازتاب را دارد و نزدیک‌ترین مود ‌طولی کاواک به λ_B کمترین تلفات را دارد. ساختار این نوع لیزرها برای اتصال به‌سایر ادوات، مانند بخش‌های جداگانه برای تنظیم پارامترهای لیزر یا مدولاسیون، مناسب می‌باشد. در این پایان‌نامه برای شبیه‌سازی و تحلیل لیزرهای FP و DBR از نرم‌افزار لومریکال ماژول اینترکانکت استفاده شده است. طراحی لیزرها در فرکانس 414/193 ترا‌هرتز انجام شده، و عنصر توری براگ با ثابت شبکه 194 نانومتر و ضریب شکست موثر 4 تنظیم شده است. برای تحریک نوری محیط فعال و به‌دست آوردن ضریب عبور لیزر FP و ضریب بازتاب لیزر DBR از یک تحلیل‌گر نوری شبکه استفاده شده و طیف حالت پایدار، توان خروجی آنی لیزر، و چگالی حامل‌های محیط بهره مورد مطالعه قرار گرفته‌اند. علاوه‌بر این، اثرات تغییر ثابت شبکه توری و تغییر دما بر طیف خروجی لیزر بررسی شده‌اند. نتایج شبیه‌سازی نشان می‌دهد که میزان توان گسیل‌شده حول فرکانس مرکزی در لیزرهای FP و DBR به‌ترتیب حدود dBm 4.48049 و dBm 11.3619 می‌باشد، که این نشان‌دهنده افزایش توان خروجی در لیزر DBRنسبت به لیزر FP به میزان dB 6.88 می‌باشد. در ادامه با تنظیم جریان‌های تزریقی به بخش‌های فاز و توری، چند طراحی بهینه برای جبران‌سازی اثر تغییرات ثابت شبکه توری براگ و دمای لیزر DBR انجام شده است.