This thesis presents research on designing, modelling, and simulating all-optical logic gates (AOLGs) utilizing photonic crystals (PHCs) to meet the growing demand for high-speed, energy-efficient computing in the digital age. As traditional electronic circuits face limitations such as heat generation, signal degradation, and bandwidth constraints, optical computing emerges as a promising alternative .The study focuses on two-dimensional photonic crystals—engineered structures capable of precisely controlling light propagation via photonic band gaps. It explores various implementation techniques for AOLGs, categorizing them into waveguided and non-waveguided approaches. Notably, the interference-based defect method is emphasized as the primary technique due to its simplicity and effectiveness in achieving desired logic functions .In this thesis, we employ the finite-difference time-domain (FDTD) method to establish a detailed simulation framework for analysing the optical behaviour of the designed gates. Key performance metrics, including contrast ratio, output power, and response time, are evaluated under different conditions. The results demonstrate the feasibility of constructing compact logic gates—such as AND, OR, NOR, NAND, XOR, and XNOR—with dimensions as small as 4 µm × 4 µm .Key findings reveal that the proposed AOLGs can achieve significant contrast ratios, ranging from 4 to 8.36 dB, ensuring clear differentiation between logic states, and response times as low as 60 femtoseconds. These characteristics highlight the suitability of the developed structures for high-speed optical applications in telecommunications and data processing.Overall, this work provides a comprehensive framework for designing and simulating photonic crystal-based AOLGs. The successful demonstration of interference-based logic gates showcases the potential of photonic systems to overcome the limitations of electronic circuits and sets the stage for future developments in integrated optical computing. The findings position photonic crystals as a transformative technology for scalable, high-performance data processing.

Over the past decades, the MOSFET has continually been scaled down insize; typical MOSFET channel lengths were once several micrometres, butnowadays with the ever increasing need for higher current drive and smallersizes MOSFETS, hence cheaper. The scaling down had to come to an endbecause of its multiple problems like SCE (Short Channel Effect), so newtechnologies had to be introduced to solve this matter. SOI had shown betterbehaviour compared to bulk MOSFET as it helps reducing SCE by using aburied oxide. The most promising nowadays reducing SCE and increasingthe scalability and giving better behaviour like more driving currents andbetter sub-threshold slopes are MUG FETS (MUltiple Gating FETS) whichintroduce better control of gates over channel hence reduce DIBL, leakagecurrent and improve the overall performance.In this thesis we are focusing more on DG MOSFETS(Double Gate) asThe DG-MOSFET seems to be a good candidate to meet the InternationalTechnology Road- map (ITRS-2009) requirements for high-performance logictechnology. so we made simulation analysis of DG mosfets performing in bothhigh temperature and high frequency to prec=dict how they behave underthose circumstances due to further applications for them in extended Thzapplications.This thesis is organized as follows, in Chapter(1) we are giving an introduction about the history of downscaling and the SCE and how to continuefollowing the roadmap with introducing new ideas and technologies, while inChapter(2) we are focusing on our interest of search (DG MOSFETS) andhow they behave with high frequency and high temperature and how theyintroduce a good candidate to the future of low power, high frequency applications. Finally in Chapter(3) we include our simulation results showinghow the behaviour of a DG MOSFET model is affected by high temperatureand high frequency at the same time. The results are pretty interesting asthere are new and no one before has searched this point.