http://dspace.mist.ac.bd:8080/xmlui/handle/123456789/58 2026-04-20T21:55:04Z http://dspace.mist.ac.bd:8080/xmlui/handle/123456789/441 Comparative Study of Dispersion and Other Losses including Nonlinear Impairments of Different Models of Photonic Crystal Fiber (PCF) by Varying Geometrical Shapes Prottasha, Soheli Noshin; Ahmed, Neti Nowrin Nilma; Afroj, Jinia This thesis paper presents detail analysis of a hexagonal, octagonal, decagonal and hybrid shaped photonic crystal fiber (PCF) with an aim to compare their performance over various parameters of communication. Deliberate study on the constructional design of the PCF models is carried out to find the optical signal guidance mechanisms through it. The COMSOL Multi-Physics 4.4 Simulation Software is used to perform the modal analysis of the designed PCFs. Three conventional PCFs such as H-PCF, O-PCF and D-PCF are constructed with four layered circular air hole rings. The hybrid structure (Hy-PCF) is also made of four air hole rings but consists of elliptical and square air holes along with the circular ones. Pure silica material is used as core-cladding materials. All the properties are analyzed for 0.80-2.00μm wavelengths range. The dispersion profile of the H-PCF is found quite varying whereas the O-PCF and D-PCF have shown zero to negative dispersion with little variation. At 1.55 μm wavelengths, the calculated dispersion for H-PCF, O-PCF and D-PCF are −2.80 ps/nm-km, −8.61 ps/nm-km and−11 ps/nm-km respectively. The Hy-PCF has exhibited more negative dispersion with almost linearly decreasing characteristics against wavelengths. The value is −81.08 ps/nm-km for 1.55 μm wavelengths. A very negligible confinement loss is obtained for H-PCF, O-PCF and D-PCF for a large wavelengths range. At 1.55 μm wavelengths the H-PCF, O-PCF, D-PCF and Hy-PCF have provided 25.42 μm2, 19.83 μm2, 15.7 μm2 and 5.15 μm2effective mode areas respectively. For the three conventional structures of similar parameters the values of nonlinear coefficient are found close to each other (3.43W-1km-1, 2.865W-1km-1 and 2.493 W-1km-1 respectively at 1.55 μm) but the Hy-PCF has shown 19.03W-1km-1. Moreover the conventional PCFs have provided negligible birefringence of the order of 10-6 only, but the Hy-PCF has provided large birefringence (4.34×10−3 at 1.55 μm wavelengths). Considering the overall system performance, it can be said that, this findings of this thesis on PCF structures will help to fabricate better kind of optical transmission media of more data rates. Loss parameter analysis of all structures studied will suggest their application in specific areas of optical communication. First of all, we would like to thank Allah for giving us the ability to complete this thesis work. We would like to express our utmost gratitude towards our honorable supervisor, Lt. Col. Md. Jahangir Hossain, without whose encouragement and guidance, this thesis would have never been completed. We are very grateful for his continuous instructions and encouragement, valuable discussions and careful review during the entire duration of the research. His thoughtful analyses and firm supervision have provided us with the right direction towards our goal. We have learned many valuable concepts of Optical fiber Communication from him throughout our study, which we tried to utilize and develop our analyzing abilities. His constant encouragement gave us the confidence to carry out our work. We would also like to thank all our teachers. They gave the knowledge and directions needed throughout my life. We express our gratitude towards our teachers from Military Institute of Science and Technology (MIST). Last but not the least; we would like to thank our parents. Their unconditional support made it possible to finish this thesis. 2017-12-01T00:00:00Z http://dspace.mist.ac.bd:8080/xmlui/handle/123456789/440 Study and Performance Analysis of Radar Cross Section for F-117A Nighthawk Stealth Aircraft Tabassum, Syeda Tahrin; Ashraf, Rezwan; Tahmid, Ragib Radio Detection and Ranging (RADAR) is a technology with which immense practical consequences can be measured and detected at high accuracy. Using radar, Air travel is thousands of times safer than travel by road, astronomers can map the contours of far-off planets, physicians can show images of internal organs, meteorologists can measure weather change in distant places on Earth. Due to its reasonable larger practical applications, the bistatic radar cross section of F117 Nighthawk Stealth Aircraft is the main focus of our thesis. The main goal of this thesis is to carry out a detail study of the Radar Cross Section with an aim to find out its performance under changing radar transmitter’s frequency variation, aspect angle configurations. In this regard, various radar parameters were swept and the best outcome was identified. Thereafter, the significant effect of radar frequency and aspect angle on F117 Nighthawk in its RCS were studied with a small introduction to complex target RCS. The significance of operating frequency and aspect angle on radar detection range has also been illustrated. An elaborate and exhaustive effort is taken to examine various antenna parameters to suggest the best possible radar configuration for better target detectability. In this regard, various correlated mathematical equations were taken into consideration, those were simulated using COMSOL Multiphysics to provide relevant plots for study and analysis. The extensive use of this toll has made the thesis extremely interesting with valuable results drawing important conclusions about the behavior of radar under changing conditions. We thank the Almighty Allah for the successful completion of the thesis. We would like to express our heartiest gratitude, profound indebtedness and deep respect to our supervisor Gp Capt Dr. Mohammad Hossam-E-Haider, PhD, BAF, Head of the Department, Department of Electrical, Electronic and Communication Engineering, MIST, for his supervision, continuous encouragement and valuable suggestions as well as constant guidance throughout the work. We are also grateful to the Department of EECE of Military Institute of Science and Technology (MIST) for providing the laboratory support during the thesis work. We are also grateful to the stuffs of the communication lab, MIST for their considerable support and patience. The availability of the radar systems in the communication lab gave us opportunity to study a practical radar system. Our cordial thanks are to them who directly or indirectly helped us for the completion of the thesis. Special thanks goes to Lec. Syed Nazmus Sakib, Department of Electrical and Telecommunication Engineering (ETE), Daffodil International University, for his valuable suggestions on various concepts and ideas. 2017-12-01T00:00:00Z http://dspace.mist.ac.bd:8080/xmlui/handle/123456789/439 PERFORMANCE ANALYSIS OF FREE SPACE OPTICAL (FSO) COMMUNICATION LINK UNDER WEAK TURBULENCE Alam, Md. Khorshed; Primula, Anika Tasnim; Mustafa, Mohammad Asif Ibna This thesis investigates the performance of terrestrial free-space optical communication (FSO) system based on the On-Off keying (OOK) and Pulse Position Modulation(PPM)inthepresenceofatmosphericturbulenceandpointingerror. The performance analysis is carried out on basis of the bit error rate (BER). Optical signal traversing the atmospheric channel suffers from attenuation due to scattering and absorption by aerosols, fog, atmospheric gases and precipitation. The effect of atmospheric turbulence of an FSO system is presented analytically and experimentally verified both in case of single hop (with OOK modulation) and multiple hop (with PPM modulation). Atmospheric turbulence has a significant impact on the quality of a laser beam propagating through the atmosphere over long distances. Turbulence causes intensity scintillation and beam wander from propagation through turbulent eddies of varying sizes and refractive index. This can severely impair the operation of target designation and FSO communications systems. In this thesis, analysis of BER is done under weak atmospheric turbulence i.e. Log-normally distributed and transmission using single hop and multi-hop which is established on amplify-andforward relays. We illustrate combined probability density function for multi-hop FSO system. Changing the modulation order, the BER performance is analyzed. Using multiple hop, the performance is also investigated and power penalty, the total transmission distance are also calculated as the derived curves for a fixed BER in this thesis. Finally, the numerically found results show that the multiple hop transmission along with PPM is a good solution for obtaining desired Bit Error Rate (BER) under the effects of weak turbulence and pointing error than OOK based single hop. All praises to almighty Allah, the most gracious and the most merciful, who bestowed upon us the will, for the successful competition of our thesis paper within the scheduled time, without which our paper would not have been possible. With due sincerity, we would like to express our heartfelt gratitude and indebtedness to the thesis supervisor Professor Dr. Satya Prasad Majumder for his valuable support and guidance in our BSc program. Throughout this entire thesis work he gave us invaluable advices, continuous guidance and constant encouragement. He has helped us to come to terms with the basic concept of free space optical communication and its forthcoming potential. We are very proud that we had the chance to work with him. We are also thankful to the Department EECE, MIST for providing us an excellent research environment and facilities. 2017-12-01T00:00:00Z http://dspace.mist.ac.bd:8080/xmlui/handle/123456789/438 PERFORMANCE ANALYSIS OF A HEXAGONAL PHOTONIC CRYSTAL FIBER(H-PCF) OVER A BROADBAND RANGE BY VARYING DOPING PARAMETERS Khan, Murtaza; Kabir, Shanzida; Mira, Zafrin Ferdous This thesis paper presents a novel design of a hexagonal four ring photonic crystal fiber (H-PCF) and its performance for different parameter such as effective mode index, dispersion, effective mode area and non-linearity parameter. COMSOL Multi-physics 4.3 software is used to design and analyze the parameters of H-PCF. The designed H-PCF consists of four layered circular air holes and gradually decreasing refractive index from core to cladding. Doping materials, doping percentage and wavelength are varied to analyze the characteristics of the designed H-PCF. MATLAB 7.6 is used to plot the simulation results. The values of Dispersion, Effective mode index, Effective mode area and Non-linearity parameter are calculated from standard equations and plotted against the wavelength. Nearly flattened dispersion is found for a wide range of wavelength from 1410 nm to 1610 nm for GeO2 doped silica at 30% doping and for BaF2doped silica at 10% doping. An increasing effective mode index of value 1.4038 to 1.4401 is found by varying doping percentage of GeO2 doped silica and an increasing effective mode index of 1.4038 to 1.4087 is found by varying doping percentage of BaF2 doped silica which is important for light confinement and total internal reflection. The proposed H-PCF shows nearly zero dispersion and don’t display flattened range of dispersion when not doped. But when the model is doped with GeO2 and BaF2, then it offers flattened dispersion for a wide range of wavelength from 1410 nm to 1610 nm. Though the effective mode area of the model decreases with increasing doping percentage, but it is in the acceptable range of fiber optic communication. Increasing non-linear parameter from 14.31 W-1Km-1 to 27.98 W-1Km-1 can be found by varying doping percentage for GeO2 doping and from 13.5 W1Km-1 to 18.91 W-1Km-1 for BaF2 doping. When the loss parameters of the proposed HPCF are compared for both type of doping, it is found that for the same percentage of doping concentration, value of effective mode area is higher for BaF2 doped silica than GeO2 doped silica and nonlinearity parameter is higher for GeO2 doping than BaF2 doping. Increase of effective mode index is higher for GeO2 doping than BaF2 doping. In summary, it can be said that the proposed H-PCF displays good performance in terms of effective mode index, effective mode area, non-linear parameter, dispersion etc. with doping of GeO2 and BaF2, which is important for optical communication. First of all, we would like to thank almighty Allah for giving us the ability to complete this thesis work. We would like to express our sincere gratitude towards our honorable supervisor, Lt. Col. Md Jahangir Hossain, te, sigs department of Electrical, Electronic and Communication Engineering (EECE), Military Institute of Science and Technology, Dhaka, Bangladesh for his patience, motivation, and immense knowledge. We couldn’t have imagined having a better supervisor and mentor for our thesis work. We are very grateful for his continuous instruction and encouragement, valuable discussions and careful review during the entire duration of the research. His thoughtful analyses and firm supervision have provided us with the right direction towards our goal. We have learned many valuable concepts of Optical Fiber Communication from him throughout our study, which we tried to utilize and develop our analyzing abilities. His encouragement gave us confidence to carry out our work. 2017-12-01T00:00:00Z