الفهرس 
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Abstract
Because information exchange is advancing quickly and there is a need to improve the effectiveness of existing communication technologies, developing optical communication systems to achieve high transmission capacity has become increasingly important. The integration of several optical components, including detectors, couplers, modulators, and multiplexers, is crucial to optical communication systems. The optical wave should be modified with the digital electronic signal to send digital signals across an optical traveling wave. Depending on the digital signal carrying the information, an electro-optical modulator switches the optical wave to pass or block. These modulators are essential parts of any optical communication system because they transform digital electronic impulses into optical signals that may be sent through optical fibers over great distances with little loss. Plasmonics have attracted attention because they have the potential to produce innovative photonics devices with distinctive optical features. The focus of this dissertation is on brand-new plasmonic device designs for photonics applications. Two different plasmonic modulator designs are offered in the current thesis and are put through computer simulations with the FEM. Phase-changing materials (PCMs), like graphene, are regarded as novel adaptive materials since they may shift from being insulating to conducting when an external electric field or temperature is applied. There has been a lot of interest in the two-dimensional type of carbon called graphene, in which the atoms are organized in a hexagonal structure. Due to its outstanding optoelectronic and photonic characteristics, like fast operation and powerful graphene light interaction and broadband operation. At room temperature, the carrier mobility exceeds 200000 cm2 / (V. s), and a pure graphene monolayer absorbs just 2.3% of the infrared and visible spectrum (Liu et al. 2011). Wang et al noticed in 2008 that the electrical gating can modify the monolayer or bilayer of graphene’s strong interband optical transitions. Firstly, a broadband plasmonic optical modulator based on a bowtie-shape waveguide and two graphene layers has been investigated. The proposed structure is designed at TE mode over a range of wavelengths extending from 1100 to 1900 nm. The performance of the modulator has been tuned by adjusting the geometry of the bowtie structure. The proposed modulator’s performance has been characterized using propagation loss, bandwidth, power consumption, and modulation depth. The obtained results show at a wavelength of 1.55 μm that the loss, modulation depth, and small footprint read 0.0257 dB/μm, 0.5829 dB/μm, and (0.5 μm×12.17 μm), respectively. Additionally, the proposed modulator offers modulation bandwidth and power consumption of about 151.7 GHz and 32.919 fJ/bit, respectively. For the second design, a broadband plasmonic optical modulator based on a dual back-to-back U-shaped silicon waveguide and double layers of graphene has been investigated. The proposed structure is designed at TE mode over a range of wavelengths extending from 1.1 to 1.9 μm. By adjusting the geometry of the U-shaped structure, the modulator’s performance has been tuned. Utilizing propagation loss, bandwidth, power consumption, and modulation depth, the proposed modulator’s performance has been characterized. According to the results, at a wavelength of 1.55 μm, the loss, modulation depth, and small footprint read 0.0415 dB/μm, 0.6337 dB/μm, and (0.5 μm×12.17 μm), respectively. Furthermore, the proposed modulator has a modulation bandwidth of about 151.7 GHz and power consumption of 21.068 fJ/bit.