دراسات نظريه لبلورات فوتونيه جرافينيه لتطبيقات مختلفه

Research Abstract

Conclusion The main idea of the present thesis is improve the applications of the one-dimensional photonic crystal (1D-PC) by using optical properties of graphene. In addition, we show how optical properties of graphene effect on three types of materials (Nanocomposite, Electro-optical, Liquid crystal) and how enhancement their optical properties. The optical properties of our structures are calculated by using the transfers' matrix method. In chapter 1, we give general information about all points in thesis. These points include photonic crystals, 1D-PC, graphene, graphene based on 1D-PC, nanocomposite based on 1D-PC, graphene- nanocomposite based on 1D-PC, Electro-optical materials based on 1D-PC, graphene- Electro-optical based on 1D-PC, thermal sensor based on 1D-PC, Liquid crystal as a thermal sensor, and graphene- liquid crystal based on 1D-PC thermal sensor with high sensitivity. In chapter 2, we present a new type of the one-dimensional photonic crystals which has unique optical characteristics. The present structure consists of graphene based on nanocomposite and dielectric layers. Here, the nanocomposite layer is designed in the form of graphene nanoparticles that embedded into in a dielectric host material. By using transfers matrix method, Maxwell – Garnett formula, and Kubo formula, the properties of photonic band gap within visible and infrared regions are discussed. Our calculations reflect the significant effect of graphene on the optical characteristics of the nanocomposite layer. Wherein, the volume fraction of graphene's nanoparticles has a significant effect on the effective permittivity of the nanocomposite layer and the properties of the photonic band gaps as well. Thus, the tunability of the photonic band gaps based on this parameter could be expected. In addition, have the effect of the constituent materials thicknesses, the chemical potential and the permittivities of the host dielectric material on the transmittance properties are demonstrated. Finally, nanocomposite-based on graphene shows significant multifunctional improvements compared to conventional composites. This design could be of potential interest in many fields of applications such as stop band filters and switches with high reflectivity. In chapter 3, we present a new (to the best of our knowledge) photonic crystal optical filters with unique optical characteristics are theoretically introduced in this research. Here, our design is composed of a defect layer inside one-dimensional photonic crystals. The main idea of our study is dependent on the tunability of the permittivity of graphene by means of the electro-optical effect. The transfer matrix method and the electro-optical effect represent the cornerstone of our methodology to investigate the numerical results of this design. The numerical results are investigated for four different configurations of the defective one-dimensional photonic crystals for the electric polarization mode. The graphene as a defect layer is deposited on two different electro-optical materials (Lithium Niobate and Polystyrene) to obtain the four different configurations. The electro-optical properties of graphene represent the main role of our numerical results. In the infrared wavelength range from 0.7 µm to 1.6 µm, the reflectance properties of the composite structures are numerically simulated by varying several parameters such as defect layer thickness, applied electrical field, and incident angle. The numerical results show that graphene could enhance the reflectance characteristics of the defect mode in comparison with the two electro-optical materials without graphene. In the presence of graphene with Lithium Niobate, the intensity of the defect mode increased by 5% beside the shift in its position with 41 nm. For the case of polystyrene, the intensity of the defect mode increased from 6.5% to 68.8%, and its position is shifted with 72 nm. Such a design could be of significant interest in the sensing and measuring of electric fields, as well as for filtering purposes. In chapter 4, we present a simple design to act as a temperature sensor based on the one dimensional photonic crystal. The main idea of the proposed sensor is depending on the inclusion of graphene deposited nematic liquid crystal as defect layer through the photonic crystal. The transfers matrix method, Kubo-Formula, and fitting experimental data represent the core axes of our theoretical treatment. Here, the proposed sensor is designed to work based on the shift of the resonant peak with the temperature variation. The performance of such sensor is demonstrated by calculating the sensitivity, figure of merit, detection limit, sensor resolution and the quality factor. The effect of the thickness of the defect layer and the mode of polarization as well on the performance of our sensor is investigated. The numerical results show that our sensor could be of interest in many fields of application due to the high values of its sensitivity and quality factor. The proposed sensor could receive to 4 nm / oC and quality factor of more than 11000. In chapter 5, we theoretically explore the transmittance properties and cutoff frequency of one-dimensional photonic crystal (1DPCs) within the terahertz frequency region, by using the transfer matrix method,. The present structure consists of high-temperature superconductor and semiconductor layers. The results of the calculations represent the effects of various parameters on the cutoff frequency. We have used the two-fluid model as well as the Drude model to describe the permittivity of superconductor and semiconductor. Further, we consider that the permittivity of both the materials is depending on the hydrostatic pressure. The present results show that with the increasing of different parameters as the operating temperature, the thickness of semiconductor, and the filling factor of semiconductor, then the cutoff frequency shifts to lower frequencies regions. By the increasing of superconductor thickness, hydrostatic pressure, doping concentration, and filling factor of the superconductor, we found the cutoff frequency shifts to higher frequencies regions. These results indicate that cutoff frequency can be modified through these different parameters. Finally, the present design could be useful for many optical systems as the optical filter, reflector, and photo electronic applications in the Terahertz regime. Chapter 5, related to the future work. We will be used graphene based on this idea which present in this chapter.

Research Keywords

دراسات نظريه لبلورات فوتونيه جرافينيه لتطبيقات مختلفه