Research On The Mechanism Of Photonic Bandgaps, Fabrication Of Different Structures Of Photonic Crystal Film And Characterization Of Their Optical Properties

Photonic crystals (PhCs) are materials that possess spatial periodicity in their dielectric constants on the order of the wavelength of light. These materials can strongly modulate light, with sufficient dielectric contrast and an appropriate geometry, and may exhibit a photonic bandgap (PBG), in which electromagnetic wave with a certain wavelength can be prohibited in a certain direction. This key feature makes PhCs capable of controlling the photons in much the same way as a semiconductor does for electrons. Just as it is predicted that PhCs may replace semiconductor to be the carrier of information and media of transmission and lead to another technological revolution, like studies on semiconductor causing the revolution in electronic industry. However, there have been yet a lot of challenges on both the theory of the formation of PBGs and the fabrication of PhCs for a subject possesses only 20 years history.This thesis firstly reviewed the concept and features of PhCs. Then a comparison was made between the electronic crystal and photonic crystal, followed with a brief introduction on the study methods of PhCs upon the basis of analyzing field equation and bandgap theory. With regards to the fabrication of PhCs, the "top-down" physical method and "bottom-up" chemical self-assembly method were summarized in this thesis. The recent development of PhCs in materials, structure and methods were discussed in details as well. Besides that, the introduction of the applications of PhCs, in particular, in the range of near-infrared, optical and microwave were made.Both theoretical study and experimental study were carried out in this thesis. There are two parts in the experimental study:1. Wave vectors of TE mode and TM mode under two dimensions were characterized and explained the difference between them. Through the derivation of general matrix of three dimensions, the complications of three-dimensional bandgaps were illustrated. And then the distributions of electromagnetic field and bandgaps were analysized by using the finite-difference time-domain (FDTD) method. This section not only gave derivations and applications on the frequently used calculation method, but also solved the problem that why this phenomenon occurs.2. Research on the PhCs building blocks:Building blocks are the fundamental of PhCs. However, a number of problems have not been solved in previous studies, such as many studies on two-dimensional PhCs were carried out without taking into account the differences between TE mode and TM mode, and few studies on asymmetric building blocks. In this study, the basic theory of building blocks was discussed and some common building blocks were introduced, and then two novel building blocks: eye-shaped and sectoral building blocks were designed independently. Through the calculation of different bandgaps, some comparison was made on the difference between the bandgaps of TE mode and TM mode. The results demonstrated that these two kinds of building blocks not only possess their own advantages in the width of PBGs, but also can tune the widths and positions of the PBGs.The experimental part can be divided into two parts:1. The fabrication of PhCs used in near-infrared wave:This part includes two chapters: Synthesis of colloidal microspheres and the fabrication of simple PhCs, and fabrication of complex PhCs and PhCs embedding with functional defects. In detail, this part not only includes the synthesis of polystyrene (PS) and silica (SiO2) colloidal microspheres, but also contains the fabrication of simple PhCs by using vertical deposition and horizontal deposition method. Moreover, this part not only contains the fabrication of SiO2 inverse opal by using PS PhCs as template, but also covers the fabrication of binary structure of PhCs and its inverse structure. In addition, the introduction of planar defects into PS and SiO2 opal and inverse opal, and embedding line defects in polystyrene PhCs were carried out as well.2. The fabrication of PhCs used in terahertz wavelength:As the diameter of spheres reaches tens of microns, the PBG of PhCs lies at the range of terahertz wavelength. However, it is a challenge to self-assemble building blocks with a diameter from ten to hundred microns. Traditionally, microfabrication methods are used to fabricate THz PhCs. To solve this problem, we firstly fabricated patterned silicon wafers by using photolithography method, and then attempted to assemble microspheres with big diameter on patterned silicon wafer.Finally, this thesis pointed out that PhCs, especially three-dimensional PhCs, can be utilized as novel functional materials for the application of information processing and communication. To achieve this goal, it is necessary to carry on further investigation on the theory of PhCs to make it more systematic. Further, among all kinds of fabrication methods, self-assembly is the cheapest and most effective method to fabricate three-dimensional PhCs though some disadvantages accompanied. Therefore, self-assembly method often combines with other methods to fabricate complicated PhCs, especially to embed all kinds of defects into PhCs to realize the functionalized PhCs. With respect to the PhCs applied in the field of terahertz wave, deep insight on the mechanism of self-assembly and improvement in assembly approaches and combining the chemical and physical method should be carried out.