| Summary: | 碩士 === 國立成功大學 === 機械工程學系碩博士班 === 96 === Metamaterials currently play an important role in providing new functionalities and enhancements to the future electronic devices and components. The major trend today is to create the fundamentally new properties required by new technologies. Metamaterials make perfect lenses that image classical electromagnetic fields with significantly higher resolution than the diffraction limit. Materials with negative refractive index attracted lots of interest recently because they can be realized with metamaterials or photonic crystals (PCs), which are usually periodic structures. Specifically, the diffraction of PCs leads to the effective negative refraction such that a so-called perfect lens is feasible and able to focusing the electromagnetic wave beyond the diffraction limit.
This research focuses on the optical properties and the sub-wavelength focusing of a novel photonic crystal (PC). We propose an innovated PC slab and investigate its optical properties and the focusing numerically by both finite-difference-time-domain and finite element methods. The PC is composed of an array of two-dimensional hexagonal with dielectric cylinders inside each unit cell. As the different radius of the cylinder varies, the plane wave expansion method is employed for solving Maxwell’s equations. Interestingly, the complex PC, whose radius of each cylinder is different, can generate focusing with an effective refractive index of �{1. The design as the antireflection structures to enhance the transmission efficiency of light at the interfaces between the air and the PC slab was proposed in this research. Numerical simulations show that the focusing resolution can be improved greatly by appropriately adding the surface of the slab. Such a mechanism of negative refraction PCs could open up a new application in optical imaging systems, such as optical lithography or near-field optical microscopy.
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