| Summary: | 碩士 === 國立成功大學 === 光電科學與工程學系 === 107 === Photonic crystals can produce many special phenomena because of its periodic dielectric structure. For example, when light travels through a photonic crystal, it can cause destructive interference due to the interaction between each layer of structure. These destructive interferences can prohibit the propagation of some frequencies, and the areas covered by these frequencies are called photonic band gaps. The band structure of photonic crystals is therefore divided into upper and lower parts. Bound states in the continuum (BICs) are found in the waveguide composed of photonic crystals. These special modes are caused by bound states outside the continuous spectrum of the wave source. And its energy is continuously rises in the continuous spectrum, so it has very high Q-factor. This makes them useful for many optical and other application. There are many reasons for the occurrence of continuum bound states. In the Fabry-Pérot cavity, the round-trip phase shifts can be used to make the two sides of the resonant cavity become perfect mirrors, so that electromagnetic waves are confined to generate BICs. In a photonic crystal waveguide, its periodic arrangement can provide good symmetry, so the horizontal wave vector of the electromagnetic field has the opportunity to be superimposed. If such a situation occurs in the continuous spectrum, BICs can be formed. In this article, we use FDTD with periodic boundary conditions to simulate the photonic crystal waveguide, and successfully find the BICs. Then we analyze the conditions of BICs to make electric field patterns to discuss the composition distribution of BIC modes. We also changed the shape of the structures to observe the BICs generated under different structures.
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