Study On The Optical Properties Of Photonic Crystal Nanobeam Cavities

Photonic crystal is a kind of artificial microstructure which is formed by the periodic arrangement of dielectric materials with different refractive index. If the defect or disorder is introduced into the photonic crystal so that the periodicity of the photonic crystal is destroyed, then the photonic crystal resonant cavity is formed. Photonic crystal nanobeam cavity(PCNC) is a typical one-dimensional photonic crystal cavity. It has smaller size, higher quality factor and smaller size comparing with two dimensional photonic crystal resonator, so it is widely used. It is urgent to propose a new model for PCNC instead of conventional optical cavity in order to further improve PCNC’s optical performance and obtain high quality factor and very small volume.In this paper, we first introduce the research background of PCNC and the photonic crystal’s characteristics and applications. Then we introduce the basic theory and main research methods of PCNC, focusing on the plane wave expansion method and the finite difference time domain method. We propose a novel PCNC model with H type air holes instead of the traditional nanobeam cavities which usually adopt circular or rectangular air holes. By using the plane wave expansion method we studied the photonic band structure of the proposed nanobeam cavity and analyzed the impact of different structural parameters on photonic band gap. We further designed periodic waveguide structure, which has strong limitations to photonic. At the same time, by using the mode matching method, the structure of periodic waveguide was modified to form a nanobeam cavity with tapered regions and mirror regions. By using the finite difference time domain method, the optical properties of the nanobeam cavity such as the quality factor and the mode volume are studied systematically. For comparison, we also designed a kind of nanobeam cavity with the same structure as the PCNC with H type air holes, but changed the air hole to rectangle one. At the same time, the photonic band structures, the quality factor and the mode volume of these two kinds of nanobeam cavities are compared. Compared with the traditional nanobeam cavities, our proposed novel nanobeam cavity with H type air holes has quality factor as high as Q=6.6×10~7 and mode volume as small as V=0.59(λ/n)~3, so that it will be widely used in low threshold lasers, high sensitivity optical sensors, filters and optomechanical systems and so on.