Design And Study Of Rectangular Wave Filter And Beam Splitters Based On Photonic Crystals

The main research contents of this dissertation are as follows:1. Firstly, the realization of rectangular wave filter based on the photonic crystals impurity band has been investigated by means of transfer matrix method. The formation of the quasi-flat bands can be achieved not only by choosing different materials with different refractive indexes but also by adjusting the structure parameters of photonic crystal(PC) itself. So the realization has a large choice range. The dissertation gives a detailed theory analysis and explanation about the rectangular wave formation mechanism. The processing when two PC atoms(signal defect) are coupled to form a PC molecule(two coupled defects) is analyzed in detail. It is found that the ratio of the PC atom linewidth to the PC molecule linewidth plays an important role in the forming of quasi-flat bands. The physical picture about the rectangular wave is also clearly illustrated in this article.Group velocity delay in optical communication will directly lead to ultra-short pulse signal distortion or attenuation. From this perspective, obtaining a relatively quasi-flat bands is very important for the ultra-short transportation without any distortion in optical communication.2. Directional coupler in optical communication can be constructed by putting five photonic crystal waveguides together. The propagation of the optical field entering this system symmetrically is analyzed numerically on the basis of self-imaging principle.1×3 beam splitter, which the length can lowly be 14.26μm. is designed by using this structure. By symmetrically tuning the effective refractive index of two dielectric rods in the coupler, accordingly inducing the redistribution of the electric field, uniform or free energy split can be achieved. By asymmetrically tuning the effective refractive index of one dielectric rod in the coupler, free energy split can also be achieved.Due to the ultracompact size and the free energy split of the output power, the device has extensive practical value in future optical communication photonic integrated circuits.