Research Of Characteristics Of Two-dimensional Photonic Crystal And Its Coupler

We have systematically introduce the basic concept, main characteristics, and analysis method of photonic crystals. By using plane wave expansion method(PWE) and with the help of BandSOLVE software, a band gap distribution map of two-dimensional triangular lattice can be obtained. A coupler based on the two-dimensional triangular lattice is designed. Using the finite-difference time-domain (FDTD) technique and FullWAVE software, we simulate the transmission and coupling characteristic of this kind of coupler, and get some significant results.First of all, we put up numerical simulations in the method of plane wave expansion method(PWE) and obtain some curves of relation between the band gap of two-dimensional photonic crystals and radii of scatterer. From the simulation results, we can also obtain the energy band diagram of two-dimensional photonic crystals which has difform scatterers (rotundity, squareness and hexagon). The results show that:There are two types of two-dimensional photonic crystals which can both generate TM,TE band gap. They are air-substrate Si columnar type and Si-substrate air pass type. The air-substrate Si columnar type is not able to generate complete band gap, but it has prodigious TM band gap. Central frequency of the band gap decreases with increasing radii of Si column. The Si-substrate air pass type can generate complete band gap, and it also has broad TE band gap. Central frequency of the band gap increases with increasing radii of air pass. The form of scatterer will differ band gap structure.Second, an air-substrate Si columnar type two-dimensional triangular lattice photonic crystal coupler has been designed. By using the finite-difference time-domain method, we have simulated the output characteristics of the coupler, numerically solved the simulation result with the help of Matlab software, and obtained some conclusions as follows:Different coupling interaction length will lead to different light intensity of the coupler's output terminal. When determining coupling interaction length, light of different wavelength will result in different coupling efficiency. For a given light frequency, envelope of the curve which describes relation between coupling interaction length and coupling efficiency is sinusoidal. The smaller the spacing between the two coupling arm is, the easier the two arms can couple. But if the spacing of the coupling arms is large to some extent, there is no coupling at all. Various light frequencies have various coupling interaction length. The relation between coupling length and frequency is nonlinear. There are some factors that can affect coupling length such as shape, size as well as the variation of the rotation angle of the scatterers between two branches.The results are important for the design of the actual manufacture of photonic crystal devices.