Study On Negative Refraction Property And Relative Applications Of Graded Index Photonic Crystals

Optics is an old subject with new developments, the proposal of photonic crystals(PC) add new energy to this subject. The concept of photonic crystals was firstly proposed by Yablonvitch and John in 1987. Photonic crystals are composed by periodic dielectric materials with different dielectric constant. Similar to electronic crystals,photonic crystals have also band structures, so they can control propagation of light inside them. Many photonic-crystals-based applications were proposed. Centeno and Cassagne put forward a new type of photonic crystals in 2005, they call it graded index photonic crystals(GRIN PC). GRIN PCs are obtained by modify relative parameters of ordinary PCs.This thesis put emphasis on GRIN PCs. Firstly fundamental theory of finite-difference time-domain(FDTD) method is described, including finite-difference scheme, absorb boundary condition and stability problem. This method is used to calculate band structures of PCs and simulate propagation behavior of light inside PCs.Then the negative refraction property is studied and the focusing property of different GRIN PCs with different parameters is compared in the thesis. During this section,following conclusions are reached:1. Obvious negative refraction phenomena exist in the second band of PC, and this phenomenon get intense in the center area of second band.2. For different GRIN PCs with different index profile, the PC with n=0.5 index profile posses better focusing property including smaller spot size and longer focal length.3. GRIN PCs with elliptical air holes have longer focal length, while GRIN PCs with rectangle air holes have smaller spot size and better transmission. The focusing property of GRIN PCs with triangle air holes is not ideal.4. With the increase of filling factor A, the focal length of GRIN PCs become longer,while the spot size become larger. In the same time, GRIN PCs with rectangle air hole is sensitive to the filling factor A, while GRIN PCs with elliptical air holes is not sensitive to the filling factor A.These conclusions will be helpful in designing PC based devices.At last, a novel optical beam splitter is put forward. The splitter consists of GRIN PCsand ordinary PC with square lattice. Because of the focusing property of GRIN PC and the band gap of square lattice PC, this splitter can both split and focus the incident plane wave. This splitter has many advantages over traditional splitters.