Abstract
Photonic band gap is the most important characteristic of photonic crystals. It is used to confine of EM waves within the crystal, so that photonic crystals perform like photonic insulators. At present, 2D photonic crystals are popularly applied. The focus is to calculate the photonic band gap. And if we can reduce the calculation of 2D to 1D, it will save us a lot of time and troubles. We had investigated a 1D effective model (a mean field theory) before, but the result of this kind of model for TE mode was not good enough. The purpose of this thesis is to improve the previous model and calculate the low-lying bands of photonic crystal simply and efficiently in a systematic way.