Defect modes in one-dimensional comblike photonic crystals

The photonic band structures and the effect of defect states on photonic band gap in a comblike waveguide geometry which were made of dangling side branches grafted periodically along an infinite monomode waveguide were investigated in this paper. It was discovered that the photonic forbidden bands originates from both the periodicity of the system and the resonance states of the grafted branches. By removing or inserting some defect branches in the star waveguide of finite number of grafted branchs, the localized states appear in the transmission spectrum as very narrow pea. The behavior of the localized states was analyzed as the functions of the length, the position and the number of the defective branches.