Modal reshaping of the electromagnetic mode density near band edges in finite one-dimensional periodic photonic band-gap structures

We show that cascading two finite one-dimensional periodic photonic band-gap structures may result, due to the multiple confinement of the electromagnetic field, in a significant modification of the modal distribution of the electromagnetic density of modes (DOM) around a band edge. As a result of the combination of the band-gap effects and the band-edge effects, the enhancement and the optimum localization of the DOM can be simultaneously obtained. The general approach is presented. The basic rules and the main steps for the design of such a structure are described. Some numerical results are given and discussed, by using alternating Ga_0.7Al _0.3As/AlAs layer quarter-wave and mixed quarter-wave/half-wave stacks. The principle of the present work, although described within the limits of linear and dispersionless materials, may be directly applied to nonlinear parametric processes.