Large forbidden band in one-dimensional multi-layered structure containing exponentially graded materials

In the present communication, we have presented band spectra and reflectance properties of one-dimensional multi-layered structure containing dielectric exponentially graded and simple dielectric layers. This study has been performed theoretically by using transfer matrix method. In this paper we have taken the multi-layered structure where refractive index of odd layers is varying continuously along the direction perpendicular to the surface of the layer in exponential form. The effect of the graded profiles are studied and compared with the conventional multi-layered structure of suitable contrast of refractive indices in detail. In this study the materials are considered as non-magnetic and layers other than the graded are taken to be homogeneous and isotropic dielectric medium of constant refractive index. It has been found that the introduction of graded layers enhanced the forbidden band gaps and affects the reflectance of electromagnetic wave spectra significantly. By changing the grading profiles and the contrast, we obtained the forbidden band gaps and the reflectance of such structural change accordingly. Therefore, introducing a graded exponential layer of dielectric in the one-dimensional multi-layered structure provides possible mechanism for enhancing the reflectance as well as the forbidden gap in the optical region. Such multi-layered structure may be useful in the design of a broadband filter. (C) 2007 Elsevier B.V. All rights reserved.