Transmission properties of perturbed optical cantor multilayer

Fractal multilayers of two distinct dielectric materials are structures exhibiting stop bands and transmission peaks in their electromagnetic response. In this work we analyze how the transmission spectrum of a Cantor fractal multilayer changes when a defect, consisting of a dielectric layer different from those constituting the multilayer, is inserted midway through its thickness. Unlike a periodic multilayer structure, no transmission peaks (defect modes) appear in the stop band by inserting a defect in a Cantor multilayer. We show that a defect in the fractal structure results in a frequency shift of its transmission spectrum and in a change of the width of both stop bands and transmission peaks. The extent of such spectrum modifications depends on either the thickness and the refractive index of the defect layer. By suitably modulating these parameters a tunable narrow band filter can be realized to cover a desired range of frequency. This feature may hold attraction for certain applications such as dense wavelength division multiplexing systems and sensors.