1. Department of Telecommunications, Faculty of Electronic Engineering, University of Niš, Aleksandra Medvedeva 14, 18000 Niš, Serbia
2. Department of Applied Mathematics and Theoretical Physics, Center for Research and Education in Optical Sciences and Applications, Delaware State University, 1200 N DuPont Highway, Dover, DE 19901, USA
3. Department of Physics and Pre-Engineering, Delaware State University, 1200 N DuPont Highway, Dover, DE 19901, USA