Ivaniga, Tomas, Petr Ivaniga, Jan Turan, and Lubos Ovsenik. 2017. “Analysis of Possibilities of Increasing the Spanned Distance Using EDFA and DRA in DWDM System”. Communications - Scientific Letters of the University of Zilina 19 (3), 88-95. http://journals.uniza.sk/index.php/communications/article/view/240.