[1] Northumbria Univ, Fac Engn & Environm, Opt Commun Res Grp, Newcastle Upon Tyne NE1 8ST, Tyne & Wear, England
[2] Univ Aveiro, Inst Telecomunicacoes, P-3810193 Aveiro, Portugal
[3] Univ Aveiro, Dept Elect Telecomunicacoes & Informat, P-3810193 Aveiro, Portugal
[4] Czech Tech Univ, Fac Elect Engn, Dept Electromagnet Field, Prague 16627, Czech Republic