[1] Dublin Inst Technol, Sch Elect & Commun Engn, Photon Res Ctr, Dublin 8, Ireland
[2] Northumbria Univ, Dept Phys & Elect Engn, Newcastle Upon Tyne NE1 8ST, Tyne & Wear, England
[3] Beijing Univ Posts & Telecommun, State Key Lab Informat Photon & Opt Commun, Beijing 100876, Peoples R China
[4] Jinan Univ, Inst Photon Technol, Guangzhou 510632, Guangdong, Peoples R China